[Sema] Extend -Wenum-compare to handle mixed enum comparisons in switch statements

[rnkovacs]

Summary

-Wenum-compare warns if two values with different enumeration types are compared in expressions with binary operators. This patch extends this diagnostic so that comparisons of mixed enumeration types are recognized in switch statements as well.

Example:

enum MixedA { A1, A2, A3 };
enum MixedB { B1, B2, B3 };

void MixedEnums(MixedA a) {
  switch (a) {
    case A1: break; // OK, same enum types.
    case B1: break; // Warn, different enum types.
  }
}

[aaron.ballman]

Can you generate the updated patch with more context (https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface)?

lib/Sema/SemaStmt.cpp

746

Cond and Case can be declared as const pointers.

758

You can lower this in to the diagnostic.

[rnkovacs]

Uploaded the full diff and addressed comments. Added const qualifiers to GetTypeBeforeIntegralPromotion() function.

[aaron.ballman]

Aside from a minor naming nit, LGTM!

lib/Sema/SemaStmt.cpp

605–608

Since you're touching the code -- can you change the names to E (or some other, more descriptive name), Cleanups and Impcast to meet the coding standards?

lib/Sema/SemaStmt.cpp

   return true;
 }
 
+static void checkEnumTypesInSwitchStmt(Sema &S, Expr *Cond, Expr *Case) {
+  QualType CondType = GetTypeBeforeIntegralPromotion(Cond);
+  QualType CaseType = Case->getType();
+
+  const EnumType *CondEnumType = CondType->getAs<EnumType>();
+  const EnumType *CaseEnumType = CaseType->getAs<EnumType>();
+  if (!CondEnumType || !CaseEnumType)
+    return;
+
+  if (S.Context.hasSameUnqualifiedType(CondType, CaseType))
+    return;
+
+  SourceLocation Loc = Case->getExprLoc();
+  S.Diag(Loc, diag::warn_comparison_of_mixed_enum_types)
+      << CondType << CaseType << Cond->getSourceRange()
+      << Case->getSourceRange();
+}
+
 StmtResult
 Sema::ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
                             Stmt *BodyStmt) {

         break;
       }
 
+      checkEnumTypesInSwitchStmt(*this, CondExpr, Lo);
+
       llvm::APSInt LoVal;
 
       if (getLangOpts().CPlusPlus11) {

test/Sema/switch.c

   case EE1_b: break;
   case EE1_c: break; // no-warning
   case EE1_d: break; // expected-warning {{case value not in enumerated type 'enum ExtendedEnum1'}}
+  // expected-warning@-1 {{comparison of two values with different enumeration types ('enum ExtendedEnum1' and 'const enum ExtendedEnum1_unrelated')}}
   }
 }
 

test/SemaCXX/warn-enum-compare.cpp

   while (getBar() > x); // expected-warning  {{comparison of two values with different enumeration types ('Bar' and 'Foo')}}
   while (getBar() < x); // expected-warning  {{comparison of two values with different enumeration types ('Bar' and 'Foo')}}
 
+  switch (a) {
+    case name1::F1: break;
+    case name1::F3: break;
+    case name2::B2: break; // expected-warning {{comparison of two values with different enumeration types ('name1::Foo' and 'name2::Baz')}}
+  }
+
+  switch (x) {
+    case FooB: break;
+    case FooC: break;
+    case BarD: break; // expected-warning {{comparison of two values with different enumeration types ('Foo' and 'Bar')}}
+  }
+
+  switch(getBar()) {
+    case BarE: break;
+    case BarF: break;
+    case FooA: break; // expected-warning {{comparison of two values with different enumeration types ('Bar' and 'Foo')}}
+  }
 }