More

* Bump FsCheck and FSharp.Core

Bumps [FsCheck](https://github.com/Fscheck/fscheck) and [FSharp.Core](https://github.com/dotnet/fsharp). These dependencies needed to be updated together.

Updates `FsCheck` from 3.1.0 to 3.2.0
- [Release notes](https://github.com/Fscheck/fscheck/releases)
- [Changelog](https://github.com/fscheck/FsCheck/blob/master/FsCheck%20Release%20Notes.md)
- [Commits](https://github.com/Fscheck/fscheck/compare/3.1.0...3.2.0)

Updates `FSharp.Core` from 4.3.4 to 5.0.2
- [Release notes](https://github.com/dotnet/fsharp/releases)
- [Changelog](https://github.com/dotnet/fsharp/blob/main/release-notes.md)
- [Commits](https://github.com/dotnet/fsharp/commits)

---
updated-dependencies:
- dependency-name: FsCheck
  dependency-version: 3.2.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: FSharp.Core
  dependency-version: 5.0.2
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* Bump FSharp.Core and WoofWare.Whippet.Fantomas

Bumps [FSharp.Core](https://github.com/dotnet/fsharp) and [WoofWare.Whippet.Fantomas](https://github.com/Smaug123/WoofWare.Whippet). These dependencies needed to be updated together.

Updates `FSharp.Core` from 4.3.4 to 6.0.1
- [Release notes](https://github.com/dotnet/fsharp/releases)
- [Changelog](https://github.com/dotnet/fsharp/blob/main/release-notes.md)
- [Commits](https://github.com/dotnet/fsharp/commits)

Updates `WoofWare.Whippet.Fantomas` from 0.3.2 to 0.5.1
- [Commits](https://github.com/Smaug123/WoofWare.Whippet/commits)

---
updated-dependencies:
- dependency-name: FSharp.Core
  dependency-version: 6.0.1
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: WoofWare.Whippet.Fantomas
  dependency-version: 0.5.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Smaug123 <3138005+Smaug123@users.noreply.github.com>

.config/dotnet-tools.json

@@ -3,13 +3,13 @@
   "isRoot": true,
   "tools": {
     "fantomas": {
-      "version": "7.0.0",
+      "version": "7.0.1",
       "commands": [
         "fantomas"
       ]
     },
     "fsharp-analyzers": {
-      "version": "0.28.0",
+      "version": "0.30.0",
       "commands": [
         "fsharp-analyzers"
       ]

.github/workflows/dotnet.yaml

@@ -29,7 +29,7 @@ jobs:
       with:
         fetch-depth: 0 # so that NerdBank.GitVersioning has access to history
     - name: Install Nix
-      uses: cachix/install-nix-action@v30
+      uses: cachix/install-nix-action@v31
       with:
         extra_nix_config: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -50,7 +50,7 @@ jobs:
         with:
           fetch-depth: 0 # so that NerdBank.GitVersioning has access to history
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -67,7 +67,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -82,7 +82,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -97,7 +97,7 @@ jobs:
         with:
           fetch-depth: 0 # so that NerdBank.GitVersioning has access to history
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -116,7 +116,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -129,7 +129,7 @@ jobs:
     steps:
       - uses: actions/checkout@master
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -142,7 +142,7 @@ jobs:
     steps:
       - uses: actions/checkout@master
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -156,7 +156,7 @@ jobs:
       with:
         fetch-depth: 0 # so that NerdBank.GitVersioning has access to history
     - name: Install Nix
-      uses: cachix/install-nix-action@v30
+      uses: cachix/install-nix-action@v31
       with:
         extra_nix_config: |
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -254,7 +254,7 @@ jobs:
           name: nuget-package-attribute
           path: packed
       - name: Attest Build Provenance
-        uses: actions/attest-build-provenance@520d128f165991a6c774bcb264f323e3d70747f4 # v2.2.0
+        uses: actions/attest-build-provenance@c074443f1aee8d4aeeae555aebba3282517141b2 # v2.2.3
         with:
           subject-path: "packed/*.nupkg"
 
@@ -273,7 +273,7 @@ jobs:
           name: nuget-package-plugin
           path: packed
       - name: Attest Build Provenance
-        uses: actions/attest-build-provenance@520d128f165991a6c774bcb264f323e3d70747f4 # v2.2.0
+        uses: actions/attest-build-provenance@c074443f1aee8d4aeeae555aebba3282517141b2 # v2.2.3
         with:
           subject-path: "packed/*.nupkg"
 
@@ -289,7 +289,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
@@ -322,7 +322,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}

.github/workflows/flake_update.yaml

@@ -34,7 +34,7 @@ jobs:
 
       - name: Create token
         id: generate-token
-        uses: actions/create-github-app-token@v1
+        uses: actions/create-github-app-token@v2
         with:
           # https://github.com/actions/create-github-app-token/issues/136
           app-id: ${{ secrets.APP_ID }}

ConsumePlugin/Args.fs

@@ -235,3 +235,9 @@ type FlagsIntoPositionalArgs' =
         [<PositionalArgs false>]
         DontGrabEverything : string list
     }
+
+[<ArgParser true>]
+type PassThru =
+    {
+        A : ParentRecordChildPos
+    }

ConsumePlugin/ArgsWithUnions.fs

@@ -0,0 +1,35 @@
+namespace ConsumePlugin.ArgsWithUnions
+
+open System
+open System.IO
+open WoofWare.Myriad.Plugins
+
+type BasicNoPositionals =
+    {
+        Foo : int
+        Bar : string
+        Baz : bool
+        Rest : int list
+    }
+
+type UsernamePasswordAuth =
+    {
+        Username : string
+        Password : string
+    }
+
+type TokenAuth =
+    {
+        Token : string
+    }
+
+type AuthOptions =
+    | UsernamePassword of UsernamePasswordAuth
+    | Token of TokenAuth
+
+[<ArgParser>]
+type DoTheThing =
+    {
+        Basics : BasicNoPositionals
+        Auth : AuthOptions
+    }

ConsumePlugin/ConsumePlugin.fsproj

@@ -12,6 +12,7 @@
   <ItemGroup>
     <None Include="myriad.toml"/>
     <Compile Include="AssemblyInfo.fs" />
+    <!--
     <Compile Include="RecordFile.fs"/>
     <Compile Include="GeneratedRecord.fs">
       <MyriadFile>RecordFile.fs</MyriadFile>
@@ -66,10 +67,16 @@
     <Compile Include="ListCata.fs">
       <MyriadFile>List.fs</MyriadFile>
     </Compile>
+    -->
     <Compile Include="Args.fs" />
     <Compile Include="GeneratedArgs.fs">
       <MyriadFile>Args.fs</MyriadFile>
     </Compile>
+    <Compile Include="ArgsWithUnions.fs" />
+    <Compile Include="GeneratedArgsWithUnions.fs">
+      <MyriadFile>ArgsWithUnions.fs</MyriadFile>
+    </Compile>
+    <!--
     <None Include="swagger-gitea.json" />
     <Compile Include="GeneratedSwaggerGitea.fs">
       <MyriadFile>swagger-gitea.json</MyriadFile>
@@ -81,6 +88,7 @@
     <Compile Include="Generated2SwaggerGitea.fs">
       <MyriadFile>GeneratedSwaggerGitea.fs</MyriadFile>
     </Compile>
+    -->
   </ItemGroup>
 
   <ItemGroup>

ConsumePlugin/GeneratedArgsWithUnions.fs

@@ -0,0 +1,686 @@
+//------------------------------------------------------------------------------
+//        This code was generated by myriad.
+//        Changes to this file will be lost when the code is regenerated.
+//------------------------------------------------------------------------------
+
+
+
+
+
+
+namespace ArgParserHelpers
+
+/// Helper types for arg parsing
+module internal ArgParseHelpers_ConsumePlugin_ArgsWithUnions =
+    open System
+    open System.IO
+    open WoofWare.Myriad.Plugins
+    open ConsumePlugin.ArgsWithUnions
+
+    /// A partially-parsed BasicNoPositionals.
+    type internal BasicNoPositionals_InProgress =
+        {
+            mutable Bar : string option
+            mutable Baz : bool option
+            mutable Foo : int option
+            mutable Rest : ResizeArray<int>
+        }
+
+        /// Freeze this in-progress type. On success, returns the frozen type and the arg (if any) which consumed the input positional args.
+        member this.Assemble_
+            (getEnvironmentVariable : string -> string)
+            (positionals : Choice<string * int, string * int> list)
+            : Result<BasicNoPositionals * string option, string list>
+            =
+            let errors = ResizeArray<string> ()
+            let positionalConsumers = ResizeArray<string> ()
+            let outOfPlacePositionals : ResizeArray<string> = ResizeArray ()
+
+            let arg0 : int =
+                match this.Foo with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "foo")
+                    Unchecked.defaultof<_>
+
+            let arg1 : string =
+                match this.Bar with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "bar")
+                    Unchecked.defaultof<_>
+
+            let arg2 : bool =
+                match this.Baz with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "baz")
+                    Unchecked.defaultof<_>
+
+            let arg3 : int list = this.Rest |> Seq.toList
+
+            if positionalConsumers.Count <= 1 then
+                if outOfPlacePositionals.Count > 0 then
+                    outOfPlacePositionals
+                    |> String.concat " "
+                    |> (fun x ->
+                        if 0 = outOfPlacePositionals.Count then
+                            "Unmatched args which look like they are meant to be flags. " + x
+                        else
+                            sprintf
+                                "Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `%s=` syntax, or place them after a trailing `--`. %s"
+                                positionalConsumers.[0]
+                                x
+                    )
+                    |> errors.Add
+                else
+                    ()
+
+                if errors.Count = 0 then
+                    Ok (
+                        {
+                            Foo = arg0
+                            Bar = arg1
+                            Baz = arg2
+                            Rest = arg3
+                        },
+                        Seq.tryExactlyOne positionalConsumers
+                    )
+                else
+                    errors |> Seq.toList |> Error
+            else
+                ("Multiple parsers consumed positional args; this is an error in the application, not an error by the user: "
+                 + String.concat ", " positionalConsumers)
+                |> List.singleton
+                |> Error
+
+        static member _Empty () : BasicNoPositionals_InProgress =
+            {
+                Bar = None
+                Baz = None
+                Foo = None
+                Rest = ResizeArray ()
+            }
+
+        /// Processes the key-value pair, returning Error if no key was matched.
+        /// If the key is an arg which can have arity 1, but throws when consuming that arg, we return Error(<the message>).
+        /// This can nevertheless be a successful parse, e.g. when the key may have arity 0.
+        member this.ProcessKeyValueSelf_
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            if System.String.Equals (key, sprintf "--%s" "rest", System.StringComparison.OrdinalIgnoreCase) then
+                value |> (fun x -> System.Int32.Parse x) |> (fun x -> x) |> this.Rest.Add
+                () |> Ok
+            else if System.String.Equals (key, sprintf "--%s" "foo", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Foo with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "foo")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Foo <- value |> (fun x -> System.Int32.Parse x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else if System.String.Equals (key, sprintf "--%s" "baz", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Baz with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "baz")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Baz <- value |> (fun x -> System.Boolean.Parse x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else if System.String.Equals (key, sprintf "--%s" "bar", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Bar with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "bar")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Bar <- value |> (fun x -> x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else
+                Error None
+
+        member this.ProcessKeyValue
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            match this.ProcessKeyValueSelf_ argNum_ errors_ key value with
+            | Ok () -> Ok ()
+            | Error None -> Error None
+            | Error (Some errorFromLeaf) -> Error (Some errorFromLeaf)
+
+        /// Returns false if we didn't set a value.
+        member this.SetFlagValue_ (errors_ : ResizeArray<string>) (key : string) : bool =
+            if System.String.Equals (key, sprintf "--%s" "baz", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Baz with
+                | Some _ ->
+                    sprintf "Flag '%s' was supplied multiple times" (sprintf "--%s" "baz")
+                    |> errors_.Add
+
+                    true
+                | None ->
+                    this.Baz <- true |> Some
+                    true
+            else
+                false
+
+        /// Compute help text for this parser, optionally noting the given prefix on each argument and indenting each line by this many spaces.
+        static member HelpText_ (prefix : string option) (indent : int) : string = failwith "TODO"
+
+    /// A partially-parsed UsernamePasswordAuth.
+    type internal UsernamePasswordAuth_InProgress =
+        {
+            mutable Password : string option
+            mutable Username : string option
+        }
+
+        /// Freeze this in-progress type. On success, returns the frozen type and the arg (if any) which consumed the input positional args.
+        member this.Assemble_
+            (getEnvironmentVariable : string -> string)
+            (positionals : Choice<string * int, string * int> list)
+            : Result<UsernamePasswordAuth * string option, string list>
+            =
+            let errors = ResizeArray<string> ()
+            let positionalConsumers = ResizeArray<string> ()
+            let outOfPlacePositionals : ResizeArray<string> = ResizeArray ()
+
+            let arg0 : string =
+                match this.Username with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "username")
+                    Unchecked.defaultof<_>
+
+            let arg1 : string =
+                match this.Password with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "password")
+                    Unchecked.defaultof<_>
+
+            if positionalConsumers.Count <= 1 then
+                if outOfPlacePositionals.Count > 0 then
+                    outOfPlacePositionals
+                    |> String.concat " "
+                    |> (fun x ->
+                        if 0 = outOfPlacePositionals.Count then
+                            "Unmatched args which look like they are meant to be flags. " + x
+                        else
+                            sprintf
+                                "Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `%s=` syntax, or place them after a trailing `--`. %s"
+                                positionalConsumers.[0]
+                                x
+                    )
+                    |> errors.Add
+                else
+                    ()
+
+                if errors.Count = 0 then
+                    Ok (
+                        {
+                            Username = arg0
+                            Password = arg1
+                        },
+                        Seq.tryExactlyOne positionalConsumers
+                    )
+                else
+                    errors |> Seq.toList |> Error
+            else
+                ("Multiple parsers consumed positional args; this is an error in the application, not an error by the user: "
+                 + String.concat ", " positionalConsumers)
+                |> List.singleton
+                |> Error
+
+        static member _Empty () : UsernamePasswordAuth_InProgress =
+            {
+                Password = None
+                Username = None
+            }
+
+        /// Processes the key-value pair, returning Error if no key was matched.
+        /// If the key is an arg which can have arity 1, but throws when consuming that arg, we return Error(<the message>).
+        /// This can nevertheless be a successful parse, e.g. when the key may have arity 0.
+        member this.ProcessKeyValueSelf_
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            if System.String.Equals (key, sprintf "--%s" "username", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Username with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "username")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Username <- value |> (fun x -> x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else if
+                System.String.Equals (key, sprintf "--%s" "password", System.StringComparison.OrdinalIgnoreCase)
+            then
+                match this.Password with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "password")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Password <- value |> (fun x -> x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else
+                Error None
+
+        member this.ProcessKeyValue
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            match this.ProcessKeyValueSelf_ argNum_ errors_ key value with
+            | Ok () -> Ok ()
+            | Error None -> Error None
+            | Error (Some errorFromLeaf) -> Error (Some errorFromLeaf)
+
+        /// Returns false if we didn't set a value.
+        member this.SetFlagValue_ (errors_ : ResizeArray<string>) (key : string) : bool = false
+        /// Compute help text for this parser, optionally noting the given prefix on each argument and indenting each line by this many spaces.
+        static member HelpText_ (prefix : string option) (indent : int) : string = failwith "TODO"
+
+    /// A partially-parsed TokenAuth.
+    type internal TokenAuth_InProgress =
+        {
+            mutable Token : string option
+        }
+
+        /// Freeze this in-progress type. On success, returns the frozen type and the arg (if any) which consumed the input positional args.
+        member this.Assemble_
+            (getEnvironmentVariable : string -> string)
+            (positionals : Choice<string * int, string * int> list)
+            : Result<TokenAuth * string option, string list>
+            =
+            let errors = ResizeArray<string> ()
+            let positionalConsumers = ResizeArray<string> ()
+            let outOfPlacePositionals : ResizeArray<string> = ResizeArray ()
+
+            let arg0 : string =
+                match this.Token with
+                | Some result -> result
+                | None ->
+                    errors.Add (sprintf "Required argument '--%s' received no value" "token")
+                    Unchecked.defaultof<_>
+
+            if positionalConsumers.Count <= 1 then
+                if outOfPlacePositionals.Count > 0 then
+                    outOfPlacePositionals
+                    |> String.concat " "
+                    |> (fun x ->
+                        if 0 = outOfPlacePositionals.Count then
+                            "Unmatched args which look like they are meant to be flags. " + x
+                        else
+                            sprintf
+                                "Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `%s=` syntax, or place them after a trailing `--`. %s"
+                                positionalConsumers.[0]
+                                x
+                    )
+                    |> errors.Add
+                else
+                    ()
+
+                if errors.Count = 0 then
+                    Ok (
+                        {
+                            Token = arg0
+                        },
+                        Seq.tryExactlyOne positionalConsumers
+                    )
+                else
+                    errors |> Seq.toList |> Error
+            else
+                ("Multiple parsers consumed positional args; this is an error in the application, not an error by the user: "
+                 + String.concat ", " positionalConsumers)
+                |> List.singleton
+                |> Error
+
+        static member _Empty () : TokenAuth_InProgress =
+            {
+                Token = None
+            }
+
+        /// Processes the key-value pair, returning Error if no key was matched.
+        /// If the key is an arg which can have arity 1, but throws when consuming that arg, we return Error(<the message>).
+        /// This can nevertheless be a successful parse, e.g. when the key may have arity 0.
+        member this.ProcessKeyValueSelf_
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            if System.String.Equals (key, sprintf "--%s" "token", System.StringComparison.OrdinalIgnoreCase) then
+                match this.Token with
+                | Some x ->
+                    sprintf
+                        "Argument '%s' was supplied multiple times: %s and %s"
+                        (sprintf "--%s" "token")
+                        (x.ToString ())
+                        (value.ToString ())
+                    |> errors_.Add
+
+                    Ok ()
+                | None ->
+                    try
+                        this.Token <- value |> (fun x -> x) |> Some
+                        Ok ()
+                    with _ as exc ->
+                        exc.Message |> Some |> Error
+            else
+                Error None
+
+        member this.ProcessKeyValue
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            match this.ProcessKeyValueSelf_ argNum_ errors_ key value with
+            | Ok () -> Ok ()
+            | Error None -> Error None
+            | Error (Some errorFromLeaf) -> Error (Some errorFromLeaf)
+
+        /// Returns false if we didn't set a value.
+        member this.SetFlagValue_ (errors_ : ResizeArray<string>) (key : string) : bool = false
+        /// Compute help text for this parser, optionally noting the given prefix on each argument and indenting each line by this many spaces.
+        static member HelpText_ (prefix : string option) (indent : int) : string = failwith "TODO"
+
+    /// A partially-parsed AuthOptions.
+    type internal AuthOptions_InProgress =
+        {
+            Token : TokenAuth_InProgress
+            UsernamePassword : UsernamePasswordAuth_InProgress
+        }
+
+        /// Freeze this in-progress type. On success, returns the frozen type and the arg (if any) which consumed the input positional args.
+        member this.Assemble_
+            (getEnvironmentVariable : string -> string)
+            (positionals : Choice<string * int, string * int> list)
+            : Result<AuthOptions * string option, string list>
+            =
+            failwith "TODO"
+
+        static member _Empty () : AuthOptions_InProgress =
+            {
+                Token = TokenAuth_InProgress._Empty ()
+                UsernamePassword = UsernamePasswordAuth_InProgress._Empty ()
+            }
+
+        /// Compute help text for this parser, optionally noting the given prefix on each argument and indenting each line by this many spaces.
+        static member HelpText_ (prefix : string option) (indent : int) : string = failwith "TODO"
+
+    /// A partially-parsed DoTheThing.
+    type internal DoTheThing_InProgress =
+        {
+            mutable Auth : AuthOptions_InProgress
+            mutable Basics : BasicNoPositionals_InProgress
+        }
+
+        /// Freeze this in-progress type. On success, returns the frozen type and the arg (if any) which consumed the input positional args.
+        member this.Assemble_
+            (getEnvironmentVariable : string -> string)
+            (positionals : Choice<string * int, string * int> list)
+            : Result<DoTheThing * string option, string list>
+            =
+            let errors = ResizeArray<string> ()
+            let positionalConsumers = ResizeArray<string> ()
+            let outOfPlacePositionals : ResizeArray<string> = ResizeArray ()
+
+            let arg0 : BasicNoPositionals =
+                match this.Basics.Assemble_ getEnvironmentVariable positionals with
+                | Ok (result, consumedPositional) ->
+                    match consumedPositional with
+                    | None -> ()
+                    | Some positionalConsumer -> positionalConsumers.Add positionalConsumer
+
+                    result
+                | Error err ->
+                    errors.AddRange err
+                    Unchecked.defaultof<_>
+
+            let arg1 : AuthOptions =
+                match this.Auth.Assemble_ getEnvironmentVariable positionals with
+                | Ok (result, consumedPositional) ->
+                    match consumedPositional with
+                    | None -> ()
+                    | Some positionalConsumer -> positionalConsumers.Add positionalConsumer
+
+                    result
+                | Error err ->
+                    errors.AddRange err
+                    Unchecked.defaultof<_>
+
+            if positionalConsumers.Count <= 1 then
+                if outOfPlacePositionals.Count > 0 then
+                    outOfPlacePositionals
+                    |> String.concat " "
+                    |> (fun x ->
+                        if 0 = outOfPlacePositionals.Count then
+                            "Unmatched args which look like they are meant to be flags. " + x
+                        else
+                            sprintf
+                                "Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `%s=` syntax, or place them after a trailing `--`. %s"
+                                positionalConsumers.[0]
+                                x
+                    )
+                    |> errors.Add
+                else
+                    ()
+
+                if errors.Count = 0 then
+                    Ok (
+                        {
+                            Basics = arg0
+                            Auth = arg1
+                        },
+                        Seq.tryExactlyOne positionalConsumers
+                    )
+                else
+                    errors |> Seq.toList |> Error
+            else
+                ("Multiple parsers consumed positional args; this is an error in the application, not an error by the user: "
+                 + String.concat ", " positionalConsumers)
+                |> List.singleton
+                |> Error
+
+        static member _Empty () : DoTheThing_InProgress =
+            {
+                Basics = BasicNoPositionals_InProgress._Empty ()
+                Auth = AuthOptions_InProgress._Empty ()
+            }
+
+        /// Passes the key-value pair to any child records, returning Error if no key was matched.
+        /// If the key is an arg which can have arity 1, but throws when consuming that arg, we return Error(<the message>).
+        /// This can nevertheless be a successful parse, e.g. when the key may have arity 0.
+        member this.ProcessKeyValueRecord_
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            let errors : ResizeArray<string> = ResizeArray ()
+
+            match this.Basics.ProcessKeyValue argNum_ errors_ key value with
+            | Ok () -> Ok ()
+            | Error e -> Error None
+
+        member this.ProcessKeyValue
+            (argNum_ : int)
+            (errors_ : ResizeArray<string>)
+            (key : string)
+            (value : string)
+            : Result<unit, string option>
+            =
+            match this.ProcessKeyValueRecord_ argNum_ errors_ key value with
+            | Ok () -> Ok ()
+            | Error errorFromRecord -> Error errorFromRecord
+
+        /// Returns false if we didn't set a value.
+        member this.SetFlagValue_ (errors_ : ResizeArray<string>) (key : string) : bool = false
+        /// Compute help text for this parser, optionally noting the given prefix on each argument and indenting each line by this many spaces.
+        static member HelpText_ (prefix : string option) (indent : int) : string = failwith "TODO"
+namespace ConsumePlugin.ArgsWithUnions
+
+open ArgParserHelpers
+open System
+open System.IO
+open WoofWare.Myriad.Plugins
+
+/// Methods to parse arguments for the type DoTheThing
+[<RequireQualifiedAccess ; CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
+module DoTheThing =
+    type internal ParseState_DoTheThing =
+        /// Ready to consume a key or positional arg
+        | AwaitingKey
+        /// Waiting to receive a value for the key we've already consumed
+        | AwaitingValue of key : string
+
+    let parse' (getEnvironmentVariable : string -> string) (args : string list) : DoTheThing =
+        let inProgress =
+            ArgParseHelpers_ConsumePlugin_ArgsWithUnions.DoTheThing_InProgress._Empty ()
+
+        let positionals : ResizeArray<Choice<string * int, string * int>> = ResizeArray ()
+        let errors_ = ResizeArray ()
+
+        let rec go (argNum_ : int) (state : ParseState_DoTheThing) (args : string list) =
+            match args with
+            | [] ->
+                match state with
+                | ParseState_DoTheThing.AwaitingKey -> ()
+                | ParseState_DoTheThing.AwaitingValue key ->
+                    if inProgress.SetFlagValue_ errors_ key then
+                        ()
+                    else
+                        sprintf
+                            "Trailing argument %s had no value. Use a double-dash to separate positional args from key-value args."
+                            key
+                        |> errors_.Add
+            | "--" :: rest -> positionals.AddRange (rest |> Seq.map (fun x -> (x, argNum_ + 1)) |> Seq.map Choice2Of2)
+            | arg :: args ->
+                match state with
+                | ParseState_DoTheThing.AwaitingKey ->
+                    if arg.StartsWith ("--", System.StringComparison.Ordinal) then
+                        if arg = "--help" then
+                            "TODO" |> failwithf "Help text requested.\n%s"
+                        else
+                            let equals = arg.IndexOf (char 61)
+
+                            if equals < 0 then
+                                go (argNum_ + 1) (ParseState_DoTheThing.AwaitingValue arg) args
+                            else
+                                let key = arg.[0 .. equals - 1]
+                                let value = arg.[equals + 1 ..]
+
+                                match inProgress.ProcessKeyValue argNum_ errors_ key value with
+                                | Ok () -> go (argNum_ + 1) ParseState_DoTheThing.AwaitingKey args
+                                | Error x ->
+                                    match x with
+                                    | None ->
+                                        positionals.Add (Choice1Of2 (arg, argNum_))
+                                        go (argNum_ + 1) ParseState_DoTheThing.AwaitingKey args
+                                    | Some msg ->
+                                        sprintf "%s (at arg %s)" msg arg |> errors_.Add
+                                        go (argNum_ + 1) ParseState_DoTheThing.AwaitingKey args
+                    else
+                        (arg, argNum_) |> Choice1Of2 |> positionals.Add
+                        go (argNum_ + 1) ParseState_DoTheThing.AwaitingKey args
+                | ParseState_DoTheThing.AwaitingValue key ->
+                    match inProgress.ProcessKeyValue argNum_ errors_ key arg with
+                    | Ok () -> go argNum_ ParseState_DoTheThing.AwaitingKey args
+                    | Error exc ->
+                        if inProgress.SetFlagValue_ errors_ key then
+                            go argNum_ ParseState_DoTheThing.AwaitingKey (arg :: args)
+                        else
+                            (key, argNum_) |> Choice1Of2 |> positionals.Add
+                            go (argNum_ + 1) ParseState_DoTheThing.AwaitingKey (arg :: args)
+
+        go 0 ParseState_DoTheThing.AwaitingKey args
+
+        if 0 = errors_.Count then
+            ()
+        else
+            errors_
+            |> String.concat System.Environment.NewLine
+            |> (fun x -> "Errors during parse!\n" + x)
+            |> failwith
+
+        match inProgress.Assemble_ getEnvironmentVariable (positionals |> Seq.toList) with
+        | Ok (result, posConsumer) ->
+            if positionals.Count > 0 && posConsumer.IsNone then
+                positionals
+                |> Seq.map (fun choiceValue ->
+                    match choiceValue with
+                    | Choice1Of2 (arg, _) -> arg
+                    | Choice2Of2 (arg, _) -> arg
+                )
+                |> String.concat " "
+                |> sprintf "Parse error: The following arguments were not consumed: %s"
+                |> failwith
+            else
+                result
+        | Error e ->
+            e
+            |> String.concat System.Environment.NewLine
+            |> (fun x -> "Errors during parse!\n" + x)
+            |> failwith
+
+    let parse (args : string list) : DoTheThing =
+        parse' System.Environment.GetEnvironmentVariable args

Directory.Build.props

@@ -10,7 +10,7 @@
     <WarnOn>FS3388,FS3559</WarnOn>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Nerdbank.GitVersioning" Version="3.7.115" PrivateAssets="all"/>
+    <PackageReference Include="Nerdbank.GitVersioning" Version="3.8.38-alpha" PrivateAssets="all"/>
     <SourceLinkGitHubHost Include="github.com" ContentUrl="https://raw.githubusercontent.com"/>
   </ItemGroup>
   <PropertyGroup Condition="'$(GITHUB_ACTION)' != ''">

Playground/Domain.fs

@@ -0,0 +1,47 @@
+namespace Playground
+
+open System
+open WoofWare.Myriad.Plugins
+
+[<ArgParser>]
+type SubMode1 =
+    {
+        Info1 : int
+        Info2 : string
+        Rest : string list
+    }
+
+[<ArgParser>]
+type SubMode2 =
+    {
+        Info1 : int
+        Info2 : string
+        Rest : int list
+    }
+
+[<ArgParser>]
+type Mode1 =
+    {
+        Things : SubMode1
+        Whatnot : int
+    }
+
+[<ArgParser>]
+type Mode2 =
+    {
+        Things : SubMode2
+        Whatnot : DateTime
+    }
+
+[<ArgParser>]
+type Modes =
+    | Mode1 of Mode1
+    | Mode2 of Mode2
+
+[<ArgParser>]
+type Args =
+    {
+        WhatToDo : Modes
+        [<PositionalArgs>]
+        OtherArgs : string list
+    }

Playground/Library.fs

@@ -0,0 +1,563 @@
+//------------------------------------------------------------------------------
+//        This code was generated by myriad.
+//        Changes to this file will be lost when the code is regenerated.
+//------------------------------------------------------------------------------
+
+namespace Playground // Assuming a namespace
+
+open System
+open System.IO
+open WoofWare.Myriad.Plugins // Assuming attributes are here
+
+// Assume original type definitions are accessible here
+// [<ArgParser>] type SubMode1 = { Info1 : int; Info2 : string; Rest : string list }
+// [<ArgParser>] type SubMode2 = { Info1 : int; Info2 : string; Rest : int list }
+// [<ArgParser>] type Mode1 = { Things : SubMode1; Whatnot : int }
+// [<ArgParser>] type Mode2 = { Things : SubMode2; Whatnot : DateTime }
+// [<ArgParser>] type Modes = | Mode1 of Mode1 | Mode2 of Mode2
+// [<ArgParser>] type Args = { WhatToDo : Modes; [<PositionalArgs>] OtherArgs : string list }
+
+
+/// Methods to parse arguments for the type Args
+[<RequireQualifiedAccess ; CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
+module Args =
+
+    //--------------------------------------------------------------------------
+    // Internal state definitions (Non-Flattened with combined Assemble/Validate)
+    //--------------------------------------------------------------------------
+
+    /// State representing the parse progress for SubMode1 record
+    type private State_SubMode1 =
+        {
+            mutable Info1 : int option
+            mutable Info2 : string option
+            Rest : ResizeArray<string> // Corresponds to --rest
+        }
+
+        static member Create () =
+            {
+                Info1 = None
+                Info2 = None
+                Rest = ResizeArray ()
+            }
+
+        /// Check completeness and assemble the SubMode1 record from state.
+        member this.Assemble () : Result<SubMode1, string list> =
+            let errors = ResizeArray<string> ()
+            let mutable complete = true
+
+            if this.Info1.IsNone then
+                complete <- false
+                errors.Add ("Argument '--info1' is required.")
+
+            if this.Info2.IsNone then
+                complete <- false
+                errors.Add ("Argument '--info2' is required.")
+            // Rest is list, always 'complete'
+
+            if complete then
+                Ok
+                    {
+                        Info1 = this.Info1.Value
+                        Info2 = this.Info2.Value
+                        Rest = this.Rest |> Seq.toList
+                    }
+            else
+                Error (errors |> Seq.toList)
+
+    /// State representing the parse progress for SubMode2 record
+    type private State_SubMode2 =
+        {
+            mutable Info1 : int option
+            mutable Info2 : string option
+            Rest : ResizeArray<int> // Corresponds to --rest
+        }
+
+        static member Create () =
+            {
+                Info1 = None
+                Info2 = None
+                Rest = ResizeArray ()
+            }
+
+        /// Check completeness and assemble the SubMode2 record from state.
+        member this.Assemble () : Result<SubMode2, string list> =
+            let errors = ResizeArray<string> ()
+
+            if this.Info1.IsNone then
+                errors.Add ("Argument '--info1' is required.")
+
+            if this.Info2.IsNone then
+                errors.Add ("Argument '--info2' is required.")
+            // Rest is list, always 'complete'
+
+            if errors.Count = 0 then
+                Ok
+                    {
+                        Info1 = this.Info1.Value
+                        Info2 = this.Info2.Value
+                        Rest = this.Rest |> Seq.toList
+                    }
+            else
+                Error (errors |> Seq.toList)
+
+
+    /// State representing the parse progress for Mode1 record (references SubMode1 state)
+    type private State_Mode1 =
+        {
+            ThingsState : State_SubMode1 // Holds state for the nested record
+            mutable Whatnot : int option
+        }
+
+        static member Create () =
+            {
+                ThingsState = State_SubMode1.Create ()
+                Whatnot = None
+            }
+
+        /// Check completeness and assemble the Mode1 record from state (including nested).
+        member this.Assemble () : Result<Mode1, string list> =
+            let errors = ResizeArray<string> ()
+
+            // Check direct fields
+            if this.Whatnot.IsNone then
+                errors.Add ("Argument '--whatnot' is required for Mode1.")
+
+            // Assemble nested state (which includes its own validation)
+            let thingsResult = this.ThingsState.Assemble ()
+            let mutable thingsValue = None
+
+            match thingsResult with
+            | Ok v -> thingsValue <- Some v
+            | Error nestedErrors -> errors.AddRange (nestedErrors |> List.map (sprintf "Things: %s")) // Add context
+
+            if errors.Count = 0 then
+                Ok
+                    {
+                        Things = thingsValue.Value
+                        Whatnot = this.Whatnot.Value
+                    }
+            else
+                Error (errors |> Seq.toList)
+
+
+    /// State representing the parse progress for Mode2 record (references SubMode2 state)
+    type private State_Mode2 =
+        {
+            ThingsState : State_SubMode2 // Holds state for the nested record
+            mutable Whatnot : DateTime option
+        }
+
+        static member Create () =
+            {
+                ThingsState = State_SubMode2.Create ()
+                Whatnot = None
+            }
+
+        /// Check completeness and assemble the Mode2 record from state (including nested).
+        member this.Assemble () : Result<Mode2, string list> =
+            let errors = ResizeArray<string> ()
+
+            // Check direct fields
+            if this.Whatnot.IsNone then
+                errors.Add ("Argument '--whatnot' is required for Mode2.")
+
+            // Assemble nested state (which includes its own validation)
+            let thingsResult = this.ThingsState.Assemble ()
+            let mutable thingsValue = Unchecked.defaultof<_>
+
+            match thingsResult with
+            | Ok v -> thingsValue <- v
+            | Error nestedErrors -> errors.AddRange (nestedErrors |> List.map (sprintf "Things: %s")) // Add context
+
+            if errors.Count = 0 then
+                {
+                    Things = thingsValue
+                    Whatnot = this.Whatnot.Value
+                }
+                |> Ok
+            else
+                Error (errors |> Seq.toList)
+
+
+    /// State for a single candidate parse path for the Modes DU (Structure unchanged)
+    type private CandidateParseState_Modes =
+        {
+            CaseName : string // "Mode1" or "Mode2"
+            mutable IsViable : bool
+            Errors : ResizeArray<string> // Errors specific to this candidate's path
+            ConsumedArgIndices : System.Collections.Generic.HashSet<int> // Indices consumed *by this candidate*
+            CaseState : obj // Holds either State_Mode1 or State_Mode2
+        }
+
+        static member CreateMode1 () =
+            {
+                CaseName = "Mode1"
+                IsViable = true
+                Errors = ResizeArray ()
+                ConsumedArgIndices = System.Collections.Generic.HashSet ()
+                CaseState = State_Mode1.Create () :> obj
+            }
+
+        static member CreateMode2 () =
+            {
+                CaseName = "Mode2"
+                IsViable = true
+                Errors = ResizeArray ()
+                ConsumedArgIndices = System.Collections.Generic.HashSet ()
+                CaseState = State_Mode2.Create () :> obj
+            }
+
+    //--------------------------------------------------------------------------
+    // Main Parser Logic
+    //--------------------------------------------------------------------------
+
+    type private ParseState_Args =
+        | AwaitingArg
+        | AwaitingValue of keyIndex : int * key : string
+
+    let parse' (getEnvironmentVariable : string -> string) (args : string list) : Args =
+        let ArgParser_errors = ResizeArray () // Global errors accumulator
+
+        let helpText () =
+            // Help text generation unchanged
+            [
+                (sprintf "%s  int32%s%s" (sprintf "--%s" "info1") "" " (for Mode1/Mode2 Things)")
+                (sprintf "%s  string%s%s" (sprintf "--%s" "info2") "" " (for Mode1/Mode2 Things)")
+                (sprintf "%s  string%s%s" (sprintf "--%s" "rest") " (can be repeated)" " (for Mode1 Things)")
+                (sprintf "%s  int32%s%s" (sprintf "--%s" "rest") " (can be repeated)" " (for Mode2 Things)")
+                (sprintf "%s  int32%s%s" (sprintf "--%s" "whatnot") "" " (for Mode1)")
+                (sprintf "%s  DateTime%s%s" (sprintf "--%s" "whatnot") "" " (for Mode2)")
+                (sprintf "%s  string%s%s" (sprintf "--%s" "other-args") " (positional args) (can be repeated)" "")
+            ]
+            |> String.concat "\n"
+
+        let arg_OtherArgs : string ResizeArray = ResizeArray ()
+
+        let mutable candidates_WhatToDo : CandidateParseState_Modes list =
+            [
+                CandidateParseState_Modes.CreateMode1 ()
+                CandidateParseState_Modes.CreateMode2 ()
+            ]
+
+        let consumedArgIndices_WhatToDo = System.Collections.Generic.HashSet<int> ()
+
+        //----------------------------------------------------------------------
+        // Helper functions for applying args (applyKeyValueToSubModeXState unchanged)
+        //----------------------------------------------------------------------
+        let applyKeyValueToSubMode1State
+            (argIndex : int)
+            (keyIndex : int)
+            (key : string)
+            (value : string)
+            (subState : State_SubMode1)
+            (candidate : CandidateParseState_Modes)
+            : unit
+            =
+            // ... (Implementation identical to previous version) ...
+            if String.Equals (key, "--info1", StringComparison.OrdinalIgnoreCase) then
+                match subState.Info1 with
+                | Some _ ->
+                    candidate.Errors.Add (sprintf "Argument '--info1' supplied multiple times (SubMode1)")
+                    candidate.IsViable <- false
+                | None ->
+                    try
+                        subState.Info1 <- Some (Int32.Parse value)
+                        candidate.ConsumedArgIndices.Add argIndex |> ignore
+                        candidate.ConsumedArgIndices.Add keyIndex |> ignore
+                    with ex ->
+                        candidate.Errors.Add (
+                            sprintf "Failed to parse '%s' for --info1 (SubMode1): %s" value ex.Message
+                        )
+
+                        candidate.IsViable <- false
+            elif String.Equals (key, "--info2", StringComparison.OrdinalIgnoreCase) then
+                match subState.Info2 with
+                | Some _ ->
+                    candidate.Errors.Add (sprintf "Argument '--info2' supplied multiple times (SubMode1)")
+                    candidate.IsViable <- false
+                | None ->
+                    subState.Info2 <- Some value
+                    candidate.ConsumedArgIndices.Add argIndex |> ignore
+                    candidate.ConsumedArgIndices.Add keyIndex |> ignore
+            elif String.Equals (key, "--rest", StringComparison.OrdinalIgnoreCase) then
+                subState.Rest.Add value
+                candidate.ConsumedArgIndices.Add argIndex |> ignore
+                candidate.ConsumedArgIndices.Add keyIndex |> ignore
+            else
+                ()
+
+        let applyKeyValueToSubMode2State
+            (argIndex : int)
+            (keyIndex : int)
+            (key : string)
+            (value : string)
+            (subState : State_SubMode2)
+            (candidate : CandidateParseState_Modes)
+            : unit
+            =
+            // ... (Implementation identical to previous version) ...
+            if String.Equals (key, "--info1", StringComparison.OrdinalIgnoreCase) then
+                match subState.Info1 with
+                | Some _ ->
+                    candidate.Errors.Add (sprintf "Argument '--info1' supplied multiple times (SubMode2)")
+                    candidate.IsViable <- false
+                | None ->
+                    try
+                        subState.Info1 <- Some (Int32.Parse value)
+                        candidate.ConsumedArgIndices.Add argIndex |> ignore
+                        candidate.ConsumedArgIndices.Add keyIndex |> ignore
+                    with ex ->
+                        candidate.Errors.Add (
+                            sprintf "Failed to parse '%s' for --info1 (SubMode2): %s" value ex.Message
+                        )
+
+                        candidate.IsViable <- false
+            elif String.Equals (key, "--info2", StringComparison.OrdinalIgnoreCase) then
+                match subState.Info2 with
+                | Some _ ->
+                    candidate.Errors.Add (sprintf "Argument '--info2' supplied multiple times (SubMode2)")
+                    candidate.IsViable <- false
+                | None ->
+                    subState.Info2 <- Some value
+                    candidate.ConsumedArgIndices.Add argIndex |> ignore
+                    candidate.ConsumedArgIndices.Add keyIndex |> ignore
+            elif String.Equals (key, "--rest", StringComparison.OrdinalIgnoreCase) then
+                try
+                    subState.Rest.Add (Int32.Parse value)
+                    candidate.ConsumedArgIndices.Add argIndex |> ignore
+                    candidate.ConsumedArgIndices.Add keyIndex |> ignore
+                with ex ->
+                    candidate.Errors.Add (
+                        sprintf "Failed to parse '%s' as int32 for --rest (SubMode2): %s" value ex.Message
+                    )
+
+                    candidate.IsViable <- false
+            else
+                ()
+
+        //----------------------------------------------------------------------
+        // Routing and Main Application Logic (applyKeyValueToCandidate unchanged)
+        //----------------------------------------------------------------------
+        let applyKeyValueToCandidate
+            (argIndex : int, keyIndex : int, key : string, value : string)
+            (candidate : CandidateParseState_Modes)
+            : unit
+            =
+            // ... (Implementation identical to previous version, calling sub-state helpers) ...
+            if not candidate.IsViable then
+                ()
+            else
+
+            match candidate.CaseName with
+            | "Mode1" ->
+                let state = candidate.CaseState :?> State_Mode1
+
+                if String.Equals (key, "--whatnot", StringComparison.OrdinalIgnoreCase) then
+                    match state.Whatnot with
+                    | Some _ ->
+                        candidate.Errors.Add (
+                            sprintf "Argument '--whatnot' supplied multiple times for Mode1 candidate"
+                        )
+
+                        candidate.IsViable <- false
+                    | None ->
+                        try
+                            state.Whatnot <- Some (Int32.Parse value)
+                            candidate.ConsumedArgIndices.Add argIndex |> ignore
+                            candidate.ConsumedArgIndices.Add keyIndex |> ignore
+                        with ex ->
+                            candidate.Errors.Add (
+                                sprintf "Failed to parse '%s' as int32 for --whatnot (Mode1): %s" value ex.Message
+                            )
+
+                            candidate.IsViable <- false
+                elif key = "--info1" || key = "--info2" || key = "--rest" then
+                    applyKeyValueToSubMode1State argIndex keyIndex key value state.ThingsState candidate
+                else
+                    ()
+            | "Mode2" ->
+                let state = candidate.CaseState :?> State_Mode2
+
+                if String.Equals (key, "--whatnot", StringComparison.OrdinalIgnoreCase) then
+                    match state.Whatnot with
+                    | Some _ ->
+                        candidate.Errors.Add (
+                            sprintf "Argument '--whatnot' supplied multiple times for Mode2 candidate"
+                        )
+
+                        candidate.IsViable <- false
+                    | None ->
+                        try
+                            state.Whatnot <- Some (DateTime.Parse value)
+                            candidate.ConsumedArgIndices.Add argIndex |> ignore
+                            candidate.ConsumedArgIndices.Add keyIndex |> ignore
+                        with ex ->
+                            candidate.Errors.Add (
+                                sprintf "Failed to parse '%s' as DateTime for --whatnot (Mode2): %s" value ex.Message
+                            )
+
+                            candidate.IsViable <- false
+                elif key = "--info1" || key = "--info2" || key = "--rest" then
+                    applyKeyValueToSubMode2State argIndex keyIndex key value state.ThingsState candidate
+                else
+                    ()
+            | _ -> failwith "Internal error: Unknown case name"
+
+        // processKeyValue, setFlagValue, and main loop `go` are identical to previous version
+        let processKeyValue (keyIndex : int, key : string, valueIndex : int, value : string) : bool =
+            let mutable handled = false
+
+            for candidate in candidates_WhatToDo do
+                let initialConsumedCount = candidate.ConsumedArgIndices.Count
+
+                if candidate.IsViable then
+                    applyKeyValueToCandidate (valueIndex, keyIndex, key, value) candidate
+
+                if candidate.IsViable && candidate.ConsumedArgIndices.Count > initialConsumedCount then
+                    handled <- true
+                    consumedArgIndices_WhatToDo.Add keyIndex |> ignore
+                    consumedArgIndices_WhatToDo.Add valueIndex |> ignore
+
+            handled
+
+        let setFlagValue (keyIndex : int) (key : string) : bool = false // No flags
+
+        let rec go (state : ParseState_Args) (args : (int * string) list) =
+            // ... (Implementation identical to previous version) ...
+            match args with
+            | [] ->
+                match state with
+                | ParseState_Args.AwaitingArg -> ()
+                | ParseState_Args.AwaitingValue (i, k) ->
+                    if not (setFlagValue i k) then
+                        ArgParser_errors.Add (sprintf "Trailing argument '%s' (at index %d) requires a value." k i)
+            | (idx, arg) :: rest ->
+                match state with
+                | ParseState_Args.AwaitingArg ->
+                    if arg = "--" then
+                        rest
+                        |> List.iter (fun (i, v) ->
+                            if not (consumedArgIndices_WhatToDo.Contains i) then
+                                arg_OtherArgs.Add v
+                        )
+
+                        go ParseState_Args.AwaitingArg []
+                    elif arg.StartsWith ("--") then
+                        if arg = "--help" then
+                            helpText () |> failwithf "Help text requested:\n%s"
+                        else
+                            let eq = arg.IndexOf ('=')
+
+                            if eq > 0 then
+                                let k = arg.[.. eq - 1]
+                                let v = arg.[eq + 1 ..]
+
+                                if not (processKeyValue (idx, k, idx, v)) then
+                                    if not (consumedArgIndices_WhatToDo.Contains idx) then
+                                        arg_OtherArgs.Add arg
+
+                                go ParseState_Args.AwaitingArg rest
+                            elif setFlagValue idx arg then
+                                consumedArgIndices_WhatToDo.Add idx |> ignore
+                                go ParseState_Args.AwaitingArg rest
+                            else
+                                go (ParseState_Args.AwaitingValue (idx, arg)) rest
+                    else
+                        if not (consumedArgIndices_WhatToDo.Contains idx) then
+                            arg_OtherArgs.Add arg
+
+                        go ParseState_Args.AwaitingArg rest
+                | ParseState_Args.AwaitingValue (keyIdx, key) ->
+                    if processKeyValue (keyIdx, key, idx, arg) then
+                        go ParseState_Args.AwaitingArg rest
+                    elif setFlagValue keyIdx key then
+                        consumedArgIndices_WhatToDo.Add keyIdx |> ignore<bool>
+                        go ParseState_Args.AwaitingArg ((idx, arg) :: rest) // Reprocess arg
+                    elif not (consumedArgIndices_WhatToDo.Contains keyIdx) then
+                        arg_OtherArgs.Add key
+
+                        if not (consumedArgIndices_WhatToDo.Contains idx) then
+                            arg_OtherArgs.Add arg
+
+                        go ParseState_Args.AwaitingArg rest
+
+        args |> List.mapi (fun i s -> (i, s)) |> go ParseState_Args.AwaitingArg
+
+        //----------------------------------------------------------------------
+        // Final Validation and Assembly (Uses new Assemble methods)
+        //----------------------------------------------------------------------
+        let viableWinners = candidates_WhatToDo |> List.filter (fun c -> c.IsViable)
+        // No longer filter based on IsComplete here; Assemble handles it.
+        // Still need to check for relative leftovers if that logic were implemented.
+
+        let whatToDoResult =
+            match viableWinners with
+            | [] ->
+                // Add specific errors from candidates that were viable *before* Assemble check
+                ArgParser_errors.Add ("No valid parse found for 'WhatToDo'.")
+
+                candidates_WhatToDo
+                |> List.iter (fun c ->
+                    if c.Errors.Count <> 0 then
+                        ArgParser_errors.Add (
+                            sprintf "  Candidate %s parse errors: %s" c.CaseName (String.concat "; " c.Errors)
+                        )
+                // Potentially try to Assemble even non-viable ones to get completion errors? Maybe too complex.
+                )
+
+                Unchecked.defaultof<_> // Error path
+
+            | [ winner ] ->
+                // Assemble the winning case, checking the Result for completion errors
+                match winner.CaseName with
+                | "Mode1" ->
+                    match (winner.CaseState :?> State_Mode1).Assemble () with
+                    | Ok mode1Value -> Modes.Mode1 mode1Value
+                    | Error completionErrors ->
+                        ArgParser_errors.Add (sprintf "Validation failed for selected candidate Mode1:")
+                        ArgParser_errors.AddRange completionErrors
+                        Unchecked.defaultof<_> // Error path
+                | "Mode2" ->
+                    match (winner.CaseState :?> State_Mode2).Assemble () with
+                    | Ok mode2Value -> Modes.Mode2 mode2Value
+                    | Error completionErrors ->
+                        ArgParser_errors.Add (sprintf "Validation failed for selected candidate Mode2:")
+                        ArgParser_errors.AddRange completionErrors
+                        Unchecked.defaultof<_> // Error path
+                | _ -> failwith "Internal error: Unknown winning case name"
+
+            | winners -> // Ambiguous parse
+                ArgParser_errors.Add ("Ambiguous parse for 'WhatToDo'. Multiple modes potentially viable:")
+
+                winners
+                |> List.iter (fun c ->
+                    ArgParser_errors.Add (
+                        sprintf
+                            "  - %s (Initial Errors: %s)"
+                            c.CaseName
+                            (if c.Errors.Count = 0 then
+                                 "None"
+                             else
+                                 String.concat "; " c.Errors)
+                    )
+                )
+
+                Unchecked.defaultof<_> // Error path
+
+        // Finalize OtherArgs (unchanged)
+        let otherArgsResult = arg_OtherArgs |> Seq.toList
+
+        // Assemble Final Result or Fail (unchanged)
+        if ArgParser_errors.Count > 0 then
+            ArgParser_errors
+            |> String.concat "\n"
+            |> failwithf "Errors during parse!\n%s\n\nHelp Text:\n%s" (helpText ())
+        else
+            {
+                WhatToDo = whatToDoResult
+                OtherArgs = otherArgsResult
+            }
+
+    let parse (args : string list) : Args =
+        parse' System.Environment.GetEnvironmentVariable args

Playground/Playground.fsproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net9.0</TargetFramework>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+      <OutputType>Exe</OutputType>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <Compile Include="Domain.fs" />
+        <Compile Include="Library.fs"/>
+        <Compile Include="Program.fs" />
+    </ItemGroup>
+
+    <ItemGroup>
+      <ProjectReference Include="..\WoofWare.Myriad.Plugins.Attributes\WoofWare.Myriad.Plugins.Attributes.fsproj" />
+    </ItemGroup>
+
+</Project>

Playground/Program.fs

@@ -0,0 +1,10 @@
+namespace Playground
+
+module Program =
+    [<EntryPoint>]
+    let main argv =
+        [ "--whatnot=2024-01-12" ; "--info1=4" ; "--info2=hi" ]
+        |> Args.parse
+        |> printfn "%O"
+
+        0

WoofWare.Myriad.Plugins.Attributes/ArgParserAttributes.fs

@@ -26,6 +26,11 @@ type ArgParserAttribute (isExtensionMethod : bool) =
 /// an argument which looks like a flag but which we don't recognise.)
 /// We will still interpret `--help` as requesting help, unless it comes after
 /// a standalone `--` separator.
+///
+/// If the type of the PositionalArgs field is `Choice<'a, 'a>`, then we will
+/// tell you whether each arg came before or after a standalone `--` separator.
+/// For example, `MyApp foo bar -- baz` with PositionalArgs of `Choice<string, string>`
+/// would yield `Choice1Of2 foo, Choice1Of2 bar, Choice2Of2 baz`.
 type PositionalArgsAttribute (includeFlagLike : bool) =
     inherit Attribute ()
 

WoofWare.Myriad.Plugins.Attributes/Test/WoofWare.Myriad.Plugins.Attributes.Test.fsproj

@@ -17,10 +17,10 @@
     </ItemGroup>
 
     <ItemGroup>
-        <PackageReference Include="ApiSurface" Version="4.1.16" />
+        <PackageReference Include="ApiSurface" Version="4.1.20" />
-        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0"/>
         <PackageReference Include="NUnit" Version="4.3.2"/>
-        <PackageReference Include="NUnit3TestAdapter" Version="4.6.0"/>
+        <PackageReference Include="NUnit3TestAdapter" Version="5.0.0"/>
     </ItemGroup>
 
     <ItemGroup>

WoofWare.Myriad.Plugins.Test/TestArgParser/TestArgParser.fs

@@ -79,11 +79,8 @@ module TestArgParser =
 
         exc.Message
         |> shouldEqual
-            """Unable to process supplied arg --non-existent. Help text follows.
+            """Errors during parse!
---foo  int32 : This is a foo!
+Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `--rest=` syntax, or place them after a trailing `--`. --non-existent"""
---bar  string
---baz  bool
---rest  string (positional args) (can be repeated) : Here's where the rest of the args go"""
 
     [<Test>]
     let ``Can supply positional args with key`` () =
@@ -318,8 +315,7 @@ Required argument '--baz' received no value"""
         exc.Message
         |> shouldEqual
             """Errors during parse!
-Input string was not in a correct format. (at arg --invariant-exact=23:59)
+Input string was not in a correct format. (at arg --invariant-exact=23:59)"""
-Required argument '--invariant-exact' received no value"""
 
         let exc =
             Assert.Throws<exn> (fun () ->
@@ -337,8 +333,7 @@ Required argument '--invariant-exact' received no value"""
         exc.Message
         |> shouldEqual
             """Errors during parse!
-Input string was not in a correct format. (at arg --exact=11:34)
+Input string was not in a correct format. (at arg --exact=11:34)"""
-Required argument '--exact' received no value"""
 
         count.Value |> shouldEqual 0
 
@@ -444,7 +439,7 @@ Required argument '--exact' received no value"""
         ]
         |> List.map TestCaseData
 
-    [<TestCaseSource(nameof (boolCases))>]
+    [<TestCaseSource(nameof boolCases)>]
     let ``Bool env vars can be populated`` (envValue : string, boolValue : bool) =
         let getEnvVar (s : string) =
             s |> shouldEqual "CONSUMEPLUGIN_THINGS"
@@ -604,7 +599,10 @@ Required argument '--exact' received no value"""
             )
 
         exc.Message
-        |> shouldEqual """Unable to process argument --do-the-thing=foo as key --do-the-thing and value foo"""
+        |> shouldEqual
+            """Errors during parse!
+Required argument '--do-something-else' received no value
+Required argument '--turn-it-on' received no value"""
 
     [<Test>]
     let ``Long-form args help text`` () =
@@ -692,7 +690,9 @@ Required argument '--exact' received no value"""
             )
 
         exc.Message
-        |> shouldEqual """Unable to process argument --b=false as key --b and value false"""
+        |> shouldEqual
+            """Errors during parse!
+Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `--dont-grab-everything=` syntax, or place them after a trailing `--`. --b=false --c"""
 
         let exc =
             Assert.Throws<exn> (fun () ->
@@ -703,4 +703,6 @@ Required argument '--exact' received no value"""
         // Again perhaps eccentric!
         // Again, we don't try to detect that the user has missed out the desired argument to `--a`.
         exc.Message
-        |> shouldEqual """Unable to process argument --c=hi as key --c and value hi"""
+        |> shouldEqual
+            """Errors during parse!
+Unmatched args which look like they are meant to be flags. If you intended them as positional args, explicitly pass them with the `--my-arg-name=` syntax, or place them after a trailing `--`. --c=hi"""

WoofWare.Myriad.Plugins.Test/TestArgParser/TestArgsWithUnions.fs

@@ -0,0 +1,21 @@
+namespace WoofWare.Myriad.Plugins.Test
+
+open FsUnitTyped
+open NUnit.Framework
+open ConsumePlugin.ArgsWithUnions
+
+[<TestFixture>]
+module TestArgsWithUnions =
+
+    let argsWithUnionsCases =
+        [
+            ["--token" ; "hello" ; "--foo" ; "3" ; "--bar=hi" ; "--baz"], { Auth = AuthOptions.Token { Token = "hello" } ; Basics = { Foo = 3 ; Bar = "hi" ; Baz = true ; Rest = [] } }
+        ]
+        |> List.map TestCaseData
+
+    [<TestCaseSource (nameof argsWithUnionsCases)>]
+    let ``foo`` (args : string list, expected : DoTheThing) : unit =
+        args
+        |> DoTheThing.parse' (fun _ -> failwith "didn't expect env var")
+        |> shouldEqual expected
+

WoofWare.Myriad.Plugins.Test/WoofWare.Myriad.Plugins.Test.fsproj

@@ -9,9 +9,11 @@
       I have not yet seen a single instance where I care about this warning
     -->
     <NoWarn>$(NoWarn),NU1903</NoWarn>
+    <TestingPlatformDotnetTestSupport>true</TestingPlatformDotnetTestSupport>
   </PropertyGroup>
 
   <ItemGroup>
+    <!--
     <Compile Include="HttpClient.fs"/>
     <Compile Include="PureGymDtos.fs"/>
     <Compile Include="TestJsonParse\TestJsonParse.fs" />
@@ -33,20 +35,24 @@
     <Compile Include="TestCataGenerator\TestGift.fs" />
     <Compile Include="TestCataGenerator\TestMyList.fs" />
     <Compile Include="TestCataGenerator\TestMyList2.fs" />
+    -->
     <Compile Include="TestArgParser\TestArgParser.fs" />
+    <Compile Include="TestArgParser\TestArgsWithUnions.fs" />
+    <!--
     <Compile Include="TestSwagger\TestSwaggerParse.fs" />
     <Compile Include="TestRemoveOptions.fs"/>
     <Compile Include="TestSurface.fs"/>
+    -->
     <None Include="../.github/workflows/dotnet.yaml" />
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="ApiSurface" Version="4.1.16"/>
+    <PackageReference Include="ApiSurface" Version="4.1.20"/>
-    <PackageReference Include="FsCheck" Version="3.1.0"/>
+    <PackageReference Include="FsCheck" Version="3.2.0"/>
-    <PackageReference Include="FsUnit" Version="6.0.1"/>
+    <PackageReference Include="FsUnit" Version="7.0.1"/>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0"/>
     <PackageReference Include="NUnit" Version="4.3.2"/>
-    <PackageReference Include="NUnit3TestAdapter" Version="4.6.0"/>
+    <PackageReference Include="NUnit3TestAdapter" Version="5.0.0"/>
   </ItemGroup>
 
   <ItemGroup>

WoofWare.Myriad.Plugins/ArgParserGenerator.fs

@@ -7,82 +7,6 @@ open Fantomas.FCS.Text.Range
 open TypeEquality
 open WoofWare.Whippet.Fantomas
 
-type internal ArgParserOutputSpec =
-    {
-        ExtensionMethods : bool
-    }
-
-type internal FlagDu =
-    {
-        Name : Ident
-        Case1Name : Ident
-        Case2Name : Ident
-        /// Hopefully this is simply the const bool True or False, but it might e.g. be a literal
-        Case1Arg : SynExpr
-        /// Hopefully this is simply the const bool True or False, but it might e.g. be a literal
-        Case2Arg : SynExpr
-    }
-
-    static member FromBoolean (flagDu : FlagDu) (value : SynExpr) =
-        SynExpr.ifThenElse
-            (SynExpr.equals value flagDu.Case1Arg)
-            (SynExpr.createLongIdent' [ flagDu.Name ; flagDu.Case2Name ])
-            (SynExpr.createLongIdent' [ flagDu.Name ; flagDu.Case1Name ])
-
-/// The default value of an argument which admits default values can be pulled from different sources.
-/// This defines which source a particular default value comes from.
-type private ArgumentDefaultSpec =
-    /// From parsing the environment variable with the given name (e.g. "WOOFWARE_DISABLE_FOO" or whatever).
-    | EnvironmentVariable of name : SynExpr
-    /// From calling the static member `{typeWeParseInto}.Default{name}()`
-    /// For example, if `type MyArgs = { Thing : Choice<int, int> }`, then
-    /// we would use `MyArgs.DefaultThing () : int`.
-    ///
-    | FunctionCall of name : Ident
-
-type private Accumulation<'choice> =
-    | Required
-    | Optional
-    | Choice of 'choice
-    | List of Accumulation<'choice>
-
-type private ParseFunction<'acc> =
-    {
-        FieldName : Ident
-        TargetVariable : Ident
-        /// Any of the forms in this set are acceptable, but make sure they all start with a dash, or we might
-        /// get confused with positional args or something! I haven't thought that hard about this.
-        /// In the default case, this is `Const("arg-name")` for the `ArgName : blah` field; note that we have
-        /// omitted the initial `--` that will be required at runtime.
-        ArgForm : SynExpr list
-        /// If this is a boolean-like field (e.g. a bool or a flag DU), the help text should look a bit different:
-        /// we should lie to the user about the value of the cases there.
-        /// Similarly, if we're reading from an environment variable with the laxer parsing rules of accepting e.g.
-        /// "0" instead of "false", we need to know if we're reading a bool.
-        /// In that case, `boolCases` is Some, and contains the construction of the flag (or boolean, in which case
-        /// you get no data).
-        BoolCases : Choice<FlagDu, unit> option
-        Help : SynExpr option
-        /// A function string -> %TargetType%, where TargetVariable is probably a `%TargetType% option`.
-        /// (Depending on `Accumulation`, we'll remove the `option` at the end of the parse, asserting that the
-        /// argument was supplied.)
-        /// This is allowed to throw if it fails to parse.
-        Parser : SynExpr
-        /// If `Accumulation` is `List`, then this is the type of the list *element*; analogously for optionals
-        /// and choices and so on.
-        TargetType : SynType
-        Accumulation : 'acc
-    }
-
-    /// A SynExpr of type `string` which we can display to the user at generated-program runtime to display all
-    /// the ways they can refer to this arg.
-    member arg.HumanReadableArgForm : SynExpr =
-        let formatString = List.replicate arg.ArgForm.Length "--%s" |> String.concat " / "
-
-        (SynExpr.applyFunction (SynExpr.createIdent "sprintf") (SynExpr.CreateConst formatString), arg.ArgForm)
-        ||> List.fold SynExpr.applyFunction
-        |> SynExpr.paren
-
 [<RequireQualifiedAccess>]
 type private ChoicePositional =
     | Normal of includeFlagLike : SynExpr option
@@ -114,14 +38,14 @@ type private ParseTree<'hasPositional> =
     /// `assemble` takes the SynExpr's (e.g. each record field contents) corresponding to each `Ident` in
     /// the branch (e.g. each record field name),
     /// and composes them into a `SynExpr` (e.g. the record-typed object).
-    | Branch of
+    | DescendRecord of
         fields : (Ident * ParseTree<HasNoPositional>) list *
         assemble : (Map<string, SynExpr> -> SynExpr) *
         Teq<'hasPositional, HasNoPositional>
     /// `assemble` takes the SynExpr's (e.g. each record field contents) corresponding to each `Ident` in
     /// the branch (e.g. each record field name),
     /// and composes them into a `SynExpr` (e.g. the record-typed object).
-    | BranchPos of
+    | DescendRecordPos of
         posField : Ident *
         fields : ParseTree<HasPositional> *
         (Ident * ParseTree<HasNoPositional>) list *
@@ -184,63 +108,6 @@ module private ParseTree =
 
         go None ([], None) subs
 
-    let rec accumulatorsNonPos (tree : ParseTree<HasNoPositional>) : ParseFunctionNonPositional list =
-        match tree with
-        | ParseTree.PositionalLeaf (_, teq) -> exFalso teq
-        | ParseTree.BranchPos (_, _, _, _, teq) -> exFalso teq
-        | ParseTree.NonPositionalLeaf (pf, _) -> [ pf ]
-        | ParseTree.Branch (trees, _, _) -> trees |> List.collect (snd >> accumulatorsNonPos)
-
-    /// Returns the positional arg separately.
-    let rec accumulatorsPos
-        (tree : ParseTree<HasPositional>)
-        : ParseFunctionNonPositional list * ParseFunctionPositional
-        =
-        match tree with
-        | ParseTree.PositionalLeaf (pf, _) -> [], pf
-        | ParseTree.NonPositionalLeaf (_, teq) -> exFalso' teq
-        | ParseTree.Branch (_, _, teq) -> exFalso' teq
-        | ParseTree.BranchPos (_, tree, trees, _, _) ->
-            let nonPos = trees |> List.collect (snd >> accumulatorsNonPos)
-
-            let nonPos2, pos = accumulatorsPos tree
-            nonPos @ nonPos2, pos
-
-    /// Collect all the ParseFunctions which are necessary to define variables, throwing away
-    /// all information relevant to composing the resulting variables into records.
-    /// Returns the list of non-positional parsers, and any positional parser that exists.
-    let accumulators<'a> (tree : ParseTree<'a>) : ParseFunctionNonPositional list * ParseFunctionPositional option =
-        // Sad duplication of some code here, but it was the easiest way to make it type-safe :(
-        match tree with
-        | ParseTree.PositionalLeaf (pf, _) -> [], Some pf
-        | ParseTree.NonPositionalLeaf (pf, _) -> [ pf ], None
-        | ParseTree.Branch (trees, _, _) -> trees |> List.collect (snd >> accumulatorsNonPos) |> (fun i -> i, None)
-        | ParseTree.BranchPos (_, tree, trees, _, _) ->
-            let nonPos = trees |> List.collect (snd >> accumulatorsNonPos)
-
-            let nonPos2, pos = accumulatorsPos tree
-            nonPos @ nonPos2, Some pos
-
-        |> fun (nonPos, pos) ->
-            let duplicateArgs =
-                // This is best-effort. We can't necessarily detect all SynExprs here, but usually it'll be strings.
-                Option.toList (pos |> Option.map _.ArgForm) @ (nonPos |> List.map _.ArgForm)
-                |> Seq.concat
-                |> Seq.choose (fun expr ->
-                    match expr |> SynExpr.stripOptionalParen with
-                    | SynExpr.Const (SynConst.String (s, _, _), _) -> Some s
-                    | _ -> None
-                )
-                |> List.ofSeq
-                |> List.groupBy id
-                |> List.choose (fun (key, v) -> if v.Length > 1 then Some key else None)
-
-            match duplicateArgs with
-            | [] -> nonPos, pos
-            | dups ->
-                let dups = dups |> String.concat " "
-                failwith $"Duplicate args detected! %s{dups}"
-
     /// Build the return value.
     let rec instantiate<'a> (tree : ParseTree<'a>) : SynExpr =
         match tree with
@@ -673,7 +540,7 @@ module internal ArgParserGenerator =
                 args
                 |> Map.toList
                 |> List.map (fun (ident, expr) -> SynLongIdent.create [ Ident.create ident ], expr)
-                |> AstHelper.instantiateRecord
+                |> SynExpr.createRecord None
             )
 
         tree, counter

WoofWare.Myriad.Plugins/AstHelper.fs

@@ -36,13 +36,6 @@ module internal AstHelper =
         | SynTypeDefnRepr.Simple (SynTypeDefnSimpleRepr.Enum _, _) -> true
         | _ -> false
 
-    let instantiateRecord (fields : (SynLongIdent * SynExpr) list) : SynExpr =
-        let fields =
-            fields
-            |> List.map (fun (rfn, synExpr) -> SynExprRecordField ((rfn, true), Some range0, Some synExpr, None))
-
-        SynExpr.Record (None, None, fields, range0)
-
     let defineRecordType (record : RecordType) : SynTypeDefn =
         let name =
             SynComponentInfo.create record.Name

WoofWare.Myriad.Plugins/InterfaceMockGenerator.fs

@@ -89,7 +89,7 @@ module internal InterfaceMockGenerator =
                      []
                  else
                      [ SynPat.unit ])
-                (AstHelper.instantiateRecord constructorFields)
+                (SynExpr.createRecord None constructorFields)
             |> SynBinding.withXmlDoc (PreXmlDoc.create "An implementation where every method throws.")
             |> SynBinding.withReturnAnnotation constructorReturnType
             |> SynMemberDefn.staticMember

WoofWare.Myriad.Plugins/JsonParseGenerator.fs

@@ -480,7 +480,7 @@ module internal JsonParseGenerator =
         let finalConstruction =
             fields
             |> List.mapi (fun i fieldData -> SynLongIdent.createI fieldData.Ident, SynExpr.createIdent $"arg_%i{i}")
-            |> AstHelper.instantiateRecord
+            |> SynExpr.createRecord None
 
         (finalConstruction, assignments)
         ||> List.fold (fun final assignment -> SynExpr.createLet [ assignment ] final)

WoofWare.Myriad.Plugins/List.fs

@@ -21,3 +21,13 @@ module private List =
             | Some head :: tail -> go (head :: acc) tail
 
         go [] l
+
+    /// Return the first error encountered, or the entire list.
+    let allOkOrError<'ok, 'err> (l : Result<'ok, 'err> list) : Result<'ok list, 'err> =
+        let rec go acc l =
+            match l with
+            | [] -> Ok (List.rev acc)
+            | Error e :: _ -> Error e
+            | Ok o :: rest -> go (o :: acc) rest
+
+        go [] l

WoofWare.Myriad.Plugins/RemoveOptionsGenerator.fs

@@ -97,7 +97,7 @@ module internal RemoveOptionsGenerator =
 
                 SynLongIdent.createI fieldData.Ident, body
             )
-            |> AstHelper.instantiateRecord
+            |> SynExpr.createRecord None
 
         SynBinding.basic
             [ functionName ]

WoofWare.Myriad.Plugins/WoofWare.Myriad.Plugins.fsproj

@@ -22,7 +22,7 @@
   <ItemGroup>
     <PackageReference Include="Myriad.Core" Version="0.8.3" />
     <PackageReference Include="TypeEquality" Version="0.3.0" />
-    <PackageReference Include="WoofWare.Whippet.Fantomas" Version="0.3.1" />
+    <PackageReference Include="WoofWare.Whippet.Fantomas" Version="0.5.1" />
     <!-- the lowest version allowed by Myriad.Core -->
     <PackageReference Update="FSharp.Core" Version="6.0.1" PrivateAssets="all"/>
   </ItemGroup>
@@ -40,7 +40,8 @@
     <Compile Include="JsonParseGenerator.fs"/>
     <Compile Include="HttpClientGenerator.fs"/>
     <Compile Include="CataGenerator.fs" />
-    <Compile Include="ArgParserGenerator.fs" />
+    <Compile Include="ShibaGenerator.fs" />
+    <None Include="ArgParserGenerator.fs" />
     <Compile Include="Swagger.fs" />
     <Compile Include="SwaggerClientGenerator.fs" />
     <None Include="ApacheLicence.txt" />

WoofWare.Myriad.sln

@@ -10,6 +10,8 @@ Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "WoofWare.Myriad.Plugins.Att
 EndProject
 Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "WoofWare.Myriad.Plugins.Attributes.Test", "WoofWare.Myriad.Plugins.Attributes\Test\WoofWare.Myriad.Plugins.Attributes.Test.fsproj", "{26DC0C94-85F2-45B4-8FA1-1B27201F7AFB}"
 EndProject
+Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "Playground", "Playground\Playground.fsproj", "{6DF8C756-DE59-4AFF-A4BB-2D05C74192A4}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -36,5 +38,9 @@ Global
 		{26DC0C94-85F2-45B4-8FA1-1B27201F7AFB}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{26DC0C94-85F2-45B4-8FA1-1B27201F7AFB}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{26DC0C94-85F2-45B4-8FA1-1B27201F7AFB}.Release|Any CPU.Build.0 = Release|Any CPU
+		{6DF8C756-DE59-4AFF-A4BB-2D05C74192A4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{6DF8C756-DE59-4AFF-A4BB-2D05C74192A4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{6DF8C756-DE59-4AFF-A4BB-2D05C74192A4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{6DF8C756-DE59-4AFF-A4BB-2D05C74192A4}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal

analyzers/analyzers.fsproj

@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageDownload Include="G-Research.FSharp.Analyzers" Version="[0.12.0]" />
+    <PackageDownload Include="G-Research.FSharp.Analyzers" Version="[0.14.0]" />
   </ItemGroup>
 
 </Project>

flake.lock

@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1739019272,
+        "lastModified": 1744502386,
-        "narHash": "sha256-7Fu7oazPoYCbDzb9k8D/DdbKrC3aU1zlnc39Y8jy/s8=",
+        "narHash": "sha256-QAd1L37eU7ktL2WeLLLTmI6P9moz9+a/ONO8qNBYJgM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "fa35a3c8e17a3de613240fea68f876e5b4896aec",
+        "rev": "f6db44a8daa59c40ae41ba6e5823ec77fe0d2124",
         "type": "github"
       },
       "original": {

nix/deps.json

@@ -1,13 +1,13 @@
 [
   {
     "pname": "ApiSurface",
-    "version": "4.1.16",
+    "version": "4.1.20",
-    "hash": "sha256-3F+dY2nZMFukUjIGrvB/h3ZsZYdLJ9jvQKRxX33qk2E="
+    "hash": "sha256-koWgO9FC9ax+Ij56ug8kxeyknl0yhLqnNLOUdxtqqo4="
   },
   {
     "pname": "fantomas",
-    "version": "7.0.0",
+    "version": "7.0.1",
-    "hash": "sha256-v4bXmvjZOYxl5RSIHuqVfDzBQdRz5SrmzZtD6SeEYTY="
+    "hash": "sha256-2aGD6Kjh83gmssRqqZ/Uihi7VbNqNUelX4otIfCuhTI="
   },
   {
     "pname": "Fantomas.Core",
@@ -21,29 +21,19 @@
   },
   {
     "pname": "FsCheck",
-    "version": "3.1.0",
+    "version": "3.2.0",
-    "hash": "sha256-u0Ha94EjClJ8evNSHu8d6+Dx9qYM3kV3sl1PEq9gF8s="
+    "hash": "sha256-ksZ4vLgWwyQOzFuK2BczdtDtWWYmedG7UBAg4pYuI8g="
   },
   {
     "pname": "fsharp-analyzers",
-    "version": "0.28.0",
+    "version": "0.30.0",
-    "hash": "sha256-BqGk9MzHHA3oRPNfWuANcM1YELsdhzWI+kLF4mUDUx8="
+    "hash": "sha256-7oaSwpHAU1opzpz4szLU/gDaJC/ww9eiFkPu0nr4Mj4="
   },
   {
     "pname": "FSharp.Core",
     "version": "4.3.4",
     "hash": "sha256-styyo+6mJy+yxE0NZG/b1hxkAjPOnJfMgd9zWzCJ5uk="
   },
-  {
-    "pname": "FSharp.Core",
-    "version": "4.5.0",
-    "hash": "sha256-7+B+8rsm/dMKvNBty8z5qB+kOxMwUzExy0F04xM88sk="
-  },
-  {
-    "pname": "FSharp.Core",
-    "version": "5.0.2",
-    "hash": "sha256-YOoosLEiszPsOOaNAkWhFGU04JJKDOFVoA/ggrZMN10="
-  },
   {
     "pname": "FSharp.Core",
     "version": "6.0.1",
@@ -51,13 +41,18 @@
   },
   {
     "pname": "FSharp.Core",
-    "version": "9.0.101",
+    "version": "9.0.202",
-    "hash": "sha256-bR4PHanvKrzD43qFQxmOmmhhpz+ZmKZMPlgGnlRNcp4="
+    "hash": "sha256-64Gub0qemmCoMa1tDus6TeTuB1+5sHfE6KD2j4o84mA="
   },
   {
     "pname": "FsUnit",
-    "version": "6.0.1",
+    "version": "7.0.1",
-    "hash": "sha256-vka/aAgWhDCl5tu+kgO7GtSaHOOvlSaWxG+tExwGXpI="
+    "hash": "sha256-K85CIdxMeFSHEKZk6heIXp/oFjWAn7dBILKrw49pJUY="
+  },
+  {
+    "pname": "Microsoft.ApplicationInsights",
+    "version": "2.22.0",
+    "hash": "sha256-mUQ63atpT00r49ca50uZu2YCiLg3yd6r3HzTryqcuEA="
   },
   {
     "pname": "Microsoft.AspNetCore.App.Ref",
@@ -86,13 +81,13 @@
   },
   {
     "pname": "Microsoft.CodeCoverage",
-    "version": "17.12.0",
+    "version": "17.13.0",
-    "hash": "sha256-lGjifppD0OBMBp28pjUfPipaeXg739n8cPhtHWoo5RE="
+    "hash": "sha256-GKrIxeyQo5Az1mztfQgea1kGtJwonnNOrXK/0ULfu8o="
   },
   {
     "pname": "Microsoft.NET.Test.Sdk",
-    "version": "17.12.0",
+    "version": "17.13.0",
-    "hash": "sha256-DKFEbhh2wPzahNeHdEoFig8tZh/LEVrFc5+zpT43Btg="
+    "hash": "sha256-sc2wvyV8cGm1FrNP2GGHEI584RCvRPu15erYCsgw5QY="
   },
   {
     "pname": "Microsoft.NETCore.App.Host.linux-arm64",
@@ -164,15 +159,45 @@
     "version": "1.1.3",
     "hash": "sha256-WLsf1NuUfRWyr7C7Rl9jiua9jximnVvzy6nk2D2bVRc="
   },
+  {
+    "pname": "Microsoft.Testing.Extensions.Telemetry",
+    "version": "1.5.3",
+    "hash": "sha256-bIXwPSa3jkr2b6xINOqMUs6/uj/r4oVFM7xq3uVIZDU="
+  },
+  {
+    "pname": "Microsoft.Testing.Extensions.TrxReport.Abstractions",
+    "version": "1.5.3",
+    "hash": "sha256-IfMRfcyaIKEMRtx326ICKtinDBEfGw/Sv8ZHawJ96Yc="
+  },
+  {
+    "pname": "Microsoft.Testing.Extensions.VSTestBridge",
+    "version": "1.5.3",
+    "hash": "sha256-XpM/yFjhLSsuzyDV+xKubs4V1zVVYiV05E0+N4S1h0g="
+  },
+  {
+    "pname": "Microsoft.Testing.Platform",
+    "version": "1.5.3",
+    "hash": "sha256-y61Iih6w5D79dmrj2V675mcaeIiHoj1HSa1FRit2BLM="
+  },
+  {
+    "pname": "Microsoft.Testing.Platform.MSBuild",
+    "version": "1.5.3",
+    "hash": "sha256-YspvjE5Jfi587TAfsvfDVJXNrFOkx1B3y1CKV6m7YLY="
+  },
   {
     "pname": "Microsoft.TestPlatform.ObjectModel",
     "version": "17.12.0",
     "hash": "sha256-3XBHBSuCxggAIlHXmKNQNlPqMqwFlM952Av6RrLw1/w="
   },
+  {
+    "pname": "Microsoft.TestPlatform.ObjectModel",
+    "version": "17.13.0",
+    "hash": "sha256-6S0fjfj8vA+h6dJVNwLi6oZhYDO/I/6hBZaq2VTW+Uk="
+  },
   {
     "pname": "Microsoft.TestPlatform.TestHost",
-    "version": "17.12.0",
+    "version": "17.13.0",
-    "hash": "sha256-rf8Sh0fQq44Sneuvs64unkkIHg8kOjDGWE35j9iLx5I="
+    "hash": "sha256-L/CJzou7dhmShUgXq3aXL3CaLTJll17Q+JY2DBdUUpo="
   },
   {
     "pname": "Myriad.Core",
@@ -186,8 +211,8 @@
   },
   {
     "pname": "Nerdbank.GitVersioning",
-    "version": "3.7.115",
+    "version": "3.8.38-alpha",
-    "hash": "sha256-sqn+i7vvBgBUtm7j82mH+SpApgI2hsmL5DYfLm1Z7gw="
+    "hash": "sha256-gPMrVbjOZxXoofczF/pn6eVkLhjVSJIyQrLO2oljrDc="
   },
   {
     "pname": "NETStandard.Library",
@@ -206,38 +231,33 @@
   },
   {
     "pname": "NuGet.Common",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-k6JAFqHFinTakwNuW666aXYPhR7TpI/rb+KbHm1S2TM="
+    "hash": "sha256-ASLa/Jigg5Eop0ZrXPl98RW2rxnJRC7pbbxhuV74hFw="
   },
   {
     "pname": "NuGet.Configuration",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-e/4lvyl7o7g4aWTAtr9S2yiGgk7V0E9p6DXpsy7GgVw="
+    "hash": "sha256-z8VW1YdRDanyyRTDYRvRkSv/XPR3c/hMM1y8cNNjx0Y="
   },
   {
     "pname": "NuGet.Frameworks",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-GGpkbas+PNLx35vvr3nyAVz5lY/aeoMx6qjmT368Lpg="
+    "hash": "sha256-caDyc+WgYOo43AUTjtbP0MyvYDb6JweEKDdIul61Cac="
   },
   {
     "pname": "NuGet.Packaging",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-3h8Nmjpt383+dCg9GJ1BJ26UirwEQsWCPcTiT0+wGeI="
+    "hash": "sha256-lhO+SFwIYZ4aPHxIGm5ubkkE2a5Ve2xgtroRbNh7hpw="
   },
   {
     "pname": "NuGet.Protocol",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-l+CHnAcit6Y9OjBxereRP5JzOuWbuZZQYkFOKsUkdQ8="
+    "hash": "sha256-5lnAHHZjy7A4vgv65AeBAs64mSNpuoUjxW3HnrMpuzY="
   },
   {
     "pname": "NuGet.Versioning",
-    "version": "6.12.1",
+    "version": "6.13.2",
-    "hash": "sha256-f/ejCuzCAwKs4N4Ec6yf2RovrhBT0nj0hRDP+03/Iy4="
+    "hash": "sha256-gmpyBpKnt+GHqgx/2uFKp+J2csbxEAy1E7WdVT117sw="
-  },
-  {
-    "pname": "NUnit",
-    "version": "4.0.1",
-    "hash": "sha256-jd1CD5nHVXkpvBNpVDJcJyfTggCHLyDBySVSvtrA8Uk="
   },
   {
     "pname": "NUnit",
@@ -246,8 +266,8 @@
   },
   {
     "pname": "NUnit3TestAdapter",
-    "version": "4.6.0",
+    "version": "5.0.0",
-    "hash": "sha256-9Yav2fYhC4w0OgsyUwU4/5rDy4FVDTpKnWHuwl/uKJQ="
+    "hash": "sha256-7jZM4qAbIzne3AcdFfMbvbgogqpxvVe6q2S7Ls8xQy0="
   },
   {
     "pname": "RestEase",
@@ -269,6 +289,16 @@
     "version": "4.3.0",
     "hash": "sha256-c5tXWhE/fYbJVl9rXs0uHh3pTsg44YD1dJvyOA0WoMs="
   },
+  {
+    "pname": "System.Collections.Immutable",
+    "version": "8.0.0",
+    "hash": "sha256-F7OVjKNwpqbUh8lTidbqJWYi476nsq9n+6k0+QVRo3w="
+  },
+  {
+    "pname": "System.Diagnostics.DiagnosticSource",
+    "version": "5.0.0",
+    "hash": "sha256-6mW3N6FvcdNH/pB58pl+pFSCGWgyaP4hfVtC/SMWDV4="
+  },
   {
     "pname": "System.Diagnostics.DiagnosticSource",
     "version": "7.0.0",
@@ -339,15 +369,10 @@
     "version": "4.5.0",
     "hash": "sha256-BkUYNguz0e4NJp1kkW7aJBn3dyH9STwB5N8XqnlCsmY="
   },
-  {
-    "pname": "System.Text.Encodings.Web",
-    "version": "8.0.0",
-    "hash": "sha256-IUQkQkV9po1LC0QsqrilqwNzPvnc+4eVvq+hCvq8fvE="
-  },
   {
     "pname": "System.Text.Json",
-    "version": "8.0.4",
+    "version": "8.0.5",
-    "hash": "sha256-g5oT7fbXxQ9Iah1nMCr4UUX/a2l+EVjJyTrw3FTbIaI="
+    "hash": "sha256-yKxo54w5odWT6nPruUVsaX53oPRe+gKzGvLnnxtwP68="
   },
   {
     "pname": "TypeEquality",
@@ -356,7 +381,7 @@
   },
   {
     "pname": "WoofWare.Whippet.Fantomas",
-    "version": "0.3.1",
+    "version": "0.5.1",
-    "hash": "sha256-i5oiqcrxzM90Ocuq5MIu2Ha5lV0aYu5nCvuwmFqp6NA="
+    "hash": "sha256-59CwnOZQAq5ZJoUkd87OiP8KUwx8xYDLMimMMTlKeZA="
   }
 ]