[clang-tidy/google-readability-casting] Disable check for Objective-C++

[benhamilton]

Summary

Previously, google-readability-casting was disabled for Objective-C.

The Google Objective-C++ style allows both Objective-C and
C++ style in the same file. Since clang-tidy doesn't have a good
way to allow multiple styles per file, this disables the
check for Objective-C++.

Test Plan: New tests added. Ran tests with:

% make -j16 check-clang-tools
Before diff, confirmed tests failed:
https://reviews.llvm.org/P8081
After diff, confirrmed tests passed.

[benhamilton]

An alternative implementation would be to allow C-style casts (either always or only for ObjC objects) within Objective-C methods inside Objective-C++ files, but that may get messy with things like shared macros.

[benhamilton]

• Change to simply disable check for Objective-C++

[benhamilton]

After discussion, I changed this diff to simply disable the check altogether for Objective-C++.

[alexfh]

LG

[stephanemoore]

clang-tidy/google/AvoidCStyleCastsCheck.cpp

103–104

In the future it would probably be good to allow configuring whether or not this is disabled but I think that disabling it for Objective-C++ completely in the interim is a positive change.

[benhamilton]

clang-tidy/google/AvoidCStyleCastsCheck.cpp

103–104

Agreed. Filed https://bugs.llvm.org/show_bug.cgi?id=37489 to follow up.

clang-tidy/google/AvoidCStyleCastsCheck.cpp

if (CastExpr->getCastKind() == CK_NoOp && !FnToFnCast) {
     if (SourceTypeAsWritten == DestTypeAsWritten) {
       diag(CastExpr->getLocStart(), "redundant cast to the same type")
           << FixItHint::CreateRemoval(ReplaceRange);
       return;
     }
   }
 
   // The rest of this check is only relevant to C++.
   if (!getLangOpts().CPlusPlus)
     return;
   // Ignore code inside extern "C" {} blocks.
   if (!match(expr(hasAncestor(linkageSpecDecl())), *CastExpr, *Result.Context)
            .empty())
     return;
   // Ignore code in .c files and headers included from them, even if they are
   // compiled as C++.
   if (getCurrentMainFile().endswith(".c"))
     return;
+  // Ignore casts between Objective-C types.
+  if (SourceType->isObjCObjectPointerType() ||
+      DestType->isObjCObjectPointerType())
+    return;
 
   SourceManager &SM = *Result.SourceManager;
 
   // Ignore code in .c files #included in other files (which shouldn't be done,
   // but people still do this for test and other purposes).
   if (SM.getFilename(SM.getSpellingLoc(CastExpr->getLocStart())).endswith(".c"))
     return;
 

test/clang-tidy/google-readability-casting.mm

+// RUN: clang-tidy %s -checks=-*,google-readability-casting -- \
+// RUN:   -xobjective-c++ -fobjc-abi-version=2 -fobjc-arc | count 0
+
+// Note: this test expects no diagnostics, but FileCheck cannot handle that,
+// hence the use of | count 0.
+
+#define nil 0
+
+@interface Foo
+@end
+
+@protocol Proto
+@end
+
+@interface Bar : Foo <Proto>
+@end
+
+@interface Baz : Foo <Proto>
+@end
+
+void foo() {
+  id nilObj = nil;
+  Foo *foo = (Foo *)nilObj;
+  Bar *bar = (Bar *)nilObj;
+  id ego = (id)foo;
+  foo = (Foo *)bar;
+  foo = (id)bar;
+  id<Proto> nilProto = (id<Proto>)bar;
+  ego = (id)nilProto;
+  bar = (Bar *)nilProto;
+  Foo<Proto> *fooProto = (Foo<Proto> *)bar;
+  Baz *baz = (Baz *)bar;
+  Class klass = (Class)nilObj;
+  ego = (id)klass;
+  void *voidStar = nullptr;
+  foo = (__bridge Foo *)voidStar;
+  nilProto = (__bridge id<Proto>)voidStar;
+  klass = (__bridge Class)voidStar;
+  voidStar = (__bridge void *)foo;
+  voidStar = (__bridge void *)nilProto;
+  voidStar = (__bridge void *)klass;
+}