Add conformance tests based on upstream Git

[pjbgf]

Expands the cli featureset mostly so that we can run the same test cases as git/git, ensuring that go-git's behaviour is aligned with upstream.

First test suites introduced:

t2008-checkout-subdir.sh
t5308-pack-detect-duplicates.sh

Results:

make conformance
./conformance/run.sh
Building gogit...
Refreshing /home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git from origin...
remote: Total 0 (delta 0), reused 0 (delta 0), pack-reused 0 (from 0)
HEAD is now at 29bd7ed The second batch
=== Running t2008-checkout-subdir.sh ===
Initialized empty Git repository in /home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir
expecting success of 2008.1 'setup':

	echo "base" > file0 &&
	git add file0 &&
	mkdir dir1 &&
	echo "hello" > dir1/file1 &&
	git add dir1/file1 &&
	mkdir dir2 &&
	echo "bonjour" > dir2/file2 &&
	git add dir2/file2 &&
	test_tick &&
	git commit -m "populate tree"


ok 1 - setup

expecting success of 2008.2 'remove and restore with relative path':

	(
		cd dir1 &&
		rm ../file0 &&
		git checkout HEAD -- ../file0 &&
		test "base" = "$(cat ../file0)" &&
		rm ../dir2/file2 &&
		git checkout HEAD -- ../dir2/file2 &&
		test "bonjour" = "$(cat ../dir2/file2)" &&
		rm ../file0 ./file1 &&
		git checkout HEAD -- .. &&
		test "base" = "$(cat ../file0)" &&
		test "hello" = "$(cat file1)"
	)


ok 2 - remove and restore with relative path

expecting success of 2008.3 'checkout with empty prefix':

	rm file0 &&
	git checkout HEAD -- file0 &&
	test "base" = "$(cat file0)"


ok 3 - checkout with empty prefix

expecting success of 2008.4 'checkout with simple prefix':

	rm dir1/file1 &&
	git checkout HEAD -- dir1 &&
	test "hello" = "$(cat dir1/file1)" &&
	rm dir1/file1 &&
	git checkout HEAD -- dir1/file1 &&
	test "hello" = "$(cat dir1/file1)"


ok 4 - checkout with simple prefix

expecting success of 2008.5 'checkout with complex relative path':
	(
		cd dir1 &&
		rm file1 &&
		git checkout HEAD -- ../dir1/../dir1/file1 &&
		test "hello" = "$(cat file1)"
	)

ok 5 - checkout with complex relative path

expecting success of 2008.6 'relative path outside tree should fail': test_must_fail git checkout HEAD -- ../../Makefile
Error: pathspec "../../Makefile" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
Usage:
  gogit checkout <tree-ish> -- <pathspec>...

Flags:
  -h, --help   help for checkout

pathspec "../../Makefile" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
ok 6 - relative path outside tree should fail

expecting success of 2008.7 'incorrect relative path to file should fail (1)': test_must_fail git checkout HEAD -- ../file0
Error: pathspec "../file0" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
Usage:
  gogit checkout <tree-ish> -- <pathspec>...

Flags:
  -h, --help   help for checkout

pathspec "../file0" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
ok 7 - incorrect relative path to file should fail (1)

expecting success of 2008.8 'incorrect relative path should fail (2)': ( cd dir1 && test_must_fail git checkout HEAD -- ./file0 )
Error: no matching paths in HEAD
Usage:
  gogit checkout <tree-ish> -- <pathspec>...

Flags:
  -h, --help   help for checkout

no matching paths in HEAD
ok 8 - incorrect relative path should fail (2)

expecting success of 2008.9 'incorrect relative path should fail (3)': ( cd dir1 && test_must_fail git checkout HEAD -- ../../file0 )
Error: pathspec "../../file0" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
Usage:
  gogit checkout <tree-ish> -- <pathspec>...

Flags:
  -h, --help   help for checkout

pathspec "../../file0" is outside worktree "/home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t2008-checkout-subdir"
ok 9 - incorrect relative path should fail (3)

# passed all 9 test(s)
1..9
=== Running t5308-pack-detect-duplicates.sh ===
Initialized empty Git repository in /home/coder/git/tasks/conformance-tests/go-git-cli/conformance/.cache/git/t/trash directory.t5308-pack-detect-duplicates
expecting success of 5308.1 'setup':
	test_oid_cache <<-EOF
	lo_oid sha1:e68fe8129b546b101aee9510c5328e7f21ca1d18
	lo_oid sha256:471819e8c52bf11513f100b2810a8aa0622d5cd3d1c913758a071dd4b3bad8fe

	missing_oid sha1:e69d000000000000000000000000000000000000
	missing_oid sha256:4720000000000000000000000000000000000000000000000000000000000000
	EOF

ok 1 - setup

expecting success of 5308.2 'pack with no duplicates':
	create_pack no-dups.pack 1 &&
	git index-pack --stdin <no-dups.pack

ok 2 - pack with no duplicates

expecting success of 5308.3 'index-pack will allow duplicate objects by default':
	clear_packs &&
	create_pack dups.pack 100 &&
	git index-pack --stdin <dups.pack

ok 3 - index-pack will allow duplicate objects by default

expecting success of 5308.4 'create batch-check test vectors':
	cat >input <<-EOF &&
	$LO_SHA1
	$HI_SHA1
	$MISSING_SHA1
	EOF
	cat >expect <<-EOF
	$LO_SHA1 blob 2
	$HI_SHA1 blob 0
	$MISSING_SHA1 missing
	EOF

ok 4 - create batch-check test vectors

expecting success of 5308.5 'lookup in duplicated pack':
	git cat-file --batch-check <input >actual &&
	test_cmp expect actual

ok 5 - lookup in duplicated pack

expecting success of 5308.6 'index-pack can reject packs with duplicates':
	clear_packs &&
	create_pack dups.pack 2 &&
	test_must_fail git index-pack --strict --stdin <dups.pack &&
	test_expect_code 1 git cat-file -e $LO_SHA1

duplicate object e68fe8129b546b101aee9510c5328e7f21ca1d18 in pack (--strict)
ok 6 - index-pack can reject packs with duplicates

# passed all 6 test(s)
1..6

Thanks @Soph for suggesting this approach. 🙇

[Copilot]

Pull request overview

Adds a conformance-test harness that runs curated upstream git/git test scripts against gogit (go-git–backed CLI), expanding the CLI feature surface to match the needs of the first imported test suites.

Changes:

• Introduces conformance/run.sh + conformance/tests.txt and a make conformance target (with CI job + TAP artifact upload on failure).
• Adds minimal gogit commands/flags needed by the initial upstream tests (e.g., init, add, commit, checkout, cat-file, index-pack, version, --exec-path, root no-args exit behavior) plus unit tests.
• Updates go-git/go-git-fixtures (and x/net indirect) versions to support the new behavior/tests.

Reviewed changes

Copilot reviewed 23 out of 25 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
Makefile	Adds conformance target to run the harness.
go.mod	Bumps go-git/go-git-fixtures versions; updates x/net indirect.
go.sum	Updates dependency sums for the version bumps.
conformance/tests.txt	Defines curated upstream test scripts to run.
conformance/run.sh	Implements the conformance runner (build gogit, fetch upstream git tests, stub test-tool, run tests, capture TAP).
cmd/gogit/main.go	Adds root behavior for conformance (--exec-path, exit code 1 on no subcommand) and sets a version string.
cmd/gogit/main_test.go	Adds integration-style tests that execute the built gogit binary.
cmd/gogit/version.go	Adds version subcommand with --build-options output.
cmd/gogit/version_test.go	Tests version --build-options output.
cmd/gogit/init.go	Adds init command (with --template compatibility flag).
cmd/gogit/init_test.go	Tests init and ignored --template.
cmd/gogit/add.go	Adds add command.
cmd/gogit/add_test.go	Tests add behavior.
cmd/gogit/commit.go	Adds commit command with env-based identity/date handling.
cmd/gogit/commit_test.go	Tests committing with env identity values.
cmd/gogit/checkout.go	Adds checkout <tree-ish> -- <pathspec>... restore behavior and directory expansion.
cmd/gogit/checkout_test.go	Tests restoring files/dirs and pathspec escape failure.
cmd/gogit/checkout_pathspec.go	Implements pathspec resolution relative to worktree root with escape prevention.
cmd/gogit/checkout_pathspec_test.go	Unit tests for pathspec resolution.
cmd/gogit/cat-file.go	Adds cat-file -e and cat-file --batch-check.
cmd/gogit/cat-file_test.go	Tests cat-file existence and batch-check output.
cmd/gogit/index-pack.go	Adds index-pack --stdin [--strict] with duplicate detection in strict mode.
cmd/gogit/index-pack_test.go	Tests strict/non-strict behavior using constructed pack data.
.gitignore	Ignores conformance cache directory.
.github/workflows/build.yml	Adds a conformance job (matrix) and an optional go_git_ref workflow input.

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