[CSSimplify] Detect and diagnose attempts to specialize non-generic types/aliases

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -13658,8 +13658,15 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
     }
   }
 
-  if (openedGenericParams.empty())
-    return SolutionKind::Error;
+  if (openedGenericParams.empty()) {
+    if (!shouldAttemptFixes())
+      return SolutionKind::Error;
+
+    return recordFix(AllowConcreteTypeSpecialization::create(
+               *this, type1, getConstraintLocator(locator)))
+               ? SolutionKind::Error
+               : SolutionKind::Solved;
+  }
 
   assert(openedGenericParams.size() == genericParams->size());
 

test/Macros/macro_and_typealias.swift

@@ -6,13 +6,15 @@
 
 @freestanding(expression) public macro Print<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 @freestanding(expression) public macro OtherPrint<each Value>(_ value: repeat each Value) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
+@freestanding(expression) public macro ConcretePrint(_ value: Any) = #externalMacro(module: "MacroDefinition", type: "PrintMacro")
 
 public struct Printer<Value> {
   init(_: (Value) -> Void) {}
 }
 
 typealias Print = Printer
 typealias OtherPrint<T> = Printer<T>
+typealias ConcretePrint = Printer<Any>
 
 struct Test {
   struct Object {
@@ -27,6 +29,11 @@ struct Test {
     let _ = OtherPrint<Object> { // Ok
       compute(root: $0, \.prop)
     }
+
+    let _ = ConcretePrint<Object> { // expected-error {{cannot specialize non-generic type 'ConcretePrint' (aka 'Printer<Any>')}}
+      compute(root: $0, \.prop) // expected-error {{value of type 'Any' has no member 'prop'}}
+      // expected-note@-1 {{cast 'Any' to 'AnyObject' or use 'as!' to force downcast to a more specific type to access members}}
+    }
   }
 
   func compute<R, V>(root: R, _: KeyPath<R, V>) {}