Respect generic arity in method uniqueness (#17804)

Author: T-Gro

docs/release-notes/.FSharp.Compiler.Service/9.0.200.md

@@ -1,7 +1,10 @@
 ### Fixed
+
+* Fix internal error when calling 'AddSingleton' and other overloads only differing in generic arity ([PR #17804](https://github.com/dotnet/fsharp/pull/17804))
 * Fix extension methods support for non-reference system assemblies ([PR #17799](https://github.com/dotnet/fsharp/pull/17799))
 * Ensure `frameworkTcImportsCache` mutations are threadsafe. ([PR #17795](https://github.com/dotnet/fsharp/pull/17795))
 
+
 ### Added
 
 

src/Compiler/AbstractIL/il.fs

@@ -5700,6 +5700,7 @@ let resolveILMethodRefWithRescope r (td: ILTypeDef) (mref: ILMethodRef) =
             mref.CallingConv = md.CallingConv
             && (md.Parameters, argTypes)
                ||> List.lengthsEqAndForall2 (fun p1 p2 -> r p1.Type = p2)
+            && md.GenericParams.Length = mref.GenericArity
             &&
             // REVIEW: this uses equality on ILType. For CMOD_OPTIONAL this is not going to be correct
             r md.Return.Type = retType)

tests/FSharp.Compiler.Private.Scripting.UnitTests/FSharpScriptTests.fs

@@ -502,3 +502,17 @@ test pfloat "1.234"
         let opt = script.Eval(code)  |> getValue
         let value = opt.Value
         Assert.True(true = downcast value.ReflectionValue)
+
+    [<Fact>]
+    member _.``Nuget package with method duplicates differing only in generic arity``() =
+        // regression test for: https://github.com/dotnet/fsharp/issues/17796
+        // Was an internal error
+        let code = """
+#r "nuget: Microsoft.Extensions.DependencyInjection.Abstractions"
+open Microsoft.Extensions.DependencyInjection
+let add (col:IServiceCollection) = 
+    col.AddSingleton<string,string>()
+"""
+        use script = new FSharpScript(additionalArgs=[| |])
+        let _value,diag = script.Eval(code)
+        Assert.Empty(diag)