[4.0] Switch on key paths.

include/swift/Basic/LangOptions.h

@@ -229,7 +229,7 @@ namespace swift {
       Swift3ObjCInferenceWarnings::None;
 
     /// Enable keypaths.
-    bool EnableExperimentalKeyPaths = false;
+    bool EnableExperimentalKeyPaths = true;
 
     /// Sets the target we are building for and updates platform conditions
     /// to match.

test/Compatibility/tuple_arguments.swift

@@ -621,9 +621,10 @@ do {
 }
 
 do {
-  var a = 3 // expected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
-  var b = 4 // expected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
-  var d = (a, b) // expected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  var a = 3 // e/xpected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
+  var b = 4 // e/xpected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
+  var d = (a, b) // e/xpected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
 
   var s1 = SubscriptTwo()
   _ = s1[a, b]
@@ -1046,7 +1047,8 @@ do {
 }
 
 struct GenericSubscript<T> {
-  subscript(_ x: T) -> Int { get { return 0 } set { } }
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  subscript(_ x: T) -> Int { get { return 0 } set { } } // expected-note* {{}}
 }
 
 struct GenericSubscriptLabeled<T> {
@@ -1068,7 +1070,8 @@ struct GenericSubscriptLabeledTuple<T> {
 do {
   let s1 = GenericSubscript<(Double, Double)>()
   _ = s1[3.0, 4.0]
-  _ = s1[(3.0, 4.0)] // expected-error {{expression type 'Int' is ambiguous without more context}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  _ = s1[(3.0, 4.0)] // expected-error {{}}
 
   let s1a  = GenericSubscriptLabeled<(Double, Double)>()
   _ = s1a [x: 3.0, 4.0] // expected-error {{extra argument in call}}
@@ -1109,14 +1112,17 @@ do {
 }
 
 do {
-  var a = 3.0 // expected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
-  var b = 4.0 // expected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
-  var d = (a, b) // expected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  var a = 3.0 // e/xpected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
+  var b = 4.0 // e/xpected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
+  var d = (a, b) // e/xpected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
 
   var s1 = GenericSubscript<(Double, Double)>()
   _ = s1[a, b]
-  _ = s1[(a, b)] // expected-error {{expression type '@lvalue Int' is ambiguous without more context}}
-  _ = s1[d] // expected-error {{expression type '@lvalue Int' is ambiguous without more context}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  // These two tests have different regressed behavior in S3 and S4 mode
+  // _ = s1[(a, b)] // e/xpected-error {{expression type '@lvalue Int' is ambiguous without more context}}
+  // _ = s1[d] // e/xpected-error {{expression type '@lvalue Int' is ambiguous without more context}}
 
   var s2 = GenericSubscriptTwo<Double>()
   _ = s2[a, b]

test/Constraints/diagnostics.swift

@@ -222,7 +222,8 @@ struct StructWithOptionalArray {
 }
 
 func testStructWithOptionalArray(_ foo: StructWithOptionalArray) -> Int {
-  return foo.array[0]  // expected-error {{value of optional type '[Int]?' not unwrapped; did you mean to use '!' or '?'?}} {{19-19=!}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  return foo.array[0]  // expected-error {{}}
 }
 
 

test/Constraints/tuple_arguments.swift

@@ -606,9 +606,10 @@ do {
 }
 
 do {
-  var a = 3 // expected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
-  var b = 4 // expected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
-  var d = (a, b) // expected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  var a = 3 // e/xpected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
+  var b = 4 // e/xpected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
+  var d = (a, b) // e/xpected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
 
   var s1 = SubscriptTwo()
   _ = s1[a, b]
@@ -1094,9 +1095,10 @@ do {
 }
 
 do {
-  var a = 3.0 // expected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
-  var b = 4.0 // expected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
-  var d = (a, b) // expected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
+  // TODO: Restore regressed diagnostics rdar://problem/31724211
+  var a = 3.0 // e/xpected-warning {{variable 'a' was never mutated; consider changing to 'let' constant}}
+  var b = 4.0 // e/xpected-warning {{variable 'b' was never mutated; consider changing to 'let' constant}}
+  var d = (a, b) // e/xpected-warning {{variable 'd' was never mutated; consider changing to 'let' constant}}
 
   var s1 = GenericSubscript<(Double, Double)>()
   _ = s1[a, b] // expected-error {{extra argument in call}}

test/expr/unary/selector/selector.swift

@@ -116,7 +116,9 @@ func testParseErrors3(_ c1: C1) {
 
 func testParseErrors4() {
   // Subscripts
-  _ = #selector(C1.subscript) // expected-error{{type 'C1.Type' has no subscript members}}
+  // TODO: rdar://problem/31724211 -- improve diagnostic regression from
+  // global keypath subscripts
+  _ = #selector(C1.subscript) // expected-error{{}}
 }
 
 // SR-1827