[code-complete] Update literal protocol to show "" for Character

... and UnicodeScalar, which is technically more correct than only
showing it for String.  This also happens to workaround a bug where we
won't show "" for string.contains.

rdar://problem/34746368

Author: benlangmuir

lib/IDE/CodeCompletion.cpp

@@ -1521,7 +1521,7 @@ protocolForLiteralKind(CodeCompletionLiteralKind kind) {
   case CodeCompletionLiteralKind::NilLiteral:
     return KnownProtocolKind::ExpressibleByNilLiteral;
   case CodeCompletionLiteralKind::StringLiteral:
-    return KnownProtocolKind::ExpressibleByStringLiteral;
+    return KnownProtocolKind::ExpressibleByUnicodeScalarLiteral;
   case CodeCompletionLiteralKind::Tuple:
     llvm_unreachable("no such protocol kind");
   }

test/IDE/complete_value_literals.swift

@@ -14,6 +14,9 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_0 | %FileCheck %s -check-prefix=STRING_0
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_1 | %FileCheck %s -check-prefix=STRING_1
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_2 | %FileCheck %s -check-prefix=STRING_2
+// RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_3 | %FileCheck %s -check-prefix=STRING_3
+// RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_4 | %FileCheck %s -check-prefix=STRING_4
+// RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=STRING_5 | %FileCheck %s -check-prefix=STRING_5
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=ARRAY_0 | %FileCheck %s -check-prefix=ARRAY_0
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=ARRAY_1 | %FileCheck %s -check-prefix=ARRAY_1
 // RUN: %target-swift-ide-test -code-completion -source-filename=%s -code-completion-token=ARRAY_2 | %FileCheck %s -check-prefix=ARRAY_2
@@ -62,6 +65,13 @@ struct MyString1: ExpressibleByStringLiteral {
   init(extendedGraphemeClusterLiteral value: String) {}
   init(stringLiteral value: String) {}
 }
+struct MyUnicodeScalar1: ExpressibleByUnicodeScalarLiteral {
+  init(unicodeScalarLiteral value: Character) {}
+}
+struct MyCharacter1: ExpressibleByExtendedGraphemeClusterLiteral {
+  init(unicodeScalarLiteral value: Character) {}
+  init(extendedGraphemeClusterLiteral value: String) {}
+}
 struct MyArray1<Element>: ExpressibleByArrayLiteral {
   init(arrayLiteral value: Element...) {}
 }
@@ -154,6 +164,19 @@ func testString2() {
 }
 // STRING_2: Literal[String]/None/TypeRelation[Identical]: "{#(abc)#}"[#String#];
 
+func testString3() {
+  let x: MyUnicodeScalar1 = #^STRING_3^#
+}
+// STRING_3: Literal[String]/None/TypeRelation[Identical]: "{#(abc)#}"[#MyUnicodeScalar1#];
+func testString4() {
+  let x: MyCharacter1 = #^STRING_4^#
+}
+// STRING_4: Literal[String]/None/TypeRelation[Identical]: "{#(abc)#}"[#MyCharacter1#];
+func testString5() {
+  let x: Character = #^STRING_5^#
+}
+// STRING_5: Literal[String]/None/TypeRelation[Identical]: "{#(abc)#}"[#Character#];
+
 func testArray0() {
   let x: Int = #^ARRAY_0^#
 }