[clang] [webkit.UncountedLambdaCapturesChecker] Fix a bug that the checker didn't take the object pointer into acccount. (PR #125662)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa created https://github.com/llvm/llvm-project/pull/125662

When a callee is a method call (e.g. calling a lambda), we need to skip the object pointer to match the parameter list with the call arguments. This manifests as a bug that the checker erroneously generate a warning for a lambda capture (L1) which is passed to a no-escape argument of another lambda (L2).

>From 775a70588362f9be3100003138eef59df348a96f Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Tue, 4 Feb 2025 02:02:19 -0800
Subject: [PATCH] [webkit.UncountedLambdaCapturesChecker] Fix a bug that the
 checker didn't take the object pointer into acccount.

When a callee is a method call (e.g. calling a lambda), we need to skip the object pointer
to match the parameter list with the call arguments. This manifests as a bug that the checker
erroneously generate a warning for a lambda capture (L1) which is passed to a no-escape argument of
another lambda (L2).
---
 .../WebKit/UncountedLambdaCapturesChecker.cpp        |  4 +++-
 .../Checkers/WebKit/uncounted-lambda-captures.cpp    | 12 +++++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
index a57499d52acd0ca..53ef423bd82e7e2 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
@@ -109,8 +109,10 @@ class UncountedLambdaCapturesChecker
       bool VisitCallExpr(CallExpr *CE) override {
         checkCalleeLambda(CE);
         if (auto *Callee = CE->getDirectCallee()) {
-          bool TreatAllArgsAsNoEscape = shouldTreatAllArgAsNoEscape(Callee);
           unsigned ArgIndex = 0;
+          if (auto *CXXCallee = dyn_cast<CXXMethodDecl>(Callee))
+            ArgIndex = CXXCallee->isInstance();
+          bool TreatAllArgsAsNoEscape = shouldTreatAllArgAsNoEscape(Callee);
           for (auto *Param : Callee->parameters()) {
             if (ArgIndex >= CE->getNumArgs())
               return true;
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
index 2173245bc7af3eb..0f5ec8d8364325e 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
@@ -252,13 +252,23 @@ struct RefCountableWithLambdaCapturingThis {
     call(lambda);
   }
 
-  void method_captures_this_with_guardian_refPtr() {
+  void method_captures_this_with_guardian_refptr() {
     auto lambda = [this, protectedThis = RefPtr { &*this }]() {
       nonTrivial();
     };
     call(lambda);
   }
 
+
+  void forEach(const WTF::Function<void(RefCountable&)>&);
+  void method_captures_this_with_lambda_with_no_escape() {
+    auto run = [&]([[clang::noescape]] const WTF::Function<void(RefCountable&)>& func) {
+      forEach(func);
+    };
+    run([&](RefCountable&) {
+      nonTrivial();
+    });
+  }
 };
 
 struct NonRefCountableWithLambdaCapturingThis {