From 2e83aa30bfcb143f31875481b8551b983427a5df Mon Sep 17 00:00:00 2001
From: Patrick Stevens <3138005+Smaug123@users.noreply.github.com>
Date: Mon, 21 Apr 2025 17:56:07 +0100
Subject: [PATCH] Add type printing for App (#33)

---
 WoofWare.Whippet.Fantomas.Test/TestSynType.fs | 38 +++++++++++++++++++
 .../WoofWare.Whippet.Fantomas.Test.fsproj     |  2 +
 WoofWare.Whippet.Fantomas/SynType.fs          |  3 ++
 3 files changed, 43 insertions(+)
 create mode 100644 WoofWare.Whippet.Fantomas.Test/TestSynType.fs

diff --git a/WoofWare.Whippet.Fantomas.Test/TestSynType.fs b/WoofWare.Whippet.Fantomas.Test/TestSynType.fs
new file mode 100644
index 0000000..4e93820
--- /dev/null
+++ b/WoofWare.Whippet.Fantomas.Test/TestSynType.fs
@@ -0,0 +1,38 @@
+namespace WoofWare.Whippet.Fantomas.Test
+
+open Fantomas.FCS.Syntax
+open Fantomas.FCS.Text
+open NUnit.Framework
+open FsUnitTyped
+open WoofWare.Whippet.Fantomas
+open Fantomas.FCS
+
+[<TestFixture>]
+module TestSynType =
+    let typeToStringCases =
+        [ "string", "string" ; "ResizeArray<int>", "ResizeArray<int32>" ]
+        |> List.map TestCaseData
+
+    [<TestCaseSource(nameof typeToStringCases)>]
+    let ``Snapshot tests for SynType.toHumanReadableString`` (fsharpTypeString : string, expected : string) =
+        let parsed, diags =
+            Parse.parseFile false (SourceText.ofString $"let x : %s{fsharpTypeString} = failwith \"\"") []
+
+        diags |> shouldBeEmpty
+
+        let (SynModuleOrNamespace (decls = parsed)) =
+            match parsed with
+            | ParsedInput.ImplFile parsedImplFileInput -> parsedImplFileInput.Contents.[0]
+            | ParsedInput.SigFile _ -> failwith "logic error"
+
+        let (SynBinding (expr = parsed)) =
+            match List.exactlyOne parsed with
+            | SynModuleDecl.Let (bindings = bindings) -> bindings.[0]
+            | _ -> failwith "logic error"
+
+        let ty =
+            match parsed with
+            | SynExpr.Typed (targetType = targetType) -> targetType
+            | _ -> failwith $"logic error: %O{parsed}"
+
+        SynType.toHumanReadableString ty |> shouldEqual expected
diff --git a/WoofWare.Whippet.Fantomas.Test/WoofWare.Whippet.Fantomas.Test.fsproj b/WoofWare.Whippet.Fantomas.Test/WoofWare.Whippet.Fantomas.Test.fsproj
index 1c148c4..9743464 100644
--- a/WoofWare.Whippet.Fantomas.Test/WoofWare.Whippet.Fantomas.Test.fsproj
+++ b/WoofWare.Whippet.Fantomas.Test/WoofWare.Whippet.Fantomas.Test.fsproj
@@ -9,10 +9,12 @@
 
     <ItemGroup>
         <Compile Include="TestSurface.fs" />
+        <Compile Include="TestSynType.fs" />
     </ItemGroup>
 
     <ItemGroup>
         <PackageReference Include="ApiSurface" Version="4.1.5" />
+        <PackageReference Include="FsUnit" Version="7.0.1" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1"/>
         <PackageReference Include="NUnit" Version="4.2.2"/>
         <PackageReference Include="NUnit3TestAdapter" Version="4.6.0"/>
diff --git a/WoofWare.Whippet.Fantomas/SynType.fs b/WoofWare.Whippet.Fantomas/SynType.fs
index 80006df..3f6ee53 100644
--- a/WoofWare.Whippet.Fantomas/SynType.fs
+++ b/WoofWare.Whippet.Fantomas/SynType.fs
@@ -508,6 +508,9 @@ module SynType =
         | DateOnly -> "DateOnly"
         | TimeSpan -> "TimeSpan"
         | SynType.LongIdent (SynLongIdent.SynLongIdent (ident, _, _)) -> ident |> List.map _.idText |> String.concat "."
+        | SynType.App (ty, _, args, _, _, _, _) ->
+            let args = args |> Seq.map toHumanReadableString |> String.concat ", "
+            $"%s{toHumanReadableString ty}<%s{args}>"
         | ty -> failwithf "could not compute human-readable string for type: %O" ty
 
     /// Guess whether the types are equal. We err on the side of saying "no, they're different".