[CodeCompletion] Analyze the parent of initializer

For `Initializer` decl context, type context analyzer should look into
its parent context because that might constrain initializer's type.

rdar://problem/48208253
(swift-5.0-version of commit fd9b6a1)

Author: rintaro

lib/IDE/CodeCompletion.cpp

@@ -5409,7 +5409,11 @@ class CodeCompletionTypeContextAnalyzer {
     // We cannot analyze without target.
     if (!ParsedExpr)
       return false;
-    DC->walkContext(Finder);
+
+    // For 'Initializer' context, we need to look into its parent because it
+    // might constrain the initializer's type.
+    auto analyzeDC = isa<Initializer>(DC) ? DC->getParent() : DC;
+    analyzeDC->walkContext(Finder);
 
     for (auto It = Finder.Ancestors.rbegin(); It != Finder.Ancestors.rend();
          ++ It) {

test/IDE/complete_in_accessors.swift

@@ -150,7 +150,7 @@ func returnsInt() -> Int {}
 
 // WITH_MEMBER_DECLS_INIT: Begin completions
 // WITH_MEMBER_DECLS_INIT-DAG: Decl[Struct]/CurrModule:          FooStruct[#FooStruct#]{{; name=.+$}}
-// WITH_MEMBER_DECLS_INIT-DAG: Decl[FreeFunction]/CurrModule:    returnsInt()[#Int#]{{; name=.+$}}
+// WITH_MEMBER_DECLS_INIT-DAG: Decl[FreeFunction]/CurrModule/TypeRelation[Identical]: returnsInt()[#Int#]{{; name=.+$}}
 // WITH_MEMBER_DECLS_INIT-DAG: Decl[InstanceMethod]/CurrNominal: instanceFunc({#self: MemberAccessors#})[#(Int) -> Float#]{{; name=.+$}}
 // WITH_MEMBER_DECLS_INIT: End completions
 

test/IDE/complete_unresolved_members.swift

@@ -78,6 +78,8 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=OVERLOADED_INIT_1 | %FileCheck %s -check-prefix=OVERLOADED_METHOD_1
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=OVERLOADED_INIT_2 | %FileCheck %s -check-prefix=OVERLOADED_METHOD_1
 
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=DECL_MEMBER_INIT_1 | %FileCheck %s -check-prefix=UNRESOLVED_3
+
 enum SomeEnum1 {
   case South
   case North
@@ -535,3 +537,7 @@ func testOverload(val: HasOverloaded) {
   let _ = HasOverloaded(e: .#^OVERLOADED_INIT_2^#)
 // Same as OVERLOADED_METHOD_1.
 }
+
+struct TestingStruct {
+  var value: SomeEnum1 = .#^DECL_MEMBER_INIT_1^#
+}