[clang] [alpha.webkit.UncountedCallArgsChecker] A return value can be erroneously treated as unsafe if it's a template parameter (PR #157993)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa updated https://github.com/llvm/llvm-project/pull/157993

>From e4334be7318658f8530747d3c275499157a41149 Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Wed, 10 Sep 2025 22:15:10 -0700
Subject: [PATCH 1/2] [alpha.webkit.UncountedCallArgsChecker] A return value
 can be erroneously treated as unsafe if it's a template parameter

When a template class takes Ref<T> as a template parameter and this template parameter is used as the return value of
a member function, the return value can be treated as unsafe (i.e. emits a false positive). The issue was caused by
getCanonicalType sometimes converting Ref<T> to T. Workaround this problem by avoid emitting a warning when the original,
non-canonical type is a safe pointer type.
---
 .../WebKit/RawPtrRefCallArgsChecker.cpp       | 17 +++++++++++++--
 .../WebKit/template-wrapper-call-arg.cpp      | 21 +++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Analysis/Checkers/WebKit/template-wrapper-call-arg.cpp

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
index e80f1749d595b..47bd13bea4abb 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
@@ -122,9 +122,22 @@ class RawPtrRefCallArgsChecker
             return;
         }
         auto *E = MemberCallExpr->getImplicitObjectArgument();
-        QualType ArgType = MemberCallExpr->getObjectType().getCanonicalType();
+        auto MemberCallQT = MemberCallExpr->getObjectType();
+        QualType ArgType = MemberCallQT.getCanonicalType();
         std::optional<bool> IsUnsafe = isUnsafeType(ArgType);
-        if (IsUnsafe && *IsUnsafe && !isPtrOriginSafe(E))
+
+        // Sometimes, canonical type erroneously turns Ref<T> into T.
+        // Workaround this problem by checking again if the original type was
+        // a SubstTemplateTypeParmType of a safe smart pointer type (e.g. Ref).
+        bool IsSafePtr = false;
+        if (auto *Subst = dyn_cast<SubstTemplateTypeParmType>(MemberCallQT)) {
+          if (auto *Decl = Subst->getAssociatedDecl()) {
+            if (auto *CXXRD = dyn_cast<CXXRecordDecl>(Decl))
+              IsSafePtr = isSafePtr(CXXRD);
+          }
+        }
+
+        if (IsUnsafe && *IsUnsafe && !IsSafePtr && !isPtrOriginSafe(E))
           reportBugOnThis(E, D);
       }
 
diff --git a/clang/test/Analysis/Checkers/WebKit/template-wrapper-call-arg.cpp b/clang/test/Analysis/Checkers/WebKit/template-wrapper-call-arg.cpp
new file mode 100644
index 0000000000000..b0ff210f9415e
--- /dev/null
+++ b/clang/test/Analysis/Checkers/WebKit/template-wrapper-call-arg.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.webkit.UncountedCallArgsChecker -verify %s
+// expected-no-diagnostics
+
+#include "mock-types.h"
+
+struct Obj {
+  void ref() const;
+  void deref() const;
+
+  void someFunction();
+};
+
+template<typename T> class Wrapper {
+public:
+  T obj();
+};
+
+static void foo(Wrapper<Ref<Obj>>&& wrapper)
+{
+  wrapper.obj()->someFunction();
+}

>From a5593c64c71a588ef30d56eb9e6b89bde7eb8ea2 Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Thu, 11 Sep 2025 12:46:18 -0700
Subject: [PATCH 2/2] Fix the failing test case. We need to be checking the
 return type of a callee, not any member call type.

---
 .../Checkers/WebKit/ASTUtils.cpp               | 18 ++++++++++++++++++
 .../WebKit/RawPtrRefCallArgsChecker.cpp        | 17 ++---------------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
index 9a7f5b71cae71..f49a6f3b16491 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
@@ -154,6 +154,24 @@ bool tryToFindPtrOrigin(
             Name == "NSClassFromString")
           return callback(E, true);
       }
+
+      // Sometimes, canonical type erroneously turns Ref<T> into T.
+      // Workaround this problem by checking again if the original type was
+      // a SubstTemplateTypeParmType of a safe smart pointer type (e.g. Ref).
+      if (auto *CalleeDecl = call->getCalleeDecl()) {
+        if (auto *FD = dyn_cast<FunctionDecl>(CalleeDecl)) {
+          auto RetType = FD->getReturnType();
+          if (auto *Subst = dyn_cast<SubstTemplateTypeParmType>(RetType)) {
+            if (auto *SubstType = Subst->desugar().getTypePtr()) {
+              if (auto *RD = dyn_cast<RecordType>(SubstType)) {
+                if (auto *CXX = dyn_cast<CXXRecordDecl>(RD->getOriginalDecl()))
+                  if (isSafePtr(CXX))
+                    return callback(E, true);
+              }
+            }
+          }
+        }
+      }
     }
     if (auto *ObjCMsgExpr = dyn_cast<ObjCMessageExpr>(E)) {
       if (auto *Method = ObjCMsgExpr->getMethodDecl()) {
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
index 47bd13bea4abb..e80f1749d595b 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefCallArgsChecker.cpp
@@ -122,22 +122,9 @@ class RawPtrRefCallArgsChecker
             return;
         }
         auto *E = MemberCallExpr->getImplicitObjectArgument();
-        auto MemberCallQT = MemberCallExpr->getObjectType();
-        QualType ArgType = MemberCallQT.getCanonicalType();
+        QualType ArgType = MemberCallExpr->getObjectType().getCanonicalType();
         std::optional<bool> IsUnsafe = isUnsafeType(ArgType);
-
-        // Sometimes, canonical type erroneously turns Ref<T> into T.
-        // Workaround this problem by checking again if the original type was
-        // a SubstTemplateTypeParmType of a safe smart pointer type (e.g. Ref).
-        bool IsSafePtr = false;
-        if (auto *Subst = dyn_cast<SubstTemplateTypeParmType>(MemberCallQT)) {
-          if (auto *Decl = Subst->getAssociatedDecl()) {
-            if (auto *CXXRD = dyn_cast<CXXRecordDecl>(Decl))
-              IsSafePtr = isSafePtr(CXXRD);
-          }
-        }
-
-        if (IsUnsafe && *IsUnsafe && !IsSafePtr && !isPtrOriginSafe(E))
+        if (IsUnsafe && *IsUnsafe && !isPtrOriginSafe(E))
           reportBugOnThis(E, D);
       }