<Project>
    <ItemGroup>
        <None Include="my-swagger-schema.json" />
        <Compile Include="Client.fs">
            <WhippetFile>my-swagger-schema.json</WhippetFile>
            <WhippetParamClassName>GiteaClient</WhippetParamClassName>
        </Compile>
    </ItemGroup>
    <ItemGroup>
        <PackageReference Include="WoofWare.Whippet.Plugin.HttpClient.Attributes" Version="" />
        <PackageReference Include="WoofWare.Whippet.Plugin.Json.Attributes" Version="" />

        <!-- Development dependencies, hence PrivateAssets="all". Note `WhippetPlugin="true"`. -->
        <PackageReference Include="WoofWare.Whippet.Plugin.Swagger" WhippetPlugin="true" Version="" />
        <PackageReference Include="WoofWare.Whippet" Version="" PrivateAssets="all" />
    </ItemGroup>
</Project>

(Note that you must supply <WhippetParamClassName>SomeClassName</WhippetParamClassName> to tell the generator what to name the type it produces.)

The generator produces code like this. Notice that it adds JsonParse and JsonSerialize attributes (i.e. it assumes you have access to WoofWare.Whippet.Plugin.Json.Attributes), and also the HttpClient attribute (i.e. it assumes you have access to WoofWare.Whippet.Plugin.HttpClient.Attributes).

/// A type which was defined in the Swagger spec
[<JsonParse true ; JsonSerialize true>]
type SwaggerType1 =
    {
        [<System.Text.Json.Serialization.JsonExtensionData>]
        AdditionalProperties : System.Collections.Generic.Dictionary<string, System.Text.Json.Nodes.JsonNode>
        Message : string
    }

/// Documentation from the Swagger spec
[<HttpClient false ; RestEase.BasePath "/api/v1">]
type IGitea =
    /// Returns the Person actor for a user
    [<RestEase.Get "/activitypub/user/{username}">]
    abstract ActivitypubPerson :
        [<RestEase.Path "username">] username : string * ?ct : System.Threading.CancellationToken ->
            ActivityPub System.Threading.Tasks.Task

That means if you choose to, you can chain other Whippet generators off this one, to generate JSON serde methods and HTTP REST clients:

<Project>
    <ItemGroup>
        <None Include="my-swagger-schema.json" />
        <Compile Include="Client.fs">
            <WhippetFile>my-swagger-schema.json</WhippetFile>
            <WhippetParamClassName>GiteaClient</WhippetParamClassName>
        </Compile>
        <Compile Include="GeneratedClientMockAndJson.fs">
            <WhippetFile>Client.fs</WhippetFile>
            <WhippetParamIGiteaClient>InterfaceMock</WhippetParamIGiteaClient>
        </Compile>
        <Compile Include="GeneratedClient.fs">
            <WhippetFile>Client.fs</WhippetFile>
            <WhippetParamIGiteaClient>HttpClient</WhippetParamIGiteaClient>
            <!-- We're consuming the `Client.fs` file *again*, so prevent the JSON generators from firing again.-->
            <WhippetSuppressPlugin>JsonParseGenerator,JsonSourceGenerator</WhippetSuppressPlugin>
        </Compile>
    </ItemGroup>
    <ItemGroup>
        <PackageReference Include="WoofWare.Whippet.Plugin.HttpClient.Attributes" Version="" />
        <PackageReference Include="WoofWare.Whippet.Plugin.Json.Attributes" Version="" />

        <PackageReference Include="WoofWare.Whippet.Plugin.HttpClient" WhippetPlugin="true" Version="" />
        <PackageReference Include="WoofWare.Whippet.Plugin.Json" WhippetPlugin="true" Version="" />
        <PackageReference Include="WoofWare.Whippet.Plugin.Swagger" WhippetPlugin="true" Version="" />
        <PackageReference Include="WoofWare.Whippet.Plugin.InterfaceMock" WhippetPlugin="true" Version="" />
        <PackageReference Include="WoofWare.Whippet" Version="" PrivateAssets="all" />
    </ItemGroup>
</Project>

The <WhippetParamClassName /> key tells us what to name the resulting interface (it gets an I prepended for you).

What's the point?

SwaggerProvider is absolutely magical, but it's kind of witchcraft. I fear no man, but that thing… it scares me.

Also, builds using SwaggerProvider appear to be inherently nondeterministic, even if the data source doesn't change.

Limitations

Swagger API specs appear to be pretty cowboy in the wild. I try to cope with invalid schemas I have seen, but I can't guarantee I do so correctly. Definitely do perform integration tests and let me know of weird specs you encounter, and bits of the (very extensive) Swagger spec I have omitted!

I have only attempted to deal with Swagger v2.0 so far.