[clang-tidy] new check misc-use-internal-linkage (#90830)

Add new check misc-use-internal-linkage to detect variable and function
can be marked as static.

---------

Co-authored-by: Danny Mösch <danny.moesch@icloud.com>

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

@@ -41,6 +41,7 @@ add_clang_library(clangTidyMiscModule
   UnusedParametersCheck.cpp
   UnusedUsingDeclsCheck.cpp
   UseAnonymousNamespaceCheck.cpp
+  UseInternalLinkageCheck.cpp
 
   LINK_LIBS
   clangTidy

clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp

@@ -31,6 +31,7 @@
 #include "UnusedParametersCheck.h"
 #include "UnusedUsingDeclsCheck.h"
 #include "UseAnonymousNamespaceCheck.h"
+#include "UseInternalLinkageCheck.h"
 
 namespace clang::tidy {
 namespace misc {
@@ -78,6 +79,8 @@ class MiscModule : public ClangTidyModule {
         "misc-unused-using-decls");
     CheckFactories.registerCheck<UseAnonymousNamespaceCheck>(
         "misc-use-anonymous-namespace");
+    CheckFactories.registerCheck<UseInternalLinkageCheck>(
+        "misc-use-internal-linkage");
   }
 };
 

clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.cpp

@@ -0,0 +1,95 @@
+//===--- UseInternalLinkageCheck.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 "UseInternalLinkageCheck.h"
+#include "../utils/FileExtensionsUtils.h"
+#include "clang/AST/Decl.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchersMacros.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/Specifiers.h"
+#include "llvm/ADT/STLExtras.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::misc {
+
+namespace {
+
+AST_MATCHER(Decl, isFirstDecl) { return Node.isFirstDecl(); }
+
+static bool isInMainFile(SourceLocation L, SourceManager &SM,
+                         const FileExtensionsSet &HeaderFileExtensions) {
+  for (;;) {
+    if (utils::isSpellingLocInHeaderFile(L, SM, HeaderFileExtensions))
+      return false;
+    if (SM.isInMainFile(L))
+      return true;
+    // not in header file but not in main file
+    L = SM.getIncludeLoc(SM.getFileID(L));
+    if (L.isValid())
+      continue;
+    // Conservative about the unknown
+    return false;
+  }
+}
+
+AST_MATCHER_P(Decl, isAllRedeclsInMainFile, FileExtensionsSet,
+              HeaderFileExtensions) {
+  return llvm::all_of(Node.redecls(), [&](const Decl *D) {
+    return isInMainFile(D->getLocation(),
+                        Finder->getASTContext().getSourceManager(),
+                        HeaderFileExtensions);
+  });
+}
+
+AST_POLYMORPHIC_MATCHER(isExternStorageClass,
+                        AST_POLYMORPHIC_SUPPORTED_TYPES(FunctionDecl,
+                                                        VarDecl)) {
+  return Node.getStorageClass() == SC_Extern;
+}
+
+} // namespace
+
+void UseInternalLinkageCheck::registerMatchers(MatchFinder *Finder) {
+  auto Common =
+      allOf(isFirstDecl(), isAllRedeclsInMainFile(HeaderFileExtensions),
+            unless(anyOf(
+                // 1. internal linkage
+                isStaticStorageClass(), isInAnonymousNamespace(),
+                // 2. explicit external linkage
+                isExternStorageClass(), isExternC(),
+                // 3. template
+                isExplicitTemplateSpecialization(),
+                // 4. friend
+                hasAncestor(friendDecl()))));
+  Finder->addMatcher(
+      functionDecl(Common, unless(cxxMethodDecl()), unless(isMain()))
+          .bind("fn"),
+      this);
+  Finder->addMatcher(varDecl(Common, hasGlobalStorage()).bind("var"), this);
+}
+
+static constexpr StringRef Message =
+    "%0 %1 can be made static or moved into an anonymous namespace "
+    "to enforce internal linkage";
+
+void UseInternalLinkageCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *FD = Result.Nodes.getNodeAs<FunctionDecl>("fn")) {
+    diag(FD->getLocation(), Message) << "function" << FD;
+    return;
+  }
+  if (const auto *VD = Result.Nodes.getNodeAs<VarDecl>("var")) {
+    diag(VD->getLocation(), Message) << "variable" << VD;
+    return;
+  }
+  llvm_unreachable("");
+}
+
+} // namespace clang::tidy::misc

clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h

@@ -0,0 +1,38 @@
+//===--- UseInternalLinkageCheck.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_MISC_USEINTERNALLINKAGECHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_USEINTERNALLINKAGECHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::misc {
+
+/// Detects variables and functions that can be marked as static or moved into
+/// an anonymous namespace to enforce internal linkage.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/misc/use-internal-linkage.html
+class UseInternalLinkageCheck : public ClangTidyCheck {
+public:
+  UseInternalLinkageCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context),
+        HeaderFileExtensions(Context->getHeaderFileExtensions()) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  FileExtensionsSet HeaderFileExtensions;
+};
+
+} // namespace clang::tidy::misc
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_USEINTERNALLINKAGECHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -148,6 +148,12 @@ New checks
   to reading out-of-bounds data due to inadequate or incorrect string null
   termination.
 
+- New :doc:`misc-use-internal-linkage
+  <clang-tidy/checks/misc/use-internal-linkage>` check.
+
+  Detects variables and functions that can be marked as static or moved into
+  an anonymous namespace to enforce internal linkage.
+
 - New :doc:`modernize-min-max-use-initializer-list
   <clang-tidy/checks/modernize/min-max-use-initializer-list>` check.
 

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

@@ -267,6 +267,7 @@ Clang-Tidy Checks
    :doc:`misc-unused-parameters <misc/unused-parameters>`, "Yes"
    :doc:`misc-unused-using-decls <misc/unused-using-decls>`, "Yes"
    :doc:`misc-use-anonymous-namespace <misc/use-anonymous-namespace>`,
+   :doc:`misc-use-internal-linkage <misc/use-internal-linkage>`,
    :doc:`modernize-avoid-bind <modernize/avoid-bind>`, "Yes"
    :doc:`modernize-avoid-c-arrays <modernize/avoid-c-arrays>`,
    :doc:`modernize-concat-nested-namespaces <modernize/concat-nested-namespaces>`, "Yes"

clang-tools-extra/docs/clang-tidy/checks/misc/use-internal-linkage.rst

@@ -0,0 +1,27 @@
+.. title:: clang-tidy - misc-use-internal-linkage
+
+misc-use-internal-linkage
+=========================
+
+Detects variables and functions that can be marked as static or moved into
+an anonymous namespace to enforce internal linkage.
+
+Static functions and variables are scoped to a single file. Marking functions
+and variables as static helps to better remove dead code. In addition, it gives
+the compiler more information and allows for more aggressive optimizations.
+
+Example:
+
+.. code-block:: c++
+
+  int v1; // can be marked as static
+
+  void fn1(); // can be marked as static
+
+  namespace {
+    // already in anonymous namespace
+    int v2;
+    void fn2();
+  }
+  // already declared as extern
+  extern int v2;

clang-tools-extra/test/clang-tidy/checkers/misc/Inputs/use-internal-linkage/func.h

@@ -0,0 +1,5 @@
+#pragma once
+
+void func_header();
+
+#include "func_h.inc"

clang-tools-extra/test/clang-tidy/checkers/misc/Inputs/use-internal-linkage/func_cpp.inc

@@ -0,0 +1 @@
+void func_cpp_inc();

clang-tools-extra/test/clang-tidy/checkers/misc/Inputs/use-internal-linkage/func_h.inc

@@ -0,0 +1 @@
+void func_h_inc();

clang-tools-extra/test/clang-tidy/checkers/misc/Inputs/use-internal-linkage/var.h

@@ -0,0 +1,3 @@
+#pragma once
+
+extern int gloabl_header;

clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-func.cpp

@@ -0,0 +1,37 @@
+// RUN: %check_clang_tidy %s misc-use-internal-linkage %t -- -- -I%S/Inputs/use-internal-linkage
+
+#include "func.h"
+
+void func() {}
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'func'
+
+template<class T>
+void func_template() {}
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'func_template'
+
+void func_cpp_inc();
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'func_cpp_inc'
+
+#include "func_cpp.inc"
+
+void func_h_inc();
+
+struct S {
+  void method();
+};
+void S::method() {}
+
+void func_header();
+extern void func_extern();
+static void func_static();
+namespace {
+void func_anonymous_ns();
+} // namespace
+
+int main(int argc, const char*argv[]) {}
+
+extern "C" {
+void func_extern_c_1() {}
+}
+
+extern "C" void func_extern_c_2() {}

clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-var.cpp

@@ -0,0 +1,40 @@
+// RUN: %check_clang_tidy %s misc-use-internal-linkage %t -- -- -I%S/Inputs/use-internal-linkage
+
+#include "var.h"
+
+int global;
+// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: variable 'global'
+
+template<class T>
+T global_template;
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: variable 'global_template'
+
+int gloabl_header;
+
+extern int global_extern;
+
+static int global_static;
+
+namespace {
+static int global_anonymous_ns;
+namespace NS {
+static int global_anonymous_ns;
+}
+}
+
+static void f(int para) {
+  int local;
+  static int local_static;
+}
+
+struct S {
+  int m1;
+  static int m2;
+};
+int S::m2;
+
+extern "C" {
+int global_in_extern_c_1;
+}
+
+extern "C" int global_in_extern_c_2;