[clang-tools-extra] [clang-tidy] Improve performance-enum-size to exclude empty enums (PR #71640)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL updated https://github.com/llvm/llvm-project/pull/71640

>From f74559586a11455e2b4c1f2c63076c5c441c527b Mon Sep 17 00:00:00 2001
From: Piotr Zegar <piotr.zegar at nokia.com>
Date: Wed, 8 Nov 2023 09:02:54 +0000
Subject: [PATCH] [clang-tidy] Improve performance-enum-size to exclude empty
 enums

Enums without enumerators (empty) are now excluded
from analysis as it's not possible to peroperly determinate
new narrowed type, and such enums can be used in diffrent
way, like as strong-types.
---
 clang-tools-extra/clang-tidy/performance/EnumSizeCheck.cpp     | 3 +++
 .../docs/clang-tidy/checks/performance/enum-size.rst           | 2 ++
 .../test/clang-tidy/checkers/performance/enum-size.cpp         | 3 +++
 3 files changed, 8 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/performance/EnumSizeCheck.cpp b/clang-tools-extra/clang-tidy/performance/EnumSizeCheck.cpp
index 0d44b8c7706c3c4..0f3e9d3ef75917b 100644
--- a/clang-tools-extra/clang-tidy/performance/EnumSizeCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/EnumSizeCheck.cpp
@@ -23,6 +23,8 @@ namespace clang::tidy::performance {
 
 namespace {
 
+AST_MATCHER(EnumDecl, hasEnumerators) { return !Node.enumerators().empty(); }
+
 const std::uint64_t Min8 =
     std::imaxabs(std::numeric_limits<std::int8_t>::min());
 const std::uint64_t Max8 = std::numeric_limits<std::int8_t>::max();
@@ -93,6 +95,7 @@ bool EnumSizeCheck::isLanguageVersionSupported(
 void EnumSizeCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       enumDecl(unless(isExpansionInSystemHeader()), isDefinition(),
+               hasEnumerators(),
                unless(matchers::matchesAnyListedName(EnumIgnoreList)))
           .bind("e"),
       this);
diff --git a/clang-tools-extra/docs/clang-tidy/checks/performance/enum-size.rst b/clang-tools-extra/docs/clang-tidy/checks/performance/enum-size.rst
index 08054123366eee4..f72b8c7eabc2221 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/performance/enum-size.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/performance/enum-size.rst
@@ -58,6 +58,8 @@ terms of memory usage and cache performance. However, it's important to
 consider the trade-offs and potential impact on code readability and
 maintainability.
 
+Enums without enumerators (empty) are excluded from analysis.
+
 Requires C++11 or above.
 Does not provide auto-fixes.
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/enum-size.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/enum-size.cpp
index 37481a8141c5c45..782c12080f5180e 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/enum-size.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/enum-size.cpp
@@ -102,4 +102,7 @@ enum class IgnoredSecondEnum
     unused2 = 2
 };
 
+enum class EnumClassWithoutValues : int {};
+enum EnumWithoutValues {};
+
 }