[Sema] C++11 opaque enums should avoid the "case value not in enumerated type" switch warning

[arphaman]

Summary

This patch ensures that the switch warning "case value not in enumerated type" isn't shown for opaque enums. We don't know the actual list of values in opaque enums, so that warning is incorrect.

[ahatanak]

lib/Sema/SemaStmt.cpp

1165

This function used to call setAllEnumCasesCovered() when parsing a switch statement with an opaque enum condition, but this patch changes the behavior. I couldn't tell whether isAllEnumCasesCovered should return true or false for such switch statements, but was this change intentional?

[arphaman]

lib/Sema/SemaStmt.cpp

1165

You're right, good catch! Originally it wasn't intentional, but I've looked over this change and it seems like the right change to me. We can't know if we actually covered all enum cases when checking an opaque enum because we don't know which cases the enum has (unless we have a switch that covers all the of possible values of the enum's integer type)! It seems that the previous behaviour was incorrect.

[ahatanak]

That makes sense. Thanks for the explanation.

lib/Sema/SemaStmt.cpp

if (!HasDependentValue) {
     // Check to see if switch is over an Enum and handles all of its
     // values.  We only issue a warning if there is not 'default:', but
     // we still do the analysis to preserve this information in the AST
     // (which can be used by flow-based analyes).
     //
     const EnumType *ET = CondTypeBeforePromotion->getAs<EnumType>();
 
     // If switch has default case, then ignore it.
-    if (!CaseListIsErroneous  && !HasConstantCond && ET) {
+    if (!CaseListIsErroneous && !HasConstantCond && ET &&
+        ET->getDecl()->isCompleteDefinition()) {
       const EnumDecl *ED = ET->getDecl();
       EnumValsTy EnumVals;
 
       // Gather all enum values, set their type and sort them,
       // allowing easier comparison with CaseVals.
       for (auto *EDI : ED->enumerators()) {
         llvm::APSInt Val = EDI->getInitVal();
         AdjustAPSInt(Val, CondWidth, CondIsSigned);
if (!CaseListIsErroneous && !HasConstantCond && ET &&
                                                    : diag::warn_missing_case)
                                << (int)UnhandledNames.size();
 
         for (size_t I = 0, E = std::min(UnhandledNames.size(), (size_t)3);
              I != E; ++I)
           DB << UnhandledNames[I];
       }
 
       if (!hasCasesNotInSwitch)
         SS->setAllEnumCasesCovered();
     }
   }
 
   if (BodyStmt)
     DiagnoseEmptyStmtBody(CondExpr->getLocEnd(), BodyStmt,
                           diag::warn_empty_switch_body);
 

test/SemaCXX/switch.cpp

template<typename T> void f(T t) {
     case 0:
       return;
     default:
       break;
     }
   }
   template void f(S); // expected-note {{instantiation of}}
 }
+
+// rdar://29230764
+namespace OpaqueEnumWarnings {
+
+enum Opaque : int;
+enum class OpaqueClass : int;
+
+enum class Defined : int;
+enum class Defined : int { a };
+
+void test(Opaque o, OpaqueClass oc, Defined d) {
+  // Don't warn that case value is not present in opaque enums.
+  switch (o) {
+  case (Opaque)1:
+    break;
+  }
+  switch (oc) {
+  case (OpaqueClass)1:
+    break;
+  }
+
+  switch (d) {
+  case Defined::a:
+    break;
+  case (Defined)2: // expected-warning {{case value not in enumerated type 'OpaqueEnumWarnings::Defined'}}
+    break;
+  }
+}
+
+}