sha1_name.c: get_describe_name() by definition groks only commits

Teach get_describe_name() to pass the disambiguation hint down the
callchain to get_short_sha1().

Also add tests to show various syntactic elements that we could take
advantage of the object type information to help disambiguration of
abbreviated object names.  Many of them are marked as broken, and
some of them will be fixed in later patches in this series.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 257 insertions, 1 deletions

diff --git a/sha1_name.c b/sha1_name.c
index 174d3df9b3..caef6e5e62 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -603,6 +603,7 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 static int get_describe_name(const char *name, int len, unsigned char *sha1)
 {
 	const char *cp;
+	unsigned flags = GET_SHA1_QUIETLY | GET_SHA1_COMMIT;
 
 	for (cp = name + len - 1; name + 2 <= cp; cp--) {
 		char ch = *cp;
@@ -613,7 +614,7 @@ static int get_describe_name(const char *name, int len, unsigned char *sha1)
 			if (ch == 'g' && cp[-1] == '-') {
 				cp++;
 				len -= cp - name;
-				return get_short_sha1(cp, len, sha1, GET_SHA1_QUIETLY);
+				return get_short_sha1(cp, len, sha1, flags);
 			}
 		}
 	}
diff --git a/t/t1512-rev-parse-disambiguation.sh b/t/t1512-rev-parse-disambiguation.sh
new file mode 100755
index 0000000000..0d3f05b992
--- /dev/null
+++ b/t/t1512-rev-parse-disambiguation.sh
@@ -0,0 +1,255 @@
+#!/bin/sh
+
+test_description='object name disambiguation
+
+Create blobs, trees, commits and a tag that all share the same
+prefix, and make sure "git rev-parse" can take advantage of
+type information to disambiguate short object names that are
+not necessarily unique.
+
+The final history used in the test has five commits, with the bottom
+one tagged as v1.0.0.  They all have one regular file each.
+
+  +-------------------------------------------+
+  |                                           |
+  |           .-------b3wettvi---- ad2uee     |
+  |          /                   /            |
+  |  a2onsxbvj---czy8f73t--ioiley5o           |
+  |                                           |
+  +-------------------------------------------+
+
+'
+
+. ./test-lib.sh
+
+test_expect_success 'blob and tree' '
+	test_tick &&
+	(
+		for i in 0 1 2 3 4 5 6 7 8 9
+		do
+			echo $i
+		done
+		echo
+		echo b1rwzyc3
+	) >a0blgqsjc &&
+
+	# create one blob 0000000000b36
+	git add a0blgqsjc &&
+
+	# create one tree 0000000000cdc
+	git write-tree
+'
+
+test_expect_success 'warn ambiguity when no candidate matches type hint' '
+	test_must_fail git rev-parse --verify 000000000^{commit} 2>actual &&
+	grep "short SHA1 000000000 is ambiguous" actual
+'
+
+test_expect_failure 'disambiguate tree-ish' '
+	# feed tree-ish in an unambiguous way
+	git rev-parse --verify 0000000000cdc:a0blgqsjc &&
+
+	# ambiguous at the object name level, but there is only one
+	# such tree-ish (the other is a blob)
+	git rev-parse --verify 000000000:a0blgqsjc
+'
+
+test_expect_failure 'disambiguate blob' '
+	sed -e "s/|$//" >patch <<-EOF &&
+	diff --git a/frotz b/frotz
+	index 000000000..ffffff 100644
+	--- a/frotz
+	+++ b/frotz
+	@@ -10,3 +10,4 @@
+	 9
+	 |
+	 b1rwzyc3
+	+irwry
+	EOF
+	(
+		GIT_INDEX_FILE=frotz &&
+		export GIT_INDEX_FILE &&
+		git apply --build-fake-ancestor frotz patch &&
+		git cat-file blob :frotz >actual
+	) &&
+	test_cmp a0blgqsjc actual
+'
+
+test_expect_failure 'disambiguate tree' '
+	commit=$(echo "d7xm" | git commit-tree 000000000) &&
+	test $(git rev-parse $commit^{tree}) = $(git rev-parse 0000000000cdc)
+'
+
+test_expect_success 'first commit' '
+	# create one commit 0000000000e4f
+	git commit -m a2onsxbvj
+'
+
+test_expect_failure 'disambiguate commit-ish' '
+	# feed commit-ish in an unambiguous way
+	git rev-parse --verify 0000000000e4f^{commit} &&
+
+	# ambiguous at the object name level, but there is only one
+	# such commit (the others are tree and blob)
+	git rev-parse --verify 000000000^{commit} &&
+
+	# likewise
+	git rev-parse --verify 000000000^0
+'
+
+test_expect_failure 'disambiguate commit' '
+	commit=$(echo "j9xqh" | git commit-tree 0000000000cdc -p 000000000) &&
+	test $(git rev-parse $commit^) = $(git rev-parse 0000000000e4f)
+'
+
+test_expect_failure 'log name1..name2 takes only commit-ishes on both ends' '
+	git log 000000000..000000000 &&
+	git log ..000000000 &&
+	git log 000000000.. &&
+	git log 000000000...000000000 &&
+	git log ...000000000 &&
+	git log 000000000...
+'
+
+test_expect_failure 'rev-parse name1..name2 takes only commit-ishes on both ends' '
+	git rev-parse 000000000..000000000 &&
+	git rev-parse ..000000000 &&
+	git rev-parse 000000000..
+'
+
+test_expect_failure 'git log takes only commit-ish' '
+	git log 000000000
+'
+
+test_expect_failure 'git reset takes only commit-ish' '
+	git reset 000000000
+'
+
+test_expect_success 'first tag' '
+	# create one tag 0000000000f8f
+	git tag -a -m j7cp83um v1.0.0
+'
+
+test_expect_failure 'two semi-ambiguous commit-ish' '
+	# Once the parser becomes ultra-smart, it could notice that
+	# 110282 before ^{commit} name many different objects, but
+	# that only two (HEAD and v1.0.0 tag) can be peeled to commit,
+	# and that peeling them down to commit yield the same commit
+	# without ambiguity.
+	git rev-parse --verify 110282^{commit} &&
+
+	# likewise
+	git log 000000000..000000000 &&
+	git log ..000000000 &&
+	git log 000000000.. &&
+	git log 000000000...000000000 &&
+	git log ...000000000 &&
+	git log 000000000...
+'
+
+test_expect_failure 'three semi-ambiguous tree-ish' '
+	# Likewise for tree-ish.  HEAD, v1.0.0 and HEAD^{tree} share
+	# the prefix but peeling them to tree yields the same thing
+	git rev-parse --verify 000000000^{tree}
+'
+
+test_expect_success 'parse describe name' '
+	# feed an unambiguous describe name
+	git rev-parse --verify v1.0.0-0-g0000000000e4f &&
+
+	# ambiguous at the object name level, but there is only one
+	# such commit (others are blob, tree and tag)
+	git rev-parse --verify v1.0.0-0-g000000000
+'
+
+test_expect_success 'more history' '
+	# commit 0000000000043
+	git mv a0blgqsjc d12cr3h8t &&
+	echo h62xsjeu >>d12cr3h8t &&
+	git add d12cr3h8t &&
+
+	test_tick &&
+	git commit -m czy8f73t &&
+
+	# commit 00000000008ec
+	git mv d12cr3h8t j000jmpzn &&
+	echo j08bekfvt >>j000jmpzn &&
+	git add j000jmpzn &&
+
+	test_tick &&
+	git commit -m ioiley5o &&
+
+	# commit 0000000005b0
+	git checkout v1.0.0^0 &&
+	git mv a0blgqsjc f5518nwu &&
+
+	for i in h62xsjeu j08bekfvt kg7xflhm
+	do
+		echo $i
+	done >>f5518nwu &&
+	git add f5518nwu &&
+
+	test_tick &&
+	git commit -m b3wettvi &&
+	side=$(git rev-parse HEAD) &&
+
+	# commit 000000000066
+	git checkout master &&
+
+	# If you use recursive, merge will fail and you will need to
+	# clean up a0blgqsjc as well.  If you use resolve, merge will
+	# succeed.
+	test_might_fail git merge --no-commit -s recursive $side &&
+	git rm -f f5518nwu j000jmpzn &&
+
+	test_might_fail git rm -f a0blgqsjc &&
+	(
+		git cat-file blob $side:f5518nwu
+		echo j3l0i9s6
+	) >ab2gs879 &&
+	git add ab2gs879 &&
+
+	test_tick &&
+	git commit -m ad2uee
+
+'
+
+test_expect_failure 'parse describe name taking advantage of generation' '
+	# ambiguous at the object name level, but there is only one
+	# such commit at generation 0
+	git rev-parse --verify v1.0.0-0-g000000000 &&
+
+	# likewise for generation 2 and 4
+	git rev-parse --verify v1.0.0-2-g000000000 &&
+	git rev-parse --verify v1.0.0-4-g000000000
+'
+
+# Note: because rev-parse does not even try to disambiguate based on
+# the generation number, this test currently succeeds for a wrong
+# reason.  When it learns to use the generation number, the previous
+# test should succeed, and also this test should fail because the
+# describe name used in the test with generation number can name two
+# commits.  Make sure that such a future enhancement does not randomly
+# pick one.
+test_expect_success 'parse describe name not ignoring ambiguity' '
+	# ambiguous at the object name level, and there are two such
+	# commits at generation 1
+	test_must_fail git rev-parse --verify v1.0.0-1-g000000000
+'
+
+test_expect_success 'ambiguous commit-ish' '
+	# Now there are many commits that begin with the
+	# common prefix, none of these should pick one at
+	# random.  They all should result in ambiguity errors.
+	test_must_fail git rev-parse --verify 110282^{commit} &&
+
+	# likewise
+	test_must_fail git log 000000000..000000000 &&
+	test_must_fail git log ..000000000 &&
+	test_must_fail git log 000000000.. &&
+	test_must_fail git log 000000000...000000000 &&
+	test_must_fail git log ...000000000 &&
+	test_must_fail git log 000000000...
+'
+
+test_done