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diffcore: add a pickaxe option to find a specific blob

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Sometimes users are given a hash of an object and they want to
identify it further (ex.: Use verify-pack to find the largest blobs,
but what are these? or [1])

One might be tempted to extend git-describe to also work with blobs,
such that `git describe <blob-id>` gives a description as
'<commit-ish>:<path>'.  This was implemented at [2]; as seen by the sheer
number of responses (>110), it turns out this is tricky to get right.
The hard part to get right is picking the correct 'commit-ish' as that
could be the commit that (re-)introduced the blob or the blob that
removed the blob; the blob could exist in different branches.

Junio hinted at a different approach of solving this problem, which this
patch implements. Teach the diff machinery another flag for restricting
the information to what is shown. For example:

    $ ./git log --oneline --find-object=v2.0.0:Makefile
    b2feb64309 Revert the whole "ask curl-config" topic for now
    47fbfded53 i18n: only extract comments marked with "TRANSLATORS:"

we observe that the Makefile as shipped with 2.0 was appeared in
v1.9.2-471-g47fbfded53 and in v2.0.0-rc1-5-gb2feb6430b.  The
reason why these commits both occur prior to v2.0.0 are evil
merges that are not found using this new mechanism.

[1] https://stackoverflow.com/questions/223678/which-commit-has-this-blob
[2] https://public-inbox.org/git/20171028004419.10139-1-sbeller@google.com/

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Stefan Beller
2018-01-04 14:50:42 -08:00
committed by Junio C Hamano
parent cf63051ada
commit 15af58c1ad
6 changed files with 134 additions and 19 deletions
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21
diff.c
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@ -4082,6 +4082,7 @@ void diff_setup(struct diff_options *options)
options->interhunkcontext = diff_interhunk_context_default;
options->ws_error_highlight = ws_error_highlight_default;
options->flags.rename_empty = 1;
options->objfind = NULL;
/* pathchange left =NULL by default */
options->change = diff_change;
@ -4487,6 +4488,23 @@ static int parse_ws_error_highlight_opt(struct diff_options *opt, const char *ar
return 1;
}
static int parse_objfind_opt(struct diff_options *opt, const char *arg)
{
struct object_id oid;
if (get_oid(arg, &oid))
return error("unable to resolve '%s'", arg);
if (!opt->objfind)
opt->objfind = xcalloc(1, sizeof(*opt->objfind));
opt->pickaxe_opts |= DIFF_PICKAXE_KIND_OBJFIND;
opt->flags.recursive = 1;
opt->flags.tree_in_recursive = 1;
oidset_insert(opt->objfind, &oid);
return 1;
}
int diff_opt_parse(struct diff_options *options,
const char **av, int ac, const char *prefix)
{
@ -4736,7 +4754,8 @@ int diff_opt_parse(struct diff_options *options,
else if ((argcount = short_opt('O', av, &optarg))) {
options->orderfile = prefix_filename(prefix, optarg);
return argcount;
}
} else if (skip_prefix(arg, "--find-object=", &arg))
return parse_objfind_opt(options, arg);
else if ((argcount = parse_long_opt("diff-filter", av, &optarg))) {
int offending = parse_diff_filter_opt(optarg, options);
if (offending)