Merge pull request #42456 from xedin/ban-unavailable-cond-from-opaque

[TypeChecker] Disallow `if #unavailable` to produce different opaque …

Author: xedin

lib/Sema/MiscDiagnostics.cpp

@@ -2848,7 +2848,9 @@ class OpaqueUnderlyingTypeChecker : public ASTWalker {
       // If this is `if #available` statement with no other dynamic
       // conditions, let's check if it returns opaque type directly.
       if (llvm::all_of(If->getCond(), [&](const auto &condition) {
-            return condition.getKind() == StmtConditionElement::CK_Availability;
+            return condition.getKind() ==
+                       StmtConditionElement::CK_Availability &&
+                   !condition.getAvailability()->isUnavailability();
           })) {
         // Check return statement directly with availability context set.
         if (auto *Then = dyn_cast<BraceStmt>(If->getThenStmt())) {

test/type/opaque_with_conditional_availability.swift

@@ -106,3 +106,15 @@ func test_fail_without_universally_available_type() -> some P {
     return Y()
   }
 }
+
+// Treat `if #unavailable` like regular conditions.
+func test_fail_with_unavailability_condition() -> some P {
+  // expected-error@-1 {{function declares an opaque return type 'some P', but the return statements in its body do not have matching underlying types}}
+  // expected-note@-2 {{add @available attribute to enclosing global function}}
+  if #unavailable(macOS 12) {
+    return X() // expected-error {{'X' is only available in macOS 11.0 or newer}} expected-note {{return statement has underlying type 'X'}}
+    // expected-note@-1 {{add 'if #available' version check}}
+  }
+
+  return Y() // expected-note {{return statement has underlying type 'Y'}}
+}