[Sema] Don't emit -Wunguarded-availability for switch cases

[erik.pilkington]

Summary

Currently, this has pretty terrible ergonomics for the fairly common case of switching over an enum which has some entries that are partial. Thanks to Nico Weber for pointing this out!

Thanks,
Erik

[arphaman]

Thanks! There are two issues that I see:

lib/Sema/SemaDeclAttr.cpp

7519

GNU case statements can also have a RHS expression in a range. You should avoid using children completely and just traverse the sub stmt instead.

7520

You should call TraverseStmt instead because we have special logic for tracking the statement stack for a fixit. We can produce an incorrect multi-statement fixit if the case's sub statement is a compound statement when we call Base::TraverseStmt.

[erik.pilkington]

Ah, good point. This new patch does that.
Thanks,
Erik

[arphaman]

LGTM

lib/Sema/SemaDeclAttr.cpp

   }
 
   void IssueDiagnostics(Stmt *S) { TraverseStmt(S); }
 
   bool TraverseIfStmt(IfStmt *If);
 
   bool TraverseLambdaExpr(LambdaExpr *E) { return true; }
 
+  bool TraverseCaseStmt(CaseStmt *CS) {
+    // for 'case X:' statements, don't bother looking at the 'X'; it can't lead
+    // to any useful diagnostics.
+    for (Stmt *Child : llvm::drop_begin(CS->children(), 1))
+      if (!Base::TraverseStmt(Child))
+        return false;
+    return true;
+  }
+
   bool VisitObjCPropertyRefExpr(ObjCPropertyRefExpr *PRE) {
     if (PRE->isClassReceiver())
       DiagnoseDeclAvailability(PRE->getClassReceiver(), PRE->getReceiverLocation());
     return true;
   }
 
   bool VisitObjCMessageExpr(ObjCMessageExpr *Msg) {
     if (ObjCMethodDecl *D = Msg->getMethodDecl())

test/SemaObjC/unguarded-availability.m

 
 @interface ClassWithNewProtocolRequirement : BaseClass <NewProtocol>
 
 @end
 
 @interface BaseClass (CategoryWithNewProtocolRequirement) <NewProtocol>
 
 @end
+
+typedef enum {
+  AK_Dodo __attribute__((availability(macos, deprecated=10.3))), // expected-note 2 {{marked deprecated here}}
+  AK_Cat __attribute__((availability(macos, introduced=10.4))),
+  AK_CyborgCat __attribute__((availability(macos, introduced=10.12))), // expected-note {{marked partial here}}
+} Animals;
+
+void switchAnimals(Animals a) {
+  switch (a) {
+  case AK_Dodo: break; // expected-warning{{'AK_Dodo' is deprecated}}
+  case AK_Cat: break;
+  case AK_Cat|AK_CyborgCat: break; // expected-warning{{case value not in enum}}
+  case AK_CyborgCat: break; // no warn
+  }
+
+  (void)AK_Dodo; // expected-warning{{'AK_Dodo' is deprecated}}
+  (void)AK_Cat; // no warning
+  (void)AK_CyborgCat; // expected-warning{{'AK_CyborgCat' is only available on macOS 10.12 or newer}} expected-note {{@available}}
+}