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[docs] adding_to_third_party.md: Prefer Git mirror

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This updates the docs to prefer (but not mandate) Git mirrors for most
third_party software added, going forward.

Change-Id: I7aff8cf4e5bce342ad557895f9acd99d15a29049
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3161637
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Jason Clinton <jclinton@chromium.org>
Cr-Commit-Position: refs/heads/main@{#926876}
This commit is contained in:
Jason D. Clinton
2021-09-30 19:19:58 +00:00
committed by Chromium LUCI CQ
parent ade1f324c2
commit b21e99b2c1
1 changed files with 22 additions and 6 deletions

28
docs/adding_to_third_party.md

@ -32,11 +32,27 @@ for your project is clear, e.g., a design doc has been circulated.
## Get the code
There are two common ways to depend on third-party code: you can reference a
Git repo directly (via entries in the DEPS file), or you can check in a
snapshot. The former is preferable if you are actively developing in it or need
access to the history; the latter is better if you don't need the full history
of the repo or don't need to pick up every single change. And, of course, if
the code you need isn't in a Git repo, you have to do the latter.
Git repo directly (via entries in the DEPS file) or you can check in a
snapshot. The former is preferable in most cases:
1. If you are actively developing in the upstream repo, then having the DEPS
file include the upstream (that's been mirrored to GoB, see below) can be a
way to include those changes into Chromium at a particular revision. The
DEPS file will be updated to a new revision when you are ready to "roll" the
new version into Chromium. This also avoids duplicate copies of the code
showing up in multiple repos leading to contributor confusion.
1. This interacts favorably with our upstream tracking automation. We
automatically consume the upstream Git hashes and match them against a
database of known upstreams to tracking drift between Chromium and upstream
sources.
1. This makes adding deps that don't need local changes easier. E.g. some of
our automation automatically converts non-GN build rules into GN build rules
without any additional CLs.
Checking in a snapshot is useful if this is effectively taking on maintenance
of an unmaintained project (e.g. an ancient library that we're going to GN-ify
that hasn't been updated in years). And, of course, if the code you need isn't
in a Git repo, then you have to snapshot.
### Node packages
@ -52,7 +68,7 @@ If the code is in a Git repo that you want to mirror, please file an [infra git
ticket](https://bugs.chromium.org/p/chromium/issues/entry?template=Infra-Git)
to get the repo mirrored onto chromium.googlesource.com; we don't allow direct
dependencies on non-Google-hosted repositories, so that we can still build
if an external repository goes down..
if an external repository goes down.
Once the mirror is set up, add an entry to [//DEPS](../DEPS) so that gclient
will pull it in. If the code is only needed on some platforms, add a condition