[Diagnostics] Add a special case diagnostic for call to init on Void with arguments

Expressions like `Void(...)` have a special locator which ends at
`FunctionArgument` instead of `ApplyArgument` which makes it possible
to type-check `Void()` call successfully. "extraneous arguments" diagnostic
needs to handle such situations specifically e.g. `Void(0)`.

Author: xedin

lib/Sema/CSDiag.cpp

@@ -1296,21 +1296,6 @@ bool FailureDiagnosis::visitApplyExpr(ApplyExpr *callExpr) {
     }
   }
 
-  // Let's check whether this is a situation when callee expects
-  // no arguments but N are given. Otherwise, just below
-  // `typeCheckArgumentChild*` is going to use `()` is a contextual type which
-  // is incorrect.
-  if (argType && argType->isVoid()) {
-    auto *argExpr = callExpr->getArg();
-    if (isa<ParenExpr>(argExpr) ||
-        (isa<TupleExpr>(argExpr) &&
-         cast<TupleExpr>(argExpr)->getNumElements() > 0)) {
-      diagnose(callExpr->getLoc(), diag::extra_argument_to_nullary_call)
-          .highlight(argExpr->getSourceRange());
-      return true;
-    }
-  }
-
   // Get the expression result of type checking the arguments to the call
   // independently, so we have some idea of what we're working with.
   //

lib/Sema/CSDiagnostics.cpp

@@ -4561,7 +4561,21 @@ bool ExtraneousArgumentsFailure::diagnoseAsNote() {
 }
 
 bool ExtraneousArgumentsFailure::diagnoseSingleExtraArgument() const {
-  auto *arguments = getArgumentListExprFor(getLocator());
+  auto *locator = getLocator();
+
+  // This specifically handles a case of `Void(...)` which generates
+  // constraints differently from other constructor invocations and
+  // wouldn't have `ApplyArgument` as a last element in the locator.
+  if (auto *call = dyn_cast<CallExpr>(getRawAnchor())) {
+    auto *TE = dyn_cast<TypeExpr>(call->getFn());
+    if (TE && getType(TE)->getMetatypeInstanceType()->isVoid()) {
+      emitDiagnostic(call->getLoc(), diag::extra_argument_to_nullary_call)
+          .highlight(call->getArg()->getSourceRange());
+      return true;
+    }
+  }
+
+  auto *arguments = getArgumentListExprFor(locator);
   if (!arguments)
     return false;