Use `Process.communicate()` instead of `Process.wait()` to ensure the
`stdin` and `stdout` OS pipe buffers don't get full and cause a deadlock
waiting for the buffers to get emptied.
The context manager would previously just terminate early on exception.
As a result, the worktree and branch would not get pruned when update script failed.
Let’s wrap the cleanup code in `finally` block as suggested by Python docs:
https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager
When updating a package using nix-update-script with `--argstr commit true`,
update.nix would not detect the changes because nix-update would stage them
and `git diff` would be empty.
We now detect both staged and unstaged changes to handle this use case.
When an update script fails, it might still modify the source tree.
These changes would then be committed in the next update attempt.
Let’s make sure the worktree is clean before updating to avoid that.
`update.nix` extracts `passthru.updateScript` attributes in the main repo
and when they are relative paths (e.g. `./update.sh`), Nix will resolve them
to absolute paths in the main repo.
Update scripts can use $(dirname $0) to get the location of files they
should update but that would point to the main repo.
We want them to modify the appropriate git worktree instead
so we replace the prefix accordingly.
`git rev-parse --show-toplevel` will resolve symlinks but, fortunately,
Nix will do that as well, so the path will match:
https://github.com/NixOS/nixpkgs/pull/98304#issuecomment-695761754
Instead of having the updateScript support returning JSON object,
it should be sufficient to specify attrPath in passthru.updateScript.
It is much easier to use.
The former is now considered experimental.
Update scripts can now declare features using
passthru.updateScript = {
command = [ ../../update.sh pname ];
supportedFeatures = [ "commit" ];
};
A `commit` feature means that when the update script finishes successfully,
it will print a JSON list like the following:
[
{
"attrPath": "volume_key",
"oldVersion": "0.3.11",
"newVersion": "0.3.12",
"files": [
"/path/to/nixpkgs/pkgs/development/libraries/volume-key/default.nix"
]
}
]
and data from that will be used when update.nix is run with --argstr commit true
to create commits.
We will create a new git worktree for each thread in the pool and run the update
script there. Then we will commit the change and cherry pick it in the main repo,
releasing the worktree for a next change.
To make updating large attribute sets faster, the update scripts
are now run in parallel.
Please note the following changes in semantics:
- The string passed to updateScript needs to be a path to an executable file.
- The updateScript can also be a list: the tail elements will then be passed
to the head as command line arguments.
