[tidy] add new check bugprone-return-const-ref-from-parameter

clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp

@@ -54,6 +54,7 @@
 #include "PosixReturnCheck.h"
 #include "RedundantBranchConditionCheck.h"
 #include "ReservedIdentifierCheck.h"
+#include "ReturnConstRefFromParameterCheck.h"
 #include "SharedPtrArrayMismatchCheck.h"
 #include "SignalHandlerCheck.h"
 #include "SignedCharMisuseCheck.h"
@@ -137,6 +138,8 @@ class BugproneModule : public ClangTidyModule {
         "bugprone-inaccurate-erase");
     CheckFactories.registerCheck<IncorrectEnableIfCheck>(
         "bugprone-incorrect-enable-if");
+    CheckFactories.registerCheck<ReturnConstRefFromParameterCheck>(
+        "bugprone-return-const-ref-from-parameter");
     CheckFactories.registerCheck<SwitchMissingDefaultCaseCheck>(
         "bugprone-switch-missing-default-case");
     CheckFactories.registerCheck<IncDecInConditionsCheck>(

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

@@ -26,6 +26,7 @@ add_clang_library(clangTidyBugproneModule
   ImplicitWideningOfMultiplicationResultCheck.cpp
   InaccurateEraseCheck.cpp
   IncorrectEnableIfCheck.cpp
+  ReturnConstRefFromParameterCheck.cpp
   SuspiciousStringviewDataUsageCheck.cpp
   SwitchMissingDefaultCaseCheck.cpp
   IncDecInConditionsCheck.cpp

clang-tools-extra/clang-tidy/bugprone/ReturnConstRefFromParameterCheck.cpp

@@ -0,0 +1,34 @@
+//===--- ReturnConstRefFromParameterCheck.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 "ReturnConstRefFromParameterCheck.h"
+#include "../utils/Matchers.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void ReturnConstRefFromParameterCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      returnStmt(hasReturnValue(declRefExpr(to(parmVarDecl(hasType(
+                     hasCanonicalType(matchers::isReferenceToConst())))))))
+          .bind("ret"),
+      this);
+}
+
+void ReturnConstRefFromParameterCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *R = Result.Nodes.getNodeAs<ReturnStmt>("ret");
+  diag(R->getRetValue()->getBeginLoc(),
+       "returning a constant reference parameter may cause a use-after-free "
+       "when the parameter is constructed from a temporary");
+}
+
+} // namespace clang::tidy::bugprone

clang-tools-extra/clang-tidy/bugprone/ReturnConstRefFromParameterCheck.h

@@ -0,0 +1,40 @@
+//===--- ReturnConstRefFromParameterCheck.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_BUGPRONE_RETURNCONSTREFFROMPARAMETERCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_RETURNCONSTREFFROMPARAMETERCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::bugprone {
+
+/// Detects return statements that return constant reference parameter as
+/// constant reference. This may cause use-after-free errors if the caller uses
+/// xvalue as arguments.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/bugprone/return-const-ref-from-parameter.html
+class ReturnConstRefFromParameterCheck : public ClangTidyCheck {
+public:
+  ReturnConstRefFromParameterCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    // Use 'AsIs' to make sure the return type is exactly the same as the
+    // parameter type.
+    return TK_AsIs;
+  }
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+};
+
+} // namespace clang::tidy::bugprone
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_RETURNCONSTREFFROMPARAMETERCHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -112,6 +112,13 @@ New checks
   Detects error-prone Curiously Recurring Template Pattern usage, when the CRTP
   can be constructed outside itself and the derived class.
 
+- New :doc:`bugprone-return-const-ref-from-parameter
+  <clang-tidy/checks/bugprone/return-const-ref-from-parameter>` check.
+
+  Detects return statements that return constant reference parameter as constant
+  reference. This may cause use-after-free errors if the caller uses xvalue as
+  arguments.
+
 - New :doc:`bugprone-suspicious-stringview-data-usage
   <clang-tidy/checks/bugprone/suspicious-stringview-data-usage>` check.
 

clang-tools-extra/docs/clang-tidy/checks/bugprone/return-const-ref-from-parameter.rst

@@ -0,0 +1,31 @@
+.. title:: clang-tidy - bugprone-return-const-ref-from-parameter
+
+bugprone-return-const-ref-from-parameter
+========================================
+
+Detects return statements that return a constant reference parameter as constant
+reference. This may cause use-after-free errors if the caller uses xvalue as
+arguments.
+
+In C++, constant reference parameters can accept xvalues which will be destructed
+after the call. When the function returns such a parameter also as constant reference,
+then the returned reference can be used after the object it refers to has been
+destroyed.
+
+Example
+-------
+
+.. code-block:: c++
+
+  struct S {
+    int v;
+    S(int);
+    ~S();
+  };
+
+  const S &fn(const S &a) {
+    return a;
+  }
+
+  const S& s = fn(S{1});
+  s.v; // use after free

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

@@ -120,6 +120,7 @@ Clang-Tidy Checks
    :doc:`bugprone-posix-return <bugprone/posix-return>`, "Yes"
    :doc:`bugprone-redundant-branch-condition <bugprone/redundant-branch-condition>`, "Yes"
    :doc:`bugprone-reserved-identifier <bugprone/reserved-identifier>`, "Yes"
+   :doc:`bugprone-return-const-ref-from-parameter <bugprone/return-const-ref-from-parameter>`
    :doc:`bugprone-shared-ptr-array-mismatch <bugprone/shared-ptr-array-mismatch>`, "Yes"
    :doc:`bugprone-signal-handler <bugprone/signal-handler>`,
    :doc:`bugprone-signed-char-misuse <bugprone/signed-char-misuse>`,

clang-tools-extra/test/clang-tidy/checkers/bugprone/return-const-ref-from-parameter.cpp

@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy %s bugprone-return-const-ref-from-parameter %t
+
+using T = int;
+using TConst = int const;
+using TConstRef = int const&;
+
+namespace invalid {
+
+int const &f1(int const &a) { return a; }
+// CHECK-MESSAGES: :[[@LINE-1]]:38: warning: returning a constant reference parameter
+
+int const &f2(T const &a) { return a; }
+// CHECK-MESSAGES: :[[@LINE-1]]:36: warning: returning a constant reference parameter
+
+int const &f3(TConstRef a) { return a; }
+// CHECK-MESSAGES: :[[@LINE-1]]:37: warning: returning a constant reference parameter
+
+int const &f4(TConst &a) { return a; }
+// CHECK-MESSAGES: :[[@LINE-1]]:35: warning: returning a constant reference parameter
+
+} // namespace invalid
+
+namespace valid {
+
+int const &f1(int &a) { return a; }
+
+int const &f2(int &&a) { return a; }
+
+int f1(int const &a) { return a; }
+
+} // namespace valid