add new check to find NSError init invocation

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

Reviewers: hokein, benhamilton

Reviewed By: benhamilton

Subscribers: klimek, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D40528

llvm-svn: 319459

clang-tools-extra/clang-tidy/objc/AvoidNserrorInitCheck.cpp

@@ -0,0 +1,37 @@
+//===--- 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: or initWithDomain:code:userInfo: to "
+       "create a new NSError");
+}
+
+}  // namespace objc
+}  // namespace tidy
+}  // namespace clang

clang-tools-extra/clang-tidy/objc/AvoidNserrorInitCheck.h

@@ -0,0 +1,36 @@
+//===--- 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-tools-extra/clang-tidy/objc/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyObjCModule
+  AvoidNSErrorInitCheck.cpp
   AvoidSpinlockCheck.cpp
   ForbiddenSubclassingCheck.cpp
   ObjCTidyModule.cpp

clang-tools-extra/clang-tidy/objc/ObjCTidyModule.cpp

@@ -10,6 +10,7 @@
 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "AvoidNSErrorInitCheck.h"
 #include "AvoidSpinlockCheck.h"
 #include "ForbiddenSubclassingCheck.h"
 #include "PropertyDeclarationCheck.h"
@@ -23,6 +24,8 @@ 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>(

clang-tools-extra/docs/ReleaseNotes.rst

@@ -158,6 +158,11 @@ Improvements to clang-tidy
   Finds uses of bitwise operations on signed integer types, which may lead to 
   undefined or implementation defined behaviour.
 
+- 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
 

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

@@ -173,6 +173,7 @@ Clang-Tidy Checks
    modernize-use-using
    mpi-buffer-deref
    mpi-type-mismatch
+   objc-avoid-nserror-init
    objc-avoid-spinlock
    objc-forbidden-subclassing
    objc-property-declaration

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

@@ -0,0 +1,13 @@
+.. 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 runtime.
+
+The corresponding information about NSError creation: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/ErrorHandlingCocoa/CreateCustomizeNSError/CreateCustomizeNSError.html

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

@@ -0,0 +1,12 @@
+// 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: or initWithDomain:code:userInfo: to create a new NSError [objc-avoid-nserror-init]
+}
+@end