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writing_gn_templates.md: Mention action_helpers.py and zip_helpers.py

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Bug: 1428082
Change-Id: Idd6f49c30e22e68a5f606903382f963d420cea55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4385435
Reviewed-by: Sam Maier <smaier@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1124874}
This commit is contained in:
Andrew Grieve
2023-03-31 20:13:44 +00:00
committed by Chromium LUCI CQ
parent 0ce81e69d0
commit f0c49bde7b
1 changed files with 10 additions and 3 deletions

13
build/docs/writing_gn_templates.md

@ -40,6 +40,9 @@ won't exist for the initial build.
depfiles.
* Stale paths in depfiles can cause ninja to complain of circular
dependencies [in some cases](https://bugs.chromium.org/p/chromium/issues/detail?id=639042).
* Use [`action_helpers.write_depfile()`] to write these.
[`action_helpers.write_depfile()`]: https://source.chromium.org/chromium/chromium/src/+/main:build/action_helpers.py?q=symbol:%5Cbwrite_depfile
### Ensuring "gn analyze" Knows About your Inputs
"gn analyze" is used by bots to run only affected tests and build only affected
@ -136,15 +139,19 @@ Outputs should be atomic and take advantage of `restat=1`.
short-circuits a build when output timestamps do not change. This feature is
the reason that the total number of build steps sometimes decreases when
building..
* Use [`build_utils.AtomicOutput()`](https://cs.chromium.org/chromium/src/build/android/gyp/util/build_utils.py?rcl=7d6ba28e92bec865a7b7876c35b4621d56fb37d8&l=128)
to perform both of these techniques.
* Use [`action_helpers.atomic_output()`] to perform both of these techniques.
[`action_helpers.atomic_output()`]: https://source.chromium.org/chromium/chromium/src/+/main:build/action_helpers.py?q=symbol:%5Cbatomic_output
Actions should be deterministic in order to avoid hard-to-reproduce bugs.
Given identical inputs, they should produce byte-for-byte identical outputs.
* Some common mistakes:
* Depending on filesystem iteration order.
* Writing timestamps in files (or in zip entries).
* Writing absolute paths in outputs.
* Writing timestamps in files (or in zip entries).
* Tip: Use [`zip_helpers.py`] when writing `.zip` files.
[`zip_helpers.py`]: https://source.chromium.org/chromium/chromium/src/+/main:build/zip_helpers.py
## Style Guide
Chromium GN files follow