Add a FIXME and corresponding test coverage for some suspicious behavior

forming composite ObjC pointer types in comparisons.

Author: zygoloid

clang/lib/Sema/SemaExpr.cpp

@@ -11055,6 +11055,9 @@ QualType Sema::CheckCompareOperands(ExprResult &LHS, ExprResult &RHS,
         diagnoseDistinctPointerComparison(*this, Loc, LHS, RHS,
                                           /*isError*/false);
       }
+      // FIXME: If LPtrToVoid, we should presumably convert the LHS rather than
+      // the RHS, but we have test coverage for this behavior.
+      // FIXME: Consider using convertPointersToCompositeType in C++.
       if (LHSIsNull && !RHSIsNull) {
         Expr *E = LHS.get();
         if (getLangOpts().ObjCAutoRefCount)

clang/test/SemaObjC/arc.m

@@ -295,6 +295,7 @@ void test11(id op, void *vp) {
   b = (vp == nil);
   b = (nil == vp);
 
+  // FIXME: Shouldn't these be consistent?
   b = (vp == op); // expected-error {{implicit conversion of Objective-C pointer type 'id' to C pointer type 'void *' requires a bridged cast}} expected-note {{use __bridge}} expected-note {{use CFBridgingRetain call}}
   b = (op == vp);
 }

clang/test/SemaObjCXX/arc-ptr-comparison.mm

@@ -22,3 +22,32 @@ int testObjCComparisonRules(void *v, id x, id y) {
   return v == (void *)0;
   return x == y;
 }
+
+@class A;
+
+int testMixedQualComparisonRules(void *v, const void *cv, A *a, const A *ca) {
+  return cv == ca;
+#ifndef NOARC
+// expected-error@-2 {{implicit conversion of Objective-C pointer type 'const A *' to C pointer type 'const void *' requires a bridged cast}}
+// expected-note@-3 {{use __bridge to convert directly (no change in ownership)}}
+// expected-note@-4 {{use __bridge_retained to make an ARC object available as a +1 'const void *'}}
+#endif
+  // FIXME: The "to" type in this diagnostic is wrong; we should convert to "const void *".
+  return v == ca;
+#ifndef NOARC
+// expected-error@-2 {{implicit conversion of Objective-C pointer type 'const A *' to C pointer type 'void *' requires a bridged cast}}
+// expected-note@-3 {{use __bridge to convert directly (no change in ownership)}}
+// expected-note@-4 {{use __bridge_retained to make an ARC object available as a +1 'void *'}}
+#endif
+  return cv == a;
+#ifndef NOARC
+// expected-error@-2 {{implicit conversion of Objective-C pointer type 'A *' to C pointer type 'const void *' requires a bridged cast}}
+// expected-note@-3 {{use __bridge to convert directly (no change in ownership)}}
+// expected-note@-4 {{use __bridge_retained to make an ARC object available as a +1 'const void *'}}
+#endif
+
+  // FIXME: Shouldn't these be rejected in ARC mode too?
+  return ca == cv;
+  return a == cv;
+  return ca == v;
+}