@llvm/pr-subscribers-clang

Author: Hans Wennborg (zmodem)

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index e8c1f8490342a..990d2fadaf5aa 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1667,8 +1667,12 @@ Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
         // Don't warn about omitted unavailable EnumConstantDecls.
         switch (EI->second->getAvailability()) {
         case AR_Deprecated:
-          // Omitting a deprecated constant is ok; it should never materialize.
+          // Deprecated enumerators still need to be handled: they may be
+          // deprecated, but can still occur.
+          break;
+
         case AR_Unavailable:
+          // Omitting an unavailable enumerator is ok; it should never occur.
           continue;
 
         case AR_NotYetIntroduced:
diff --git a/clang/test/Sema/switch-availability.c b/clang/test/Sema/switch-availability.c
index 888edddac463d..b4f8726addc0b 100644
--- a/clang/test/Sema/switch-availability.c
+++ b/clang/test/Sema/switch-availability.c
@@ -15,7 +15,7 @@ enum SwitchTwo {
 };
 
 void testSwitchTwo(enum SwitchTwo st) {
-  switch (st) {} // expected-warning{{enumeration values 'Vim' and 'Emacs' not handled in switch}}
+  switch (st) {} // expected-warning{{enumeration values 'Ed', 'Vim' and 'Emacs' not handled in switch}}
 }
 
 enum SwitchThree {

Fly-by comment: I drafted the following alternative comment in another thread. Please feel free to disregard as I don't know the tone and style of comments in these files. (But I appreciate your consideration for the contents in the message I'd like to see!)

      // We currently treat deprecated constants as if they don't exist;
      // however, note that this current behavior leads to compile-time
      // false negatives for coverage checking of switch statements. If
      // a switch is missing a case for a deprecated constant, we will not
      // emit a diagnostic, even though the deprecated constant might still
      // be present in legacy use.

Fly-by comment: I drafted the following alternative comment in another thread. Please feel free to disregard as I don't know the tone and style of comments in these files. (But I appreciate your consideration for the contents in the message I'd like to see!)

      // We currently treat deprecated constants as if they don't exist;
      // however, note that this current behavior leads to compile-time
      // false negatives for coverage checking of switch statements. If
      // a switch is missing a case for a deprecated constant, we will not
      // emit a diagnostic, even though the deprecated constant might still
      // be present in legacy use.

My patch changes the behavior so that deprecated constants are not ignored by the switch coverage warning.

I wonder if we should also do something special about the -Wdeprecated-declarations diagnostic in switches.

If the user fixes the -Wswitch / -Wreturn-type warnings from testSwitchFour the natural way:

int testSwitchFour(enum SwitchFour e) {
  switch (e) {
  case Red:   return 1;
  case Green: return 2;
  case Blue:  return 3;
  }
} 

They will get warning: 'Blue' is deprecated [-Wdeprecated-declarations] instead.

Maybe we should suppress that warning for switch cases? Or suggest adding a default label instead?