mirror of https://github.com/bazelbuild/platforms
86 lines
3.5 KiB
Markdown
86 lines
3.5 KiB
Markdown
# [Bazel Platforms](https://bazel.build)
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This repository houses all canonical
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[constraint_setting()](https://docs.bazel.build/versions/master/be/platform.html#constraint_setting)s,
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[constraint_value()](https://docs.bazel.build/versions/master/be/platform.html#constraint_value)s
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and
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[platform()](https://docs.bazel.build/versions/master/be/platform.html#platform)s
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that are universally useful across languages and Bazel projects.
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For questions or concerns please email
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[bazel-discuss@googlegroups.com](mailto://bazel-discuss@googlegroups.com).
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# Motivation
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Constraints must be carefully organized to avoid fragmentation. If two different
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declarations for, say, cpu=x86_64 were to exist at the same time then select()
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statements and toolchain selection would stop working across languages and
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projects.
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# Process
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This repository only includes truly ubiquitous constraints.
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Most common constraints -- that is settings and values that can be used across
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projects - fall into specific areas like "Apple" or "Java". These are declared
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in those areas' respective repositories.
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A very few constraints (such as OS and cpu) are relevant for essentially all
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projects across all areas. These are what this repository is for.
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# Adding a canonical constraint value
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To add a new canonical constraint value, prepare a PR adding it to that the
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appropriate BUILD file.
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Note that even global constraint values are typically area values. For example,
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ios is an area value for the global setting os but belongs in the apple area.
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For the PR's reviewer(s) choose an owner of this repository plus an owner of the
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area repository this references..
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A constraint value should be:
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- semantically clear, particularly in its distinctions from other values of
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the same setting
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- well-named: consistent with existing values of the same setting and easy to
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understand at usage sites
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- well-documented
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Remember that this value will apply for the entire Bazel community and its
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semantics will be difficult to impossible to change once it starts being used.
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# Adding a canonical constraint setting
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New canonical constraint settings should be rare and well-justified.
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To add a new setting, prepare a design document according to Bazel's design
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review process. This document should explain the need for a new setting and why
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it belongs here vs. area-specific repositories. It should clearly explain
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semantics, initial values, and criteria for adding new values.
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Once the design is approved prepare a PR for the actual change. If any values
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are area-specific, include the area repositories' owners as reviewers.
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# Private changes to global constraints
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If you'd like to experiment with changes to global settings or values, you can
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fork this repo for experimental purposes. But in the interest of community
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health and interoperability please don't share your changes with anyone not
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involved with the experiment. For wider distribution, submit a proper change
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here.
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Note that you can declare constraint_values in your own repo that are members of
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the global constraint_settings. This lets you "extend" global settings within
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the confines of your own project. But don't do this if you expect other projects
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to use these changes - this can easily lead to fragmentation conflicts.
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If you need custom constaint_settings, just declare them in your own repo. They
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are, by definition, not global.
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If you really need a permanent global change and it isn't design-approved for
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this repo, contact
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[bazel-dev@googlegroups.com](mailto://bazel-dev@googlegroups.com) to discuss
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options.
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