introduce commit_in_branch.py script to help devs figure this out

It's been pointed out to me that determining whether a commit is present
in a stable branch is non-trivial (cherry-picks are a pain to search for)
and the commands are hard to remember, making it too much to ask.

This script aims to solve that problem; at its simplest form, it only
takes a commit and a branch and tells the user whether that commit
predates the branch, was cherry-picked to it, or is not present in any
form in the branch.

    $ bin/commit_in_branch.py e58a10af64 fdo/20.1
    Commit e58a10af64 is in branch 20.1
    $ echo $?
    0

    $ bin/commit_in_branch.py dd2bd68fa6 fdo/20.1
    Commit dd2bd68fa6 was backported to branch 20.1 as commit d043d24654c851f0be57dbbf48274b5373dea42b
    $ echo $?
    0

    $ bin/commit_in_branch.py master fdo/20.1
    Commit 2fbcfe170bf50fcbcd2fc70a564a4d69096d968c is NOT in branch 20.1
    $ echo $?
    1

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5306>

bin/commit_in_branch_test.py

@@ -0,0 +1,116 @@
+import argparse
+import pytest  # type: ignore
+import subprocess
+
+from .commit_in_branch import (
+    is_commit_valid,
+    branch_has_commit,
+    branch_has_backport_of_commit,
+    canonicalize_commit,
+    validate_branch,
+)
+
+
+def get_upstream() -> str:
+    # Let's assume master is bound to the upstream remote and not a fork
+    out = subprocess.check_output(['git', 'for-each-ref',
+                                   '--format=%(upstream)',
+                                   'refs/heads/master'],
+                                  stderr=subprocess.DEVNULL)
+    return out.decode().strip().split('/')[2]
+
+
+@pytest.mark.parametrize(
+    'commit, expected',
+    [
+        ('20.1-branchpoint', True),
+        ('master', True),
+        ('e58a10af640ba58b6001f5c5ad750b782547da76', True),
+        ('d043d24654c851f0be57dbbf48274b5373dea42b', True),
+        ('dd2bd68fa69124c86cd008b256d06f44fab8e6cd', True),
+        ('0000000000000000000000000000000000000000', False),
+        ('not-even-a-valid-commit-format', False),
+    ])
+def test_canonicalize_commit(commit: str, expected: bool) -> None:
+    if expected:
+        assert canonicalize_commit(commit)
+    else:
+        try:
+            assert canonicalize_commit(commit)
+        except argparse.ArgumentTypeError:
+            return
+        assert False
+
+
+@pytest.mark.parametrize(
+    'commit, expected',
+    [
+        (get_upstream() + '/20.1', True),
+        (get_upstream() + '/master', True),
+        ('20.1', False),
+        ('master', False),
+        ('e58a10af640ba58b6001f5c5ad750b782547da76', False),
+        ('d043d24654c851f0be57dbbf48274b5373dea42b', False),
+        ('dd2bd68fa69124c86cd008b256d06f44fab8e6cd', False),
+        ('0000000000000000000000000000000000000000', False),
+        ('not-even-a-valid-commit-format', False),
+    ])
+def test_validate_branch(commit: str, expected: bool) -> None:
+    if expected:
+        assert validate_branch(commit)
+    else:
+        try:
+            assert validate_branch(commit)
+        except argparse.ArgumentTypeError:
+            return
+        assert False
+
+
+@pytest.mark.parametrize(
+    'commit, expected',
+    [
+        ('master', True),
+        ('20.1-branchpoint', True),
+        ('20.1', False),
+        (get_upstream() + '/20.1', True),
+        ('e58a10af640ba58b6001f5c5ad750b782547da76', True),
+        ('d043d24654c851f0be57dbbf48274b5373dea42b', True),
+        ('dd2bd68fa69124c86cd008b256d06f44fab8e6cd', True),
+        ('0000000000000000000000000000000000000000', False),
+        ('not-even-a-valid-commit-format', False),
+    ])
+def test_is_commit_valid(commit: str, expected: bool) -> None:
+    assert is_commit_valid(commit) == expected
+
+
+@pytest.mark.parametrize(
+    'branch, commit, expected',
+    [
+        ('20.1', '20.1-branchpoint', True),
+        ('20.1', '20.0', False),
+        ('20.1', 'master', False),
+        ('20.1', 'e58a10af640ba58b6001f5c5ad750b782547da76', True),
+        ('20.1', 'd043d24654c851f0be57dbbf48274b5373dea42b', True),
+        ('20.1', 'dd2bd68fa69124c86cd008b256d06f44fab8e6cd', False),
+        ('master', 'dd2bd68fa69124c86cd008b256d06f44fab8e6cd', True),
+        ('20.0', 'd043d24654c851f0be57dbbf48274b5373dea42b', False),
+    ])
+def test_branch_has_commit(branch: str, commit: str, expected: bool) -> None:
+    upstream = get_upstream()
+    assert branch_has_commit(upstream, branch, commit) == expected
+
+
+@pytest.mark.parametrize(
+    'branch, commit, expected',
+    [
+        ('20.1', 'dd2bd68fa69124c86cd008b256d06f44fab8e6cd', 'd043d24654c851f0be57dbbf48274b5373dea42b'),
+        ('20.1', '20.1-branchpoint', ''),
+        ('20.1', '20.0', ''),
+        ('20.1', '20.2', ''),
+        ('20.1', 'master', ''),
+        ('20.1', 'd043d24654c851f0be57dbbf48274b5373dea42b', ''),
+        ('20.0', 'dd2bd68fa69124c86cd008b256d06f44fab8e6cd', ''),
+    ])
+def test_branch_has_backport_of_commit(branch: str, commit: str, expected: bool) -> None:
+    upstream = get_upstream()
+    assert branch_has_backport_of_commit(upstream, branch, commit) == expected