[PATCH] D40058: add check to avoid throwing objc exception according to Google Objective-C guide

[Ben Hamilton via Phabricator via cfe-commits]

benhamilton requested changes to this revision.
benhamilton added a comment.
This revision now requires changes to proceed.

Almost there.



================
Comment at: clang-tidy/google/AvoidThrowingObjcExceptionCheck.cpp:22
+void AvoidThrowingObjcExceptionCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(objcThrowStmt().bind("throwStmt"), this);
+}
----------------
It looks like we also need to catch (no pun intended :) people who invoke the following class methods:

```
+[NSException raise:format:]
+[NSException raise:format:arguments:]
```

We actually have a few places that use these:

http://google3/googlemac/iPhone/Maps/SDK/Maps/GMSServices.mm?l=412&rcl=174266104
http://google3/googlemac/iPhone/Bigtop/Source/Actions/ActionHandler.m?l=1942&rcl=174353485
http://google3/googlemac/iPhone/Applecrisp/Sketchy/Classes/Sketchy/SketchyLib/SketchyApplicationContext.mm?l=398&rcl=175173348



================
Comment at: clang-tidy/google/AvoidThrowingObjcExceptionCheck.cpp:30
+  diag(MatchedStmt->getThrowLoc(),
+       "avoid using @throw to handle Objective-C exceptions");
+}
----------------
Suggested wording:

"Pass in NSError ** instead of using @throw to indicate Objective-C errors"


================
Comment at: clang-tidy/google/AvoidThrowingObjcExceptionCheck.h:1
+//===--- AvoidThrowingObjcExceptionCheck.h - clang-tidy----------*- C++ -*-===//
+//
----------------
Naming nit-pick: We are currently using `ObjC`, not `Objc`.


================
Comment at: clang-tidy/google/AvoidThrowingObjcExceptionCheck.h:21-22
+/// The check is to find usage of @throw invocation in Objective-C code.
+/// We should avoid using @throw for Objective-C exceptions according to
+/// Google Objective-C Style Guide.
+///
----------------
Grammar nit:

according to Google Objective-C Style Guide -> according to the Google Objective-C Style Guide


================
Comment at: clang-tidy/google/AvoidThrowingObjcExceptionCheck.h:26
+/// http://clang.llvm.org/extra/clang-tidy/checks/google-objc-avoid-throwing-exception.html
+class AvoidThrowingObjcExceptionCheck : public ClangTidyCheck {
+ public:
----------------
`Objc` -> `ObjC`



================
Comment at: docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst:6-7
+
+This check finds @throw usages in Objective-C files. According to Google's Objective-C
+Guide, we should not use @throw to handle exceptions.
+
----------------
How about:

This check finds @throw usages in Objective-C files. [For the same reasons as the Google C++ style guide](https://google.github.io/styleguide/cppguide.html#Exceptions), we [prefer not throwing exceptions from Objective-C code](http://google.github.io/styleguide/objcguide.html#avoid-throwing-exceptions).

Instead, prefer passing in `NSError **` and return `BOOL` to indicate success or failure. A counterexample:

```lang=objectivec
- (void)readFile {
  if ([self isError]) {
    @throw [NSException exceptionWithName:...];
  }
}
```

Instead, returning an error via `NSError **` is preferred:

```lang=objectivec
- (BOOL)readFileWithError:(NSError **)error {
  if ([self isError]) {
    *error = [NSError errorWithDomain:...];
    return NO;
  }
  return YES;
}
```



================
Comment at: docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst:10
+The corresponding style guide rule:
+http://go/objc-style#Avoid_Throwing_Exceptions
----------------
hokein wrote:
> Use the public link: http://google.github.io/styleguide/objcguide.html#avoid-throwing-exceptions
+1


https://reviews.llvm.org/D40058