1# How to Contribute to Abseil
2
3We'd love to accept your patches and contributions to this project. There are
4just a few small guidelines you need to follow.
5
6NOTE: If you are new to GitHub, please start by reading [Pull Request
7howto](https://help.github.com/articles/about-pull-requests/)
8
9## Contributor License Agreement
10
11Contributions to this project must be accompanied by a Contributor License
12Agreement. You (or your employer) retain the copyright to your contribution,
13this simply gives us permission to use and redistribute your contributions as
14part of the project. Head over to <https://cla.developers.google.com/> to see
15your current agreements on file or to sign a new one.
16
17You generally only need to submit a CLA once, so if you've already submitted one
18(even if it was for a different project), you probably don't need to do it
19again.
20
21## Contribution Guidelines
22
23Potential contributors sometimes ask us if the Abseil project is the appropriate
24home for their utility library code or for specific functions implementing
25missing portions of the standard. Often, the answer to this question is "no".
26We’d like to articulate our thinking on this issue so that our choices can be
27understood by everyone and so that contributors can have a better intuition
28about whether Abseil might be interested in adopting a new library.
29
30### Priorities
31
32Although our mission is to augment the C++ standard library, our goal is not to
33provide a full forward-compatible implementation of the latest standard. For us
34to consider a library for inclusion in Abseil, it is not enough that a library
35is useful. We generally choose to release a library when it meets at least one
36of the following criteria:
37
38*   **Widespread usage** - Using our internal codebase to help gauge usage, most
39    of the libraries we've released have tens of thousands of users.
40*   **Anticipated widespread usage** - Pre-adoption of some standard-compliant
41    APIs may not have broad adoption initially but can be expected to pick up
42    usage when it replaces legacy APIs. `absl::from_chars`, for example,
43    replaces existing code that converts strings to numbers and will therefore
44    likely see usage growth.
45*   **High impact** - APIs that provide a key solution to a specific problem,
46    such as `absl::FixedArray`, have higher impact than usage numbers may signal
47    and are released because of their importance.
48*   **Direct support for a library that falls under one of the above** - When we
49    want access to a smaller library as an implementation detail for a
50    higher-priority library we plan to release, we may release it, as we did
51    with portions of `absl/meta/type_traits.h`. One consequence of this is that
52    the presence of a library in Abseil does not necessarily mean that other
53    similar libraries would be a high priority.
54
55### API Freeze Consequences
56
57Via the
58[Abseil Compatibility Guidelines](https://abseil.io/about/compatibility), we
59have promised a large degree of API stability. In particular, we will not make
60backward-incompatible changes to released APIs without also shipping a tool or
61process that can upgrade our users' code. We are not yet at the point of easily
62releasing such tools. Therefore, at this time, shipping a library establishes an
63API contract which is borderline unchangeable. (We can add new functionality,
64but we cannot easily change existing behavior.) This constraint forces us to
65very carefully review all APIs that we ship.
66
67
68## Coding Style
69
70To keep the source consistent, readable, diffable and easy to merge, we use a
71fairly rigid coding style, as defined by the
72[google-styleguide](https://github.com/google/styleguide) project. All patches
73will be expected to conform to the style outlined
74[here](https://google.github.io/styleguide/cppguide.html).
75
76## Guidelines for Pull Requests
77
78*   If you are a Googler, it is preferable to first create an internal CL and
79    have it reviewed and submitted. The code propagation process will deliver
80    the change to GitHub.
81
82*   Create **small PRs** that are narrowly focused on **addressing a single
83    concern**. We often receive PRs that are trying to fix several things at a
84    time, but if only one fix is considered acceptable, nothing gets merged and
85    both author's & review's time is wasted. Create more PRs to address
86    different concerns and everyone will be happy.
87
88*   For speculative changes, consider opening an [Abseil
89    issue](https://github.com/abseil/abseil-cpp/issues) and discussing it first.
90    If you are suggesting a behavioral or API change, consider starting with an
91    [Abseil proposal template](ABSEIL_ISSUE_TEMPLATE.md).
92
93*   Provide a good **PR description** as a record of **what** change is being
94    made and **why** it was made. Link to a GitHub issue if it exists.
95
96*   Don't fix code style and formatting unless you are already changing that
97    line to address an issue. Formatting of modified lines may be done using
98   `git clang-format`. PRs with irrelevant changes won't be merged. If
99    you do want to fix formatting or style, do that in a separate PR.
100
101*   Unless your PR is trivial, you should expect there will be reviewer comments
102    that you'll need to address before merging. We expect you to be reasonably
103    responsive to those comments, otherwise the PR will be closed after 2-3
104    weeks of inactivity.
105
106*   Maintain **clean commit history** and use **meaningful commit messages**.
107    PRs with messy commit history are difficult to review and won't be merged.
108    Use `rebase -i upstream/master` to curate your commit history and/or to
109    bring in latest changes from master (but avoid rebasing in the middle of a
110    code review).
111
112*   Keep your PR up to date with upstream/master (if there are merge conflicts,
113    we can't really merge your change).
114
115*   **All tests need to be passing** before your change can be merged. We
116    recommend you **run tests locally** (see below)
117
118*   Exceptions to the rules can be made if there's a compelling reason for doing
119    so. That is - the rules are here to serve us, not the other way around, and
120    the rules need to be serving their intended purpose to be valuable.
121
122*   All submissions, including submissions by project members, require review.
123
124## Running Tests
125
126If you have [Bazel](https://bazel.build/) installed, use `bazel test
127--test_tag_filters="-benchmark" ...` to run the unit tests.
128
129If you are running the Linux operating system and have
130[Docker](https://www.docker.com/) installed, you can also run the `linux_*.sh`
131scripts under the `ci/`(https://github.com/abseil/abseil-cpp/tree/master/ci)
132directory to test Abseil under a variety of conditions.
133
134## Abseil Committers
135
136The current members of the Abseil engineering team are the only committers at
137present.
138
139## Release Process
140
141Abseil lives at head, where latest-and-greatest code can be found.
142