[clang-tools-extra] [clang-tidy] ignore local variable with [maybe_unused] attribute in bugprone-unused-local-non-trivial-variable (PR #81563)

[Congcong Cai via cfe-commits]

https://github.com/HerrCai0907 created https://github.com/llvm/llvm-project/pull/81563

Fixes: #81419.

>From fefe52614837d14858d056783dca8b08745de9d4 Mon Sep 17 00:00:00 2001
From: Congcong Cai <congcongcai0907 at 163.com>
Date: Tue, 13 Feb 2024 09:47:52 +0800
Subject: [PATCH] [clang-tidy] ignore local variable with [maybe_unused]
 attribute in bugprone-unused-local-non-trivial-variable

Fixes: #81419.
---
 .../bugprone/UnusedLocalNonTrivialVariableCheck.cpp           | 1 +
 clang-tools-extra/docs/ReleaseNotes.rst                       | 4 ++++
 .../checks/bugprone/unused-local-non-trivial-variable.rst     | 1 +
 .../checkers/bugprone/unused-local-non-trivial-variable.cpp   | 1 +
 4 files changed, 7 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/bugprone/UnusedLocalNonTrivialVariableCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UnusedLocalNonTrivialVariableCheck.cpp
index 1b763d291082b6..37baae7a6f0c3a 100644
--- a/clang-tools-extra/clang-tidy/bugprone/UnusedLocalNonTrivialVariableCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/UnusedLocalNonTrivialVariableCheck.cpp
@@ -60,6 +60,7 @@ void UnusedLocalNonTrivialVariableCheck::registerMatchers(MatchFinder *Finder) {
       varDecl(isLocalVarDecl(), unless(isReferenced()),
               unless(isExceptionVariable()), hasLocalStorage(), isDefinition(),
               unless(hasType(isReferenceType())), unless(hasType(isTrivial())),
+              unless(hasAttr(attr::Kind::Unused)),
               hasType(hasUnqualifiedDesugaredType(
                   anyOf(recordType(hasDeclaration(namedDecl(
                             matchesAnyListedName(IncludeTypes),
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index ee68c8f49b3df2..f2fba9aa1450d6 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -121,6 +121,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/too-small-loop-variable>` check by incorporating
   better support for ``const`` loop boundaries.
 
+- Improved :doc:`bugprone-unused-local-non-trivial-variable
+  <clang-tidy/checks/bugprone/unused-local-non-trivial-variable>` check by
+  ignoring local variable with ``[maybe_unused]`` attribute.
+
 - Cleaned up :doc:`cppcoreguidelines-prefer-member-initializer
   <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>`
   by removing enforcement of rule `C.48
diff --git a/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-local-non-trivial-variable.rst b/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-local-non-trivial-variable.rst
index 7531f19f3ebc15..9f283de78fbdec 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-local-non-trivial-variable.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-local-non-trivial-variable.rst
@@ -11,6 +11,7 @@ The following types of variables are excluded from this check:
 * exception variables in catch clauses
 * static or thread local
 * structured bindings
+* variables with ``[[maybe_unused]]`` attribute
 
 This check can be configured to warn on all non-trivial variables by setting
 `IncludeTypes` to `.*`, and excluding specific types using `ExcludeTypes`.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-local-non-trivial-variable.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-local-non-trivial-variable.cpp
index 19f2344de4a650..3fdc24b94a6cb2 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-local-non-trivial-variable.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-local-non-trivial-variable.cpp
@@ -77,6 +77,7 @@ T qux(T Generic) {
     // CHECK-MESSAGES: :[[@LINE-1]]:22: warning: unused local variable 'TemplateType' of type 'async::Future<T>' [bugprone-unused-local-non-trivial-variable]
     a::Future<T> AliasTemplateType;
     // CHECK-MESSAGES: :[[@LINE-1]]:18: warning: unused local variable 'AliasTemplateType' of type 'a::Future<T>' (aka 'Future<type-parameter-0-0>') [bugprone-unused-local-non-trivial-variable]
+    [[maybe_unused]] async::Future<Units> MaybeUnused;
     return Generic;
 }