releng: automatically figure out if we should tag latest for docker

For example, when releasing from release-2.90, if `main` has a 2.91 tag
ancestor, we know that 2.91 was released, so we should *not* tag latest.

Change-Id: Ia56b17a2ee03bbec74b7c271c742858c690d450d

releng/__init__.py

@@ -11,6 +11,7 @@ from . import version
 from . import cli
 from . import docker
 from . import docker_assemble
+from . import gitutils
 
 rootLogger = logging.getLogger()
 rootLogger.setLevel(logging.DEBUG)
@@ -35,3 +36,4 @@ def reload():
     importlib.reload(cli)
     importlib.reload(docker)
     importlib.reload(docker_assemble)
+    importlib.reload(gitutils)

releng/create_release.xsh

@@ -11,6 +11,7 @@ from .environment import RelengEnvironment
 from . import keys
 from . import docker
 from .version import VERSION, RELEASE_NAME, MAJOR
+from .gitutils import verify_are_on_tag, git_preconditions
 
 $RAISE_SUBPROC_ERROR = True
 $XONSH_SHOW_TRACEBACK = True
@@ -38,15 +39,6 @@ def setup_creds(env: RelengEnvironment):
     $AWS_ENDPOINT_URL = environment.S3_ENDPOINT
 
 
-def git_preconditions():
-    # verify there is nothing in index ready to stage
-    proc = !(git diff-index --quiet --cached HEAD --)
-    assert proc.rtn == 0
-    # verify there is nothing *stageable* and tracked
-    proc = !(git diff-files --quiet)
-    assert proc.rtn == 0
-
-
 def official_release_commit_tag(force_tag=False):
     print('[+] Setting officialRelease in flake.nix and tagging')
     prev_branch = $(git symbolic-ref --short HEAD).strip()
@@ -240,11 +232,6 @@ def prepare_release_notes():
     git commit -m @(commit_msg)
 
 
-def verify_are_on_tag():
-    current_tag = $(git describe --tag).strip()
-    assert current_tag == VERSION
-
-
 def upload_artifacts(env: RelengEnvironment, noconfirm=False, no_check_git=False, force_push_tag=False):
     if not no_check_git:
         verify_are_on_tag()

releng/environment.py

@@ -64,7 +64,7 @@ STAGING = RelengEnvironment(
     releases_bucket='s3://staging-releases',
     git_repo='ssh://git@git.lix.systems/lix-project/lix-releng-staging',
     docker_targets=[
-        # FIXME: how do we make sure that latest gets the latest of the *most recent* branch?
+        # latest will be auto tagged if appropriate
         DockerTarget('git.lix.systems/lix-project/lix-releng-staging',
                      tags=['{version}', '{major}']),
         DockerTarget('ghcr.io/lix-project/lix-releng-staging',

releng/gitutils.xsh

@@ -0,0 +1,37 @@
+import subprocess
+import json
+
+
+def version_compare(v1: str, v2: str):
+    return json.loads($(nix-instantiate --eval --json --argstr v1 @(v1) --argstr v2 @(v2) --expr '{v1, v2}: builtins.compareVersions v1 v2'))
+
+
+def latest_tag_on_branch(branch: str) -> str:
+    return $(git describe --abbrev=0 @(branch) e>/dev/null).strip()
+
+
+def is_maintenance_branch(branch: str) -> bool:
+    try:
+        main_tag = latest_tag_on_branch('main')
+        current_tag = latest_tag_on_branch(branch)
+
+        return version_compare(current_tag, main_tag) < 0
+    except subprocess.CalledProcessError:
+        # This is the case before Lix releases 2.90, since main *has* no
+        # release tag on it.
+        # FIXME: delete this case after 2.91
+        return False
+
+
+def verify_are_on_tag():
+    current_tag = $(git describe --tag).strip()
+    assert current_tag == VERSION
+
+
+def git_preconditions():
+    # verify there is nothing in index ready to stage
+    proc = !(git diff-index --quiet --cached HEAD --)
+    assert proc.rtn == 0
+    # verify there is nothing *stageable* and tracked
+    proc = !(git diff-files --quiet)
+    assert proc.rtn == 0