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Bazaar Design Principles
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We have learned or adopted a few general principles for code in Bazaar.
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Generally we will try to follow them in future, either for consistency or
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because they've been proven to work well, or both.
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We may need to depart from these principles in particular special cases,
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or modify them as we learn more, or we might be diverging for them for no
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very good reason but just because of bugs. If in doubt, ask.
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See also: `Bazaar Developer Document Catalog <index.html>`_.
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Untested code is broken code.
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So if a function is removed from the normal flow of execution (perhaps
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because a new default format was introduced) we have to make sure we can
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still execute and test the old code -- or remove it altogether.
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Fixing code once it's released is easy; fixing a problematic data format
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once people have started using it is more difficult. We should document
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and review formats separately from the code that implements them.
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Data formats should have clear format markers that allow us to support new
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formats in future. It should be easy to read the format without reading
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The format marker should be a string understandable by a user that names
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the format and gives the bzr release that introduced it. If the bzr
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program doesn't understand that format, it can at least show that format
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Once we mark a format as supported, we'll continue supporting it for
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several future releases, and support upgrading from it
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Once we've released a format, we normally don't change it. Adding new
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optional elements can cause problems when older clients don't understand
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those changes, or don't propagate them properly.
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We clearly distinguish internal files from user files. Files inside
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``.bzr/`` are only written to by bzr and we discourage users from editing
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them. Within bzr, code addressing the abstract interface of the Branch,
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BzrDir, etc shouldn't know where or how the internal files are stored. If
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anything else is written in there, it won't be propagated when pushing or
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pulling, and won't be converted when upgrading. (This is not quite true
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though; there is a ``branch.conf``.)
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User files within the tree, by contrast, we always store and return
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verbatim. It's OK for Bazaar to read and act on these files (as we do
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with ``.bzrignore``), and to update them (as ``bzr ignore`` does), but
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they remain clearly user files and can be directly edited.
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doc/developers/principles.txt
