[clang-tidy] bugprone-exception-escape didn't detech catching of an exception with pointer type by void * exception handler

[hanickadot]

As in title, code which checks eligibility of exceptions with pointer types to be handled by exception handler of type void * disallowed this case. It was working like this:

if (isStandardPointerConvertible(ExceptionCanTy, HandlerCanTy) &&
          isUnambiguousPublicBaseClass(
              ExceptionCanTy->getTypePtr()->getPointeeType().getTypePtr(),
              HandlerCanTy->getTypePtr()->getPointeeType().getTypePtr())) {

but in isUnambiguousPublicBaseClass there was code which looked for definitions:

bool isUnambiguousPublicBaseClass(const Type *DerivedType,
                                  const Type *BaseType) {
  const auto *DerivedClass =
      DerivedType->getCanonicalTypeUnqualified()->getAsCXXRecordDecl();
  const auto *BaseClass =
      BaseType->getCanonicalTypeUnqualified()->getAsCXXRecordDecl();
  if (!DerivedClass || !BaseClass)
    return false;

This code disallowed usage of void * type which was already correctly detected in isStandardPointerConvertible.

AFAIK this seems like misinterpretation of specification:

14.4 Handling an exception
a standard pointer conversion not involving conversions to pointers to private or protected or ambiguous classes
(https://eel.is/c++draft/except.handle#3.3.1)

and

7.3.12 Pointer conversions
... If B is an inaccessible ([class.access]) or ambiguous ([class.member.lookup]) base class of D, a program that necessitates this conversion is ill-formed. ...
(https://eel.is/c++draft/conv.ptr#3)

14.4 is carving out private, protected, and ambiguous base classes, but they are already carved out in 7.3.12 and implemented in isStandardPointerConvertible

[llvmbot]

@llvm/pr-subscribers-clang-tidy

@llvm/pr-subscribers-clang-tools-extra

Author: Hana Dusíková (hanickadot)

Changes

As in title, code which check eligibility of exceptions with pointer types to be handled by exception handler of type void * disallowed this case. It was check:

if (isStandardPointerConvertible(ExceptionCanTy, HandlerCanTy) &&
          isUnambiguousPublicBaseClass(
              ExceptionCanTy->getTypePtr()->getPointeeType().getTypePtr(),
              HandlerCanTy->getTypePtr()->getPointeeType().getTypePtr())) {

but in isUnambiguousPublicBaseClass there was code which looked for definitions:

bool isUnambiguousPublicBaseClass(const Type *DerivedType,
                                  const Type *BaseType) {
  const auto *DerivedClass =
      DerivedType->getCanonicalTypeUnqualified()->getAsCXXRecordDecl();
  const auto *BaseClass =
      BaseType->getCanonicalTypeUnqualified()->getAsCXXRecordDecl();
  if (!DerivedClass || !BaseClass)
    return false;

This code disallowed usage of void * type which was correctly detected in isStandardPointerConvertible.

AFAIK this seems like misinterpretation of specification:

> 14.4 Handling an exception
> a standard pointer conversion not involving conversions to pointers to private or protected or ambiguous classes
(https://eel.is/c++draft/except.handle#3.3.1)

and

> 7.3.12 Pointer conversions
> ... If B is an inaccessible ([class.access]) or ambiguous ([class.member.lookup]) base class of D, a program that necessitates this conversion is ill-formed[.](https://eel.is/c++draft/conv.ptr#3.sentence-2) ...
(https://eel.is/c++draft/conv.ptr#3)

14.4 is carving out private, protected, and ambiguous base classes, but they are already carved out in 7.3.12 and implemented in isStandardPointerConvertible

---

Full diff: https://github.com/llvm/llvm-project/pull/99773.diff

3 Files Affected:

• (modified) clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp (+5-5)
• (modified) clang-tools-extra/docs/ReleaseNotes.rst (+4)
• (modified) clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp (+18)

diff --git a/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp b/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
index 6ae46e2b1262a..9bfb7e2677533 100644
--- a/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
+++ b/clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp
@@ -141,7 +141,10 @@ bool isStandardPointerConvertible(QualType From, QualType To) {
     if (RD->isCompleteDefinition() &&
         isBaseOf(From->getPointeeType().getTypePtr(),
                  To->getPointeeType().getTypePtr())) {
-      return true;
+      // If B is an inaccessible or ambiguous base class of D, a program
+      // that necessitates this conversion is ill-formed
+      return isUnambiguousPublicBaseClass(From->getPointeeType().getTypePtr(),
+                                          To->getPointeeType().getTypePtr());
     }
   }
 
@@ -375,10 +378,7 @@ bool ExceptionAnalyzer::ExceptionInfo::filterByCatch(
         isPointerOrPointerToMember(ExceptionCanTy->getTypePtr())) {
       // A standard pointer conversion not involving conversions to pointers to
       // private or protected or ambiguous classes ...
-      if (isStandardPointerConvertible(ExceptionCanTy, HandlerCanTy) &&
-          isUnambiguousPublicBaseClass(
-              ExceptionCanTy->getTypePtr()->getPointeeType().getTypePtr(),
-              HandlerCanTy->getTypePtr()->getPointeeType().getTypePtr())) {
+      if (isStandardPointerConvertible(ExceptionCanTy, HandlerCanTy)) {
         TypesToDelete.push_back(ExceptionTy);
       }
       // A function pointer conversion ...
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index a23483e6df6d2..8e8c0cd0cc3d8 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -518,6 +518,10 @@ Changes in existing checks
   usages of ``std::string_view::compare``. Added a `StringLikeClasses` option
   to detect usages of ``compare`` method in custom string-like classes.
 
+- Improved :doc:`exception-escape <clang-tidy/checks/bugprone/exception-escape>`
+  check to correctly detect exception handler of type `CV void *` as catching all 
+  `CV` compatible pointer types.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
index f5e74df1621ce..26c443b139629 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp
@@ -756,3 +756,21 @@ struct test_implicit_throw {
 };
 
 }}
+
+void pointer_exception_can_not_escape_with_const_void_handler() noexcept {
+  // CHECK-MESSAGES-NOT: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'pointer_exception_can_not_escape_with_const_void_handler' which should not throw exceptions
+  const int value = 42;
+  try {
+    throw &value;
+  } catch (const void *) {
+  }
+}
+
+void pointer_exception_can_not_escape_with_void_handler() noexcept {
+  // CHECK-MESSAGES-NOT: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'pointer_exception_can_not_escape_with_void_handler' which should not throw exceptions
+  int value = 42;
+  try {
+    throw &value;
+  } catch (void *) {
+  }
+}

[PiotrZSL]

Except bug in release notes looks fine for me.