[clang-tools-extra] [clang-tidy] fix false negative in cppcoreguidelines-missing-std-forward (PR #83987)

[Qizhi Hu via cfe-commits]

https://github.com/jcsxky created https://github.com/llvm/llvm-project/pull/83987

Try to fix https://github.com/llvm/llvm-project/issues/83845
When `std::forward` is invoked in a function, make sure it uses correct parameter by checking if the bounded `var` equals the parameter.

>From 67e7001dee4fdcc1da3d267a9a120d3bc65ae69b Mon Sep 17 00:00:00 2001
From: huqizhi <huqizhi at feysh.com>
Date: Tue, 5 Mar 2024 18:02:01 +0800
Subject: [PATCH] [clang-tidy] fix false negative in
 cppcoreguidelines-missing-std-forward

---
 .../cppcoreguidelines/MissingStdForwardCheck.cpp       | 10 ++++++----
 clang-tools-extra/docs/ReleaseNotes.rst                |  3 ++-
 .../checkers/cppcoreguidelines/missing-std-forward.cpp | 10 ++++++++++
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
index c633683570f748..87fd8adf997082 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/MissingStdForwardCheck.cpp
@@ -112,10 +112,12 @@ void MissingStdForwardCheck::registerMatchers(MatchFinder *Finder) {
 
   auto ForwardCallMatcher = callExpr(
       callExpr().bind("call"), argumentCountIs(1),
-      hasArgument(
-          0, declRefExpr(to(
-                 varDecl(optionally(equalsBoundNode("param"))).bind("var")))),
-      forCallable(anyOf(equalsBoundNode("func"), CapturedInLambda)),
+      hasArgument(0, declRefExpr(to(varDecl().bind("var")))),
+      forCallable(
+          anyOf(allOf(equalsBoundNode("func"),
+                      functionDecl(hasAnyParameter(parmVarDecl(allOf(
+                          equalsBoundNode("param"), equalsBoundNode("var")))))),
+                CapturedInLambda)),
       callee(unresolvedLookupExpr(hasAnyDeclaration(
           namedDecl(hasUnderlyingDecl(hasName("::std::forward")))))),
 
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 143ae230fc443c..1abe45bae8a84d 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -156,7 +156,8 @@ Changes in existing checks
 
 - Improved :doc:`cppcoreguidelines-missing-std-forward
   <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by no longer
-  giving false positives for deleted functions.
+  giving false positives for deleted functions and fix false negative when one
+  parameter is forwarded, but some other parameter isn't.
 
 - Cleaned up :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>`
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 20e43f04180ff3..29af67b60614c8 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
@@ -95,6 +95,16 @@ void lambda_value_capture_copy(T&& t) {
   [&,t]() { T other = std::forward<T>(t); };
 }
 
+template <typename X>
+void use(const X &x) {}
+
+template <typename X, typename Y>
+void foo(X &&x, Y &&y) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:21: warning: forwarding reference parameter 't' is never forwarded inside the function body [cppcoreguidelines-missing-std-forward]
+    use(std::forward<X>(x));
+    use(y);
+}
+
 } // namespace positive_cases
 
 namespace negative_cases {