[clang-tidy] New check to warn when storing dispatch_once_t in non-static, non-global storage.

[mwyman]

Summary

Creates a new darwin ClangTidy module and adds the darwin-dispatch-once-nonstatic check that warns about dispatch_once_t variables not in static or global storage. This catches a missing static for local variables in e.g. singleton initialization behavior, and also warns on storing dispatch_once_t values in Objective-C instance variables. C/C++ struct/class instances may potentially live in static/global storage, and are ignored for this check.

The osx.API static analysis checker can find the non-static storage use of dispatch_once_t; I thought it useful to also catch this issue in clang-tidy when possible.

This is a re-land of https://reviews.llvm.org/D67567

[Eugene.Zelenko]

clang-tools-extra/docs/ReleaseNotes.rst

85

Please synchronize with first sentence in documentation.

[mwyman]

Tweaked release notes to match first sentence of documentation.

[stephanemoore]

Looks good 👌

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

 endif()
 
 add_subdirectory(android)
 add_subdirectory(abseil)
 add_subdirectory(boost)
 add_subdirectory(bugprone)
 add_subdirectory(cert)
 add_subdirectory(cppcoreguidelines)
+add_subdirectory(darwin)
 add_subdirectory(fuchsia)
 add_subdirectory(google)
 add_subdirectory(hicpp)
 add_subdirectory(linuxkernel)
 add_subdirectory(llvm)
 add_subdirectory(misc)
 add_subdirectory(modernize)
 if(CLANG_ENABLE_STATIC_ANALYZER)

clang-tools-extra/clang-tidy/ClangTidyForceLinker.h

 static int LLVM_ATTRIBUTE_UNUSED LLVMModuleAnchorDestination =
     LLVMModuleAnchorSource;
 
 // This anchor is used to force the linker to link the CppCoreGuidelinesModule.
 extern volatile int CppCoreGuidelinesModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED CppCoreGuidelinesModuleAnchorDestination =
     CppCoreGuidelinesModuleAnchorSource;
 
+// This anchor is used to force the linker to link the DarwinModule.
+extern volatile int DarwinModuleAnchorSource;
+static int LLVM_ATTRIBUTE_UNUSED DarwinModuleAnchorDestination =
+    DarwinModuleAnchorSource;
+
 // This anchor is used to force the linker to link the FuchsiaModule.
 extern volatile int FuchsiaModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED FuchsiaModuleAnchorDestination =
     FuchsiaModuleAnchorSource;
 
 // This anchor is used to force the linker to link the GoogleModule.
 extern volatile int GoogleModuleAnchorSource;
 static int LLVM_ATTRIBUTE_UNUSED GoogleModuleAnchorDestination =

clang-tools-extra/clang-tidy/darwin/CMakeLists.txt

+set(LLVM_LINK_COMPONENTS support)
+
+add_clang_library(clangTidyDarwinModule
+  DarwinTidyModule.cpp
+  DispatchOnceNonstaticCheck.cpp
+
+  LINK_LIBS
+  clangAnalysis
+  clangAST
+  clangASTMatchers
+  clangBasic
+  clangLex
+  clangTidy
+  clangTidyUtils
+  )

clang-tools-extra/clang-tidy/darwin/DarwinTidyModule.cpp

+//===--- MiscTidyModule.cpp - clang-tidy ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "../ClangTidy.h"
+#include "../ClangTidyModule.h"
+#include "../ClangTidyModuleRegistry.h"
+#include "DispatchOnceNonstaticCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace darwin {
+
+class DarwinModule : public ClangTidyModule {
+public:
+  void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<DispatchOnceNonstaticCheck>(
+        "darwin-dispatch-once-nonstatic");
+  }
+};
+
+} // namespace darwin
+
+// Register the DarwinTidyModule using this statically initialized variable.
+static ClangTidyModuleRegistry::Add<darwin::DarwinModule>
+    X("misc-module", "Adds miscellaneous lint checks.");
+
+// This anchor is used to force the linker to link in the generated object file
+// and thus register the DarwinModule.
+volatile int DarwinModuleAnchorSource = 0;
+
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/darwin/DispatchOnceNonstaticCheck.h

+//===--- DispatchOnceNonstaticCheck.h - clang-tidy --------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_DARWIN_DISPATCHONCENONSTATICCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_DARWIN_DISPATCHONCENONSTATICCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace darwin {
+
+/// Finds variables of type dispatch_once_t that do not have static or global
+/// storage duration, as required by the libdispatch documentation.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/darwin-dispatch-once-nonstatic.html
+class DispatchOnceNonstaticCheck : public ClangTidyCheck {
+public:
+  DispatchOnceNonstaticCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace darwin
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_DARWIN_DISPATCHONCENONSTATICCHECK_H

clang-tools-extra/clang-tidy/darwin/DispatchOnceNonstaticCheck.cpp

+//===--- DispatchOnceNonstaticCheck.cpp - clang-tidy ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DispatchOnceNonstaticCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclObjC.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Basic/Diagnostic.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace darwin {
+
+void DispatchOnceNonstaticCheck::registerMatchers(MatchFinder *Finder) {
+  // Find variables without static or global storage. VarDecls do not include
+  // struct/class members, which are FieldDecls.
+  Finder->addMatcher(
+      varDecl(hasLocalStorage(), hasType(asString("dispatch_once_t")))
+          .bind("non-static-var"),
+      this);
+
+  // Members of structs or classes might be okay, if the use is at static or
+  // global scope. These will be ignored for now. But ObjC ivars can be
+  // flagged immediately, since they cannot be static.
+  Finder->addMatcher(
+      objcIvarDecl(hasType(asString("dispatch_once_t"))).bind("ivar"), this);
+}
+
+void DispatchOnceNonstaticCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *VD = Result.Nodes.getNodeAs<VarDecl>("non-static-var")) {
+    if (const auto *PD = dyn_cast<ParmVarDecl>(VD)) {
+      // Catch function/method parameters, as any dispatch_once_t should be
+      // passed by pointer instead.
+      diag(PD->getTypeSpecStartLoc(),
+           "dispatch_once_t variables must have static or global storage "
+           "duration; function parameters should be pointer references");
+    } else {
+      diag(VD->getTypeSpecStartLoc(), "dispatch_once_t variables must have "
+                                      "static or global storage duration")
+          << FixItHint::CreateInsertion(VD->getTypeSpecStartLoc(), "static ");
+    }
+  }
+
+  if (const auto *D = Result.Nodes.getNodeAs<ObjCIvarDecl>("ivar")) {
+    diag(D->getTypeSpecStartLoc(),
+         "dispatch_once_t variables must have static or global storage "
+         "duration and cannot be Objective-C instance variables");
+  }
+}
+
+} // namespace darwin
+} // namespace tidy
+} // namespace clang

clang-tools-extra/clang-tidy/plugin/CMakeLists.txt

 add_clang_library(clangTidyPlugin
   ClangTidyPlugin.cpp
 
   LINK_LIBS
   clangAST
   clangASTMatchers
   clangBasic
   clangFrontend
   clangSema
   clangTidy
   clangTidyAbseilModule
   clangTidyAndroidModule
   clangTidyBoostModule
   clangTidyBugproneModule
   clangTidyCERTModule
   clangTidyCppCoreGuidelinesModule
+  clangTidyDarwinModule
   clangTidyFuchsiaModule
   clangTidyGoogleModule
   clangTidyHICPPModule
   clangTidyLinuxKernelModule
   clangTidyLLVMModule
   clangTidyMiscModule
   clangTidyModernizeModule
   clangTidyObjCModule

clang-tools-extra/clang-tidy/tool/CMakeLists.txt

target_link_libraries(clang-tidy
   clangBasic
   clangTidy
   clangTidyAndroidModule
   clangTidyAbseilModule
   clangTidyBoostModule
   clangTidyBugproneModule
   clangTidyCERTModule
   clangTidyCppCoreGuidelinesModule
+  clangTidyDarwinModule
   clangTidyFuchsiaModule
   clangTidyGoogleModule
   clangTidyHICPPModule
   clangTidyLinuxKernelModule
   clangTidyLLVMModule
   clangTidyMiscModule
   clangTidyModernizeModule
   clangTidyObjCModule

clang-tools-extra/clangd/CMakeLists.txt

add_clang_library(clangDaemon
   clangSerialization
   clangTidy
   clangTidyAndroidModule
   clangTidyAbseilModule
   clangTidyBoostModule
   clangTidyBugproneModule
   clangTidyCERTModule
   clangTidyCppCoreGuidelinesModule
+  clangTidyDarwinModule
   clangTidyFuchsiaModule
   clangTidyGoogleModule
   clangTidyHICPPModule
   clangTidyLinuxKernelModule
   clangTidyLLVMModule
   clangTidyMiscModule
   clangTidyModernizeModule
   clangTidyObjCModule

clang-tools-extra/docs/ReleaseNotes.rst

- New :doc:`bugprone-dynamic-static-initializers
   dynamically in header files.
 
 - New :doc:`bugprone-infinite-loop
   <clang-tidy/checks/bugprone-infinite-loop>` check.
 
   Finds obvious infinite loops (loops where the condition variable is not
   changed at all).
 
+- New :doc:`darwin-dispatch-once-nonstatic
+  <clang-tidy/checks/darwin-dispatch-once-nonstatic>` check.
+
+  Finds instances of ``dispatch_once_t`` variables not having static or global
+  storage.
+
 - New :doc:`linuxkernel-must-use-errs
   <clang-tidy/checks/linuxkernel-must-use-errs>` check.
 
   Checks Linux kernel code to see if it uses the results from the functions in
   ``linux/err.h``.
 
 - New :doc:`google-upgrade-googletest-case
   <clang-tidy/checks/google-upgrade-googletest-case>` check.

clang-tools-extra/docs/clang-tidy/checks/darwin-dispatch-once-nonstatic.rst

+.. title:: clang-tidy - darwin-dispatch-once-nonstatic
+
+darwin-dispatch-once-nonstatic
+==============================
+
+Finds declarations of ``dispatch_once_t`` variables without static or global
+storage. The behavior of using ``dispatch_once_t`` predicates with automatic or
+dynamic storage is undefined by libdispatch, and should be avoided.
+
+It is a common pattern to have functions initialize internal static or global
+data once when the function runs, but programmers have been known to miss the
+static on the ``dispatch_once_t`` predicate, leading to an uninitialized flag
+value at the mercy of the stack.
+
+Programmers have also been known to make ``dispatch_once_t`` variables be
+members of structs or classes, with the intent to lazily perform some expensive
+struct or class member initialization only once; however, this violates the
+libdispatch requirements.
+
+See the discussion section of
+`Apple's dispatch_once documentation <https://developer.apple.com/documentation/dispatch/1447169-dispatch_once>`_
+for more information.

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

.. toctree::
    cppcoreguidelines-pro-type-cstyle-cast
    cppcoreguidelines-pro-type-member-init
    cppcoreguidelines-pro-type-reinterpret-cast
    cppcoreguidelines-pro-type-static-cast-downcast
    cppcoreguidelines-pro-type-union-access
    cppcoreguidelines-pro-type-vararg
    cppcoreguidelines-slicing
    cppcoreguidelines-special-member-functions
+   darwin-dispatch-once-nonstatic
    fuchsia-default-arguments-calls
    fuchsia-default-arguments-declarations
    fuchsia-header-anon-namespaces (redirects to google-build-namespaces) <fuchsia-header-anon-namespaces>
    fuchsia-multiple-inheritance
    fuchsia-overloaded-operator
    fuchsia-restrict-system-includes
    fuchsia-statically-constructed-objects
    fuchsia-trailing-return

clang-tools-extra/test/clang-tidy/darwin-dispatch-once-nonstatic.mm

+// RUN: %check_clang_tidy %s darwin-dispatch-once-nonstatic %t -- -- -fblocks
+
+typedef int dispatch_once_t;
+extern void dispatch_once(dispatch_once_t *pred, void(^block)(void));
+
+
+void bad_dispatch_once(dispatch_once_t once, void(^block)(void)) {}
+// CHECK-MESSAGES: :[[@LINE-1]]:24: warning: dispatch_once_t variables must have static or global storage duration; function parameters should be pointer references [darwin-dispatch-once-nonstatic]
+
+// file-scope dispatch_once_ts have static storage duration.
+dispatch_once_t global_once;
+static dispatch_once_t file_static_once;
+namespace {
+dispatch_once_t anonymous_once;
+} // end anonymous namespace
+
+int Correct(void) {
+  static int value;
+  static dispatch_once_t once;
+  dispatch_once(&once, ^{
+    value = 1;
+  });
+  return value;
+}
+
+int Incorrect(void) {
+  static int value;
+  dispatch_once_t once;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: dispatch_once_t variables must have static or global storage duration [darwin-dispatch-once-nonstatic]
+  // CHECK-FIXES: static dispatch_once_t once;
+  dispatch_once(&once, ^{
+    value = 1;
+  });
+  return value;
+}
+
+struct OnceStruct {
+  static dispatch_once_t staticOnce; // Allowed
+  int value;
+  dispatch_once_t once;  // Allowed (at this time)
+};
+
+@interface MyObject {
+  dispatch_once_t _once;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: dispatch_once_t variables must have static or global storage duration and cannot be Objective-C instance variables [darwin-dispatch-once-nonstatic]
+  // CHECK-FIXES: dispatch_once_t _once;
+}
+@end