Fix some bad behavior around static methods (#1289)

These are steps towards a fix for the problem of not being able to call a static method as follows:

    SomeType::someMethod();

One problem in the above is that the parser gets confused and parses an (anonynmous!) function declaration. This change doesn't address that problem, but *does* fix the problem that when checking fails to coerce `SomeType::someMethod` into a type it was triggering an unimplemented-feature exception rather than a real error message.

Another problem was that if the above is re-written to try to avoid the parser bug:

    (SomeType::someMethod)();

we end up with a call where the base expression (the callee) is a `ParenExpr` and the code for handling calls wasn't expecting that. Instead, it sent the overload resolution logic into an unimplemented case that was bailing by throwing an arbitrary C++ exception instead of emitting a diagnostic.

This latter issue was fixed in two ways. First, the code path that failed to emit a diagnostic now emits a reasonable one for the unimplemented feature (this still ends up being a fatal compiler error). Second, we properly handle the case of trying to call a `ParenExpr` by unwrapping it and using the base expression instead, so that `(<func>)(<args>)` is always treated the same as `<func>(<args>)`.

3 files changed, 18 insertions, 22 deletions

diff --git a/source/slang/slang-check-overload.cpp b/source/slang/slang-check-overload.cpp
index 92d390bf0..0cad2875a 100644
--- a/source/slang/slang-check-overload.cpp
+++ b/source/slang/slang-check-overload.cpp
@@ -849,25 +849,11 @@ namespace Slang
     }
 
     void SemanticsVisitor::AddFuncOverloadCandidate(
-        RefPtr<FuncType>		/*funcType*/,
-        OverloadResolveContext&	/*context*/)
+        RefPtr<FuncType>        funcType,
+        OverloadResolveContext& context)
     {
-#if 0
-        if (funcType->decl)
-        {
-            AddFuncOverloadCandidate(funcType->decl, context);
-        }
-        else if (funcType->Func)
-        {
-            AddFuncOverloadCandidate(funcType->Func->SyntaxNode, context);
-        }
-        else if (funcType->Component)
-        {
-            AddComponentFuncOverloadCandidate(funcType->Component, context);
-        }
-#else
-        throw "unimplemented";
-#endif
+        SLANG_UNUSED(funcType);
+        getSink()->diagnose(context.loc, Diagnostics::unimplemented, "call on expression of function type");
     }
 
     void SemanticsVisitor::AddCtorOverloadCandidate(
@@ -1093,9 +1079,19 @@ namespace Slang
     }
 
     void SemanticsVisitor::AddOverloadCandidates(
-        RefPtr<Expr>	funcExpr,
-        OverloadResolveContext&			context)
+        RefPtr<Expr>            funcExpr,
+        OverloadResolveContext& context)
     {
+        // A call of the form `(<something>)(<args>)` should be
+        // resolved as if the user wrote `<something>(<args>)`,
+        // so that we avoid introducing intermediate expressions
+        // of function type in cases where they are not needed.
+        //
+        while(auto parenExpr = as<ParenExpr>(funcExpr))
+        {
+            funcExpr = parenExpr->base;
+        }
+
         auto funcExprType = funcExpr->type;
 
         if (auto declRefExpr = as<DeclRefExpr>(funcExpr))
diff --git a/source/slang/slang-check-type.cpp b/source/slang/slang-check-type.cpp
index 68e14c462..f0ec54061 100644
--- a/source/slang/slang-check-type.cpp
+++ b/source/slang/slang-check-type.cpp
@@ -86,7 +86,7 @@ namespace Slang
             return expr;
         }
 
-        getSink()->diagnose(expr, Diagnostics::unimplemented, "expected a type");
+        getSink()->diagnose(expr, Diagnostics::expectedAType, expr->type);
         return CreateErrorExpr(expr);
     }
 
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index 2fbd373cc..a28bfe77e 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -252,7 +252,7 @@ DIAGNOSTIC(30051, Error, invalidValueForArgument, "invalid value for argument '$
 DIAGNOSTIC(30052, Error, invalidSwizzleExpr, "invalid swizzle pattern '$0' on type '$1'")
 DIAGNOSTIC(30043, Error, getStringHashRequiresStringLiteral, "getStringHash parameter can only accept a string literal")
 
-DIAGNOSTIC(30060, Error, expectedAType, "expected a type got a '$0'")
+DIAGNOSTIC(30060, Error, expectedAType, "expected a type, got a '$0'")
 
 DIAGNOSTIC(30100, Error, staticRefToNonStaticMember, "type '$0' cannot be used to refer to non-static member '$1'")