Merge pull request #82239 from hamishknight/cod-cycle-6.2

[6.2] [Sema] Scale back CodingKeys hack in `TypeChecker::lookupUnqualifiedType`

Author: hamishknight

lib/Sema/TypeCheckNameLookup.cpp

@@ -325,9 +325,6 @@ TypeChecker::lookupUnqualifiedType(DeclContext *dc, DeclNameRef name,
                                    NameLookupOptions options) {
   auto &ctx = dc->getASTContext();
 
-  // HACK: Synthesize CodingKeys if needed.
-  synthesizeCodingKeysIfNeededForUnqualifiedLookup(ctx, dc, name);
-
   auto ulOptions = convertToUnqualifiedLookupOptions(options) |
                    UnqualifiedLookupFlags::TypeLookup;
   {
@@ -336,8 +333,15 @@ TypeChecker::lookupUnqualifiedType(DeclContext *dc, DeclNameRef name,
         name, dc, loc,
         ulOptions - UnqualifiedLookupFlags::AllowProtocolMembers);
 
-    auto lookup =
-        evaluateOrDefault(ctx.evaluator, UnqualifiedLookupRequest{desc}, {});
+    UnqualifiedLookupRequest req(desc);
+    auto lookup = evaluateOrDefault(ctx.evaluator, req, {});
+
+    // HACK: Try synthesize CodingKeys if we got an empty result.
+    if (lookup.allResults().empty() && name.isSimpleName(ctx.Id_CodingKeys)) {
+      synthesizeCodingKeysIfNeededForUnqualifiedLookup(ctx, dc, name);
+      lookup = evaluateOrDefault(ctx.evaluator, req, {});
+    }
+
     if (!lookup.allResults().empty())
       return lookup;
   }

test/Sema/rdar153096639.swift

@@ -0,0 +1,18 @@
+// RUN: %target-typecheck-verify-swift
+
+// Make sure we don't run into a request cycle for the below use of 'CodingKeys'
+// in an `init(from:)` signature.
+
+protocol P {
+  associatedtype X
+}
+
+struct S: Codable {
+  var foo: String?
+
+  enum CodingKeys: CodingKey {
+    case foo
+  }
+
+  init<T: P>(from: T) where T.X == CodingKeys {}
+}