[clang-tools-extra] [clang-tidy] Change AllowCastToVoid default to true in bugprone-unused-return-value (PR #200173)

Endre Fülöp via cfe-commits cfe-commits at lists.llvm.org
Thu Sep 17 02:58:51 PDT 2026 

https://github.com/gamesh411 updated https://github.com/llvm/llvm-project/pull/200173

>From 46ac1618dd287acb91fce09a7e525fda12c4ee4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Endre=20F=C3=BCl=C3=B6p?= <endre.fulop at sigmatechnology.com>
Date: Thu, 28 May 2026 14:55:21 +0200
Subject: [PATCH 1/2] [clang-tidy] Change AllowCastToVoid default to true in
 bugprone-unused-return-value

Casting to (void) is the standard C/C++ idiom for intentionally
discarding a return value. The check should respect this by default
rather than requiring users to opt in.

Both coding standard aliases that used this check (cert-err33-c and the
now-removed hicpp-ignored-remove-result) overrode AllowCastToVoid to
true, confirming that (void) casts are a legitimate suppression
mechanism.
---
 .../clang-tidy/bugprone/UnusedReturnValueCheck.cpp            | 2 +-
 clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp          | 1 -
 clang-tools-extra/docs/ReleaseNotes.rst                       | 4 ++++
 .../docs/clang-tidy/checks/bugprone/unused-return-value.rst   | 2 +-
 .../checkers/bugprone/unused-return-value-custom.cpp          | 1 -
 .../checkers/bugprone/unused-return-value-remove.cpp          | 2 +-
 .../test/clang-tidy/checkers/bugprone/unused-return-value.cpp | 3 +--
 7 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
index c5792cd17b9b2..9156c32078e9c 100644
--- a/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/UnusedReturnValueCheck.cpp
@@ -145,7 +145,7 @@ UnusedReturnValueCheck::UnusedReturnValueCheck(StringRef Name,
                                             "^::std::errc$;"
                                             "^::std::expected$;"
                                             "^::boost::system::error_code$"))),
-      AllowCastToVoid(Options.get("AllowCastToVoid", false)) {}
+      AllowCastToVoid(Options.get("AllowCastToVoid", true)) {}
 
 UnusedReturnValueCheck::UnusedReturnValueCheck(
     StringRef Name, ClangTidyContext *Context,
diff --git a/clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp b/clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
index ee1ce59d80b0d..4e952b59cdfe6 100644
--- a/clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
@@ -353,7 +353,6 @@ class CERTModule : public ClangTidyModule {
     Opts["cert-arr39-c.WarnOnSizeOfPointerToAggregate"] = "false";
     Opts["cert-dcl16-c.NewSuffixes"] = "L;LL;LU;LLU";
     Opts["cert-err33-c.CheckedFunctions"] = CertErr33CCheckedFunctions;
-    Opts["cert-err33-c.AllowCastToVoid"] = "true";
     Opts["cert-oop54-cpp.WarnOnlyIfThisHasSuspiciousField"] = "false";
     Opts["cert-str34-c.DiagnoseSignedUnsignedCharComparisons"] = "false";
     return Options;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 0b3bb091307e7..8e496edbb8d4e 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -423,6 +423,10 @@ Changes in existing checks
   ``std::get_temporary_buffer`` to the default list of unsafe functions. (This
   function is unsafe, useless, deprecated in C++17 and removed in C++20).
 
+- Improved :doc:`bugprone-unused-return-value
+  <clang-tidy/checks/bugprone/unused-return-value>` check by changing the
+  default of the ``AllowCastToVoid`` option from `false` to `true`.
+
 - Improved :doc:`bugprone-use-after-move
   <clang-tidy/checks/bugprone/use-after-move>` check:
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-return-value.rst b/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-return-value.rst
index 725403a6eb818..9395d9fef5b47 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-return-value.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/bugprone/unused-return-value.rst
@@ -63,7 +63,7 @@ Options
 
 .. option:: AllowCastToVoid
 
-   Controls whether casting return values to ``void`` is permitted. Default: `false`.
+   Controls whether casting return values to ``void`` is permitted. Default: `true`.
 
 :doc:`cert-err33-c <../cert/err33-c>` is an alias of this check that checks a
 fixed and large set of standard library functions.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-custom.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-custom.cpp
index 3035183573ccd..5bf21d20d3302 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-custom.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-custom.cpp
@@ -53,7 +53,6 @@ void warning() {
   // CHECK-MESSAGES: [[@LINE-1]]:4: warning: the value returned by this function should not be disregarded; neglecting it may lead to errors
 
   (void)fun();
-  // CHECK-MESSAGES: [[@LINE-1]]:9: warning: the value returned by this function should not be disregarded; neglecting it may lead to errors
 
   ns::Outer::Inner ObjA1;
   ObjA1.memFun();
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-remove.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-remove.cpp
index 2934db6dd2d2c..fee75469ca297 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-remove.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value-remove.cpp
@@ -1,5 +1,5 @@
 // RUN: %check_clang_tidy %s bugprone-unused-return-value %t -- \
-// RUN:   -config='{CheckOptions: {bugprone-unused-return-value.CheckedFunctions: "^::std::remove$;^::std::remove_if$;^::std::unique$", bugprone-unused-return-value.CheckedReturnTypes: "", bugprone-unused-return-value.AllowCastToVoid: true}}'
+// RUN:   -config='{CheckOptions: {bugprone-unused-return-value.CheckedFunctions: "^::std::remove$;^::std::remove_if$;^::std::unique$", bugprone-unused-return-value.CheckedReturnTypes: ""}}'
 // RUN: %check_clang_tidy -check-suffixes=NOCAST %s bugprone-unused-return-value %t -- \
 // RUN:   -config='{CheckOptions: {bugprone-unused-return-value.CheckedFunctions: "^::std::remove$;^::std::remove_if$;^::std::unique$", bugprone-unused-return-value.CheckedReturnTypes: "", bugprone-unused-return-value.AllowCastToVoid: false}}'
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value.cpp b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value.cpp
index 3fa87b94dc6b4..9aaa8d3c8a35f 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/unused-return-value.cpp
@@ -1,5 +1,4 @@
-// RUN: %check_clang_tidy %s bugprone-unused-return-value %t -- \
-// RUN:   --config="{CheckOptions: {bugprone-unused-return-value.AllowCastToVoid: true}}" -- -fexceptions
+// RUN: %check_clang_tidy %s bugprone-unused-return-value %t -- -- -fexceptions
 #include <vector>
 #include <memory>
 

>From afd9ee1266af27fe184f74f5f62ca49794e95837 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Endre=20F=C3=BCl=C3=B6p?= <endre.fulop at sigmatechnology.com>
Date: Thu, 17 Sep 2026 11:56:14 +0200
Subject: [PATCH 2/2] move release note to potentially breaking changes

---
 clang-tools-extra/docs/ReleaseNotes.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/clang-tools-extra/docs/ReleaseNotes.md b/clang-tools-extra/docs/ReleaseNotes.md
index 5e77736293c37..fb1cb91e2eeab 100644
--- a/clang-tools-extra/docs/ReleaseNotes.md
+++ b/clang-tools-extra/docs/ReleaseNotes.md
@@ -56,6 +56,10 @@ infrastructure are described first, followed by tool-specific sections.
 
 ### Potentially Breaking Changes
 
+- Improved {doc}`bugprone-unused-return-value
+  <clang-tidy/checks/bugprone/unused-return-value>` check by changing the
+  default of the `AllowCastToVoid` option from `false` to `true`.
+
 - The deprecated `zircon` clang-tidy module has been removed. Users of
   `zircon-temporary-objects` should migrate to {doc}`fuchsia-temporary-objects
   <clang-tidy/checks/fuchsia/temporary-objects>`.
@@ -188,10 +192,6 @@ infrastructure are described first, followed by tool-specific sections.
   <clang-tidy/checks/bugprone/std-namespace-modification>` when checking
   lambda closure types used as template arguments.
 
-- Improved {doc}`bugprone-unused-return-value
-  <clang-tidy/checks/bugprone/unused-return-value>` check by changing the
-  default of the `AllowCastToVoid` option from `false` to `true`.
-
 - Improved {doc}`cppcoreguidelines-missing-std-forward
   <clang-tidy/checks/cppcoreguidelines/missing-std-forward>` check by diagnosing
   unforwarded `auto&&` parameters in C++20 abbreviated function templates.

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