[Sema] Diagnose use of unavailable protocols in type erasing expressions (e.g. let x: P = S where S conforms to P).

Resolves rdar://83731428.

Author: tshortli

lib/Sema/TypeCheckAvailability.cpp

@@ -2863,6 +2863,12 @@ class ExprAvailabilityWalker : public ASTWalker {
         return skipChildren();
       }
     }
+    
+    if (auto EE = dyn_cast<ErasureExpr>(E)) {
+      for (ProtocolConformanceRef C : EE->getConformances()) {
+        diagnoseConformanceAvailability(E->getLoc(), C, Where);
+      }
+    }
 
     return visitChildren();
   }

test/Sema/conformance_availability.swift

@@ -4,6 +4,7 @@
 
 public protocol Horse {}
 func takesHorse<T : Horse>(_: T) {}
+func takesHorseExistential(_: Horse) {}
 
 extension Horse {
   func giddyUp() {}
@@ -17,10 +18,11 @@ public struct HasUnavailableConformance1 {}
 
 @available(*, unavailable)
 extension HasUnavailableConformance1 : Horse {}
-// expected-note@-1 6{{conformance of 'HasUnavailableConformance1' to 'Horse' has been explicitly marked unavailable here}}
+// expected-note@-1 7{{conformance of 'HasUnavailableConformance1' to 'Horse' has been explicitly marked unavailable here}}
 
 func passUnavailableConformance1(x: HasUnavailableConformance1) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance1' to 'Horse' is unavailable}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance1' to 'Horse' is unavailable}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance1' to 'Horse' is unavailable}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance1' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance1' to 'Horse' is unavailable}}
@@ -30,6 +32,7 @@ func passUnavailableConformance1(x: HasUnavailableConformance1) {
 @available(*, unavailable)
 func passUnavailableConformance1a(x: HasUnavailableConformance1) {
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = x[keyPath: \.isGalloping]
@@ -41,10 +44,11 @@ public struct HasUnavailableConformance2 {}
 
 @available(macOS, unavailable)
 extension HasUnavailableConformance2 : Horse {}
-// expected-note@-1 5{{conformance of 'HasUnavailableConformance2' to 'Horse' has been explicitly marked unavailable here}}
+// expected-note@-1 6{{conformance of 'HasUnavailableConformance2' to 'Horse' has been explicitly marked unavailable here}}
 
 func passUnavailableConformance2(x: HasUnavailableConformance2) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance2' to 'Horse' is unavailable in macOS}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance2' to 'Horse' is unavailable in macOS}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance2' to 'Horse' is unavailable in macOS}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance2' to 'Horse' is unavailable in macOS}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance2' to 'Horse' is unavailable in macOS}}
@@ -55,6 +59,7 @@ func passUnavailableConformance2(x: HasUnavailableConformance2) {
 func passUnavailableConformance2a(x: HasUnavailableConformance2) {
   // This is allowed
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = x[keyPath: \.isGalloping]
@@ -65,10 +70,11 @@ public struct HasUnavailableConformance3 {}
 
 @available(swift 12)
 extension HasUnavailableConformance3 : Horse {}
-// expected-note@-1 10{{conformance of 'HasUnavailableConformance3' to 'Horse' was introduced in Swift 12}}
+// expected-note@-1 12{{conformance of 'HasUnavailableConformance3' to 'Horse' was introduced in Swift 12}}
 
 func passUnavailableConformance3(x: HasUnavailableConformance3) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
@@ -78,6 +84,7 @@ func passUnavailableConformance3(x: HasUnavailableConformance3) {
 @available(swift 12)
 func passUnavailableConformance3a(x: HasUnavailableConformance3) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance3' to 'Horse' is unavailable}}
@@ -89,10 +96,11 @@ public struct HasUnavailableConformance4 {}
 
 @available(macOS, obsoleted: 10.1)
 extension HasUnavailableConformance4 : Horse {}
-// expected-note@-1 10{{conformance of 'HasUnavailableConformance4' to 'Horse' was obsoleted in macOS 10.1}}
+// expected-note@-1 12{{conformance of 'HasUnavailableConformance4' to 'Horse' was obsoleted in macOS 10.1}}
 
 func passUnavailableConformance4(x: HasUnavailableConformance4) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable}}
@@ -102,6 +110,7 @@ func passUnavailableConformance4(x: HasUnavailableConformance4) {
 @available(macOS, obsoleted: 10.1)
 func passUnavailableConformance4a(x: HasUnavailableConformance4) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable in macOS}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance4' to 'Horse' is unavailable}}
@@ -113,10 +122,11 @@ public struct HasUnavailableConformance5 {}
 
 @available(swift, obsoleted: 4)
 extension HasUnavailableConformance5 : Horse {}
-// expected-note@-1 10{{conformance of 'HasUnavailableConformance5' to 'Horse' was obsoleted in Swift 4}}
+// expected-note@-1 12{{conformance of 'HasUnavailableConformance5' to 'Horse' was obsoleted in Swift 4}}
 
 func passUnavailableConformance5(x: HasUnavailableConformance5) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
@@ -126,6 +136,7 @@ func passUnavailableConformance5(x: HasUnavailableConformance5) {
 @available(swift, obsoleted: 4)
 func passUnavailableConformance5a(x: HasUnavailableConformance5) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance5' to 'Horse' is unavailable}}
@@ -137,10 +148,11 @@ public struct HasUnavailableConformance6 {}
 
 @available(*, unavailable, message: "This conformance is bad")
 extension HasUnavailableConformance6 : Horse {}
-// expected-note@-1 5{{conformance of 'HasUnavailableConformance6' to 'Horse' has been explicitly marked unavailable here}}
+// expected-note@-1 6{{conformance of 'HasUnavailableConformance6' to 'Horse' has been explicitly marked unavailable here}}
 
 func passUnavailableConformance6(x: HasUnavailableConformance6) {
   takesHorse(x) // expected-error {{conformance of 'HasUnavailableConformance6' to 'Horse' is unavailable: This conformance is bad}}
+  takesHorseExistential(x) // expected-error {{conformance of 'HasUnavailableConformance6' to 'Horse' is unavailable: This conformance is bad}}
   x.giddyUp() // expected-error {{conformance of 'HasUnavailableConformance6' to 'Horse' is unavailable: This conformance is bad}}
   _ = x.isGalloping // expected-error {{conformance of 'HasUnavailableConformance6' to 'Horse' is unavailable: This conformance is bad}}
   _ = x[keyPath: \.isGalloping] // expected-error {{conformance of 'HasUnavailableConformance6' to 'Horse' is unavailable: This conformance is bad}}
@@ -155,6 +167,7 @@ extension HasDeprecatedConformance1 : Horse {}
 
 func passDeprecatedConformance1(x: HasDeprecatedConformance1) {
   takesHorse(x) // expected-warning {{conformance of 'HasDeprecatedConformance1' to 'Horse' is deprecated}}
+  takesHorseExistential(x) // expected-warning {{conformance of 'HasDeprecatedConformance1' to 'Horse' is deprecated}}
   x.giddyUp() // expected-warning {{conformance of 'HasDeprecatedConformance1' to 'Horse' is deprecated}}
   _ = x.isGalloping // expected-warning {{conformance of 'HasDeprecatedConformance1' to 'Horse' is deprecated}}
   _ = x[keyPath: \.isGalloping] // expected-warning {{conformance of 'HasDeprecatedConformance1' to 'Horse' is deprecated}}
@@ -164,6 +177,7 @@ func passDeprecatedConformance1(x: HasDeprecatedConformance1) {
 @available(*, deprecated)
 func passDeprecatedConformance1a(x: HasDeprecatedConformance1) {
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = x[keyPath: \.isGalloping]
@@ -178,6 +192,7 @@ extension HasDeprecatedConformance2 : Horse {}
 
 func passDeprecatedConformance2(x: HasDeprecatedConformance2) {
   takesHorse(x) // expected-warning {{conformance of 'HasDeprecatedConformance2' to 'Horse' is deprecated: This conformance is deprecated}}
+  takesHorseExistential(x) // expected-warning {{conformance of 'HasDeprecatedConformance2' to 'Horse' is deprecated: This conformance is deprecated}}
   x.giddyUp() // expected-warning {{conformance of 'HasDeprecatedConformance2' to 'Horse' is deprecated: This conformance is deprecated}}
   _ = x.isGalloping // expected-warning {{conformance of 'HasDeprecatedConformance2' to 'Horse' is deprecated: This conformance is deprecated}}
   _ = x[keyPath: \.isGalloping] // expected-warning {{conformance of 'HasDeprecatedConformance2' to 'Horse' is deprecated: This conformance is deprecated}}
@@ -187,6 +202,7 @@ func passDeprecatedConformance2(x: HasDeprecatedConformance2) {
 @available(*, deprecated)
 func passDeprecatedConformance2a(x: HasDeprecatedConformance2) {
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = x[keyPath: \.isGalloping]
@@ -201,6 +217,7 @@ extension HasDeprecatedConformance3 : Horse {}
 
 func passDeprecatedConformance3(x: HasDeprecatedConformance3) {
   takesHorse(x) // expected-warning {{conformance of 'HasDeprecatedConformance3' to 'Horse' was deprecated in macOS 10.8}}
+  takesHorseExistential(x) // expected-warning {{conformance of 'HasDeprecatedConformance3' to 'Horse' was deprecated in macOS 10.8}}
   x.giddyUp() // expected-warning {{conformance of 'HasDeprecatedConformance3' to 'Horse' was deprecated in macOS 10.8}}
   _ = x.isGalloping // expected-warning {{conformance of 'HasDeprecatedConformance3' to 'Horse' was deprecated in macOS 10.8}}
   _ = x[keyPath: \.isGalloping] // expected-warning {{conformance of 'HasDeprecatedConformance3' to 'Horse' was deprecated in macOS 10.8}}
@@ -213,6 +230,7 @@ func passDeprecatedConformance3a(x: HasDeprecatedConformance3) {
     // This branch is dead with our minimum deployment target, so don't emit
     // deprecation diagnostics in it.
     takesHorse(x)
+    takesHorseExistential(x)
     x.giddyUp()
     _ = x.isGalloping
     _ = x[keyPath: \.isGalloping]
@@ -231,10 +249,13 @@ extension HasAvailableConformance1 : Horse {}
 // in test/Sema/conformance_availability_warn.swift for the same example
 // but without this flag.
 
-func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 5{{add @available attribute to enclosing global function}}
+func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 6{{add @available attribute to enclosing global function}}
   takesHorse(x) // expected-error {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
   // expected-note@-1 {{add 'if #available' version check}}
 
+  takesHorseExistential(x) // expected-error {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
+  // expected-note@-1 {{add 'if #available' version check}}
+
   x.giddyUp() // expected-error {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
   // expected-note@-1 {{add 'if #available' version check}}
 
@@ -251,6 +272,7 @@ func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 5
 @available(macOS 100, *)
 func passAvailableConformance1a(x: HasAvailableConformance1) {
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = x[keyPath: \.isGalloping]

test/Sema/conformance_availability_warn.swift

@@ -4,6 +4,7 @@
 
 public protocol Horse {}
 func takesHorse<T : Horse>(_: T) {}
+func takesHorseExistential(_: Horse) {}
 
 extension Horse {
   func giddyUp() {}
@@ -23,10 +24,13 @@ extension HasAvailableConformance1 : Horse {}
 // test case in test/Sema/conformance_availability.swift for the same
 // example but with this flag.
 
-func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 5{{add @available attribute to enclosing global function}}
+func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 6{{add @available attribute to enclosing global function}}
   takesHorse(x) // expected-warning {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
   // expected-note@-1 {{add 'if #available' version check}}
 
+  takesHorseExistential(x) // expected-warning {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
+  // expected-note@-1 {{add 'if #available' version check}}
+  
   x.giddyUp() // expected-warning {{conformance of 'HasAvailableConformance1' to 'Horse' is only available in macOS 100 or newer}}
   // expected-note@-1 {{add 'if #available' version check}}
 
@@ -43,6 +47,7 @@ func passAvailableConformance1(x: HasAvailableConformance1) { // expected-note 5
 @available(macOS 100, *)
 func passAvailableConformance1a(x: HasAvailableConformance1) {
   takesHorse(x)
+  takesHorseExistential(x)
   x.giddyUp()
   _ = x.isGalloping
   _ = UsesHorse<HasAvailableConformance1>.self