add new check to find NSError init invocation

[Wizard]

Summary

This check will find out improper initialization of NSError objects.

According to Apple developer document, we should always use factory method errorWithDomain:code:userInfo: to create new NSError objects instead of [NSError alloc] init]. Otherwise it will lead to a warning message during runtime in Xcode.

The corresponding information about NSError creation: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/ErrorHandlingCocoa/CreateCustomizeNSError/CreateCustomizeNSError.html

[Wizard]

new line for doc

[hokein]

docs/clang-tidy/checks/objc-avoid-nserror-init.rst

10

What's the warning message in Xcode? I suspect whether there is a diagnostic flag in clang already.

[Wizard]

docs/clang-tidy/checks/objc-avoid-nserror-init.rst

10

It was discussed originally here https://buganizer.corp.google.com/issues/62445078 I think

[hokein]

clang-tidy/objc/AvoidNserrorInitCheck.cpp

31

not sure what's the best message here.

From apple's document:

You create an error object either by allocating it and then initializing it with the initWithDomain:code:userInfo: method of NSError or by using the class factory method errorWithDomain:code:userInfo:.

errorWithDomain:code:userInfo: is not the only way to create an NSError.

clang-tidy/objc/AvoidNserrorInitCheck.h

24

I'd name it AvoidNSErrorInitCheck.

docs/clang-tidy/checks/objc-avoid-nserror-init.rst

10

Thanks. Please don't include any internal links next time.

Looks like the error message (https://stackoverflow.com/questions/33720042/why-does-nserror-alloc-init-in-xcode-throw-an-error) is shown during runtime, instead of compilation. Could you please confirm it, and update the document here?

[NSError init] called; this results in an invalid NSError instance. It will raise an exception in a future release. Please call errorWithDomain:code:userInfo: or initWithDomain:code:userInfo:. This message shown only once.

[Wizard]

address comments

docs/clang-tidy/checks/objc-avoid-nserror-init.rst

10

Oh yes it is shown during runtime. Will update the doc

[Wizard]

change file name cases

[Wizard]

restore file names

clang-tidy/objc/AvoidNserrorInitCheck.h

+//===--- AvoidNserrorInitCheck.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_OBJC_AVOIDNSERRORINITCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_OBJC_AVOIDNSERRORINITCHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace objc {
+
+/// Finds usages of [NSSError init]. It is not the proper way of creating
+/// NSError. errorWithDomain:code:userInfo: should be used instead.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/objc-avoid-nserror-init.html
+class AvoidNserrorInitCheck : public ClangTidyCheck {
+ public:
+  AvoidNserrorInitCheck(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 tidy
+}  // namespace clang
+
+#endif  // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_OBJC_AVOIDNSERRORINITCHECK_H

clang-tidy/objc/AvoidNserrorInitCheck.cpp

+//===--- AvoidNserrorInitCheck.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 "AvoidNserrorInitCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace objc {
+
+void AvoidNserrorInitCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(objcMessageExpr(hasSelector("init"),
+                                     hasReceiverType(asString("NSError *")))
+                         .bind("nserrorInit"),
+                     this);
+}
+
+void AvoidNserrorInitCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedExpr =
+      Result.Nodes.getNodeAs<ObjCMessageExpr>("nserrorInit");
+  diag(MatchedExpr->getLocStart(),
+       "use errorWithDomain:code:userInfo: to create a new NSError");
+}
+
+}  // namespace objc
+}  // namespace tidy
+}  // namespace clang

clang-tidy/objc/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyObjCModule
+  AvoidNserrorInitCheck.cpp
   AvoidSpinlockCheck.cpp
   ForbiddenSubclassingCheck.cpp
   ObjCTidyModule.cpp
   PropertyDeclarationCheck.cpp
 
   LINK_LIBS
   clangAST
   clangASTMatchers
   clangBasic
   clangLex
   clangTidy
   clangTidyUtils
   )

clang-tidy/objc/ObjCTidyModule.cpp

 //===--- ObjCTidyModule.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 "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "AvoidNserrorInitCheck.h"
 #include "AvoidSpinlockCheck.h"
 #include "ForbiddenSubclassingCheck.h"
 #include "PropertyDeclarationCheck.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace objc {
 
 class ObjCModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<AvoidNserrorInitCheck>(
+        "objc-avoid-nserror-init");
     CheckFactories.registerCheck<AvoidSpinlockCheck>(
         "objc-avoid-spinlock");
     CheckFactories.registerCheck<ForbiddenSubclassingCheck>(
         "objc-forbidden-subclassing");
     CheckFactories.registerCheck<PropertyDeclarationCheck>(
         "objc-property-declaration");
   }
 };

docs/ReleaseNotes.rst

 Improvements to clang-rename
 ----------------------------
 
 The improvements are...
 
 Improvements to clang-tidy
 --------------------------
 
+- New `objc-avoid-nserror-init
+  <http://clang.llvm.org/extra/clang-tidy/checks/objc-avoid-nserror-init.html>`_ check
+
+  Add new check to detect the use of [NSError init].
+
 - New `objc-avoid-spinlock
   <http://clang.llvm.org/extra/clang-tidy/checks/objc-avoid-spinlock.html>`_ check
 
   Add new check to detect the use of OSSpinlock.
 
 - The 'misc-move-constructor-init' check was renamed to `performance-move-constructor-init
   <http://clang.llvm.org/extra/clang-tidy/checks/performance-move-constructor-init.html>`_
 

docs/clang-tidy/checks/list.rst

.. toctree::
    modernize-use-equals-delete
    modernize-use-noexcept
    modernize-use-nullptr
    modernize-use-override
    modernize-use-transparent-functors
    modernize-use-using
    mpi-buffer-deref
    mpi-type-mismatch
+   objc-avoid-nserror-init
    objc-avoid-spinlock
    objc-forbidden-subclassing
    objc-property-declaration
    performance-faster-string-find
    performance-for-range-copy
    performance-implicit-conversion-in-loop
    performance-inefficient-algorithm
    performance-inefficient-string-concatenation

docs/clang-tidy/checks/objc-avoid-nserror-init.rst

+.. title:: clang-tidy - objc-avoid-nserror-init
+
+objc-avoid-nserror-init
+=======================
+
+This check will find out improper initialization of NSError objects.
+
+According to Apple developer document, we should always use factory method 
+``errorWithDomain:code:userInfo:`` to create new NSError objects instead
+of ``[NSError alloc] init]``. Otherwise it will lead to a warning message
+during compilation in Xcode.
+
+The corresponding information about NSError creation: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/ErrorHandlingCocoa/CreateCustomizeNSError/CreateCustomizeNSError.html

test/clang-tidy/objc-avoid-nserror-init.m

+// RUN: %check_clang_tidy %s objc-avoid-nserror-init %t
+@interface NSError
++ (instancetype)alloc;
+- (instancetype)init;
+@end
+
+@implementation foo
+- (void)bar {
+    NSError *error = [[NSError alloc] init];
+    // CHECK-MESSAGES: :[[@LINE-1]]:22: warning: use errorWithDomain:code:userInfo: to create a new NSError [objc-avoid-nserror-init]
+}
+@end