[clang] [alpha.webkit.UncountedLocalVarsChecker] Ignore a VarDecl in "if" with trivial "then" (PR #171764)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa updated https://github.com/llvm/llvm-project/pull/171764

>From ef9a5c9e9593fdb1fc0f414ba8f73be108f46c1a Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Wed, 10 Dec 2025 21:21:11 -0800
Subject: [PATCH 1/3] [alpha.webkit.UncountedLocalVarsChecker] Ignore a VarDecl
 in "if" with trivial "then"

Don't emit a warning when a variable declaration appears within the "if" condition
and if its "then" statement is trivial.
---
 .../WebKit/RawPtrRefLocalVarsChecker.cpp      |  4 ++
 .../local-vars-checked-const-member.cpp       |  4 +-
 .../local-vars-counted-const-member.cpp       |  4 +-
 .../Checkers/WebKit/uncounted-local-vars.cpp  | 40 ++++++++++++++++++-
 4 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLocalVarsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLocalVarsChecker.cpp
index f2235e7c25ab2..404ec0783dd64 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLocalVarsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/RawPtrRefLocalVarsChecker.cpp
@@ -234,6 +234,10 @@ class RawPtrRefLocalVarsChecker
       }
 
       bool TraverseIfStmt(IfStmt *IS) override {
+        if (IS->getConditionVariable()) {
+          if (auto *Then = IS->getThen(); !Then || TFA.isTrivial(Then))
+            return true;
+        }
         if (!TFA.isTrivial(IS))
           return DynamicRecursiveASTVisitor::TraverseIfStmt(IS);
         return true;
diff --git a/clang/test/Analysis/Checkers/WebKit/local-vars-checked-const-member.cpp b/clang/test/Analysis/Checkers/WebKit/local-vars-checked-const-member.cpp
index be04cf26be2e8..bf58e676f3bb0 100644
--- a/clang/test/Analysis/Checkers/WebKit/local-vars-checked-const-member.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/local-vars-checked-const-member.cpp
@@ -21,10 +21,8 @@ class Foo {
   CheckedObj& ensureObj4() {
     if (!m_obj4)
       const_cast<CheckedPtr<CheckedObj>&>(m_obj4) = new CheckedObj;
-    if (auto* next = m_obj4->next()) {
-      // expected-warning at -1{{Local variable 'next' is unchecked and unsafe [alpha.webkit.UncheckedLocalVarsChecker]}}
+    if (auto* next = m_obj4->next())
       return *next;
-    }
     return *m_obj4;
   }
 
diff --git a/clang/test/Analysis/Checkers/WebKit/local-vars-counted-const-member.cpp b/clang/test/Analysis/Checkers/WebKit/local-vars-counted-const-member.cpp
index e12c9b900a423..5f35535bde3aa 100644
--- a/clang/test/Analysis/Checkers/WebKit/local-vars-counted-const-member.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/local-vars-counted-const-member.cpp
@@ -21,10 +21,8 @@ class Foo {
   RefCountable& ensureObj4() {
     if (!m_obj4)
       const_cast<RefPtr<RefCountable>&>(m_obj4) = RefCountable::create();
-    if (auto* next = m_obj4->next()) {
-      // expected-warning at -1{{Local variable 'next' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    if (auto* next = m_obj4->next())
       return *next;
-    }
     return *m_obj4;
   }
 
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
index 3364637369799..bf093dcf3fdd3 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
@@ -492,4 +492,42 @@ namespace virtual_function {
     auto* baz = &*obj;
     // expected-warning at -1{{Local variable 'baz' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
   }
-}
\ No newline at end of file
+}
+
+namespace vardecl_in_if_condition {
+  RefCountable* provide();
+
+  RefCountable* get() {
+    if (auto* obj = provide())
+      return obj; // no warning
+    return nullptr;
+  }
+
+  RefCountable* get_non_trivial_then() {
+    if (auto* obj = provide()) // expected-warning{{Local variable 'obj' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+      return obj->next();
+    return nullptr;
+  }
+
+  RefCountable* get_non_trivial_else() {
+    if (auto* obj = provide())
+      return obj;
+    else
+      return provide()->next();
+    return nullptr;
+  }
+
+  RefCountable& get_ref() {
+    if (auto* obj = provide())
+      return *obj; // no warning
+    static Ref<RefCountable> empty = RefCountable::create();
+    return empty.get();
+  }
+
+  RefCountable* get_non_trivial_condition() {
+    if (auto* obj = provide(); obj && obj->next())
+      return obj; // expected-warning at -1{{Local variable 'obj' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+    return nullptr;
+  }
+
+}

>From f65b25fabc65b1fdf72fcee859ff25c37bcd0c09 Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Thu, 11 Dec 2025 08:01:38 -0800
Subject: [PATCH 2/3] Add one more test case per a review comment

---
 .../test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
index bf093dcf3fdd3..e1536be0b53c9 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
@@ -530,4 +530,11 @@ namespace vardecl_in_if_condition {
     return nullptr;
   }
 
+  RefCountable* get_non_trivial_else() {
+    if (auto* obj = provide(); !obj) // expected-warning@{{Local variable 'obj' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
+      return nullptr;
+    else
+      return obj;
+  }
+
 }

>From 08a0a84dc825fdf3191f9800800b62c0561a8078 Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rniwa at webkit.org>
Date: Thu, 11 Dec 2025 08:03:20 -0800
Subject: [PATCH 3/3] Fix the last test case so that else is non-trivial.

---
 clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
index e1536be0b53c9..1abb7d63984ba 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
@@ -534,7 +534,7 @@ namespace vardecl_in_if_condition {
     if (auto* obj = provide(); !obj) // expected-warning@{{Local variable 'obj' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
       return nullptr;
     else
-      return obj;
+      return obj->next();
   }
 
 }