[clang-tidy][NFC] Add mention of running 'clang-tidy' on changes in Contributing.rst

[vbvictor]

Follow up to #147793.

Originally suggested by @carlosgalvezp in #147793 (comment)

[llvmbot]

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

Author: Baranov Victor (vbvictor)

Changes

Follow up to #147793.

Originally suggested in #147793 (comment)

---

Full diff: https://github.com/llvm/llvm-project/pull/148547.diff

1 Files Affected:

• (modified) clang-tools-extra/docs/clang-tidy/Contributing.rst (+23)

diff --git a/clang-tools-extra/docs/clang-tidy/Contributing.rst b/clang-tools-extra/docs/clang-tidy/Contributing.rst
index 9611c655886f2..66c0abadc6a40 100644
--- a/clang-tools-extra/docs/clang-tidy/Contributing.rst
+++ b/clang-tools-extra/docs/clang-tidy/Contributing.rst
@@ -657,6 +657,29 @@ directory.  The path to this directory is available in a lit test with the varia
 .. _FileCheck: https://llvm.org/docs/CommandGuide/FileCheck.html
 .. _test/clang-tidy/checkers/google/readability-casting.cpp: https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
 
+
+Submitting a Pull Request
+-------------------------
+
+Before submitting a pull request, contributors are encouraged to run
+:program:`clang-tidy` and :program:`clang-format` on their changes to ensure
+code quality and catch potential issues. While :program:`clang-tidy` is not
+currently enforced in CI, following this practice helps maintain code
+consistency and prevent common errors.
+
+Here's useful command to check your staged changes:
+
+.. code-block:: console
+
+  $ git diff --staged -U0 | ./clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py \
+      -j $(nproc) -path build/ -p1 -only-check-in-db
+  $ git clang-format
+
+Note that some warnings may be false positives or require careful consideration
+before fixing. Use your judgment and feel free to discuss in the pull request
+if you're unsure about a particular warning.
+
+
 Out-of-tree check plugins
 -------------------------
 

[llvmbot]

@llvm/pr-subscribers-clang-tidy

Author: Baranov Victor (vbvictor)

Changes

Follow up to #147793.

Originally suggested in #147793 (comment)

---

Full diff: https://github.com/llvm/llvm-project/pull/148547.diff

1 Files Affected:

• (modified) clang-tools-extra/docs/clang-tidy/Contributing.rst (+23)

diff --git a/clang-tools-extra/docs/clang-tidy/Contributing.rst b/clang-tools-extra/docs/clang-tidy/Contributing.rst
index 9611c655886f2..66c0abadc6a40 100644
--- a/clang-tools-extra/docs/clang-tidy/Contributing.rst
+++ b/clang-tools-extra/docs/clang-tidy/Contributing.rst
@@ -657,6 +657,29 @@ directory.  The path to this directory is available in a lit test with the varia
 .. _FileCheck: https://llvm.org/docs/CommandGuide/FileCheck.html
 .. _test/clang-tidy/checkers/google/readability-casting.cpp: https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/test/clang-tidy/checkers/google/readability-casting.cpp
 
+
+Submitting a Pull Request
+-------------------------
+
+Before submitting a pull request, contributors are encouraged to run
+:program:`clang-tidy` and :program:`clang-format` on their changes to ensure
+code quality and catch potential issues. While :program:`clang-tidy` is not
+currently enforced in CI, following this practice helps maintain code
+consistency and prevent common errors.
+
+Here's useful command to check your staged changes:
+
+.. code-block:: console
+
+  $ git diff --staged -U0 | ./clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py \
+      -j $(nproc) -path build/ -p1 -only-check-in-db
+  $ git clang-format
+
+Note that some warnings may be false positives or require careful consideration
+before fixing. Use your judgment and feel free to discuss in the pull request
+if you're unsure about a particular warning.
+
+
 Out-of-tree check plugins
 -------------------------
 

[EugeneZelenko]

Clang-Tidy pull requests are usually small, so is -j really necessary?

[carlosgalvezp]

LGTM, thank you!

[vbvictor]

Clang-Tidy pull requests are usually small, so is -j really necessary?

I may say why not to use all cores when we can.
If PR only touches 1 file, clang-tidy-diff will not load other cores.
If PR touches multiple files, the user can have N times faster linting time, which is always great.

To put into perspective, average lint time of a single .cpp check-file is ~20-24 seconds on my machine, so if it is a refactor change in multiple checks at once -j can make a huge difference.

[vbvictor]

IMO, we should implicitly call multiprocessing.cpu_count() in run-clang-tidy and clang-tidy-diff and use that number if user didn't specify -j explicitly.

P.S. running lint over all clang-tidy is not so fast with single core now:)

$ time run-clang-tidy -p build/ clang-tools-extra/clang-tidy/
real    5m27.460s
user    163m43.110s
sys     2m5.180s