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PiperOrigin-RevId: 251636029
Change-Id: Idef5972b0d729bd723550905d224eadcfb583516
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+# How to Contribute
+We'd love to accept your patches and contributions to this project. There are
+just a few small guidelines you need to follow.
+## Contributor License Agreement
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution;
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <> to see
+your current agreements on file or to sign a new one.
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+## Code reviews
+All submissions, including submissions by project members, require review. We
+use GitHub pull requests for this purpose. Consult
+[GitHub Help]( for more
+information on using pull requests.
+## Community Guidelines
+This project follows
+[Google's Open Source Community Guidelines](
diff --git a/LICENSE b/LICENSE
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+# [Bazel Platforms](
+This repository houses all canonical
+that are universally useful across languages and Bazel projects.
+For questions or concerns please email
+# Motivation
+Constraints must be carefully organized to avoid fragmentation. If two different
+declarations for, say, cpu=x86_64 were to exist at the same time then select()
+statements and toolchain selection would stop working across languages and
+# Process
+This repository only includes truly ubiquitous constraints.
+Most common constraints -- that is settings and values that can be used across
+projects - fall into specific areas like "Apple" or "Java". These are declared
+in those areas' respective repositories.
+A very few constraints (such as OS and cpu) are relevant for essentially all
+projects across all areas. These are what this repository is for.
+# Adding a canonical constraint value
+To add a new canonical constraint value, prepare a PR adding it to that the
+appropriate BUILD file.
+Note that even global constraint values are typically area values. For example,
+ios is an area value for the global setting os but belongs in the apple area.
+For the PR's reviewer(s) choose an owner of this repository plus an owner of the
+area repository this references..
+A constraint value should be:
+-   semantically clear, particularly in its distinctions from other values of
+    the same setting
+-   well-named: consistent with existing values of the same setting and easy to
+    understand at usage sites
+-   well-documented
+Remember that this value will apply for the entire Bazel community and its
+semantics will be difficult to impossible to change once it starts being used.
+# Adding a canonical constraint setting
+New canonical constraint settings should be rare and well-justified.
+To add a new setting, prepare a design document according to Bazel's design
+review process. This document should explain the need for a new setting and why
+it belongs here vs. area-specific repositories. It should clearly explain
+semantics, initial values, and criteria for adding new values.
+Once the design is approved prepare a PR for the actual change. If any values
+are area-specific, include the area repositories' owners as reviewers.
+# Private changes to global constraints
+If you'd like to experiment with changes to global settings or values, you can
+fork this repo for experimental purposes. But in the interest of community
+health and interoperability please don't share your changes with anyone not
+involved with the experiment. For wider distribution, submit a proper change
+Note that you can declare constraint_values in your own repo that are members of
+the global constraint_settings. This lets you "extend" global settings within
+the confines of your own project. But don't do this if you expect other projects
+to use these changes - this can easily lead to fragmentation conflicts.
+If you need custom constaint_settings, just declare them in your own repo. They
+are, by definition, not global.
+If you really need a permanent global change and it isn't design-approved for
+this repo, contact
+[](mailto:// to discuss