[clang-tidy] Add fix-it for C-style cast of nullptr #173159

SonareMradul · 2025-12-20T17:37:07Z

Adds a fix-it for C-style casts of nullptr in google-readability-casting,
suggesting static_cast<T*>(nullptr).

github-actions · 2025-12-20T17:37:24Z

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llvmbot · 2025-12-20T17:37:53Z

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

@llvm/pr-subscribers-clang-tidy

Author: Mradul Sonare (SonareMradul)

Changes

Adds a fix-it for C-style casts of nullptr in google-readability-casting,
suggesting static_cast<T*>(nullptr).

Fixes #<173147>

Full diff: https://github.com/llvm/llvm-project/pull/173159.diff

1 Files Affected:

(modified) clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp (+5)

diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp b/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
index 76f2030158c81..2e7fc0f364b48 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
@@ -218,6 +218,11 @@ void AvoidCStyleCastCheck::check(const MatchFinder::MatchResult &Result) {
       ReplaceWithNamedCast("static_cast");
     return;
   case CK_NoOp:
+  if (isa<CXXNullPtrLiteralExpr>(CastExpr->getSubExprAsWritten()->IgnoreImpCasts())) {
+  ReplaceWithNamedCast("static_cast");
+  return;
+}
+
     if (FnToFnCast) {
       ReplaceWithNamedCast("static_cast");
       return;

github-actions · 2025-12-20T17:45:31Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff origin/main HEAD --extensions cpp -- clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-style-cast.cpp --diff_from_common_commit

⚠️
The reproduction instructions above might return results for more than one PR
in a stack if you are using a stacked PR workflow. You can limit the results by
changing origin/main to the base branch/commit you want to compare against.
⚠️

View the diff from clang-format here.

diff --git a/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp b/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
index 2e7fc0f36..6c49869cf 100644
--- a/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp
@@ -218,10 +218,11 @@ void AvoidCStyleCastCheck::check(const MatchFinder::MatchResult &Result) {
       ReplaceWithNamedCast("static_cast");
     return;
   case CK_NoOp:
-  if (isa<CXXNullPtrLiteralExpr>(CastExpr->getSubExprAsWritten()->IgnoreImpCasts())) {
-  ReplaceWithNamedCast("static_cast");
-  return;
-}
+    if (isa<CXXNullPtrLiteralExpr>(
+            CastExpr->getSubExprAsWritten()->IgnoreImpCasts())) {
+      ReplaceWithNamedCast("static_cast");
+      return;
+    }
 
     if (FnToFnCast) {
       ReplaceWithNamedCast("static_cast");

localspook · 2025-12-20T17:51:06Z

The change looks good, but please:

add a release note in clang-tools-extra/docs/ReleaseNotes.rst
add tests for the change in clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-style-cast.cpp
edit your PR message to change Fixes #<173147> to Fixes #173147 (that way, when this PR is merged, Github will close that issue automatically)

zeyi2 · 2025-12-21T08:41:21Z

clang-tools-extra/docs/ReleaseNotes.rst

  on Windows when the check was enabled with a 32-bit :program:`clang-tidy`
  binary.
-
+- Fixed google-readability-casting to provide a fix-it for C-style casts of


Please follow the existing style of documenting changes:

- - Fixed google-readability-casting to provide a fix-it for C-style casts of - nullptr. + - Improved :doc:`modernize-avoid-c-style-cast + <clang-tidy/checks/modernize/avoid-c-style-cast>` by providing correct fixes + for C-style casts of nullptr

zeyi2 · 2025-12-21T08:42:24Z

clang-tools-extra/clang-tidy/modernize/AvoidCStyleCastCheck.cpp

      ReplaceWithNamedCast("static_cast");
    return;
  case CK_NoOp:
+  if (isa<CXXNullPtrLiteralExpr>(CastExpr->getSubExprAsWritten()->IgnoreImpCasts())) {


Seems like a formatting issue? You can run git clang-format HEAD~1 to fix it :)

github-actions · 2025-12-21T09:00:00Z

🐧 Linux x64 Test Results

3057 tests passed
7 tests skipped
1 test failed

Failed Tests

(click on a test name to see its output)

Clang Tools

Clang Tools.clang-tidy/infrastructure/alphabetical-order.test

Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/usr/bin/python3 /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# executed command: /usr/bin/python3 /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# note: command had no output on stdout or stderr
# RUN: at line 2
diff --strip-trailing-cr /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../docs/clang-tidy/checks/list.rst /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# executed command: diff --strip-trailing-cr /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../docs/clang-tidy/checks/list.rst /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# note: command had no output on stdout or stderr
# RUN: at line 4
/usr/bin/python3 /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.ReleaseNotes.rst
# executed command: /usr/bin/python3 /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.ReleaseNotes.rst
# .---command stderr------------
# | 
# | Entries in 'clang-tools-extra/docs/ReleaseNotes.rst' are not alphabetically sorted.
# | Fix the ordering by applying diff printed below.
# | 
# `-----------------------------
# RUN: at line 5
diff --strip-trailing-cr /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../docs/ReleaseNotes.rst /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.ReleaseNotes.rst
# executed command: diff --strip-trailing-cr /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../docs/ReleaseNotes.rst /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.ReleaseNotes.rst
# .---command stdout------------
# | *** /home/gha/actions-runner/_work/llvm-project/llvm-project/clang-tools-extra/test/clang-tidy/infrastructure/../../../docs/ReleaseNotes.rst
# | --- /home/gha/actions-runner/_work/llvm-project/llvm-project/build/tools/clang/tools/extra/test/clang-tidy/infrastructure/Output/alphabetical-order.test.tmp.ReleaseNotes.rst
# | ***************
# | *** 521,526 ****
# | --- 521,530 ----
# |     <clang-tidy/checks/modernize/avoid-c-arrays>` to not diagnose array types
# |     which are part of an implicit instantiation of a template.
# |   
# | + - Improved :doc:`modernize-avoid-c-style-cast  
# | +   <clang-tidy/checks/modernize/avoid-c-style-cast>` by providing correct fixes 
# | +   for C-style casts of nullptr.
# | +   
# |   - Improved :doc:`modernize-use-constraints
# |     <clang-tidy/checks/modernize/use-constraints>` check by fixing a crash on
# |     uses of non-standard ``enable_if`` with a signature different from
# | ***************
# | *** 544,553 ****
# |     on Windows when the check was enabled with a 32-bit :program:`clang-tidy`
# |     binary.
# |   
# | - - Improved :doc:`modernize-avoid-c-style-cast  
# | -   <clang-tidy/checks/modernize/avoid-c-style-cast>` by providing correct fixes 
# | -   for C-style casts of nullptr.
# | -   
# |   - Improved :doc:`modernize-use-override
# |     <clang-tidy/checks/modernize/use-override>` by fixing an issue where
# |     the check would sometimes suggest inserting ``override`` in an invalid
# | --- 548,553 ----
# `-----------------------------
# error: command failed with exit status: 1

--

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the infrastructure label.

github-actions · 2025-12-21T09:00:01Z

🪟 Windows x64 Test Results

2995 tests passed
30 tests skipped
1 test failed

Failed Tests

(click on a test name to see its output)

Clang Tools

Clang Tools.clang-tidy/infrastructure/alphabetical-order.test

Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
C:/Python312/python.exe C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# executed command: C:/Python312/python.exe 'C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py' -o 'C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.clang-tidy-checks-list.rst'
# note: command had no output on stdout or stderr
# RUN: at line 2
diff --strip-trailing-cr C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../docs/clang-tidy/checks/list.rst C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.clang-tidy-checks-list.rst
# executed command: diff --strip-trailing-cr 'C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../docs/clang-tidy/checks/list.rst' 'C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.clang-tidy-checks-list.rst'
# note: command had no output on stdout or stderr
# RUN: at line 4
C:/Python312/python.exe C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py -o C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.ReleaseNotes.rst
# executed command: C:/Python312/python.exe 'C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../clang-tidy/tool/check_alphabetical_order.py' -o 'C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.ReleaseNotes.rst'
# .---command stderr------------
# | 
# | Entries in 'clang-tools-extra/docs/ReleaseNotes.rst' are not alphabetically sorted.
# | Fix the ordering by applying diff printed below.
# | 
# `-----------------------------
# RUN: at line 5
diff --strip-trailing-cr C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../docs/ReleaseNotes.rst C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.ReleaseNotes.rst
# executed command: diff --strip-trailing-cr 'C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../docs/ReleaseNotes.rst' 'C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.ReleaseNotes.rst'
# .---command stdout------------
# | *** C:\_work\llvm-project\llvm-project\clang-tools-extra\test\clang-tidy\infrastructure/../../../docs/ReleaseNotes.rst
# | --- C:\_work\llvm-project\llvm-project\build\tools\clang\tools\extra\test\clang-tidy\infrastructure\Output\alphabetical-order.test.tmp.ReleaseNotes.rst
# | ***************
# | *** 521,526 ****
# | --- 521,530 ----
# |     <clang-tidy/checks/modernize/avoid-c-arrays>` to not diagnose array types
# |     which are part of an implicit instantiation of a template.
# |   
# | + - Improved :doc:`modernize-avoid-c-style-cast  
# | +   <clang-tidy/checks/modernize/avoid-c-style-cast>` by providing correct fixes 
# | +   for C-style casts of nullptr.
# | +   
# |   - Improved :doc:`modernize-use-constraints
# |     <clang-tidy/checks/modernize/use-constraints>` check by fixing a crash on
# |     uses of non-standard ``enable_if`` with a signature different from
# | ***************
# | *** 544,553 ****
# |     on Windows when the check was enabled with a 32-bit :program:`clang-tidy`
# |     binary.
# |   
# | - - Improved :doc:`modernize-avoid-c-style-cast  
# | -   <clang-tidy/checks/modernize/avoid-c-style-cast>` by providing correct fixes 
# | -   for C-style casts of nullptr.
# | -   
# |   - Improved :doc:`modernize-use-override
# |     <clang-tidy/checks/modernize/use-override>` by fixing an issue where
# |     the check would sometimes suggest inserting ``override`` in an invalid
# | --- 548,553 ----
# `-----------------------------
# error: command failed with exit status: 1

--

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the infrastructure label.

SonareMradul · 2025-12-21T15:14:01Z

@zeyi2 Could you please advise what is required from my side to get the Linux and Windows checks to paas?

zeyi2 · 2025-12-21T15:20:48Z

clang-tools-extra/docs/ReleaseNotes.rst

  on Windows when the check was enabled with a 32-bit :program:`clang-tidy`
  binary.

+- Improved :doc:`modernize-avoid-c-style-cast  


In Clang-Tidy documentations, we want entries in Changes in existing checks to keep alphabetical order, so this new entries should be placed between modernize-avoid-c-arrays and modernize-use-constraints :)

zeyi2 · 2025-12-21T15:26:34Z

what is required from my side to get the Linux and Windows checks to paas

You can try building check-clang-tools on your local machine to verify the test cases pass (though it will take some time). Since CI runs need to be manually approved for new contributors, local testing is usually faster for debugging.

If you notice any failures on GitHub, the specific output will be available in the comments to help you troubleshoot.

EugeneZelenko · 2025-12-21T15:56:32Z

clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-style-cast.cpp

+}
+// CHECK-MESSAGES: warning: C-style casts are discouraged
+// CHECK-FIXES: f(static_cast<int*>(nullptr));
+


Excessive newline.

EugeneZelenko · 2025-12-21T15:56:58Z

clang-tools-extra/test/clang-tidy/checkers/modernize/avoid-c-style-cast.cpp


  throw S2(5.0f);
 }
+void f(int *);


Will be good idea to separate with newline.

[clang-tidy] Add fix-it for C-style cast of nullptr

c44ca1e

llvmbot added clang-tools-extra clang-tidy labels Dec 20, 2025

localspook requested review from vbvictor, zeyi2 and zwuis December 20, 2025 17:45

SonareMradul added 2 commits December 21, 2025 07:24

[clang-tidy] Add test and release note for nullptr cast fix.

0715c6c

[clang-tidy] Add test and release note for nullptr cast fix

e66f785

zeyi2 requested changes Dec 21, 2025

View reviewed changes

SonareMradul and others added 4 commits December 21, 2025 18:18

Merge branch 'main' into main

453e29f

Fix releaseNotes fromatting to follow existing style

3dccf96

Merge branch 'main' of https://github.com/SonareMradul/llvm-project

d699397

Merge branch 'main' into main

abc62a2

zeyi2 reviewed Dec 21, 2025

View reviewed changes

EugeneZelenko requested review from HerrCai0907 and localspook December 21, 2025 15:55

EugeneZelenko reviewed Dec 21, 2025

View reviewed changes

[clang-tidy] Add fix-it for C-style cast of nullptr #173159

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[clang-tidy] Add fix-it for C-style cast of nullptr #173159

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