[stdlib] Add fast string interpolation for metatypes

stdlib/public/core/StringInterpolation.swift

@@ -178,7 +178,12 @@ public struct DefaultStringInterpolation: StringInterpolationProtocol {
   public mutating func appendInterpolation<T>(_ value: T) {
     _print_unlocked(value, &self)
   }
-
+
+  @_alwaysEmitIntoClient
+  public mutating func appendInterpolation(_ value: Any.Type) {
+	  _typeName(value, qualified: false).write(to: &self)
+  }
+
   /// Creates a string from this instance, consuming the instance in the
   /// process.
   @inlinable

test/IDE/complete_at_top_level.swift

@@ -471,7 +471,7 @@ var stringInterp = "\(#^STRING_INTERP_3^#)"
 _ = "" + "\(#^STRING_INTERP_4^#)" + ""
 // STRING_INTERP: Begin completions
 // STRING_INTERP-DAG: Decl[InstanceMethod]/CurrNominal/IsSystem: ['(']{#(value): T#}[')'][#Void#];
-// STRING_INTERP-DAG: Decl[Struct]/CurrModule: FooStruct[#FooStruct#];
+// STRING_INTERP-DAG: Decl[Struct]/CurrModule/TypeRelation[Convertible]: FooStruct[#FooStruct#]; name=FooStruct
 // STRING_INTERP-DAG: Decl[FreeFunction]/CurrModule/TypeRelation[Invalid]: fooFunc1()[#Void#];
 // STRING_INTERP-DAG: Decl[FreeFunction]/CurrModule: optStr()[#String?#];
 // STRING_INTERP-DAG: Decl[GlobalVar]/Local: fooObject[#FooStruct#];

test/stdlib/TypeNameInterpolation.swift

@@ -0,0 +1,105 @@
+// RUN: %target-build-swift -O %s -module-name=test -Xfrontend -sil-verify-all -emit-sil | %FileCheck %s
+// RUN: %target-build-swift -Onone %s -module-name=test -Xfrontend -sil-verify-all -emit-sil | %FileCheck %s
+// RUN: %target-run-simple-swift
+// REQUIRES: executable_test
+
+import StdlibUnittest
+
+let TypeNameTests = TestSuite("TypeName")
+
+class C {}
+struct S {}
+enum E {}
+
+protocol P {}
+protocol P2 {}
+protocol P3 {}
+protocol AssociatedTypes {
+  associatedtype A
+  associatedtype B
+  associatedtype C
+}
+
+class Model : AssociatedTypes {
+  typealias A = C
+  typealias B = S
+  typealias C = E
+}
+
+struct Model2 : AssociatedTypes {
+  typealias A = C
+  typealias B = S
+  typealias C = E
+}
+
+class GC<T : AssociatedTypes> {}
+struct GS<T : AssociatedTypes> {}
+enum GE<T : AssociatedTypes> {}
+class GC2<T : AssociatedTypes, U : AssociatedTypes> {}
+
+class SomeOuterClass {
+  struct SomeInnerStruct {}
+  struct SomeInnerGenericStruct<T> {}
+}
+
+class SomeOuterGenericClass<T> {
+  struct SomeInnerStruct {}
+  struct SomeInnerGenericStruct<U> {}
+}
+
+extension SomeOuterGenericClass {
+  struct OtherInnerStruct {}
+  struct OtherInnerGenericStruct<U> {}
+}
+
+@inline(never)
+func printTypename(_ s: String) {
+  print(s)
+}
+
+// CHECK-LABEL: sil {{.*}} @$s4test0A21TypenameInterpolationyyF :
+// CHECK-NOT:     $ss26DefaultStringInterpolationV06appendC0yyxlF
+// CHECK-NOT:     _print_unlocked
+// CHECK:       } // end sil function '$s4test0A21TypenameInterpolationyyF'
+@inline(never)
+func testTypenameInterpolation() {
+  expectEqual("Int", "\(Int.self)")
+  expectEqual("C", "\(C.self)")
+  expectEqual("S", "\(S.self)")
+  expectEqual("E", "\(E.self)")
+  expectEqual("GC<Model>",
+    "\(GC<Model>.self)")
+  expectEqual("GS<Model>",
+    "\(GS<Model>.self)")
+  expectEqual("GE<Model>",
+    "\(GE<Model>.self)")
+  expectEqual("GC2<Model, Model2>",
+    "\(GC2<Model, Model2>.self)")
+
+  expectEqual("P", "\(P.self)")
+  typealias PP2 = P & P2
+  expectEqual("P & P2",
+    "\(PP2.self)")
+  expectEqual("Any", "\(Any.self)")
+  expectEqual("P & P2", "\((P & P2).self)")
+
+
+  expectEqual("SomeInnerStruct",
+              "\(SomeOuterClass.SomeInnerStruct.self)")
+  expectEqual("SomeInnerGenericStruct<Int>",
+              "\(SomeOuterClass.SomeInnerGenericStruct<Int>.self)")
+  expectEqual("SomeInnerStruct",
+              "\(SomeOuterGenericClass<Int>.SomeInnerStruct.self)")
+  expectEqual("SomeInnerGenericStruct<Int>",
+              "\(SomeOuterGenericClass<String>.SomeInnerGenericStruct<Int>.self)")
+  expectEqual("OtherInnerStruct",
+              "\(SomeOuterGenericClass<Int>.OtherInnerStruct.self)")
+  expectEqual("OtherInnerGenericStruct<String>",
+              "\(SomeOuterGenericClass<Int>.OtherInnerGenericStruct<String>.self)")
+}
+
+TypeNameTests.test("Interpolation") {
+  testTypenameInterpolation()
+}
+
+runAllTests()