JHBuild Updates

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The progress on JHBuild has continued (although I haven’t done much in the last week or so). Frederic Peters of JhAutobuild fame now has a CVS account to maintain the client portion of that project in tree.

Perl Modules (#342638)

One of the other things that Frederic has been working on is support for building Perl modules (which use a Makefile.PL instead of a configure script). His initial patchworked fine for tarballs, but by switching over to the new generic version control code in jhbuild it was possible to support Perl modules maintained in any of the supported version control systems without extra effort.

Speed Up Builds (#313997)

One of the other suggestions for jhbuild that came up a while ago was to make it “eleventy billion times faster”. In essence, adding a mode where it would only rebuild modules that had changed. While the idea has merrit, the proposed implementation had some problems (it used the output of “cvs update” to decide whether things had changed).

I’d like to get something like this implemented, preferably with three possible behaviours:

  1. Build everything (the current behaviour).
  2. Build only modules that have changed.
  3. Build only modules that have changed, or have dependencies that have changed.

The second option is obviously the fastest, and is a useful option for collections of modules that should be API stable. The third option is essentially an optimisation of the first option. For both the second and third option, it is necessary to be able to tell if the code in a module has been updated. The easiest way to do this is to record an identifier for the tree state, and the identifier is different after an update.

The identifier should be cheap to calculate too, so will probably be dependent on the underlying version control system:

  • CVS – a hash of the names and versions of all files in the tree. Something like this, maybe (can be constructed by reading the CVS/Root, CVS/Repository and CVS/Entries files in the tree).
  • Subversion – a combination of (a) the repository UUID, (b) the path of the tree inside the repository and (c) the youngest revision for this subtree in the repository.
  • Arch – the output of “baz tree-id“.
  • Bzr – the working tree’s revision ID.
  • Darcs – a hash of the sequence of patches representing the tree, maybe?
  • Tarballs – the version number for the tarball.

On a successful build, the ID for the tree would be recorded. On subsequent builds, the ID gets recalculated after updating the tree. The new and old IDs are then used to decide on whether to build the module or not, according to the chosen policy.