[PATCH v3 2/3] range-diff/format-patch: handle commit ranges other than A..B

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In the `SPECIFYING RANGES` section of gitrevisions[7], two ways are
described to specify commit ranges that `range-diff` does not yet
accept: "<commit>^!" and "<commit>^-<n>".

Let's accept them.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 range-diff.c          | 14 +++++++++++++-
 t/t3206-range-diff.sh |  8 ++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/range-diff.c b/range-diff.c
index 9b93e08e840..0c6ac4f954d 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -567,5 +567,17 @@ int show_range_diff(const char *range1, const char *range2,
 
 int is_range_diff_range(const char *arg)
 {
-	return !!strstr(arg, "..");
+	static regex_t *regex;
+
+	if (strstr(arg, ".."))
+		return 1;
+
+	/* match `<rev>^!` and `<rev>^-<n>` */
+	if (!regex) {
+		regex = xmalloc(sizeof(*regex));
+		if (regcomp(regex, "\\^(!|-[0-9]*)$", REG_EXTENDED) < 0)
+			BUG("could not compile range-diff regex");
+	}
+
+	return !regexec(regex, arg, 0, NULL, 0);
 }
diff --git a/t/t3206-range-diff.sh b/t/t3206-range-diff.sh
index 6eb344be031..e217cecac9e 100755
--- a/t/t3206-range-diff.sh
+++ b/t/t3206-range-diff.sh
@@ -150,6 +150,14 @@ test_expect_success 'simple A B C (unmodified)' '
 	test_cmp expect actual
 '
 
+test_expect_success 'A^! and A^-<n> (unmodified)' '
+	git range-diff --no-color topic^! unmodified^-1 >actual &&
+	cat >expect <<-EOF &&
+	1:  $(test_oid t4) = 1:  $(test_oid u4) s/12/B/
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success 'trivial reordering' '
 	git range-diff --no-color master topic reordered >actual &&
 	cat >expect <<-EOF &&
-- 
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