[clang-tidy] Let bugprone-use-after-move also handle calls to std::forward (#82673)

Add support for std::forward.

Fixes #82023

Author: AMS21

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

@@ -330,7 +330,8 @@ void UseAfterMoveFinder::getReinits(
                             traverse(TK_AsIs, DeclRefMatcher),
                             unless(parmVarDecl(hasType(
                                 references(qualType(isConstQualified())))))),
-                        unless(callee(functionDecl(hasName("::std::move")))))))
+                        unless(callee(functionDecl(
+                            hasAnyName("::std::move", "::std::forward")))))))
           .bind("reinit");
 
   Stmts->clear();
@@ -359,24 +360,46 @@ void UseAfterMoveFinder::getReinits(
   }
 }
 
+enum class MoveType {
+  Move,    // std::move
+  Forward, // std::forward
+};
+
+static MoveType determineMoveType(const FunctionDecl *FuncDecl) {
+  if (FuncDecl->getName() == "move")
+    return MoveType::Move;
+  if (FuncDecl->getName() == "forward")
+    return MoveType::Forward;
+
+  llvm_unreachable("Invalid move type");
+}
+
 static void emitDiagnostic(const Expr *MovingCall, const DeclRefExpr *MoveArg,
                            const UseAfterMove &Use, ClangTidyCheck *Check,
-                           ASTContext *Context) {
-  SourceLocation UseLoc = Use.DeclRef->getExprLoc();
-  SourceLocation MoveLoc = MovingCall->getExprLoc();
+                           ASTContext *Context, MoveType Type) {
+  const SourceLocation UseLoc = Use.DeclRef->getExprLoc();
+  const SourceLocation MoveLoc = MovingCall->getExprLoc();
+
+  const bool IsMove = (Type == MoveType::Move);
 
-  Check->diag(UseLoc, "'%0' used after it was moved")
-      << MoveArg->getDecl()->getName();
-  Check->diag(MoveLoc, "move occurred here", DiagnosticIDs::Note);
+  Check->diag(UseLoc, "'%0' used after it was %select{forwarded|moved}1")
+      << MoveArg->getDecl()->getName() << IsMove;
+  Check->diag(MoveLoc, "%select{forward|move}0 occurred here",
+              DiagnosticIDs::Note)
+      << IsMove;
   if (Use.EvaluationOrderUndefined) {
-    Check->diag(UseLoc,
-                "the use and move are unsequenced, i.e. there is no guarantee "
-                "about the order in which they are evaluated",
-                DiagnosticIDs::Note);
+    Check->diag(
+        UseLoc,
+        "the use and %select{forward|move}0 are unsequenced, i.e. "
+        "there is no guarantee about the order in which they are evaluated",
+        DiagnosticIDs::Note)
+        << IsMove;
   } else if (UseLoc < MoveLoc || Use.DeclRef == MoveArg) {
     Check->diag(UseLoc,
-                "the use happens in a later loop iteration than the move",
-                DiagnosticIDs::Note);
+                "the use happens in a later loop iteration than the "
+                "%select{forward|move}0",
+                DiagnosticIDs::Note)
+        << IsMove;
   }
 }
 
@@ -388,7 +411,9 @@ void UseAfterMoveCheck::registerMatchers(MatchFinder *Finder) {
   auto TryEmplaceMatcher =
       cxxMemberCallExpr(callee(cxxMethodDecl(hasName("try_emplace"))));
   auto CallMoveMatcher =
-      callExpr(argumentCountIs(1), callee(functionDecl(hasName("::std::move"))),
+      callExpr(argumentCountIs(1),
+               callee(functionDecl(hasAnyName("::std::move", "::std::forward"))
+                          .bind("move-decl")),
                hasArgument(0, declRefExpr().bind("arg")),
                unless(inDecltypeOrTemplateArg()),
                unless(hasParent(TryEmplaceMatcher)), expr().bind("call-move"),
@@ -436,6 +461,7 @@ void UseAfterMoveCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *CallMove = Result.Nodes.getNodeAs<CallExpr>("call-move");
   const auto *MovingCall = Result.Nodes.getNodeAs<Expr>("moving-call");
   const auto *Arg = Result.Nodes.getNodeAs<DeclRefExpr>("arg");
+  const auto *MoveDecl = Result.Nodes.getNodeAs<FunctionDecl>("move-decl");
 
   if (!MovingCall || !MovingCall->getExprLoc().isValid())
     MovingCall = CallMove;
@@ -470,7 +496,8 @@ void UseAfterMoveCheck::check(const MatchFinder::MatchResult &Result) {
     UseAfterMoveFinder Finder(Result.Context);
     UseAfterMove Use;
     if (Finder.find(CodeBlock, MovingCall, Arg->getDecl(), &Use))
-      emitDiagnostic(MovingCall, Arg, Use, this, Result.Context);
+      emitDiagnostic(MovingCall, Arg, Use, this, Result.Context,
+                     determineMoveType(MoveDecl));
   }
 }
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -144,6 +144,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/unused-return-value>` check by updating the
   parameter `CheckedFunctions` to support regexp.
 
+- Improved :doc:`bugprone-use-after-move
+  <clang-tidy/checks/bugprone/use-after-move>` check to also handle
+  calls to ``std::forward``.
+
 - Improved :doc:`cppcoreguidelines-missing-std-forward
   <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by no longer
   giving false positives for deleted functions.

clang-tools-extra/docs/clang-tidy/checks/bugprone/use-after-move.rst

@@ -177,6 +177,18 @@ When analyzing the order in which moves, uses and reinitializations happen (see
 section `Unsequenced moves, uses, and reinitializations`_), the move is assumed
 to occur in whichever function the result of the ``std::move`` is passed to.
 
+The check also handles perfect-forwarding with ``std::forward`` so the
+following code will also trigger a use-after-move warning.
+
+.. code-block:: c++
+
+  void consume(int);
+
+  void f(int&& i) {
+    consume(std::forward<int>(i));
+    consume(std::forward<int>(i)); // use-after-move
+  }
+
 Use
 ---
 

clang-tools-extra/test/clang-tidy/checkers/bugprone/use-after-move.cpp

@@ -111,6 +111,18 @@ constexpr typename std::remove_reference<_Tp>::type &&move(_Tp &&__t) noexcept {
   return static_cast<typename remove_reference<_Tp>::type &&>(__t);
 }
 
+template <class _Tp>
+constexpr _Tp&&
+forward(typename std::remove_reference<_Tp>::type& __t) noexcept {
+  return static_cast<_Tp&&>(__t);
+}
+
+template <class _Tp>
+constexpr _Tp&&
+forward(typename std::remove_reference<_Tp>::type&& __t) noexcept {
+  return static_cast<_Tp&&>(__t);
+}
+
 } // namespace std
 
 class A {
@@ -1525,3 +1537,28 @@ class PR38187 {
 private:
   std::string val_;
 };
+
+namespace issue82023
+{
+
+struct S {
+  S();
+  S(S&&);
+};
+
+void consume(S s);
+
+template <typename T>
+void forward(T&& t) {
+  consume(std::forward<T>(t));
+  consume(std::forward<T>(t));
+  // CHECK-NOTES: [[@LINE-1]]:27: warning: 't' used after it was forwarded
+  // CHECK-NOTES: [[@LINE-3]]:11: note: forward occurred here
+}
+
+void create() {
+  S s;
+  forward(std::move(s));
+}
+
+} // namespace issue82023