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MozReview-Commit-ID: 3P1d5l0xOyk Differential Revision: https://phabricator.services.mozilla.com/D2460 --HG-- extra : moz-landing-system : lando
107 lines
4.2 KiB
ReStructuredText
107 lines
4.2 KiB
ReStructuredText
.. _tup:
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===========
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Tup Backend
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===========
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The Tup build backend is an alternative to the default Make backend. The `Tup
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build system <http://gittup.org/tup/>`_ is designed for fast and correct
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incremental builds. A top-level no-op build should be under 2 seconds, and
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clobbers should rarely be required. It is currently only available for Linux
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Desktop builds -- other platforms like Windows or OSX are planned for the
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future.
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As part of the mozbuild architecture, the Tup backend shares a significant
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portion of frontend (developer-facing) code in the build system. When using the
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Tup backend, ``mach build`` is still the entry point to run the build system,
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and moz.build files are still used for the build description. Familiar parts of
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the build system like configure and generating the build files (the
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``Reticulating splines...`` step) are virtually identical in both backends. The
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difference is that ``mach`` invokes Tup instead of Make under the hood to do
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the actual work of determining what needs to be rebuilt. Tup is able to perform
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this work more efficiently by loading only the parts of the DAG that are
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required for an incremental build. Additionally, Tup instruments processes to
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see what files are read from and written to in order to verify that
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dependencies are correct.
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For more detailed information on the rationale behind Tup, see the `Build
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System Rules and Algorithms
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<http://gittup.org/tup/build_system_rules_and_algorithms.pdf>`_ paper.
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Installation
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============
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You'll need to install the Tup executable, as well as the nightly rust/cargo
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toolchain::
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cd ~/.mozbuild && mach artifact toolchain --from-build linux64-tup
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rustup install nightly
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rustup default nightly
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Configuration
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=============
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Your mozconfig needs to describe how to find the executable if it's not in your
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PATH, and enable the Tup backend::
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export TUP=~/.mozbuild/tup/tup
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ac_add_options --enable-build-backends=Tup
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What Works
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==========
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You should expect a Linux desktop build to generate a working Firefox binary
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from a ``mach build``, and be able to run test suites against it (eg:
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mochitests, xpcshell, gtest). Top-level incremental builds should be fast
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enough to use them during a regular compile/edit/test cycle. If you wish to
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stop compilation partway through the build to more quickly iterate on a
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particular file, you can expect ``mach build objdir/path/to/file.o`` to
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correctly produce all inputs required to build file.o before compiling it. For
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example, you don't have to run the build system in various subdirectories to
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get generated headers built in the right order.
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Currently Unsupported / Future Work
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===================================
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There are a number of features that you may use in the Make backend that are
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currently unsupported for the Tup backend. We plan to add support for these in
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the future according to developer demand and build team availability.
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* sccache - This is currently under active development to support icecream-like
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functionality, which likely impacts the same parts that would affect Tup's
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dependency checking mechanisms. Note that icecream itself should work with
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Tup.
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* Incremental Rust compilation - see `bug 1468527 <https://bugzilla.mozilla.org/show_bug.cgi?id=1468527>`_
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* Watchman integration - This will allow Tup to skip the initial ``Scanning
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filesystem...`` step, saving 1-2 seconds of startup overhead.
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* More platform support (Windows, OSX, etc.)
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* Packaging in automation - This is still quite intertwined with Makefiles
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* Tests in automation - Requires packaging
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How to Contribute
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=================
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At the moment we're looking for early adopters who are developing on the Linux
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desktop to try out the Tup backend, and share your experiences with the build
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team (see `Contact`_).
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* Are there particular issues or missing features that prevent you from using
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the Tup backend at this time?
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* Do you find that top-level incremental builds are fast enough to use for
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every build invocation?
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* Have you needed to perform a clobber build to fix an issue?
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Contact
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========
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If you have any issues, feel free to file a bug blocking `buildtup
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<https://bugzilla.mozilla.org/show_bug.cgi?id=827343>`_, or contact mshal or
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chmanchester in #build on IRC.
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