[clang-tools-extra] [clang-tidy] Fix FP/FN in cppcoreguidelines-missing-std-forward (PR #178651)

[via cfe-commits]

https://github.com/zeyi2 created https://github.com/llvm/llvm-project/pull/178651

Closes #176873

>From bab89778820a11949f63dce48b9a404a41a025aa Mon Sep 17 00:00:00 2001
From: mtx <mitchell.xu2 at gmail.com>
Date: Wed, 28 Jan 2026 23:39:33 +0800
Subject: [PATCH] [clang-tidy] Fix FP/FN in
 cppcoreguidelines-missing-std-forward

---
 .../MissingStdForwardCheck.cpp                | 18 ++++----
 clang-tools-extra/docs/ReleaseNotes.rst       |  8 ++++
 .../cppcoreguidelines/missing-std-forward.cpp | 46 +++++++++++++++++++
 3 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
index d1d81d510c8fb..77517a629030f 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
@@ -107,19 +107,21 @@ void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
 
   auto CapturedInLambda = hasDeclContext(cxxRecordDecl(
       isLambda(),
-      hasParent(lambdaExpr(forCallable(equalsBoundNode("func")),
-                           anyOf(CapturedInCaptureList, CapturedInBody)))));
+      hasAncestor(lambdaExpr(forCallable(equalsBoundNode("func")),
+                             anyOf(CapturedInCaptureList, CapturedInBody)))));
 
   auto ToParam = hasAnyParameter(parmVarDecl(equalsBoundNode("param")));
 
   auto ForwardCallMatcher = callExpr(
       callExpr().bind("call"), argumentCountIs(1),
-      hasArgument(0, declRefExpr(to(varDecl().bind("var")))),
-      forCallable(
-          anyOf(allOf(equalsBoundNode("func"),
-                      functionDecl(hasAnyParameter(parmVarDecl(allOf(
-                          equalsBoundNode("param"), equalsBoundNode("var")))))),
-                CapturedInLambda)),
+      hasArgument(
+          0, declRefExpr(to(
+                 varDecl(anyOf(equalsBoundNode("param"),
+                               hasSameNameAsBoundNode("param"),
+                               hasInitializer(ignoringParenImpCasts(
+                                   declRefExpr(to(equalsBoundNode("param")))))))
+                     .bind("var")))),
+      forCallable(anyOf(equalsBoundNode("func"), CapturedInLambda)),
       callee(unresolvedLookupExpr(hasAnyDeclaration(
           namedDecl(hasUnderlyingDecl(hasName(ForwardFunction)))))),
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 754880bd1a381..6faf18fc96b55 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -136,6 +136,14 @@ Changes in existing checks
   the invalidating function in the warning message when a custom invalidation
   function is used (via the `InvalidationFunctions` option).
 
+- Improved :doc:`cppcoreguidelines-missing-std-forward
+  <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by:
+
+  - Correctly handling forwarding in deeply nested lambdas.
+
+  - Fixing a false negative when multiple parameters are used in a lambda and
+    only some of them are forwarded.
+
 - Improved :doc:`llvm-use-ranges
   <clang-tidy/checks/llvm/use-ranges>` check by adding support for the following
   algorithms: ``std::accumulate``, ``std::replace_copy``, and
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
index 98c592db7ce22..47e2977d6fc12 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/missing-std-forward.cpp
@@ -105,6 +105,26 @@ void foo(X &&x, Y &&y) {
     use(y);
 }
 
+template <typename T>
+void nested_but_no_forward(T &&arg) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:32: warning: forwarding reference parameter 'arg' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward]
+	[&]()
+	{
+		[&]()
+		{ consumes_all(arg); }();
+	}();
+}
+
+template <typename T, typename U>
+void nested_forward_only_one(T &&arg1, U &&arg2) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:44: warning: forwarding reference parameter 'arg2' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward]
+	[&]()
+	{
+		[&]()
+		{ consumes_all(std::forward<T>(arg1)); }();
+	}();
+}
+
 } // namespace positive_cases
 
 namespace negative_cases {
@@ -182,6 +202,32 @@ void lambda_value_reference_auxiliary_var(T&& t) {
   [&x = t]() { T other = std::forward<T>(x); };
 }
 
+template <typename T>
+void nested_forward(T &&arg) {
+	[&]()
+	{
+		[&]()
+		{ consumes_all(std::forward<T>(arg)); }();
+	}();
+}
+
+template <typename T>
+void triple_nested_forward(T &&arg) {
+	[&]()
+	{
+		[&]()
+		{
+			[&]()
+			{ consumes_all(std::forward<T>(arg)); }();
+		}();
+	}();
+}
+
+template <class T>
+void lambda_renamed_capture(T&& t) {
+  [&a = t]() { consumes_all(std::forward<T>(a)); };
+}
+
 } // namespace negative_cases
 
 namespace deleted_functions {