[clang-tidy] Portability Avoid Unprototyped Functions Check

clang-tools-extra/clang-tidy/ClangTidy.cpp

@@ -20,6 +20,7 @@
 #include "ClangTidyModuleRegistry.h"
 #include "ClangTidyProfiling.h"
 #include "ExpandModularHeadersPPCallbacks.h"
+#include "GlobList.h"
 #include "clang-tidy-config.h"
 #include "clang/AST/ASTConsumer.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
@@ -581,7 +582,32 @@ runClangTidy(clang::tidy::ClangTidyContext &Context,
         return AdjustedArgs;
       };
 
+  // Add extra arguments required by clang-additional-diagnostic-* checks.
+  ArgumentsAdjuster ClangAdditionalDiagnosticArgumentsInserter =
+      [&Context](const CommandLineArguments &Args, StringRef Filename) {
+        ClangTidyOptions Opts = Context.getOptionsForFile(Filename);
+        if (!Opts.Checks)
+          return Args;
+
+        CommandLineArguments AdjustedArgs = Args;
+        CachedGlobList Filter(*Opts.Checks);
+
+        for (StringRef Flag : clang::DiagnosticIDs::getDiagnosticFlags()) {
+          if (Flag.starts_with("-Wno"))
+            continue;
+
+          std::string CheckName = "clang-additional-diagnostic-";
+          CheckName += Flag.drop_front(2);
+
+          if (Filter.contains(CheckName))
+            AdjustedArgs.insert(AdjustedArgs.end(), Flag.str());
+        }
+
+        return AdjustedArgs;
+      };
+
   Tool.appendArgumentsAdjuster(PerFileExtraArgumentsInserter);
+  Tool.appendArgumentsAdjuster(ClangAdditionalDiagnosticArgumentsInserter);
   Tool.appendArgumentsAdjuster(getStripPluginsAdjuster());
   Context.setEnableProfiling(EnableCheckProfile);
   Context.setProfileStoragePrefix(StoreCheckProfile);

clang-tools-extra/clang-tidy/portability/AvoidUnprototypedFunctionsCheck.cpp

@@ -0,0 +1,58 @@
+//===--- AvoidUnprototypedFunctionsCheck.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 "AvoidUnprototypedFunctionsCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::portability {
+
+void AvoidUnprototypedFunctionsCheck::registerMatchers(MatchFinder *Finder) {
+  auto FunctionTypeMatcher =
+      forEachDescendant(functionType(unless(functionProtoType())));
+  Finder->addMatcher(declaratorDecl(FunctionTypeMatcher).bind("declaratorDecl"),
+                     this);
+  Finder->addMatcher(typedefDecl(FunctionTypeMatcher).bind("typedefDecl"),
+                     this);
+}
+
+void AvoidUnprototypedFunctionsCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  if (const auto *MatchedTypedefDecl =
+          Result.Nodes.getNodeAs<TypedefDecl>("typedefDecl")) {
+    diag(MatchedTypedefDecl->getLocation(),
+         "avoid unprototyped functions in typedef; explicitly add a 'void' "
+         "parameter if the function takes no arguments");
+    return;
+  }
+
+  const auto *MatchedDeclaratorDecl =
+      Result.Nodes.getNodeAs<Decl>("declaratorDecl");
+  if (!MatchedDeclaratorDecl) {
+    return;
+  }
+
+  if (const auto *MatchedFunctionDecl =
+          llvm::dyn_cast<FunctionDecl>(MatchedDeclaratorDecl)) {
+    if (MatchedFunctionDecl->isMain() ||
+        MatchedFunctionDecl->hasWrittenPrototype())
+      return;
+
+    diag(MatchedFunctionDecl->getLocation(),
+         "avoid unprototyped function declarations; explicitly spell out a "
+         "single 'void' parameter if the function takes no argument");
+    return;
+  }
+
+  diag(MatchedDeclaratorDecl->getLocation(),
+       "avoid unprototyped functions in type specifiers; explicitly add a "
+       "'void' parameter if the function takes no arguments");
+}
+
+} // namespace clang::tidy::portability

clang-tools-extra/clang-tidy/portability/AvoidUnprototypedFunctionsCheck.h

@@ -0,0 +1,33 @@
+//===--- AvoidUnprototypedFunctionsCheck.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_PORTABILITY_AVOIDUNPROTOTYPEDFUNCTIONSCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PORTABILITY_AVOIDUNPROTOTYPEDFUNCTIONSCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::portability {
+
+/// Checks if unprototyped function types are used in the source code.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/portability/avoid-unprototyped-functions.html
+class AvoidUnprototypedFunctionsCheck : public ClangTidyCheck {
+public:
+  AvoidUnprototypedFunctionsCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return !LangOpts.CPlusPlus;
+  }
+};
+
+} // namespace clang::tidy::portability
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PORTABILITY_AVOIDUNPROTOTYPEDFUNCTIONSCHECK_H

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

@@ -6,6 +6,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_clang_library(clangTidyPortabilityModule STATIC
   AvoidPragmaOnceCheck.cpp
+  AvoidUnprototypedFunctionsCheck.cpp
   PortabilityTidyModule.cpp
   RestrictSystemIncludesCheck.cpp
   SIMDIntrinsicsCheck.cpp

clang-tools-extra/clang-tidy/portability/PortabilityTidyModule.cpp

@@ -10,6 +10,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "AvoidPragmaOnceCheck.h"
+#include "AvoidUnprototypedFunctionsCheck.h"
 #include "RestrictSystemIncludesCheck.h"
 #include "SIMDIntrinsicsCheck.h"
 #include "StdAllocatorConstCheck.h"
@@ -23,6 +24,8 @@ class PortabilityModule : public ClangTidyModule {
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<AvoidPragmaOnceCheck>(
         "portability-avoid-pragma-once");
+    CheckFactories.registerCheck<AvoidUnprototypedFunctionsCheck>(
+        "portability-avoid-unprototyped-functions");
     CheckFactories.registerCheck<RestrictSystemIncludesCheck>(
         "portability-restrict-system-includes");
     CheckFactories.registerCheck<SIMDIntrinsicsCheck>(

clang-tools-extra/docs/ReleaseNotes.rst

@@ -208,6 +208,11 @@ New checks
 
   Detect redundant parentheses.
 
+- New :doc:`portability-avoid-unprototyped-functions
+  <clang-tidy/checks/portability/avoid-unprototyped-functions>` check.
+
+  Checks if unprototyped function types are used in the source code.
+
 New check aliases
 ^^^^^^^^^^^^^^^^^
 

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

@@ -362,6 +362,7 @@ Clang-Tidy Checks
    :doc:`performance-unnecessary-copy-initialization <performance/unnecessary-copy-initialization>`, "Yes"
    :doc:`performance-unnecessary-value-param <performance/unnecessary-value-param>`, "Yes"
    :doc:`portability-avoid-pragma-once <portability/avoid-pragma-once>`,
+   :doc:`portability-avoid-unprototyped-functions <portability/avoid-unprototyped-functions>`,
    :doc:`portability-restrict-system-includes <portability/restrict-system-includes>`, "Yes"
    :doc:`portability-simd-intrinsics <portability/simd-intrinsics>`,
    :doc:`portability-std-allocator-const <portability/std-allocator-const>`,

clang-tools-extra/docs/clang-tidy/checks/portability/avoid-unprototyped-functions.rst

@@ -0,0 +1,73 @@
+.. title:: clang-tidy - portability-avoid-unprototyped-functions
+
+portability-avoid-unprototyped-functions
+========================================
+
+Checks if unprototyped function types are used in the source code.
+
+For example:
+
+.. code-block:: c
+
+  void foo();         // Bad: unprototyped function declaration
+  void foo(void);     // Good: a function declaration that takes no parameters
+
+  void (*ptr)();      // Bad: pointer to an unprototyped function
+  void (*ptr)(void);  // Good: pointer to a function that takes no parameters
+
+Before C23 ``void foo()`` means a function that takes any number of parameters, so the following snippet is valid.
+
+.. code-block:: c
+
+  // -std=c17
+  void foo();
+
+  int main() {
+    foo(1, 2, 3);
+
+    return 0;
+  }
+
+Starting from C23 however, ``void foo()`` means a function that takes no parameters, so the same snippet is invalid.
+
+.. code-block:: c
+
+  // -std=c23
+  void foo();
+
+  int main() {
+    foo(1, 2, 3);
+  //    ^ error: too many arguments to function call, expected 0, have 3
+
+    return 0;
+  }
+
+Similarly a pointer to an unprototyped function binds to any function before C23, so the following snippet is considered valid.
+
+.. code-block:: c
+
+  // -std=c17
+  void foo(int x, int y);
+
+  int main() {
+    void (*ptr)() = &foo;
+
+    return 0;
+  }
+
+From C23 however, the smae pointer will only bind to functions that take no parameters.
+
+.. code-block:: c
+
+  // -std=c23
+  void foo(int x, int y);
+
+  int main() {
+    void (*ptr)() = &foo;
+    //    ^ error: incompatible function pointer types initializing 'void (*)(void)' with an expression of type 'void (*)(int, int)'
+
+    return 0;
+  }
+
+Some codebases might explicitly take advantage of the pre-C23 behavior, but these codebases should also be aware that
+their solution might not be fully portable between compilers.

clang-tools-extra/test/clang-tidy/checkers/portability/avoid-unprototyped-functions.c

@@ -0,0 +1,32 @@
+// RUN: %check_clang_tidy %s portability-avoid-unprototyped-functions %t
+struct S {
+  int (*UnprototypedFunctionPtrField)();
+  // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: avoid unprototyped functions in type specifiers; explicitly add a 'void' parameter if the function takes no arguments
+};
+
+void unprototypedFunction();
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: avoid unprototyped function declarations; explicitly spell out a single 'void' parameter if the function takes no argument
+
+void unprototypedParamter(int (*UnprototypedFunctionPtrParameter)());
+// CHECK-MESSAGES: :[[@LINE-1]]:33: warning: avoid unprototyped functions in type specifiers; explicitly add a 'void' parameter if the function takes no arguments
+
+void unprototypedVariable() {
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: avoid unprototyped function declarations; explicitly spell out a single 'void' parameter if the function takes no argument
+
+  int (*UnprototypedFunctionPtrVariable)();
+  // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: avoid unprototyped functions in type specifiers; explicitly add a 'void' parameter if the function takes no arguments
+}
+
+typedef int (*UnprototypedFunctionPtrArray[13])();
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: avoid unprototyped functions in typedef; explicitly add a 'void' parameter if the function takes no arguments
+
+void unprototypedTypeAliasParameter(UnprototypedFunctionPtrArray);
+
+#define ANYARG
+
+void unprototypedMacroParameter(ANYARG);
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: avoid unprototyped function declarations; explicitly spell out a single 'void' parameter if the function takes no argument
+
+void functionWithNoArguments(void);
+
+int main();