[CodeCompletion] Don't suggest underscored module name

Underscored modules (e.g. '_Concurrency') are usually not meant be
written explicitly in source code. They are usually implicitly imported
with other modules. Code completion should not suggest them in type and
expression context.

rdar://78232229

Author: rintaro

lib/IDE/CodeCompletion.cpp

@@ -2078,6 +2078,12 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
     IncludeInstanceMembers = true;
   }
 
+  bool isHiddenModuleName(Identifier Name) {
+    return (Name.str().startswith("_") ||
+            Name == Ctx.SwiftShimsModuleName ||
+            Name.str() == SWIFT_ONONE_SUPPORT);
+  }
+
   void addSubModuleNames(std::vector<std::pair<std::string, bool>>
       &SubModuleNameVisibilityPairs) {
     for (auto &Pair : SubModuleNameVisibilityPairs) {
@@ -2142,10 +2148,7 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
 
     auto mainModuleName = CurrModule->getName();
     for (auto ModuleName : ModuleNames) {
-      if (ModuleName.str().startswith("_") ||
-          ModuleName == mainModuleName ||
-          ModuleName == Ctx.SwiftShimsModuleName ||
-          ModuleName.str() == SWIFT_ONONE_SUPPORT)
+      if (ModuleName == mainModuleName || isHiddenModuleName(ModuleName))
         continue;
 
       auto MD = ModuleDecl::create(ModuleName, Ctx);
@@ -6257,8 +6260,10 @@ static void deliverCompletionResults(CodeCompletionContext &CompletionContext,
         RequestedModules.push_back({std::move(K), TheModule,
           Request.OnlyTypes, Request.OnlyPrecedenceGroups});
 
+        auto TheModuleName = TheModule->getName();
         if (Request.IncludeModuleQualifier &&
-            seenModuleNames.insert(TheModule->getName()).second)
+            !Lookup.isHiddenModuleName(TheModuleName) &&
+            seenModuleNames.insert(TheModuleName).second)
           Lookup.addModuleName(TheModule);
       }
     };

test/IDE/complete_modulename.swift

@@ -0,0 +1,53 @@
+// BEGIN MyModule.swift
+public struct MyModuleTy {}
+public func myModuleFunc() {}
+
+
+// BEGIN _Hidden.swift
+public struct HiddenTy {}
+public func hiddenFunc() {}
+
+// BEGIN App.swift
+
+import MyModule
+import _Hidden
+
+func test() {
+ let _ = #^EXPR^#
+
+ func test() -> #^TYPE^#
+}
+
+// EXPR: Begin completion
+// EXPR-NOT: _Concurrency[#Module#]
+// EXPR-NOT: SwiftShims[#Module#]
+// EXPR-NOT: SwiftOnoneSupport[#Module#]
+// EXPR-DAG: Decl[Module]/None:                  swift_ide_test[#Module#]; name=swift_ide_test
+// EXPR-DAG: Decl[Module]/None/IsSystem:         Swift[#Module#]; name=Swift
+// EXPR-DAG: Decl[Module]/None:                  MyModule[#Module#]; name=MyModule
+// EXPR-DAG: Decl[Struct]/OtherModule[MyModule]: MyModuleTy[#MyModuleTy#]; name=MyModuleTy
+// EXPR-DAG: Decl[Struct]/OtherModule[_Hidden]:  HiddenTy[#HiddenTy#]; name=HiddenTy
+// EXPR-DAG: Decl[FreeFunction]/OtherModule[MyModule]: myModuleFunc()[#Void#]; name=myModuleFunc()
+// EXPR-DAG: Decl[FreeFunction]/OtherModule[_Hidden]: hiddenFunc()[#Void#]; name=hiddenFunc()
+// EXPR: End completions
+
+// TYPE: Begin completion
+// TYPE-NOT: _Concurrency[#Module#]
+// TYPE-NOT: SwiftShims[#Module#]
+// TYPE-NOT: SwiftOnoneSupport[#Module#]
+// TYPE-DAG: Decl[Module]/None:                  swift_ide_test[#Module#]; name=swift_ide_test
+// TYPE-DAG: Decl[Module]/None/IsSystem:         Swift[#Module#]; name=Swift
+// TYPE-DAG: Decl[Module]/None:                  MyModule[#Module#]; name=MyModule
+// TYPE-DAG: Decl[Struct]/OtherModule[MyModule]: MyModuleTy[#MyModuleTy#]; name=MyModuleTy
+// TYPE-DAG: Decl[Struct]/OtherModule[_Hidden]:  HiddenTy[#HiddenTy#]; name=HiddenTy
+// TYPE: End completions
+
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+
+// RUN: %empty-directory(%t/Modules)
+// RUN: %target-swift-frontend -emit-module -module-name MyModule -o %t/Modules %t/MyModule.swift
+// RUN: %target-swift-frontend -emit-module -module-name _Hidden -o %t/Modules %t/_Hidden.swift
+
+// RUN: %empty-directory(%t/Out)
+// RUN: %target-swift-ide-test -batch-code-completion -source-filename %t/App.swift -filecheck %raw-FileCheck -completion-output-dir %t/Out -I %t/Modules