[CSFix] Improve missing .rawValue fix in ambiguity conditions

Author: xedin

include/swift/Sema/CSFix.h

@@ -2287,6 +2287,10 @@ class UseRawValue final : public ConstraintFix {
 
   bool diagnose(const Solution &solution, bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
   static UseRawValue *create(ConstraintSystem &cs, Type rawReprType,
                              Type expectedType, ConstraintLocator *locator);
 

lib/Sema/CSSimplify.cpp

@@ -7328,7 +7328,11 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
             TypeChecker::conformsToProtocol(rawValue, protocol,
                                             DC->getParentModule())) {
           auto *fix = UseRawValue::create(*this, type, protocolTy, loc);
-          return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
+          // Since this is a conformance requirement failure (where the
+          // source is most likely an argument), let's increase its impact
+          // to disambiguate vs. conversion failure of the same kind.
+          return recordFix(fix, /*impact=*/2) ? SolutionKind::Error
+                                              : SolutionKind::Solved;
         }
       }
 

test/Sema/enum_raw_representable.swift

@@ -146,10 +146,10 @@ rdar32431165_2(42, E_32431165.bar)
 // or constructing raw representable type from second, both ways are valid.
 do {
   E_32431165.bar == "bar"
-  // expected-error@-1 {{binary operator '==' cannot be applied to operands of type 'E_32431165' and 'String'}} expected-note@-1 {{partially matching parameter lists: (String, String)}}
+  // expected-error@-1 {{cannot convert value of type 'E_32431165' to expected argument type 'String'}} {{17-17=.rawValue}}
 
   "bar" == E_32431165.bar
-  // expected-error@-1 {{binary operator '==' cannot be applied to operands of type 'String' and 'E_32431165'}} expected-note@-1 {{partially matching parameter lists: (String, String)}}
+  // expected-error@-1 {{cannot convert value of type 'E_32431165' to expected argument type 'String'}} {{26-26=.rawValue}}
 }
 
 func rdar32431165_overloaded() -> Int { 42 }     // expected-note {{'rdar32431165_overloaded()' produces 'Int', not the expected contextual result type 'E_32431165'}}