[Deserialization] Require labels to match when looking for closely-matching clang declarations

Author: DougGregor

include/swift/AST/Types.h

@@ -372,6 +372,8 @@ enum class TypeMatchFlags {
   IgnoreSendability = 1 << 7,
   /// Ignore global actor isolation attributes on functions when matching types.
   IgnoreFunctionGlobalActorIsolation = 1 << 8,
+  /// Require parameter labels to match.
+  RequireMatchingParameterLabels = 1 << 9,
 };
 using TypeMatchOptions = OptionSet<TypeMatchFlags>;
 

lib/AST/Type.cpp

@@ -3604,6 +3604,11 @@ static bool matches(CanType t1, CanType t2, TypeMatchOptions matchMode,
                      OptionalUnwrapping::None)) {
           return false;
         }
+
+        if (matchMode.contains(TypeMatchFlags::RequireMatchingParameterLabels)&&
+            fn1Params[i].getLabel() != fn2Params[i].getLabel()) {
+          return false;
+        }
       }
 
       // Results are covariant.

lib/Serialization/Deserialization.cpp

@@ -2013,7 +2013,8 @@ namespace {
       return TypeComparison::Equal;
 
     if (nearMatchOk) {
-      TypeMatchOptions options = TypeMatchFlags::AllowTopLevelOptionalMismatch;
+      TypeMatchOptions options = TypeMatchFlags::RequireMatchingParameterLabels;
+      options |= TypeMatchFlags::AllowTopLevelOptionalMismatch;
       options |= TypeMatchFlags::AllowNonOptionalForIUOParam;
       options |= TypeMatchFlags::IgnoreNonEscapingForOptionalFunctionParam;
       options |= TypeMatchFlags::IgnoreFunctionSendability;