[clang-tidy ObjC] [3/3] New check objc-forbidden-subclassing

Summary:
This is part 3 of 3 of a series of changes to improve Objective-C
linting in clang-tidy.

This adds a new clang-tidy check `objc-forbidden-subclassing` which
ensures clients do not create subclasses of Objective-C classes which
are not designed to be subclassed.

(Note that for code under your control, you should use
__attribute__((objc_subclassing_restricted)) instead -- this
is intended for third-party APIs which cannot be modified.)

By default, the following classes (which are publicly documented
as not supporting subclassing) are forbidden from subclassing:

ABNewPersonViewController
ABPeoplePickerNavigationController
ABPersonViewController
ABUnknownPersonViewController
NSHashTable
NSMapTable
NSPointerArray
NSPointerFunctions
NSTimer
UIActionSheet
UIAlertView
UIImagePickerController
UITextInputMode
UIWebView

Clients can set a CheckOption
`objc-forbidden-subclassing.ClassNames` to a semicolon-separated
list of class names, which overrides this list.

Test Plan: `ninja check-clang-tools`

Patch by Ben Hamilton!

Reviewers: hokein, alexfh

Reviewed By: hokein

Subscribers: saidinwot, Wizard, srhines, mgorny, xazax.hun

Differential Revision: https://reviews.llvm.org/D39142

llvm-svn: 316744

1 files changed, 118 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/objc/ForbiddenSubclassingCheck.cpp b/clang-tools-extra/clang-tidy/objc/ForbiddenSubclassingCheck.cpp
new file mode 100644
index 00000000000..a8d79f55844
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/objc/ForbiddenSubclassingCheck.cpp
@@ -0,0 +1,118 @@
+//===--- ForbiddenSubclassingCheck.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 "ForbiddenSubclassingCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/SmallVector.h"
+#include "../utils/OptionsUtils.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace objc {
+
+namespace {
+
+constexpr char DefaultForbiddenSuperClassNames[] =
+    "ABNewPersonViewController;"
+    "ABPeoplePickerNavigationController;"
+    "ABPersonViewController;"
+    "ABUnknownPersonViewController;"
+    "NSHashTable;"
+    "NSMapTable;"
+    "NSPointerArray;"
+    "NSPointerFunctions;"
+    "NSTimer;"
+    "UIActionSheet;"
+    "UIAlertView;"
+    "UIImagePickerController;"
+    "UITextInputMode;"
+    "UIWebView";
+
+/// \brief Matches Objective-C classes that directly or indirectly
+/// have a superclass matching \c Base.
+///
+/// Note that a class is not considered to be a subclass of itself.
+///
+/// Example matches Y, Z
+/// (matcher = objcInterfaceDecl(hasName("X")))
+/// \code
+///   @interface X
+///   @end
+///   @interface Y : X  // directly derived
+///   @end
+///   @interface Z : Y  // indirectly derived
+///   @end
+/// \endcode
+AST_MATCHER_P(ObjCInterfaceDecl, isSubclassOf,
+              ast_matchers::internal::Matcher<ObjCInterfaceDecl>, Base) {
+  for (const auto *SuperClass = Node.getSuperClass();
+       SuperClass != nullptr;
+       SuperClass = SuperClass->getSuperClass()) {
+    if (Base.matches(*SuperClass, Finder, Builder)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+} // namespace
+
+ForbiddenSubclassingCheck::ForbiddenSubclassingCheck(
+    StringRef Name,
+    ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      ForbiddenSuperClassNames(
+          utils::options::parseStringList(
+              Options.get("ClassNames", DefaultForbiddenSuperClassNames))) {
+}
+
+void ForbiddenSubclassingCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      objcInterfaceDecl(
+          isSubclassOf(
+              objcInterfaceDecl(
+                  hasAnyName(
+                      std::vector<StringRef>(
+                          ForbiddenSuperClassNames.begin(),
+                          ForbiddenSuperClassNames.end())))
+              .bind("superclass")))
+      .bind("subclass"),
+      this);
+}
+
+void ForbiddenSubclassingCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *SubClass = Result.Nodes.getNodeAs<ObjCInterfaceDecl>(
+      "subclass");
+  assert(SubClass != nullptr);
+  const auto *SuperClass = Result.Nodes.getNodeAs<ObjCInterfaceDecl>(
+      "superclass");
+  assert(SuperClass != nullptr);
+  diag(SubClass->getLocation(),
+       "Objective-C interface %0 subclasses %1, which is not "
+       "intended to be subclassed")
+      << SubClass
+      << SuperClass;
+}
+
+void ForbiddenSubclassingCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(
+      Opts,
+      "ForbiddenSuperClassNames",
+      utils::options::serializeStringList(ForbiddenSuperClassNames));
+}
+
+} // namespace objc
+} // namespace tidy
+} // namespace clang