Unexpected scoping on type parameter of local function parameter

[jcouv]

        [Fact]
        public void TypeParameterScope_InParameterAttribute()
        {
            var comp = CreateCompilation(@"
class C
{
    void M()
    {
        local<object>(0);

        void local<TParameter>([My(TParameter)] int i) => throw null;
    }

    void M2<TParameter>([My(TParameter)] int i) => throw null;
}

public class MyAttribute : System.Attribute
{
    public MyAttribute(string name1) { }
}
");
            // TParameter unexpectedly was found in local function case
            comp.VerifyDiagnostics(
                // (8,36): error CS0119: 'TParameter' is a type, which is not valid in the given context
                //         void local<TParameter>([My(TParameter)] int i) => throw null;
                Diagnostic(ErrorCode.ERR_BadSKunknown, "TParameter").WithArguments("TParameter", "type").WithLocation(8, 36),
                // (11,29): error CS0103: The name 'TParameter' does not exist in the current context
                //     void M2<TParameter>([My(TParameter)] int i) => throw null;
                Diagnostic(ErrorCode.ERR_NameNotInContext, "TParameter").WithArguments("TParameter").WithLocation(11, 29)
                );
        }

Note: this is a different than #59775
The difference in behavior between the method and the local function is this code in BindIdentifier:

            if (!IsInMethodBody && !IsInsideNameof)
            {
                Debug.Assert((options & LookupOptions.NamespacesOrTypesOnly) == 0);
                options |= LookupOptions.MustNotBeMethodTypeParameter;
            }

Relates to test plan #38801

[Youssef1313]

Is semantic model having the same issue?

roslyn/src/Compilers/CSharp/Portable/Compilation/CSharpSemanticModel.cs

Lines 1596 to 1608 in 98b3931

	if (!binder.IsInMethodBody &&
	(options & (LookupOptions.NamespaceAliasesOnly | LookupOptions.NamespacesOrTypesOnly | LookupOptions.LabelsOnly)) == 0)
	{
	// Method type parameters are not in scope outside a method
	// body unless the position is either:
	// a) in a type-only context inside an expression, or
	// b) inside of an XML name attribute in an XML doc comment.
	var parentExpr = token.Parent as ExpressionSyntax;
	if (parentExpr != null && !(parentExpr.Parent is XmlNameAttributeSyntax) && !SyntaxFacts.IsInTypeOnlyContext(parentExpr))
	{
	options |= LookupOptions.MustNotBeMethodTypeParameter;
	}
	}

Tests for semantic model may include nameof(TParameter) to make sure the behavior matches BindIdentifier. Then, the above comment should include c) inside of a nameof

[Youssef1313]

There are only 3 usages of IsInMethodBody. Does it make sense to rename it to IsInMethodBodyOrLocalFunction?

The usages are:

roslyn/src/Compilers/CSharp/Portable/Compilation/CSharpSemanticModel.cs

Line 1596 in 98b3931

if (!binder.IsInMethodBody &&

roslyn/src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

Line 1482 in 98b3931

if (!IsInMethodBody && !IsInsideNameof)

roslyn/src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

Line 3704 in 98b3931

inLegalPosition = (IsInMethodBody || IsLocalFunctionsScopeBinder) && node.IsLegalCSharp73SpanStackAllocPosition();

[RikkiGibson]

It seems like usage of the type parameter outside of nameof() always results in an error here. It's perhaps not urgent to address this unless some new valid way of using the type parameter in an attribute arises.

[AlekseyTs]

I think it would be interesting to test with typeof as well.