[PATCH 2/3] range-diff: 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>
---
 builtin/range-diff.c  | 21 ++++++++++++++++++++-
 t/t3206-range-diff.sh |  8 ++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/builtin/range-diff.c b/builtin/range-diff.c
index 551d3e689cb..6097635c432 100644
--- a/builtin/range-diff.c
+++ b/builtin/range-diff.c
@@ -13,7 +13,26 @@ NULL
 
 static int is_range(const char *range)
 {
-	return !!strstr(range, "..");
+	size_t i;
+	char c;
+
+	if (strstr(range, ".."))
+		return 1;
+
+	i = strlen(range);
+	c = i ? range[--i] : 0;
+	if (c == '!')
+		i--; /* might be ...^! or ...^@ */
+	else if (isdigit(c)) {
+		/* handle ...^-<n> */
+		while (i > 2 && isdigit(range[--i]))
+			; /* keep trimming trailing digits */
+		if (i < 2 || range[i--] != '-')
+			return 0;
+	} else
+		return 0;
+
+	return i > 0 && range[i] == '^';
 }
 
 int cmd_range_diff(int argc, const char **argv, const char *prefix)
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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