sema: accept enum element reference as compile-time const value

Author: nkcsgexi

lib/Sema/CSFix.cpp

@@ -1129,7 +1129,8 @@ RemoveReturn *RemoveReturn::create(ConstraintSystem &cs, Type resultTy,
 NotCompileTimeConst::NotCompileTimeConst(ConstraintSystem &cs, Type paramTy,
                                          ConstraintLocator *locator):
   ContextualMismatch(cs, FixKind::NotCompileTimeConst, paramTy,
-                     cs.getASTContext().TheEmptyTupleType, locator) {}
+                     cs.getASTContext().TheEmptyTupleType, locator,
+                     /*warning*/true) {}
 
 NotCompileTimeConst *
 NotCompileTimeConst::create(ConstraintSystem &cs, Type paramTy,
@@ -1138,7 +1139,14 @@ NotCompileTimeConst::create(ConstraintSystem &cs, Type paramTy,
 }
 
 bool NotCompileTimeConst::diagnose(const Solution &solution, bool asNote) const {
-  NotCompileTimeConstFailure failure(solution, getLocator());
+  auto *locator = getLocator();
+  // Referencing an enum element directly is considered a compile-time literal.
+  if (auto *d = solution.resolveLocatorToDecl(locator).getDecl()) {
+    if (isa<EnumElementDecl>(d)) {
+      return true;
+    }
+  }
+  NotCompileTimeConstFailure failure(solution, locator);
   return failure.diagnose(asNote);
 }
 

lib/Sema/CSSimplify.cpp

@@ -1506,8 +1506,17 @@ ConstraintSystem::TypeMatchResult constraints::matchCallArguments(
       }
       if (!argument.isCompileTimeConst() && param.isCompileTimeConst()) {
         if (cs.shouldAttemptFixes()) {
-          cs.recordFix(NotCompileTimeConst::create(cs, paramTy,
-                                                   cs.getConstraintLocator(loc)));
+          auto *locator = cs.getConstraintLocator(loc);
+          SourceRange range;
+          // simplify locator so the anchor is the exact argument.
+          locator = simplifyLocator(cs, locator, range);
+          if (locator->getPath().empty() &&
+              locator->getAnchor().isExpr(ExprKind::UnresolvedMemberChainResult)) {
+            locator =
+              cs.getConstraintLocator(cast<UnresolvedMemberChainResultExpr>(
+                locator->getAnchor().get<Expr*>())->getChainBase());
+          }
+          cs.recordFix(NotCompileTimeConst::create(cs, paramTy, locator));
         }
       }
 

test/Sema/const_enum_elements.swift

@@ -0,0 +1,30 @@
+// RUN: %target-typecheck-verify-swift
+
+enum CarKind {
+	case coupe
+	case sedan
+	case other(String)
+}
+
+extension CarKind {
+	static var myCoupe: CarKind {
+		return .coupe
+	}
+}
+
+func getCarKind() -> CarKind { return .sedan }
+
+func drive(_ k1: _const CarKind, k2: _const CarKind) {}
+
+func main() {
+	drive(.coupe, k2: .sedan)
+	drive(.sedan, k2: .coupe)
+	drive(CarKind.coupe, k2: CarKind.sedan)
+	drive(CarKind.sedan, k2: CarKind.coupe)
+	drive(.other(""), k2: .sedan)
+
+	drive(.myCoupe, k2: .sedan) // expected-error {{expect a compile-time constant literal}}
+	drive(.coupe, k2: .myCoupe) // expected-error {{expect a compile-time constant literal}}
+	drive(.coupe, k2: getCarKind()) // expected-error {{expect a compile-time constant literal}}
+	drive(getCarKind(), k2: .coupe) // expected-error {{expect a compile-time constant literal}}
+}