An HTTPS URL starts with an alphanumeric scheme followed by a colon.
That means that they will be recognized as trailers in a trailer block.
That turns out to be a problem in practice. Let’s stop recognizing these
as trailers by failing the trailer parsing when we:
1. find the separator;
2. the separator and the next two characters form `://`; and
3. we haven’t parsed any whitespace yet.
The simplest example of how this can be a problem is for people who do
not use trailers but may leave URLs at the end of the commit message.
Now, while these authors might not use trailers themselves, other
authors may have used trailers and this metadata confusion can become a
problem once someone tries to extract that metadata (and non-metadata).
Let’s now look at some examples in the Linux Kernel[1] to see how this
is a problem in practice.
There are commits which contain intended non-trailer lines which start
with URLs. These are comments. Example with just the trailers:[2]
Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
[bhelgaas: squash fixes:
https://lore.kernel.org/r/20260108013956.14351-2-bagasdotme@gmail.comhttps://lore.kernel.org/r/20260108013956.14351-3-bagasdotme@gmail.com]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/20251210132907.58799-4-xueshuai@linux.alibaba.com
Those `[]` pairs delimit the “squash fixes” comment.
Now, any of these two commands:
git log --format='%(trailers:only)' -1 <commit>
git log -1 --format=%B <commit> |
git interpret-trailers --only-trailers
Will both wrongly (according to the surmised user intent) include these
two URL lines as trailers and also mangle the URLs, e.g.:
https: //lore.kernel.org/r/20260108013956.14351-2-bagasdotme@gmail.com
Because the `--only-trailers` mode (or `only` for the git-log(1) format)
normalizes the output to a colon and a space.
Another example is linewrapping mistakes; a `Link` trailer with a
URL where the URL ended up on the next line, presumably because the
user’s editor linewrapped the “too long” line. Example with just the
trailers:[3]
Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-4-c2efa4f74cb7@kernel.org
Link:
https://lore.kernel.org/3cnmtqmakpbb2uwhenrj7kdqu3uefykiykjllgfbtpkiwhaa4s@sghkevv7jned [1]
Acked-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Now, this intended trailer is already ruined, but interpreting the URL
as a standalone trailer only compounds the mistake.
Yet another example is the trailer machinery normalizing the trailer
block before application, resulting in a `https` trailer key in the
commit message itself. Example with just the trailers:[4]
https: //sashiko.dev/#/patchset/20260429114208.941011-1-holger.brunck%40hitachienergy.com
Fixes: c19b6d246a35 ("drivers/net: support hdlc function for QE-UCC")
Signed-off-by: Holger Brunck <holger.brunck@hitachienergy.com>
Link: https://patch.msgid.link/20260507155332.3452319-1-holger.brunck@hitachienergy.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
We have a helpful `Link` that points to the original patch.[5] Following
it we can see that that `https` trailer was indeed a URL
originally (again just the trailer block here):
https://sashiko.dev/#/patchset/20260429114208.941011-1-holger.brunck%40hitachienergy.com
Fixes: c19b6d246a35 ("drivers/net: support hdlc function for QE-UCC")
Signed-off-by: Holger Brunck <holger.brunck@hitachienergy.com>
So how did it end up as a `https` trailer? My theory is that the trailer
block was normalized on patch application, causing a URL comment to be
wrongly normalized and cemented in the commit message as a trailer.[6]
† 1: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/
† 2: commit 8236fc613d44e59f6736d6c3e9efffaf26ab7f00
† 3: commit 5bd97f5c5f241a5610c4412d1b93995a26241f81
† 4: commit 496c0c4c53bbe1bad97e82cd12103df61a6e459d
† 5: https://patch.msgid.link/20260507155332.3452319-1-holger.brunck@hitachienergy.com
† 6: There are only four commits in the Linux Kernel of this kind, and
three of them have the same recurring person in the signoff chain.
***
Note that this check has some benign false positives. A trailer key
can start with a digit, but a URL scheme can not start with a digit.
That means that a line that starts with `1://` will be rejected even
though it cannot be a URL. I don’t think this will reject any real
trailers, so I think the implementation simplicity is worth it.
And these false positives are just for a limited start fragment check;
a mere heuristic, not a URL parser.
Helped-by: Jeff King <peff@peff.net>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Comment lines have always been ignored but this is not documented.
The primary motivation here is to be reasonably complete in the
documentation of how trailers are parsed; this is after all the only
documentation page that documents this format. However, and going beyond
that point, we could imagine that someone would want to use this format
outside a commit (or tag) message context, like say in Git notes.
On the other hand, it seems far-fetched that someone would be caught
off guard by this considering that comment characters/strings are not
likely to be alphanumeric,[1] which would mean that these comment lines
would be treated as non-trailer lines if they were *not* detected and
removed as comment lines.
† 1: A notable exception is that Jujutsu VCS uses `JJ:` as
the comment string
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Two commits ago we moved new-trailers paragraph next to each other.
But there is something curious about two of them:
By default the new trailer will appear at the end of the trailer
block. [...]
Then a source block and a paragraph later:
By default, a `<key>=<value>` or `<key>:<value>` argument given
using `--trailer` will be appended after the existing trailers only
if [...]
Why are there two paragraphs that talk about how “By default” a trailer
will be appended?
We can make these paragraphs flow better, and with a more distinct
character each, by dividing the flow like this:
1. Declare that we are about to talk about `--trailer` appending
2. Explain the default behavior
3. Explain how this affects the trailer block
4. Then discuss what each trailer line will look like
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We chose to introduce the term “trailer block” into the documentation a
few commits ago.[1] It is used in the code though, so it is not a newly
invented term.
That term was useful to explain where the trailers are found (they
*trail* the message). But it is also useful here, where we explain
how trailers are added to existing messages, how trailer blocks are
found (beyond the simple case in the introduction), and how the end
of the message is found.
Also note that we simplify the “blank line” point. The text says:
A blank line will be added before the new trailer if there isn't one
already.
But this isn’t quite coherent. The previous sentence says “If there is
no existing trailer”, so we are in one of these modes:
1. discussing trailer blocks in general; or
2. discussing creating a new trailer block in particular.
If (1), then we shouldn’t add a blank line before the new trailer if
there exists a trailer block already. And if (2), then the “if there
isn’t one already” is redundant.[2] So just talking about the higher-
level “trailer block” simplifies the text, since we don’t have to worry
about the different contexts that *trailers* can find themselves in.
† 1: in commit “explain the format after the intro”
† 2: Note that non-trailer lines don’t matter here; if you have a
trailer block consisting of `(cherry picked from commit <commit>)`,
then you still shouldn’t insert a blank line before the new trailer
since that would create a new trailer block
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are three paragraphs that talk about how a new trailer is added.
But the first one is separated from the other two by two paragraphs
about how `key-alias` can make using `--trailer` more convenient. This
short how-to does not follow thematically from the previous paragraph,
and can wait until we have fully described how a new trailer is
added. So let’s move the three paragraphs about the new-trailer topic
together and move the how-to paragraphs after that.
***
Let’s now review the history of the document. Even if the document
is not quite correct in its current state, just doing the apparently
obvious edit without considering the history does not respect the
effort that went into changing the document in the past.
These three paragraphs were originally next to each other, in the first
version of the doc.[1] But extra sentences about this how-to topic was
added to the first paragraph nine years later:[2]
[...]
`': '` (one colon followed by one space). For convenience, the
<token> can be a shortened string key (e.g., "sign") instead of the
full string which should [...]
And then it was split into it’s own paragraph a little later.[3]
This evolution shows, in my opinion, that this how-to never followed
thematically from the existing topic. Which means that there is nothing
that was potentially lost to time that we need to restore or respect.
† 1: dfd66ddf (Documentation: add documentation for 'git
interpret-trailers', 2014-10-13)
† 2: eda2c44c (doc: trailer: mention 'key' in DESCRIPTION, 2023-06-15)
† 3: 6ccbc667 (trailer doc: <token> is a <key> or <keyAlias>, not both,
2023-09-07)
Suggested-by: D. Ben Knoble <ben.knoble+github@gmail.com>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All of the examples speak of the Happy Path where everything works
as intended. But failure examples can also be instructive. Especially
for explaining again, by example, the key format (see previous commit).
This also allows us to demonstrate trailer block detection with a
concrete example.
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A trailer key must consist of ASCII alphanumeric characters and
hyphens *only*. Let’s document it explicitly instead of relying on
readers being conservative and only basing their trailer keys on the
documentation examples.[1]
The previous commit provided us with an appropriate paragraph to
describe the key format.
† 1: Technically they would then miss out on using digits in them since
all of the example keys just use letters and hyphens
Reported-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
You need to read the entire “Description” section in order to understand
the full trailer format. But there are many nuances, so that’s fine.
As a starter though we have an introductory example.[1] That turns out
to be crucial; the rest of this section talks about the mechanics of the
command and only incidentally the format itself.
Now, although the example might arguably be self-explanatory, we can
add a little preamble which defines the format in its simplest form as
well as define the most important terms.
Note that we name the “blank line” rule since I want to use that term
every time it comes up. It gets very mildly obfuscated if you call it
a “blank line” in one place[2] and “empty (or whitespace-only) ...” in
another one.[3]
We will define the format of the *key* in the next commit.
† 1: from d57fa7fc (doc: trailer: add more examples in DESCRIPTION,
2023-06-15)
† 2: `Documentation/git-interpret-trailers.adoc:86` in
5361983c (The 22nd batch, 2026-03-27)
† 3: `Documentation/git-interpret-trailers.adoc:93` in
5361983c (The 22nd batch, 2026-03-27)
Suggested-by: D. Ben Knoble <ben.knoble+github@gmail.com>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This command doesn’t interface with commits directly. You can
interpret or modify any kind of text, even though commit messages
are the most relevant.
The git(1) suite also isn’t restricted to only direct commit support
since git-tag(1) learned `--trailer` in 066cef77 (builtin/tag: add
--trailer option, 2024-05-05)
Now, we already introduce the command in the “Name” section as dealing
with commit messages as well. That is fine since that intro line needs
to remain pretty short.
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We now since the previous commit introduce the format as “trailer
metadata”. We can replace “structured information” with “metadata”
in the “Name” section to be consistent.
While “structured information” does emphasize that the data is not
loosely structured, we also say that this command adds to or parses
this format. I don’t think that we need to emphasize that it is
structured since clearly there is some structure there.
Both “metadata” and “structured information” can convey the same
information. But “metadata” is shorter and easier to deploy since
it’s just one word.
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We removed the initial comparison to email headers in the previous
commit. Now the introduction paragraph just says “trailer lines”, and
the only hint that this is metadata/structured information is the
“otherwise free-form” phrase.
Let’s replace “lines” with “metadata” since that is their purpose.
This also makes the introduction more consistent with how I chose
to define trailers in the glossary:[1] “Key-value metadata”. (We will
introduce “key–value” in the upcoming commit “explain the format after
the intro”.)
† 1: 68e3c69e (Documentation/glossary: describe "trailer", 2024-11-17)
Let’s not emphasize “trailer” here since we are going to define the term
in the upcoming commit “explain the format after the intro”.
Let’s call it “trailer metadata” rather than “trailers metadata”.
At first it seemed better to use the latter:
1. We’re introducing the jargon, and the format is often discussed as
plural “trailers”, with its constituent parts being singular
“trailer”
2. What this replaces uses “trailer”, but it rescues the plural mood
with “lines”
3. This is very soon going to go into the constituent parts, including
each trailer, so we’re contrasting the concept name (trailers) with
its parts
But:
1. The former reads better (most important)
2. “Trailer *metadata*” suggests plurality, similar to “trailer *lines*”
Helped-by: Matt Hunter <m@lfurio.us>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This command handles the trailer metadata format. But the command
isn’t introduced as such; it is instead introduced by stating that
these trailer lines look similar to RFC 822 email headers.
This is overwrought; most people do not deal directly with email
headers, and certainly not email RFCs.
Trailers are just key–value pairs that, like email headers, use colon
as the separator. The format in its simplest form is easy to describe
directly without comparing it to anything else; we will do that in the
upcoming commit “explain the format after the intro”.
For now, let’s:
• remove the first mention of email headers;
• keep the second, innocuous comparison with email line folding in the
middle; and
• remove the now-unneeded disclaimer that trailers do not share many of
the features of RFC 822 email headers—there is no invitation to
speculate that trailers would follow any other email format rules
since we do not compare them directly any more.
***
Talking about trailers as an RFC 822/2822-like format seems to go back
to the `--fixes`/`Fixes:` trailer topic,[1] the thread that precipitated
this command and in turn the first trailer support in git(1) beyond
adding s-o-b lines.
† 1: https://lore.kernel.org/all/20131027071407.GA11683@leaf/
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some negated options are missing according to
`git interpret-trailers -h`.
Also normalize to the “stuck form” (see gitcli(7)) like what was done
in 806337c7 (doc: notes: use stuck form throughout, 2025-05-27).[1]
Also normalize the order of the regular and negated options according to
the current convention.[2]
Also note that `--no-trailer` will reset the list.
† 1: See also https://lore.kernel.org/git/6f7d027e-088a-4d66-92af-b8d1c32d730c@app.fastmail.com/
† 2: https://lore.kernel.org/git/xmqqcyct1mtq.fsf@gitster.g/
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
See e.g. 0ae23ab5 (doc: convert git worktree to synopsis style,
2025-10-05) for the markup rules for this style.
There aren’t many subtleties to the transformation of this doc since it
doesn’t use any advanced constructs. The only thing is that "`:`{nbsp}" is
used instead of `': '` to refer to effective inline-verbatim with
a space (␠).[1] I also use (_) for emphasis although (') gives the
same result.
Also prefer linking to Git commands instead of saying e.g. `git
format-patch`. But for this command we can type out git-interpret-
trailers(1) to avoid a self-reference.
Also replace camel case `<keyAlias>` with kebab case `<key-alias>`.
And while doing that make sure to replace `trailer.*` with
`trailer.<key-alias>`.
† 1: Similar to "`tag:`{nbsp}" in `Documentation/pretty-formats.adoc`
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All the documentation .txt files have been renamed to .adoc to help
content aware editors.
* bc/doc-adoc-not-txt:
Remove obsolete ".txt" extensions for AsciiDoc files
doc: use .adoc extension for AsciiDoc files
gitattributes: mark AsciiDoc files as LF-only
editorconfig: add .adoc extension
doc: update gitignore for .adoc extension
We presently use the ".txt" extension for our AsciiDoc files. While not
wrong, most editors do not associate this extension with AsciiDoc,
meaning that contributors don't get automatic editor functionality that
could be useful, such as syntax highlighting and prose linting.
It is much more common to use the ".adoc" extension for AsciiDoc files,
since this helps editors automatically detect files and also allows
various forges to provide rich (HTML-like) rendering. Let's do that
here, renaming all of the files and updating the includes where
relevant. Adjust the various build scripts and makefiles to use the new
extension as well.
Note that this should not result in any user-visible changes to the
documentation.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Kristoffer Haugsbakk