[clang-tools-extra] [clang-tidy] Fixed bugprone-non-zero-enum-to-bool-conversion (PR #131407)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL created https://github.com/llvm/llvm-project/pull/131407

Improved bugprone-non-zero-enum-to-bool-conversion check to 
ignore enums without enumerators and enums with bool as underlying type.

Fixes #130762

>From f54b035af44fca80ac52e3661680d50fff5b64e5 Mon Sep 17 00:00:00 2001
From: Piotr Zegar <me at piotrzegar.pl>
Date: Fri, 14 Mar 2025 23:48:27 +0000
Subject: [PATCH] [clang-tidy] Fixed bugprone-non-zero-enum-to-bool-conversion

Improved bugprone-non-zero-enum-to-bool-conversion check to
ignore enums without enumerators and enums with bool as
underlying type.

Fixes #130762
---
 .../bugprone/NonZeroEnumToBoolConversionCheck.cpp   | 11 +++++++++--
 clang-tools-extra/docs/ReleaseNotes.rst             |  4 ++++
 .../bugprone/non-zero-enum-to-bool-conversion.rst   |  3 ++-
 .../non-zero-enum-to-bool-conversion-cpp11.cpp      | 13 +++++++++++++
 .../bugprone/non-zero-enum-to-bool-conversion.cpp   |  6 ++++++
 5 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/bugprone/NonZeroEnumToBoolConversionCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/NonZeroEnumToBoolConversionCheck.cpp
index e0323848870bd..d81be621005be 100644
--- a/clang-tools-extra/clang-tidy/bugprone/NonZeroEnumToBoolConversionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/NonZeroEnumToBoolConversionCheck.cpp
@@ -19,9 +19,10 @@ namespace clang::tidy::bugprone {
 
 namespace {
 
-AST_MATCHER(EnumDecl, isCompleteAndHasNoZeroValue) {
+AST_MATCHER(EnumDecl, isCompleteNonEmptyAndHasNoZeroValue) {
   const EnumDecl *Definition = Node.getDefinition();
   return Definition && Node.isComplete() &&
+         Definition->enumerator_begin() != Definition->enumerator_end() &&
          std::none_of(Definition->enumerator_begin(),
                       Definition->enumerator_end(),
                       [](const EnumConstantDecl *Value) {
@@ -29,6 +30,11 @@ AST_MATCHER(EnumDecl, isCompleteAndHasNoZeroValue) {
                       });
 }
 
+AST_MATCHER(EnumDecl, hasBoolAsUnderlyingType) {
+  const QualType UnderlyingType = Node.getIntegerType();
+  return !UnderlyingType.isNull() && UnderlyingType->isBooleanType();
+}
+
 } // namespace
 
 NonZeroEnumToBoolConversionCheck::NonZeroEnumToBoolConversionCheck(
@@ -59,7 +65,8 @@ void NonZeroEnumToBoolConversionCheck::registerMatchers(MatchFinder *Finder) {
                unless(isExpansionInSystemHeader()), hasType(booleanType()),
                hasSourceExpression(
                    expr(hasType(qualType(hasCanonicalType(hasDeclaration(
-                            enumDecl(isCompleteAndHasNoZeroValue(),
+                            enumDecl(isCompleteNonEmptyAndHasNoZeroValue(),
+                                     unless(hasBoolAsUnderlyingType()),
                                      unless(matchers::matchesAnyListedName(
                                          EnumIgnoreList)))
                                 .bind("enum"))))),
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 0ad52f83fad85..68af57564b793 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -118,6 +118,10 @@ New check aliases
 Changes in existing checks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+- Improved :doc:`bugprone-non-zero-enum-to-bool-conversion
+  <clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion>` check to
+  ignore enums without enumerators and enums with ``bool`` as underlying type.
+
 - Improved :doc:`bugprone-optional-value-conversion
   <clang-tidy/checks/bugprone/optional-value-conversion>` check to detect
   conversion in argument of ``std::make_optional``.
diff --git a/clang-tools-extra/docs/clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion.rst b/clang-tools-extra/docs/clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion.rst
index 168ed71674773..de842099a71c3 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/bugprone/non-zero-enum-to-bool-conversion.rst
@@ -12,7 +12,8 @@ and maintainability and can result in bugs.
 May produce false positives if the ``enum`` is used to store other values
 (used as a bit-mask or zero-initialized on purpose). To deal with them,
 ``// NOLINT`` or casting first to the underlying type before casting to ``bool``
-can be used.
+can be used. Enums without enumerators and enums that use ``bool`` as the
+underlying type are ignored.
 
 It is important to note that this check will not generate warnings if the
 definition of the enumeration type is not available.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion-cpp11.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion-cpp11.cpp
index 42927c615ffc7..36892ce0231b0 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion-cpp11.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion-cpp11.cpp
@@ -106,5 +106,18 @@ bool testEnumConversion(const EResult& value) {
 }
 
 }
+}
+
+namespace without::issue {
+namespace enum_bool {
 
+enum EResult : bool {
+  OK = 1
+};
+
+bool testEnumConversion(const EResult& value) {
+  return value;
+}
+
+}
 }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion.cpp
index 3375f69b59111..22d931cd35f42 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/non-zero-enum-to-bool-conversion.cpp
@@ -126,4 +126,10 @@ void testCustomOperator(CustomOperatorEnum e) {
     if (!(e & E1)) {}
 }
 
+enum EmptyEnum {};
+
+bool testCustomOperator(EmptyEnum value) {
+  return value;
+}
+
 }