Re: gitattributes export-subst and software versioning

[Eli Schwartz <eschwartz@archlinux.org>]

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On 2/8/21 2:46 PM, René Scharfe wrote:
> git archive uses the pretty format code for export-subst.  It is used by
> git log and others as well.  git describe uses all object flags to find
> the best description.  Simply plugging it into the pretty format code
> would clash with the object flag use of git log.

Yeah, I was afraid there might be bad interactions with a pretty
archive-centric placeholder and something that isn't git-archive.

On the other hand, with my zero knowledge of the code but having read
lots of man pages... %S documents that it "only works with git log", so
maybe it is possible to add an option that is documented to only work
for git archive?

e.g. if you do use it,

$ cat VERSION
$Format:%d$
$Format:%S$

$ git archive HEAD | bsdtar -xOf - VERSION
 (HEAD -> master, tag: 1.0)
%S

It's apparently completely ignored and treated as raw characters. The
same restriction could theoretically be added in the other direction for
a new placeholder.

This would neatly resolve Junio's concern about the resource-intensive
nature of "describe" not being a good fit for "log".

> And replacing the flags with a commit slab doesn't seem to be enough,
> either -- I get good results lots of commits, but for some git log with
> the new placeholder would just show some nonsensical output, as it
> seems to get the depth calculation wrong for them somehow.

You mean git describe <commit> produces wrong results for those?

> Anyway, we can of course do something like in the patch below.  It
> works, it's easy, it's fast enough for git archive, and it's quite
> hideous.  Hopefully it's bad enough to motivate someone to come up with
> a cleaner, faster solution.

:D :D an important part of the resolution process, to be sure.

> ---
>  pretty.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/pretty.c b/pretty.c
> index 3922f6f9f2..bbfb5ca3e7 100644
> --- a/pretty.c
> +++ b/pretty.c
> @@ -12,6 +12,7 @@
>  #include "reflog-walk.h"
>  #include "gpg-interface.h"
>  #include "trailer.h"
> +#include "run-command.h"
> 
>  static char *user_format;
>  static struct cmt_fmt_map {
> @@ -1213,6 +1214,21 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
>  		return parse_padding_placeholder(placeholder, c);
>  	}
> 
> +	if (skip_prefix(placeholder, "(describe)", &arg)) {
> +		struct child_process cmd = CHILD_PROCESS_INIT;
> +		struct strbuf out = STRBUF_INIT;
> +
> +		cmd.git_cmd = 1;
> +		strvec_push(&cmd.args, "describe");
> +		strvec_push(&cmd.args, "--always");
> +		strvec_push(&cmd.args, oid_to_hex(&commit->object.oid));
> +		pipe_command(&cmd, NULL, 0, &out, 0, NULL, 0);
> +		strbuf_rtrim(&out);
> +		strbuf_addbuf(sb, &out);
> +		strbuf_release(&out);
> +		return arg - placeholder;
> +	}
> +
>  	/* these depend on the commit */
>  	if (!commit->object.parsed)
>  		parse_object(the_repository, &commit->object.oid);
> --
> 2.30.0
> 


-- 
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User


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