This is the first post in a small series of posts which will show off some of the new functionality you can expect in the next major version of monotone. While there is no fixed release date set for it yet, we plan to release it in fall this year. If you look at the roadmap you see that most things have already been implemented and merged into mainline, so we’re definitely on plan 🙂
Anyways, lets begin this little series with the selector rewrite Tim merged a couple of weeks ago. Selectors are one of the main concepts in monotone to pick revisions other than by their 40 byte long hash id and are therefor very useful to “navigate” between different development lines.
Monotone up until 0.48 knows already many selectors – you can select revisions by tag, by branch, by author, by custom cert values and so on. Selectors can be combined to calculate the intersection between two single sets, like “show me all revisions from author ‘Jon’ on branch ‘my.project'” which would essentially look like this:
$ mtn automate select "a:jon/b:my.project"
The syntax for these selectors is all nice and simple – each selector is prefixed with a unique character and multiple selectors are concatenated with a single slash. While these old-style selectors solved many use cases, some however kept unresolved in the past and users from other DVCS like Darcs had a rather hard time figuring out how to accomplish a certain selection in monotone.
A particular good example is “how can I easily view the changes of a development branch since the last merge point?”. Up until now you either had to figure out manually the revision of the merge point by looking at the output of log or use some scary construct like the following:
$ mtn au common_ancestors $(mtn au select h:main.branch) \
$(mtn au select h:) | mtn au erase_ancestors -@-
Enter selector functions
Luckily, you don’t have to write these things anymore starting from 0.99 onwards. Give the new selector functions a warm applause!
$ mtn au select "lca(h:main.branch;h:feature.branch)"
In this example “lca” stands for the “least common ancestors” function which takes two arguments, i.e. two other selectors. The syntax is extra short in a workspace where an empty head selector h: defaults to the branch recorded in the workspace options, so if you’re in the feature.branch workspace, just type:
$ mtn au select "lca(h:main.branch;h:)"
Quite convenient, eh? This is not only short, but up to five times faster than the above complex command line. Of course the selector can be directly used in a call to diff or log, like so:
$ mtn diff -r "lca(h:main.branch;h:)" $ mtn log --to children(lca(h:main.branch;h:))"
But huh, whats that nested children call you ask? Well, the lca function picks the merge point in the _main branch_ and if the revision graph goes around that, log would otherwise happily log more parents (earlier revisions) on the feature branch. The call to children ensures that we pick the merge revision in the feature branch and therefor really stop logging at this revision.
Test drive
There are many more of these selector functions and explaining them all in detail is out of scope here, please have a look at “composite selectors” in the nightly built manual.
And if you want to have an early look at this and play around without having to compile it yourself – at least if you’re on openSUSE or Fedora – just download the binaries from our nightly builds.