[PATCH v2 3/3] pretty: add abbrev option to %(describe)

[Eli Schwartz <eschwartz@archlinux.org>]

The %(describe) placeholder by default, like `git describe`, uses a
seven-character abbreviated commit object name. This may not be
sufficient to fully describe all commits in a given repository,
resulting in a placeholder replacement changing its length because the
repository grew in size.  This could cause the output of git-archive to
change.

Add the --abbrev option to `git describe` to the placeholder interface
in order to provide tools to the user for fine-tuning project defaults
and ensure reproducible archives.

One alternative would be to just always specify --abbrev=40 but this may
be a bit too biased...

Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>
---

Notes:
    With regard to validating that an integer is passed, I attempt to parse the
    result using the same mechanism git-describe itself does in the abbrev
    callback, just with slightly different validation of what we have at the end...
    because of course here argval is the entire rest of the format string,
    including the ")".
    
    While testing that this actually does what it's supposed to do, I noticed that
    it doesn't validate junk like leading whitespace or plus signs... this is a
    problem for `git describe --abbrev='    +15'` too so I guess it's not my
    problem to fix...

 Documentation/pretty-formats.txt |  4 ++++
 pretty.c                         | 16 +++++++++++++++-
 t/t4205-log-pretty-formats.sh    |  8 ++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/Documentation/pretty-formats.txt b/Documentation/pretty-formats.txt
index 86ed801aad..57fd84f579 100644
--- a/Documentation/pretty-formats.txt
+++ b/Documentation/pretty-formats.txt
@@ -222,6 +222,10 @@ The placeholders are:
 +
 ** 'tags[=<BOOL>]': Instead of only considering annotated tags,
    consider lightweight tags as well.
+** 'abbrev=<N>': Instead of using the default number of hexadecimal digits
+   (which will vary according to the number of objects in the repository with a
+   default of 7) of the abbreviated object name, use <n> digits, or as many digits
+   as needed to form a unique object name.
 ** 'match=<pattern>': Only consider tags matching the given
    `glob(7)` pattern, excluding the "refs/tags/" prefix.
 ** 'exclude=<pattern>': Do not consider tags matching the given
diff --git a/pretty.c b/pretty.c
index 16b5366fed..44bfc49b38 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1218,9 +1218,10 @@ static size_t parse_describe_args(const char *start, struct strvec *args)
 {
 	struct {
 		char *name;
-		enum { OPT_BOOL, OPT_STRING, } type;
+		enum { OPT_BOOL, OPT_INTEGER, OPT_STRING, } type;
 	}  option[] = {
 		{ "tags", OPT_BOOL},
+		{ "abbrev", OPT_INTEGER },
 		{ "exclude", OPT_STRING },
 		{ "match", OPT_STRING },
 	};
@@ -1245,6 +1246,19 @@ static size_t parse_describe_args(const char *start, struct strvec *args)
 					found = 1;
 				}
 				break;
+			case OPT_INTEGER:
+				if (match_placeholder_arg_value(arg, option[i].name, &arg,
+								&argval, &arglen) && arglen) {
+					if (!arglen)
+						return 0;
+					char* endptr;
+					strtol(argval, &endptr, 10);
+					if (endptr - argval != arglen)
+						return 0;
+					strvec_pushf(args, "--%s=%.*s", option[i].name, (int)arglen, argval);
+					found = 1;
+				}
+				break;
 			case OPT_STRING:
 				if (match_placeholder_arg_value(arg, option[i].name, &arg,
 								&argval, &arglen) && arglen) {
diff --git a/t/t4205-log-pretty-formats.sh b/t/t4205-log-pretty-formats.sh
index d4acf8882f..35eef4c865 100755
--- a/t/t4205-log-pretty-formats.sh
+++ b/t/t4205-log-pretty-formats.sh
@@ -1010,4 +1010,12 @@ test_expect_success '%(describe:tags) vs git describe --tags' '
 	test_cmp expect actual
 '
 
+test_expect_success '%(describe:abbrev=...) vs git describe --abbrev=...' '
+	test_when_finished "git tag -d tagname" &&
+	git tag -a -m tagged tagname &&
+	git describe --abbrev=15 >expect &&
+	git log -1 --format="%(describe:abbrev=15)" >actual &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.33.1