object-name tests: add tests for ambiguous object blind spots

Extend the tests for ambiguous objects to check how we handle objects
where we return OBJ_BAD when trying to parse them. As noted in [1] we
have a blindspot when it comes to this behavior.

Since we need to add new test data here let's extend these tests to be
tested under SHA-256, in d7a2fc8 (t1512: skip test if not using
SHA-1, 2018-05-13) all of the existing tests were skipped, as they
rely on specific SHA-1 object IDs.

For these tests it only matters that the first 4 characters of the OID
prefix are the same for both SHA-1 and SHA-256. This uses strings that
I mined, and have the same prefix when hashed with both.

We "test_cmp" the full output to guard against any future regressions,
and because a subsequent commit will tweak it. Showing a diff of how
the output changes is helpful to explain those subsequent commits.

The "sed" invocation in test_cmp_failed_rev_parse() doesn't need a
"/g" because under both SHA-1 and SHA-256 we'll wildcard match any
trailing part of the OID after our known starting prefix. We'd like to
convert all of that to just "..." for the "test_cmp" which follows.

1. https://lore.kernel.org/git/[email protected]/

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t1512-rev-parse-disambiguation.sh

@@ -25,6 +25,88 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 . ./test-lib.sh
 
+test_cmp_failed_rev_parse () {
+	dir=$1
+	rev=$2
+
+	cat >expect &&
+	test_must_fail git -C "$dir" rev-parse "$rev" 2>actual.raw &&
+	sed "s/\($rev\)[0-9a-f]*/\1.../" <actual.raw >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'ambiguous blob output' '
+	git init --bare blob.prefix &&
+	(
+		cd blob.prefix &&
+
+		# Both start with "dead..", under both SHA-1 and SHA-256
+		echo brocdnra | git hash-object -w --stdin &&
+		echo brigddsv | git hash-object -w --stdin &&
+
+		# Both start with "beef.."
+		echo 1agllotbh | git hash-object -w --stdin &&
+		echo 1bbfctrkc | git hash-object -w --stdin
+	) &&
+
+	test_must_fail git -C blob.prefix rev-parse dead &&
+	test_cmp_failed_rev_parse blob.prefix beef <<-\EOF
+	error: short object ID beef... is ambiguous
+	hint: The candidates are:
+	hint:   beef... blob
+	hint:   beef... blob
+	fatal: ambiguous argument '\''beef...'\'': unknown revision or path not in the working tree.
+	Use '\''--'\'' to separate paths from revisions, like this:
+	'\''git <command> [<revision>...] -- [<file>...]'\''
+	EOF
+'
+
+test_expect_success 'ambiguous loose bad object parsed as OBJ_BAD' '
+	git init --bare blob.bad &&
+	(
+		cd blob.bad &&
+
+		# Both have the prefix "bad0"
+		echo xyzfaowcoh | git hash-object -t bad -w --stdin --literally &&
+		echo xyzhjpyvwl | git hash-object -t bad -w --stdin --literally
+	) &&
+
+	test_cmp_failed_rev_parse blob.bad bad0 <<-\EOF
+	error: short object ID bad0... is ambiguous
+	hint: The candidates are:
+	fatal: invalid object type
+	EOF
+'
+
+test_expect_success POSIXPERM 'ambigous zlib corrupt loose blob' '
+	git init --bare blob.corrupt &&
+	(
+		cd blob.corrupt &&
+
+		# Both have the prefix "cafe"
+		echo bnkxmdwz | git hash-object -w --stdin &&
+		oid=$(echo bmwsjxzi | git hash-object -w --stdin) &&
+
+		oidf=objects/$(test_oid_to_path "$oid") &&
+		chmod 755 $oidf &&
+		echo broken >$oidf
+	) &&
+
+	test_cmp_failed_rev_parse blob.corrupt cafe <<-\EOF
+	error: short object ID cafe... is ambiguous
+	hint: The candidates are:
+	error: inflate: data stream error (incorrect header check)
+	error: unable to unpack cafe... header
+	error: inflate: data stream error (incorrect header check)
+	error: unable to unpack cafe... header
+	hint:   cafe... unknown type
+	hint:   cafe... blob
+	fatal: ambiguous argument '\''cafe...'\'': unknown revision or path not in the working tree.
+	Use '\''--'\'' to separate paths from revisions, like this:
+	'\''git <command> [<revision>...] -- [<file>...]'\''
+	EOF
+'
+
 if ! test_have_prereq SHA1
 then
 	skip_all='not using SHA-1 for objects'