[CodeCompletion] Add '.Protocol' completion for protocol in type context

Author: rintaro

lib/IDE/CodeCompletion.cpp

@@ -3730,11 +3730,15 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
     Kind = LookupKind::Type;
     this->BaseType = BaseType;
     NeedLeadingDot = !HaveDot;
-    Type MetaBase = MetatypeType::get(BaseType);
-    lookupVisibleMemberDecls(*this, MetaBase,
+    lookupVisibleMemberDecls(*this, MetatypeType::get(BaseType),
                              CurrDeclContext, TypeResolver,
                              IncludeInstanceMembers);
-    addKeyword("Type", MetaBase);
+    if (BaseType->isAnyExistentialType()) {
+      addKeyword("Protocol", MetatypeType::get(BaseType));
+      addKeyword("Type", ExistentialMetatypeType::get(BaseType));
+    } else {
+      addKeyword("Type", MetatypeType::get(BaseType));
+    }
   }
 
   static bool canUseAttributeOnDecl(DeclAttrKind DAK, bool IsInSil,

test/IDE/complete_type.swift

@@ -396,6 +396,8 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=GENERIC_ARGS_LOCAL_PARAM | %FileCheck %s -check-prefix=WITH_GLOBAL_TYPES
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=GENERIC_ARGS_LOCAL_RETURN | %FileCheck %s -check-prefix=WITH_GLOBAL_TYPES
 
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=PROTOCOL_DOT_1 | %FileCheck %s -check-prefix=PROTOCOL_DOT_1
+
 //===--- Helper types that are used in this test
 
 struct FooStruct {
@@ -1082,3 +1084,12 @@ func _testForGenericArg_() {
   func foo1(x: GenStruct<#^GENERIC_ARGS_LOCAL_PARAM^#
   func foo2() -> GenStruct<#^GENERIC_ARGS_LOCAL_RETURN^#
 }
+
+func testProtocol() {
+  let _: FooProtocol.#^PROTOCOL_DOT_1^#
+// PROTOCOL_DOT_1: Begin completions, 3 items
+// PROTOCOL_DOT_1-DAG: Decl[AssociatedType]/CurrNominal:   FooTypeAlias1; name=FooTypeAlias1
+// PROTOCOL_DOT_1-DAG: Keyword/None:                       Protocol[#FooProtocol.Protocol#]; name=Protocol
+// PROTOCOL_DOT_1-DAG: Keyword/None:                       Type[#FooProtocol.Type#]; name=Type
+// PROTOCOL_DOT_1: End completions
+}