[CodeCompletion] Don't emit failable initialization for member types

in unresolved member completion.

Author: rintaro

lib/IDE/CodeCompletion.cpp

@@ -2637,6 +2637,10 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
       for (auto *init : initializers) {
         if (shouldHideDeclFromCompletionResults(init))
           continue;
+        if (IsUnresolvedMember &&
+            cast<ConstructorDecl>(init)->getFailability() == OTK_Optional) {
+          continue;
+        }
         addConstructorCall(cast<ConstructorDecl>(init), Reason, type, None,
                            /*IsOnType=*/true, name);
       }

test/IDE/complete_unresolved_members.swift

@@ -431,6 +431,8 @@ func testInStringInterpolation() {
 class BaseClass {
   class SubClass : BaseClass { init() {} }
   static var subInstance: SubClass = SubClass()
+  init() {}
+  init?(failable: Void) {}
 }
 protocol MyProtocol {
   typealias Concrete1 = BaseClass
@@ -442,6 +444,7 @@ func testSubType() {
   var _: BaseClass = .#^SUBTYPE_1^#
 }
 // SUBTYPE_1: Begin completions, 4 items
+// SUBTYPE_1-NOT: init(failable:
 // SUBTYPE_1-DAG: Decl[Constructor]/CurrNominal/TypeRelation[Identical]: init()[#BaseClass#];
 // SUBTYPE_1-DAG: Decl[Constructor]/CurrNominal/TypeRelation[Convertible]: SubClass()[#BaseClass.SubClass#];
 // SUBTYPE_1-DAG: Decl[StaticVar]/CurrNominal/TypeRelation[Convertible]: subInstance[#BaseClass.SubClass#];
@@ -452,6 +455,7 @@ func testMemberTypealias() {
   var _: MyProtocol = .#^SUBTYPE_2^#
 }
 // SUBTYPE_2: Begin completions, 2 items
+// SUBTYPE_1-NOT: Concrete1(failable:
 // SUBTYPE_2-DAG: Decl[Constructor]/CurrNominal/TypeRelation[Convertible]: Concrete1()[#BaseClass#];
 // SUBTYPE_2-DAG: Decl[Constructor]/CurrNominal/TypeRelation[Convertible]: Concrete2()[#AnotherTy#];
 // SUBTYPE_2: End completions