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44 строки
2.0 KiB
ReStructuredText
44 строки
2.0 KiB
ReStructuredText
.. _unified-builds:
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==============
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Unified Builds
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==============
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The Firefox build system uses the technique of "unified builds" (or elsewhere
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called "`unity builds <https://en.wikipedia.org/wiki/Unity_build>`_") to
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improve compilation performance. Rather than compiling source files individually,
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groups of files in the same directory are concatenated together, then compiled once
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in a single batch.
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Unified builds can be configured using the ``UNIFIED_SOURCES`` variable in ``moz.build`` files.
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.. _unified_build_compilation_failures:
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Why are there unrelated compilation failures when I change files?
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=================================================================
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Since multiple files are concatenated together in a unified build, it's possible for a change
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in one file to cause the compilation of a seemingly unrelated file to fail.
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This is usually because source files become implicitly dependent on each other for:
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* ``#include`` statements
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* ``using namespace ...;`` statements
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* Other symbol imports or definitions
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One of the more common cases of unexpected failures are when source code files are added or
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removed, and the "chunking" is changed. There's a limit on the number of files that are combined
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together for a single compilation, so sometimes the addition of a new file will cause another one
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to be bumped into a different chunk. If that other chunk doesn't meet the implicit requirements
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of the bumped file, there will be a tough-to-debug compilation failure.
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Other notes:
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============
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* Some IDEs (such as VSCode with ``clangd``) build files in standalone mode, so they may show
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more failures than a ``mach build``.
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* The amount of files per chunk can be adjusted in ``moz.build`` files with the
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``FILES_PER_UNIFIED_FILE`` variable. Note that changing the chunk size can introduce
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compilation failures as described :ref:`above<unified_build_compilation_failures>`.
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* We are happy to accept patches that fix problematic unified build chunks (such as by adding
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includes or namespace annotations).
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