[SR-8081] Store @_implements synonyms in .swiftmodules.

include/swift/Serialization/ModuleFormat.h

@@ -55,7 +55,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t VERSION_MINOR = 448; // Last change: assoc type default is interface type
+const uint16_t VERSION_MINOR = 449; // Last change: serialize @_implements names
 
 using DeclIDField = BCFixed<31>;
 

lib/Serialization/Serialization.cpp

@@ -1814,6 +1814,16 @@ void Serializer::writeMembers(DeclID parentID,
         (*memberTable)[parentID].push_back(memberID);
       }
 
+      // Same as above, but for @_implements attributes
+      if (auto A = VD->getAttrs().getAttribute<ImplementsAttr>()) {
+        std::unique_ptr<DeclMembersTable> &memberTable =
+          DeclMemberNames[A->getMemberName().getBaseName()].second;
+        if (!memberTable) {
+          memberTable = llvm::make_unique<DeclMembersTable>();
+        }
+        (*memberTable)[parentID].push_back(memberID);
+      }
+
       // Possibly add a record to ClassMembersForDynamicLookup too.
       if (isClass) {
         if (VD->canBeAccessedByDynamicLookup()) {

test/attr/attr_implements_serial.swift

@@ -0,0 +1,33 @@
+// RUN: %empty-directory(%t)
+// RUN: echo 'client()' >%t/main.swift
+// RUN: %target-swiftc_driver -module-name AttrImplFP -emit-module -emit-module-path %t/AttrImplFP.swiftmodule -emit-library -o %t/library.%target-dylib-extension %S/attr_implements_fp.swift
+// RUN: %target-swiftc_driver -I %t -o %t/a.out %s %t/main.swift %t/library.%target-dylib-extension
+// RUN: %target-run %t/a.out | %FileCheck %s
+// REQUIRES: executable_test
+
+// This test just checks that the lookup-table entries for @_implements are
+// also written-to and read-from serialized .swiftmodules
+
+import AttrImplFP
+
+public func client() {
+  assert(compare_Comparables(Fauxt.one, Fauxt.two))
+  assert(comparedAsComparablesCount == 1)
+  // CHECK: compared as Comparables
+  assert(compare_Comparables(Fauxt.one, Fauxt.nan))
+  assert(comparedAsComparablesCount == 2)
+  // CHECK: compared as Comparables
+  assert(!compare_Comparables(Fauxt.nan, Fauxt.one))
+  assert(comparedAsComparablesCount == 3)
+  // CHECK: compared as Comparables
+
+  assert(compare_Fauxts(Fauxt.one, Fauxt.two))
+  assert(comparedAsFauxtsCount == 1)
+  // CHECK: compared as Fauxts
+  assert(!compare_Fauxts(Fauxt.one, Fauxt.nan))
+  assert(comparedAsFauxtsCount == 2)
+  // CHECK: compared as Fauxts
+  assert(!compare_Fauxts(Fauxt.nan, Fauxt.one))
+  assert(comparedAsFauxtsCount == 3)
+  // CHECK: compared as Fauxts
+}