Sema: Also diagnose availability inside keypath index expressions

Author: slavapestov

lib/Sema/TypeCheckAvailability.cpp

@@ -2307,8 +2307,7 @@ class AvailabilityWalker : public ASTWalker {
       }
     }
     if (auto KP = dyn_cast<KeyPathExpr>(E)) {
-      walkKeyPath(KP);
-      return skipChildren();
+      maybeDiagKeyPath(KP);
     }
     if (auto A = dyn_cast<AssignExpr>(E)) {
       walkAssignExpr(A);
@@ -2406,7 +2405,7 @@ class AvailabilityWalker : public ASTWalker {
 
   /// Walk a keypath expression, checking all of its components for
   /// availability.
-  void walkKeyPath(KeyPathExpr *KP) {
+  void maybeDiagKeyPath(KeyPathExpr *KP) {
     for (auto &component : KP->getComponents()) {
       switch (component.getKind()) {
       case KeyPathExpr::Component::Kind::Property:

test/expr/unary/keypath/keypath.swift

@@ -62,6 +62,11 @@ struct Deprecated {
   subscript(x: Sub) -> Int { get { } set { } }
 }
 
+@available(*, deprecated)
+func getDeprecatedSub() -> Sub {
+  return Sub()
+}
+
 extension Array where Element == A {
   var property: Prop { fatalError() }
 }
@@ -202,6 +207,8 @@ func testKeyPath(sub: Sub, optSub: OptSub,
 
   let _ = \Deprecated.deprecatedProperty // expected-warning {{'deprecatedProperty' is deprecated}}
   let _ = \Deprecated.[sub] // expected-warning {{'subscript' is deprecated}}
+
+  let _ = \A.[getDeprecatedSub()] // expected-warning {{'getDeprecatedSub()' is deprecated}}
 }
 
 func testKeyPathInGenericContext<H: Hashable, X>(hashable: H, anything: X) {