[clang-tools-extra] [clang-tidy] Fix crash on pointer arithmetic with an incomplete type in bugprone-pointer-arithmetic-on-polymorphic-object (PR #215724)

[via cfe-commits]

https://github.com/Hao-Chen2337 updated https://github.com/llvm/llvm-project/pull/215724

>From 92d5c5a0032614a66965f73dd4f2816f3198a652 Mon Sep 17 00:00:00 2001
From: Hao-Chen2337 <2113996104 at qq.com>
Date: Wed, 12 Aug 2026 11:13:14 +0800
Subject: [PATCH] [clang-tidy] Fix crash on pointer arithmetic with an
 incomplete type in bugprone-pointer-arithmetic-on-polymorphic-object

---
 .../PointerArithmeticOnPolymorphicObjectCheck.cpp      |  8 ++++++--
 .../pointer-arithmetic-on-polymorphic-object-all.cpp   | 10 ++++++++++
 ...nter-arithmetic-on-polymorphic-object-decl-only.cpp | 10 ++++++++++
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/bugprone/PointerArithmeticOnPolymorphicObjectCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/PointerArithmeticOnPolymorphicObjectCheck.cpp
index ef5fee9f3d2c3..e54a77953283a 100644
--- a/clang-tools-extra/clang-tidy/bugprone/PointerArithmeticOnPolymorphicObjectCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/PointerArithmeticOnPolymorphicObjectCheck.cpp
@@ -15,8 +15,12 @@ using namespace clang::ast_matchers;
 namespace clang::tidy::bugprone {
 
 namespace {
-AST_MATCHER(CXXRecordDecl, isAbstract) { return Node.isAbstract(); }
-AST_MATCHER(CXXRecordDecl, isPolymorphic) { return Node.isPolymorphic(); }
+AST_MATCHER(CXXRecordDecl, isAbstract) {
+  return Node.hasDefinition() && Node.isAbstract();
+}
+AST_MATCHER(CXXRecordDecl, isPolymorphic) {
+  return Node.hasDefinition() && Node.isPolymorphic();
+}
 } // namespace
 
 PointerArithmeticOnPolymorphicObjectCheck::
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-all.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-all.cpp
index f8163a2fd3fb8..80be193a41535 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-all.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-all.cpp
@@ -150,3 +150,13 @@ struct TemplateHolder : Base {
     (void)x;
   }
 };
+
+// pointer arithmetic on an incomplete type must not crash the matcher.
+template <typename T>
+struct IncompletePointeeCrash {
+  struct Incomplete;
+  void f(Incomplete *p) {
+    p[0];
+    // no-warning
+  }
+};
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-decl-only.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-decl-only.cpp
index 48757bbc9b10e..f8a741cb5b174 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-decl-only.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/pointer-arithmetic-on-polymorphic-object-decl-only.cpp
@@ -139,3 +139,13 @@ void typeAliases(BaseAlias *b, DerivedAlias *d, FinalDerivedAlias *fd,
   fdp += 1;
   // no-warning
 }
+
+// pointer arithmetic on an incomplete type must not crash the matcher.
+template <typename T>
+struct IncompletePointeeCrash {
+  struct Incomplete;
+  void f(Incomplete *p) {
+    p[0];
+    // no-warning
+  }
+};