[Sema] Don't warn about omitting unavailable enum constants in a switch

[erik.pilkington]

Summary

rdar://42717026

Thanks for taking a look!

[arphaman]

LGTM.

cfe/trunk/lib/Sema/SemaStmt.cpp

if (!CaseListIsErroneous && !CaseListIsIncomplete && !HasConstantCond &&
 
       // Check which enum vals aren't in switch
       auto CI = CaseVals.begin();
       auto RI = CaseRanges.begin();
       bool hasCasesNotInSwitch = false;
 
       SmallVector<DeclarationName,8> UnhandledNames;
 
-      for (EI = EnumVals.begin(); EI != EIEnd; EI++){
+      for (EI = EnumVals.begin(); EI != EIEnd; EI++) {
+        // Don't warn about omitted unavailable EnumConstantDecls.
+        switch (EI->second->getAvailability()) {
+        case AR_Deprecated:
+          // Omitting a deprecated constant is ok; it should never materialize.
+        case AR_Unavailable:
+          continue;
+
+        case AR_NotYetIntroduced:
+          // Partially available enum constants should be present. Note that we
+          // suppress -Wunguarded-availability diagnostics for such uses.
+        case AR_Available:
+          break;
+        }
+
         // Drop unneeded case values
         while (CI != CaseVals.end() && CI->first < EI->first)
           CI++;
 
         if (CI != CaseVals.end() && CI->first == EI->first)
           continue;
 
         // Drop unneeded case ranges

cfe/trunk/test/Sema/switch-availability.c

+// RUN: %clang_cc1 -verify -Wswitch -triple x86_64-apple-macosx10.12 %s
+
+enum SwitchOne {
+  Unavail __attribute__((availability(macos, unavailable))),
+};
+
+void testSwitchOne(enum SwitchOne so) {
+  switch (so) {} // no warning
+}
+
+enum SwitchTwo {
+  Ed __attribute__((availability(macos, deprecated=10.12))),
+  Vim __attribute__((availability(macos, deprecated=10.13))),
+  Emacs,
+};
+
+void testSwitchTwo(enum SwitchTwo st) {
+  switch (st) {} // expected-warning{{enumeration values 'Vim' and 'Emacs' not handled in switch}}
+}
+
+enum SwitchThree {
+  New __attribute__((availability(macos, introduced=1000))),
+};
+
+void testSwitchThree(enum SwitchThree st) {
+  switch (st) {} // expected-warning{{enumeration value 'New' not handled in switch}}
+}