[IDE] Completion after a qualifying module should return symbols from its shadowing cross-import overlays.

Author: Nathan Hawes

lib/IDE/CodeCompletion.cpp

@@ -1763,7 +1763,7 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
   }
 
   void addModuleName(
-      const ModuleDecl *MD,
+      ModuleDecl *MD,
       Optional<CodeCompletionResult::NotRecommendedReason> R = None) {
 
     // Don't add underscored cross-import overlay modules.
@@ -3293,16 +3293,29 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
   bool tryModuleCompletions(Type ExprType, bool TypesOnly = false) {
     if (auto MT = ExprType->getAs<ModuleType>()) {
       ModuleDecl *M = MT->getModule();
-      if (CurrModule != M) {
-        // Only use the cache if it is not the current module.
+
+      // Only lookup this module's symbols from the cache if it is not the
+      // current module.
+      if (M == CurrModule)
+        return false;
+
+      // If the module is shadowed by a separately imported overlay(s), look up
+      // the symbols from the overlay(s) instead.
+      SmallVector<ModuleDecl *, 1> ShadowingOrOriginal;
+      if (auto *SF = CurrDeclContext->getParentSourceFile()) {
+        SF->getSeparatelyImportedOverlays(M, ShadowingOrOriginal);
+        if (ShadowingOrOriginal.empty())
+          ShadowingOrOriginal.push_back(M);
+      }
+      for (ModuleDecl *M: ShadowingOrOriginal) {
         RequestedResultsTy Request = RequestedResultsTy::fromModule(M)
             .needLeadingDot(needDot())
             .withModuleQualifier(false);
         if (TypesOnly)
           Request = Request.onlyTypes();
         RequestedCachedResults.push_back(Request);
-        return true;
       }
+      return true;
     }
     return false;
   }

test/IDE/complete_cross_import.swift

@@ -7,6 +7,10 @@
 // RUN: %FileCheck --input-file %t/results.tmp --check-prefix=IMPORT %s
 // RUN: %FileCheck --input-file %t/results.tmp --check-prefix=IMPORT-NEGATIVE %s
 
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -enable-cross-import-overlays -I %S/Inputs/CrossImport -code-completion-token=SCOPED > %t/results.tmp
+// RUN: %FileCheck --input-file %t/results.tmp --check-prefix=SCOPED %s
+// RUN: %FileCheck --input-file %t/results.tmp --check-prefix=SCOPED-NEGATIVE %s
+
 import A
 import B
 
@@ -39,3 +43,17 @@ import #^IMPORT^#
 // IMPORT-NEGATIVE-NOT: _ABAdditions
 // IMPORT-NEGATIVE-NOT: __ABAdditionsDAdditions
 
+
+func bar() {
+	A.#^SCOPED^#
+}
+
+// SCOPED-DAG: Decl[FreeFunction]/OtherModule[A]:  from_ABAdditions()[#Void#]; name=from_ABAdditions()
+// SCOPED-DAG: Decl[FreeFunction]/OtherModule[A]:  fromA()[#Void#]; name=fromA()
+
+// SCOPED-NEGATIVE-NOT: name=_ABAdditions
+// SCOPED-NEGATIVE-NOT: name=__ABAdditionsDAdditions
+// SCOPED-NEGATIVE-NOT: name=fromB
+// SCOPED-NEGATIVE-NOT: [_ABAdditions]
+// SCOPED-NEGATIVE-NOT: [__ABAdditionsDAdditions]
+