sha1_name.c: teach get_sha1_1 "-" shorthand for "@{-1}"

This patch introduces "-" as a method to refer to a revision, and adds tests to
test that git-log works with this shorthand.

This change will touch the following commands (through
revision.c:setup_revisions):

* builtin/blame.c
* builtin/diff.c
* builtin/diff-files.c
* builtin/diff-index.c
* builtin/diff-tree.c
* builtin/log.c
* builtin/rev-list.c
* builtin/shortlog.c
* builtin/fast-export.c
* builtin/fmt-merge-msg.c
builtin/add.c
builtin/checkout.c
builtin/commit.c
builtin/merge.c
builtin/pack-objects.c
builtin/revert.c

* marked commands are information-only.

As most commands in this list are not of the rm-variety, (i.e a command that
would delete something), this change does not make it easier for people to
delete. (eg: "git branch -d -" is *not* enabled by this patch)

Suffixes like "-@{yesterday}" and "-@{2.days.ago}" are not enabled by this
patch. This is something that needs to be fixed later by making changes deeper
down the callchain.

Signed-off-by: Siddharth Kannan <kannan.siddharth12@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 111 insertions, 0 deletions

diff --git a/sha1_name.c b/sha1_name.c
index 73a915ff1b..2f86bc9c73 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -947,6 +947,11 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1, unsigned l
 	if (!ret)
 		return 0;
 
+	if (*name == '-' && len == 1) {
+		name = "@{-1}";
+		len = 5;
+	}
+
 	ret = get_sha1_basic(name, len, sha1, lookup_flags);
 	if (!ret)
 		return 0;
diff --git a/t/t4214-log-shorthand.sh b/t/t4214-log-shorthand.sh
new file mode 100755
index 0000000000..8be2de1bb9
--- /dev/null
+++ b/t/t4214-log-shorthand.sh
@@ -0,0 +1,106 @@
+#!/bin/sh
+
+test_description='log can show previous branch using shorthand - for @{-1}'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit first &&
+	test_commit second &&
+	test_commit third &&
+	test_commit fourth &&
+	test_commit fifth &&
+	test_commit sixth &&
+	test_commit seventh
+'
+
+test_expect_success '"log -" should not work initially' '
+	test_must_fail git log -
+'
+
+test_expect_success 'setup branches for testing' '
+	git checkout -b testing-1 master^ &&
+	git checkout -b testing-2 master~2 &&
+	git checkout master
+'
+
+test_expect_success '"log -" should work' '
+	git log testing-2 >expect &&
+	git log - >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'symmetric revision range should work when one end is left empty' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log ...@{-1} >expect.first_empty &&
+	git log @{-1}... >expect.last_empty &&
+	git log ...- >actual.first_empty &&
+	git log -... >actual.last_empty &&
+	test_cmp expect.first_empty actual.first_empty &&
+	test_cmp expect.last_empty actual.last_empty
+'
+
+test_expect_success 'asymmetric revision range should work when one end is left empty' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log ..@{-1} >expect.first_empty &&
+	git log @{-1}.. >expect.last_empty &&
+	git log ..- >actual.first_empty &&
+	git log -.. >actual.last_empty &&
+	test_cmp expect.first_empty actual.first_empty &&
+	test_cmp expect.last_empty actual.last_empty
+'
+
+test_expect_success 'symmetric revision range should work when both ends are given' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log -...testing-1 >expect &&
+	git log testing-2...testing-1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'asymmetric revision range should work when both ends are given' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log -..testing-1 >expect &&
+	git log testing-2..testing-1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'multiple separate arguments should be handled properly' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log - - >expect.1 &&
+	git log @{-1} @{-1} >actual.1 &&
+	git log - HEAD >expect.2 &&
+	git log @{-1} HEAD >actual.2 &&
+	test_cmp expect.1 actual.1 &&
+	test_cmp expect.2 actual.2
+'
+
+test_expect_success 'revision ranges with same start and end should be empty' '
+	git checkout testing-2 &&
+	git checkout master &&
+	test 0 -eq $(git log -...- | wc -l) &&
+	test 0 -eq $(git log -..- | wc -l)
+'
+
+test_expect_success 'suffixes to - should work' '
+	git checkout testing-2 &&
+	git checkout master &&
+	git log -~ >expect.1 &&
+	git log @{-1}~ >actual.1 &&
+	git log -~2 >expect.2 &&
+	git log @{-1}~2 >actual.2 &&
+	git log -^ >expect.3 &&
+	git log @{-1}^ >actual.3 &&
+	# git log -@{yesterday} >expect.4 &&
+	# git log @{-1}@{yesterday} >actual.4 &&
+	test_cmp expect.1 actual.1 &&
+	test_cmp expect.2 actual.2 &&
+	test_cmp expect.3 actual.3
+	# test_cmp expect.4 actual.4
+'
+
+test_done