[clang] [webkit.UncountedLambdaCapturesChecker] Ignore DeclRefExpr to a lambda in an no-escape argument (PR #155025)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa created https://github.com/llvm/llvm-project/pull/155025

Fix a bug that webkit.UncountedLambdaCapturesChecker was erroneously emitting a warning for a DeclRefExpr which is passed in as an argument to a no-escape function argument. The bug was caused by findLambdaInArg not adding DeclRefExpr to the ignored set even when a lambda was identified as an argument.

>From e526eb02550c02dcce8de3239829cc26b764fd8d Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Fri, 22 Aug 2025 13:06:08 -0700
Subject: [PATCH] [webkit.UncountedLambdaCapturesChecker] Ignore DeclRefExpr to
 a lambda in an no-escape argument

Fix a bug that webkit.UncountedLambdaCapturesChecker was erroneously emitting a warning for
a DeclRefExpr which is passed in as an argument to a no-escape function argument. The bug was
caused by findLambdaInArg not adding DeclRefExpr to the ignored set even when a lambda was
identified as an argument.
---
 .../WebKit/RawPtrRefLambdaCapturesChecker.cpp |  7 +++++-
 .../WebKit/uncounted-lambda-captures.cpp      | 23 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLambdaCapturesChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLambdaCapturesChecker.cpp
index 27a91132fa9be..81b08dd0831da 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLambdaCapturesChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLambdaCapturesChecker.cpp
@@ -232,14 +232,19 @@ class RawPtrRefLambdaCapturesChecker
         if (!Init)
           return nullptr;
         if (auto *Lambda = dyn_cast<LambdaExpr>(Init)) {
+          DeclRefExprsToIgnore.insert(DRE);
           updateIgnoreList();
           return Lambda;
         }
         TempExpr = dyn_cast<CXXBindTemporaryExpr>(Init->IgnoreParenCasts());
         if (!TempExpr)
           return nullptr;
+        auto *Lambda = dyn_cast_or_null<LambdaExpr>(TempExpr->getSubExpr());
+        if (!Lambda)
+          return nullptr;
+        DeclRefExprsToIgnore.insert(DRE);
         updateIgnoreList();
-        return dyn_cast_or_null<LambdaExpr>(TempExpr->getSubExpr());
+        return Lambda;
       }
 
       void checkCalleeLambda(CallExpr *CE) {
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
index 3079f8e833fcd..1dfab439c58dd 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
@@ -448,4 +448,27 @@ void ranges_for_each(RefCountable* obj) {
     obj->method();
     ++(*static_cast<unsigned*>(item));
   });
+}
+
+class RefCountedObj {
+public:
+  void ref();
+  void deref();
+
+  void call() const;
+  void callLambda([[clang::noescape]] const WTF::Function<void ()>& callback) const;
+  void doSomeWork() const;
+};
+
+void RefCountedObj::callLambda([[clang::noescape]] const WTF::Function<void ()>& callback) const
+{
+    callback();
+}
+
+void RefCountedObj::call() const
+{
+    auto lambda = [&] {
+        doSomeWork();
+    };
+    callLambda(lambda);
 }
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