With Mercurial, how to run a job for each changeset when doing an update? - mercurial

Question

Question: When I update my working directory from one revision to the other, I'd like to run a script for each revision passed. How can I do this?
Important Constraints
The script is always the same
Traversal should happen iteratively (I don't want to do all this by hand for 100 revisions...)
The incoming hook is no option. It must happen not only after pushes or pulls, but for all updates, no matter how often I switch between revisions.
For illustration:
r1(*) -- r2 -- r3 -- r4(head)
Basically, I'd like to do
r1(*) --> r2 (then run script) --> r3 (then run script) --> r4 (then...
Let's say, my working directory is currently at r1, and now I want to update it to r4. Instead of doing a direct update (like with hg update), I'd like to update to r2 first and then run a script (update-my-database, for example). Afterwards I'd like to update to r3, then run the same script and so on.

Answer 1

It is doable but we must be careful to select a linear piece from the revision graph.
Consider a minimal repository with two heads (same thing would be if two branches or two bookmarks):
$ hg log -G --template "{rev}\n"
o 4
|
| o 3
| |
| o 2
|/
o 1
|
o 0
Say we start from 1. We want to go along either head 4 (so the linear piece would be: 1, 4) or along head 3 (so the linear piece would be: 1, 2, 3).
So we will use a script with two parameters: the beginning and the end of the linear piece.
This is bare-bones but works:
for rev in `hg log -r "descendants(1) and ancestors(3)" --template "{rev}\n"`
do
echo Updating to $rev:
hg update $rev
echo Executing our script:
hg id --id --num
done
Here is the output:
Updating to 1:
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
Executing our script:
4d5aba4313ce 1
Updating to 2:
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Executing our script:
f0de0712ec00 2
Updating to 3:
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
Executing our script:
d052bd7c310b 3
The script works no matter what is the current revision of the working directory.
Before starting it, you have to do hg fetch to get the changes from the remote without applying them to the working directory and hg log --graph to understand the topology and so select the starting and ending points of the linear piece.
You also have to replace the hardcoded 1 and 3 with the $1 and $2 shell positional parameters and replace the hg id line with your actual script :-)
To understand how it works, we use a feature of mercurial called revsets (do hg help revsets to learn more) that allows to perform queries on the history graph (a bit like SQL :-)