The output of git-fetch(1) is obviously designed for consumption by
users, only: we neatly columnize data, we abbreviate reference names, we
print neat arrows and we don't provide information about actual object
IDs that have changed. This makes the output format basically unusable
in the context of scripted invocations of git-fetch(1) that want to
learn about the exact changes that the command performs.
Introduce a new machine-parseable "porcelain" output format that is
supposed to fix this shortcoming. This output format is intended to
provide information about every reference that is about to be updated,
the old object ID that the reference has been pointing to and the new
object ID it will be updated to. Furthermore, the output format provides
the same flags as the human-readable format to indicate basic conditions
for each reference update like whether it was a fast-forward update, a
branch deletion, a rejected update or others.
The output format is quite simple:
```
<flag> <old-object-id> <new-object-id> <local-reference>\n
```
We assume two conditions which are generally true:
- The old and new object IDs have fixed known widths and cannot
contain spaces.
- References cannot contain newlines.
With these assumptions, the output format becomes unambiguously
parseable. Furthermore, given that this output is designed to be
consumed by scripts, the machine-readable data is printed to stdout
instead of stderr like the human-readable output is. This is mostly done
so that other data printed to stderr, like error messages or progress
meters, don't interfere with the parseable data.
A notable ommission here is that the output format does not include the
remote from which a reference was fetched, which might be important
information especially in the context of multi-remote fetches. But as
such a format would require us to print the remote for every single
reference update due to parallelizable fetches it feels wasteful for the
most likely usecase, which is when fetching from a single remote.
In a similar spirit, a second restriction is that this cannot be used
with `--recurse-submodules`. This is because any reference updates would
be ambiguous without also printing the repository in which the update
happens.
Considering that both multi-remote and submodule fetches are user-facing
features, using them in conjunction with `--porcelain` that is intended
for scripting purposes is likely not going to be useful in the majority
of cases. With that in mind these restrictions feel acceptable. If
usecases for either of these come up in the future though it is easy
enough to add a new "porcelain-v2" format that adds this information.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
`store_updated_refs()` parses the remote reference for two purposes:
- It gets used as a note when writing FETCH_HEAD.
- It is passed through to `display_ref_update()` to display
updated references in the following format:
```
* branch master -> master
```
In most cases, the parsed remote reference is the prettified reference
name and can thus be used for both cases. But if the remote reference is
HEAD, the parsed remote reference becomes empty. This is intended when
we write the FETCH_HEAD, where we skip writing the note in that case.
But when displaying the updated references this leads to inconsistent
output where the left-hand side of reference updates is missing in some
cases:
```
$ git fetch origin HEAD HEAD:explicit-head :implicit-head main
From https://github.com/git/git
* branch HEAD -> FETCH_HEAD
* [new ref] -> explicit-head
* [new ref] -> implicit-head
* branch main -> FETCH_HEAD
```
This behaviour has existed ever since the table-based output has been
introduced for git-fetch(1) via 165f390250 (git-fetch: more terse fetch
output, 2007-11-03) and was never explicitly documented either in the
commit message or in any of our tests. So while it may not be a bug per
se, it feels like a weird inconsistency and not like it was a concious
design decision.
The logic of how we compute the remote reference name that we ultimately
pass to `display_ref_update()` is not easy to follow. There are three
different cases here:
- When the remote reference name is "HEAD" we set the remote
reference name to the empty string. This is the case that causes
the left-hand side to go missing, where we would indeed want to
print "HEAD" instead of the empty string. This is what
`prettify_refname()` would return.
- When the remote reference name has a well-known prefix then we
strip this prefix. This matches what `prettify_refname()` does.
- Otherwise, we keep the fully qualified reference name. This also
matches what `prettify_refname()` does.
As the return value of `prettify_refname()` would do the correct thing
for us in all three cases, we can thus fix the inconsistency by passing
through the full remote reference name to `display_ref_update()`, which
learns to call `prettify_refname()`. At the same time, this also
simplifies the code a bit.
Note that this patch also changes formatting of the block that computes
the "kind" (which is the category like "branch" or "tag") and "what"
(which is the prettified reference name like "master" or "v1.0")
variables. This is done on purpose so that it is part of the diff,
hopefully making the change easier to comprehend.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a testcase that exercises the logic when an invalid output format is
passed via the `fetch.output` configuration.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We're about to introduce a new porcelain mode for the output of
git-fetch(1). As part of that we'll be introducing a set of new tests
that only relate to the output of this command.
Split out tests that exercise the output format of git-fetch(1) so that
it becomes easier to verify this functionality as a standalone unit. As
the tests assume that the default branch is called "main" we set up the
corresponding GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME environment variable
accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
