Content Filters

Content formats

Bazaar’s content filtering allows you to store files in a different format from the copy in your working tree. This lets you, or your co-developers, use Windows development tools that expect CRLF files on projects that use other line-ending conventions. Among other things, content filters also let Linux developers more easily work on projects using Windows line-ending conventions, keyword expansion/compression, and trailing spaces on lines in text files to be implicitly stripped when committed.

To generalize, there are two content formats supported by Bazaar:

  • a canonical format - how files are stored internally
  • a convenience format - how files are created in a working tree.

Format conversion

The conversion between these formats is done by content filters. A content filter has two parts:

  • a read converter - converts from convenience to canonical format
  • a write converter - converts from canonical to convenience format.

Many of these converters will provide round-trip conversion, i.e. applying the read converter followed by the write converter gives back the original content. However, others may provide an asymmetric conversion. For example, a read converter might strip trailing whitespace off lines in source code while the matching write converter might pass content through unchanged.

Enabling content filters

Content filters are typically provided by plugins, so the first step in using them is to install the relevant plugins and read their documentation. Some plugins may be very specific about which files they filter, e.g. only files ending in .java or .php. In other cases, the plugin may leave it in the user’s hands to define which files are to be filtered. This is typically done using rule-based preferences. See bzr help rules for general information about defining these.

Impact on commands

Read converters are only applied to commands that read content from a working tree, e.g. status, diff and commit. For example, bzr diff will apply read converters to files in the working tree, then compare the results to the content last committed.

Write converters are only applied by commands that create files in a working tree, e.g. branch, checkout, update. If you wish to see the canonical format of a file or tree, use bzr cat or bzr export respectively.

Note: bzr commit does not implicitly apply write converters after comitting files. If this makes sense for a given plugin providing a content filter, the plugin can usually achieve this effect by using a start_commit or post_commit hook say. See Hooks for more information on hooks.

Refreshing your working tree

For performance reasons, Bazaar caches the timestamps of files in a working tree, and assumes files are unchanged if their timestamps match the cached values. As a consequence, there are times when you may need to explicitly ask for content filtering to be reapplied in one or both directions, e.g. after installing or reconfiguring plugins providing it.

Here are some general guidelines for doing this:

  • To reapply read converters, touch files, i.e. update their timestamp. Operations like bzr status should then reapply the relevant read converters and compare the end result with the canonical format.
  • To reapply write converters, ensure there are no local changes, delete the relevant files and run bzr revert on those files.

Note: In the future, it is likely that additional options will be added to commands to make this refreshing process faster and safer.

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