add check to avoid throwing objc exception according to Google Objective-C guide

[Wizard]

Summary

This is a small check to avoid throwing objc exceptions.
In specific it will detect the usage of @throw statement and throw warning.

[Wizard]

new line

[hokein]

LGTM with a few nits, I'd like to see whether @benhamilton has comments before committing it.

docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst

4 ↗

(On Diff #122953)

nit: remove the extra ===

10 ↗

(On Diff #122953)

Use the public link: http://google.github.io/styleguide/objcguide.html#avoid-throwing-exceptions

test/clang-tidy/google-objc-avoid-throwing-exception.m

11 ↗

(On Diff #122953)

nit: remove the empty line.

[benhamilton]

This comment was removed by benhamilton.

clang-tidy/google/AvoidThrowingObjcExceptionCheck.cpp

22 ↗

(On Diff #122953)

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

30 ↗

(On Diff #122953)

Suggested wording:

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

clang-tidy/google/AvoidThrowingObjcExceptionCheck.h

1 ↗

(On Diff #122953)

Naming nit-pick: We are currently using ObjC, not Objc.

21–22 ↗

(On Diff #122953)

Grammar nit:

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

26 ↗

(On Diff #122953)

Objc -> ObjC

docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst

6–7 ↗

(On Diff #122953)

How about:

This check finds @throw usages in Objective-C files. For the same reasons as the Google C++ style guide, we prefer not throwing exceptions from Objective-C code.

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

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

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

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

10 ↗

(On Diff #122953)

+1

[hokein]

clang-tidy/google/AvoidThrowingObjcExceptionCheck.h

1 ↗

(On Diff #122953)

We also need to rename the file name.

docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst

6–7 ↗

(On Diff #122953)

+1 on an illustrated sample :)

[Wizard]

address comments

[benhamilton]

Looking good. Please rename the files correctly, or it will not build on Linux.

clang-tidy/google/AvoidThrowingObjcExceptionCheck.cpp

23 ↗

(On Diff #123079)

Also need to match raise:format:arguments:.

clang-tidy/google/AvoidThrowingObjcExceptionCheck.h

1 ↗

(On Diff #123079)

Don't forget to rename the file to AvoidThrowingObjcExceptionCheck.h.

clang-tidy/google/CMakeLists.txt

5 ↗

(On Diff #123079)

Rename to AvoidThrowingObjCExceptionCheck.cpp

clang-tidy/google/GoogleTidyModule.cpp

18 ↗

(On Diff #123079)

I think you renamed the #include but not the file.. should test on Linux, it won't work with a case-sensitive file system ;)

docs/ReleaseNotes.rst

63 ↗

(On Diff #123079)

detect usage of @throw -> detect throwing exceptions

docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst

6 ↗

(On Diff #123079)

Can you include the link to the C++ style guide section here instead of at the end? http://google.github.io/styleguide/cppguide.html#Exceptions

6 ↗

(On Diff #123079)

finds @throw usages -> finds uses of throwing exceptions

[benhamilton]

clang-tidy/google/AvoidThrowingObjcExceptionCheck.h

1 ↗

(On Diff #123079)

Oops! I mean, rename the file to AvoidThrowingObjCExceptionCheck.h. :)

test/clang-tidy/google-objc-avoid-throwing-exception.m

17–20 ↗

(On Diff #123079)

Would be nice to have a test that confirms sending -raise:format: to a different object does not hit the warning.

[Wizard]

address comments

[Wizard]

rename file

[Wizard]

rename again

[benhamilton]

File names look good now, thanks.

clang-tidy/google/AvoidThrowingObjCExceptionCheck.cpp

1 ↗

(On Diff #123091)

Objc -> ObjC

[Wizard]

nit fix

[benhamilton]

LGTM

clang-tools-extra/trunk/clang-tidy/google/AvoidThrowingObjCExceptionCheck.h

+//===--- AvoidThrowingObjCExceptionCheck.h - clang-tidy----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_OBJC_AVOID_THROWING_EXCEPTION_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_OBJC_AVOID_THROWING_EXCEPTION_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace google {
+namespace objc {
+
+/// The check is to find usage of @throw invocation in Objective-C code.
+/// We should avoid using @throw for Objective-C exceptions according to
+/// the Google Objective-C Style Guide.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/google-objc-avoid-throwing-exception.html
+class AvoidThrowingObjCExceptionCheck : public ClangTidyCheck {
+ public:
+  AvoidThrowingObjCExceptionCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+}  // namespace objc
+}  // namespace google
+}  // namespace tidy
+}  // namespace clang
+
+#endif  // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_OBJC_AVOID_THROWING_EXCEPTION_H

clang-tools-extra/trunk/clang-tidy/google/AvoidThrowingObjCExceptionCheck.cpp

+//===--- AvoidThrowingObjCExceptionCheck.cpp - clang-tidy------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AvoidThrowingObjCExceptionCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace google {
+namespace objc {
+
+void AvoidThrowingObjCExceptionCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(objcThrowStmt().bind("throwStmt"), this);
+  Finder->addMatcher(
+      objcMessageExpr(anyOf(hasSelector("raise:format:"),
+                            hasSelector("raise:format:arguments:")),
+                      hasReceiverType(asString("NSException")))
+          .bind("raiseException"),
+      this);
+}
+
+void AvoidThrowingObjCExceptionCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *MatchedStmt =
+      Result.Nodes.getNodeAs<ObjCAtThrowStmt>("throwStmt");
+  const auto *MatchedExpr =
+      Result.Nodes.getNodeAs<ObjCMessageExpr>("raiseException");
+  auto SourceLoc = MatchedStmt == nullptr ? MatchedExpr->getSelectorStartLoc()
+                                          : MatchedStmt->getThrowLoc();
+  diag(SourceLoc,
+       "pass in NSError ** instead of throwing exception to indicate "
+       "Objective-C errors");
+}
+
+}  // namespace objc
+}  // namespace google
+}  // namespace tidy
+}  // namespace clang

clang-tools-extra/trunk/clang-tidy/google/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyGoogleModule
   AvoidCStyleCastsCheck.cpp
+  AvoidThrowingObjCExceptionCheck.cpp
   DefaultArgumentsCheck.cpp
   ExplicitConstructorCheck.cpp
   ExplicitMakePairCheck.cpp
   GlobalNamesInHeadersCheck.cpp
   GlobalVariableDeclarationCheck.cpp
   GoogleTidyModule.cpp
   IntegerTypesCheck.cpp
   NonConstReferences.cpp

clang-tools-extra/trunk/clang-tidy/google/GoogleTidyModule.cpp

 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "../readability/BracesAroundStatementsCheck.h"
 #include "../readability/FunctionSizeCheck.h"
 #include "../readability/NamespaceCommentCheck.h"
 #include "../readability/RedundantSmartptrGetCheck.h"
 #include "AvoidCStyleCastsCheck.h"
+#include "AvoidThrowingObjCExceptionCheck.h"
 #include "DefaultArgumentsCheck.h"
 #include "ExplicitConstructorCheck.h"
 #include "ExplicitMakePairCheck.h"
 #include "GlobalNamesInHeadersCheck.h"
 #include "GlobalVariableDeclarationCheck.h"
 #include "IntegerTypesCheck.h"
 #include "NonConstReferences.h"
 #include "OverloadedUnaryAndCheck.h"
void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<build::UsingNamespaceDirectiveCheck>(
         "google-build-using-namespace");
     CheckFactories.registerCheck<DefaultArgumentsCheck>(
         "google-default-arguments");
     CheckFactories.registerCheck<ExplicitConstructorCheck>(
         "google-explicit-constructor");
     CheckFactories.registerCheck<readability::GlobalNamesInHeadersCheck>(
         "google-global-names-in-headers");
+    CheckFactories.registerCheck<objc::AvoidThrowingObjCExceptionCheck>(
+        "google-objc-avoid-throwing-exception");
     CheckFactories.registerCheck<objc::GlobalVariableDeclarationCheck>(
         "google-objc-global-variable-declaration");
     CheckFactories.registerCheck<runtime::IntegerTypesCheck>(
         "google-runtime-int");
     CheckFactories.registerCheck<runtime::OverloadedUnaryAndCheck>(
         "google-runtime-operator");
     CheckFactories.registerCheck<runtime::NonConstReferences>(
         "google-runtime-references");

clang-tools-extra/trunk/docs/ReleaseNotes.rst

 Improvements to clang-rename
 ----------------------------
 
 The improvements are...
 
 Improvements to clang-tidy
 --------------------------
 
+- New `google-avoid-throwing-objc-exception
+  <http://clang.llvm.org/extra/clang-tidy/checks/google-objc-avoid-throwing-exception.html>`_ check
+
+  Add new check to detect throwing exceptions in Objective-C code, which should be avoided.
+
 - New `objc-property-declaration
   <http://clang.llvm.org/extra/clang-tidy/checks/objc-property-declaration.html>`_ check
 
   Add new check for Objective-C code to ensure property
   names follow the naming convention of Apple's programming
   guide.
 
 - New `google-objc-global-variable-declaration

clang-tools-extra/trunk/docs/clang-tidy/checks/google-objc-avoid-throwing-exception.rst

+.. title:: clang-tidy - google-objc-avoid-throwing-exception
+
+google-objc-avoid-throwing-exception
+====================================
+
+This check finds finds uses of throwing exceptions usages in Objective-C files.
+For the same reason as the Google C++ style guide, we prefer not throwing 
+exceptions from Objective-C code.
+
+The corresponding C++ style guide rule:
+https://google.github.io/styleguide/cppguide.html#Exceptions
+
+Instead, prefer passing in ``NSError **`` and return ``BOOL`` to indicate success or failure.
+
+A counterexample:
+
+.. code-block:: objc
+
+  - (void)readFile {
+    if ([self isError]) {
+      @throw [NSException exceptionWithName:...];
+    }
+  }
+
+Instead, returning an error via ``NSError **`` is preferred:
+
+.. code-block:: objc
+
+  - (BOOL)readFileWithError:(NSError **)error {
+    if ([self isError]) {
+      *error = [NSError errorWithDomain:...];
+      return NO;
+    }
+    return YES;
+  }
+
+The corresponding style guide rule:
+http://google.github.io/styleguide/objcguide.html#avoid-throwing-exceptions

clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst

.. toctree::
    cppcoreguidelines-slicing
    cppcoreguidelines-special-member-functions
    google-build-explicit-make-pair
    google-build-namespaces
    google-build-using-namespace
    google-default-arguments
    google-explicit-constructor
    google-global-names-in-headers
+   google-objc-avoid-throwing-exception
    google-objc-global-variable-declaration
    google-readability-braces-around-statements (redirects to readability-braces-around-statements) <google-readability-braces-around-statements>
    google-readability-casting
    google-readability-function-size (redirects to readability-function-size) <google-readability-function-size>
    google-readability-namespace-comments (redirects to llvm-namespace-comment) <google-readability-namespace-comments>
    google-readability-redundant-smartptr-get (redirects to readability-redundant-smartptr-get) <google-readability-redundant-smartptr-get>
    google-readability-todo
    google-runtime-int

clang-tools-extra/trunk/test/clang-tidy/google-objc-avoid-throwing-exception.m

+// RUN: %check_clang_tidy %s google-objc-avoid-throwing-exception %t
+@class NSString;
+
+@interface NSException
+
++ (void)raise:(NSString *)name format:(NSString *)format;
++ (void)raise:(NSString *)name format:(NSString *)format arguments:(NSString *)args; // using NSString type since va_list cannot be recognized here
+
+@end
+
+@interface NotException
+
++ (void)raise:(NSString *)name format:(NSString *)format;
+
+@end
+
+@implementation Foo
+- (void)f {
+    NSString *foo = @"foo";
+    @throw foo;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: pass in NSError ** instead of throwing exception to indicate Objective-C errors [google-objc-avoid-throwing-exception]
+}
+
+- (void)f2 {
+    [NSException raise:@"TestException" format:@"Test"];
+    // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: pass in NSError ** instead of throwing exception to indicate Objective-C errors [google-objc-avoid-throwing-exception]
+    [NSException raise:@"TestException" format:@"Test %@" arguments:@"bar"];
+    // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: pass in NSError ** instead of throwing exception to indicate Objective-C errors [google-objc-avoid-throwing-exception]
+    [NotException raise:@"NotException" format:@"Test"];
+}
+@end
+