headless_api: add merge-remote action (bug 1980701)

src/lando/headless_api/api.py

@@ -5,6 +5,7 @@
 from io import StringIO
 from typing import Annotated, Literal
 
+from django.conf import settings
 from django.core.exceptions import PermissionDenied
 from django.core.handlers.wsgi import WSGIRequest
 from django.db import transaction
@@ -16,6 +17,7 @@
 from ninja.responses import codes_4xx
 from ninja.security import HttpBearer
 from pydantic import Field, TypeAdapter
+from pydantic.types import StringConstraints
 
 from lando.headless_api.models.automation_job import (
     AutomationAction,
@@ -324,13 +326,48 @@ def process(
         raise NotImplementedError()
 
 
+class MergeRemoteAction(Schema):
+    """Merge changes from a remote repository"""
+
+    action: Literal["merge-remote"]
+    commit_message: str
+    repo: str
+    commit: Annotated[str, StringConstraints(pattern="[0-9a-fA-F]{40}")]
+    allow_unrelated: bool = False
+
+    def process(
+        self, job: AutomationJob, repo: Repo, scm: AbstractSCM, index: int
+    ) -> bool:
+        if self.repo not in settings.ALLOWED_MERGE_REMOTE_REPOS:
+            raise AutomationActionException(
+                message=f"Merges from {repo} not allowed",
+                job_action=JobAction.FAIL,
+                is_fatal=True,
+            )
+        try:
+            scm.merge_remote(
+                commit_message=self.commit_message,
+                remote=self.repo,
+                commit=self.commit,
+                allow_unrelated=self.allow_unrelated,
+            )
+        except Exception as exc:
+            message = f"Aborting, could not `merge-remote`, action #{index}.\n{exc}"
+            raise AutomationActionException(
+                message=message, job_action=JobAction.FAIL, is_fatal=True
+            ) from exc
+
+        return True
+
+
 Action = (
     AddCommitAction
     | AddCommitBase64Action
     | CreateCommitAction
     | MergeOntoAction
     | AddBranchAction
     | TagAction
+    | MergeRemoteAction
 )
 
 ActionAdapter = TypeAdapter(Action)

src/lando/headless_api/migrations/0009_alter_automationaction_action_type.py

@@ -0,0 +1,27 @@
+# Generated by Django 5.2.5 on 2025-09-01 15:03
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("headless_api", "0008_alter_automationjob_requester_email"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="automationaction",
+            name="action_type",
+            field=models.CharField(
+                choices=[
+                    ("add-commit", "Add commit"),
+                    ("add-commit-base64", "Add base64 commit"),
+                    ("create-commit", "Create commit"),
+                    ("tag", "Tag"),
+                    ("merge-onto", "Merge onto"),
+                    ("merge-remote", "Merge commit from remote repository"),
+                ]
+            ),
+        ),
+    ]

src/lando/headless_api/models/automation_job.py

@@ -80,6 +80,7 @@ class ActionTypeChoices(models.TextChoices):
     CREATE_COMMIT = "create-commit", gettext_lazy("Create commit")
     TAG = "tag", gettext_lazy("Tag")
     MERGE_ONTO = "merge-onto", gettext_lazy("Merge onto")
+    MERGE_REMOTE = "merge-remote", gettext_lazy("Merge commit from remote repository")
 
 
 class AutomationAction(BaseModel):

src/lando/headless_api/tests/test_automation_api.py

@@ -10,6 +10,7 @@
 from typing import Callable
 
 import pytest
+from django.conf import settings
 from django.contrib.auth.hashers import check_password
 
 from lando.api.legacy.workers.automation_worker import AutomationWorker
@@ -1928,3 +1929,45 @@ def test_automation_job_processing(automation_job):
     assert (
         job_from_db.duration_seconds > 0
     ), "`processing` should set and save the job duration."
+
+
+@pytest.mark.django_db
+def test_automation_job_merge_remote_success_git(
+    repo_mc,
+    treestatusdouble,
+    git_automation_worker,
+    monkeypatch,
+    request,
+    automation_job,
+):
+    repo = repo_mc(SCM_TYPE_GIT)
+    scm = repo.scm
+    scm.push = mock.MagicMock()
+
+    settings.ALLOWED_MERGE_REMOTE_REPOS = [repo.path]
+
+    # Create a repo with diverging history
+    main_commit, main_file, feature_commit, feature_file = (
+        _create_split_branches_for_merge(request, scm, repo.system_path)
+    )
+
+    job, _actions = automation_job(
+        actions=[
+            {
+                "action": "merge-remote",
+                "commit_message": "No bug: Remote merge test",
+                "repo": repo.path,
+                "commit": feature_commit,
+            }
+        ],
+        status=JobStatus.SUBMITTED,
+        requester_email="test@example.com",
+        target_repo=repo,
+    )
+
+    git_automation_worker.worker_instance.applicable_repos.add(repo)
+
+    assert git_automation_worker.run_job(job)
+    assert job.status == JobStatus.LANDED, f"Job unexpectedly failed: {job.error}"
+    assert scm.push.called
+    assert len(job.landed_commit_id) == 40

src/lando/main/scm/abstract_scm.py

@@ -292,3 +292,12 @@ def tag(self, name: str, target: str | None):
 
         If `target` is `None`, use the currently checked out commit.
         """
+
+    @abstractmethod
+    def merge_remote(
+        self, commit_message: str, remote: str, commit: str, allow_unrelated: bool
+    ) -> str:
+        """Merge changes from the referenced remote and commit.
+
+        Return the SHA of the newly created merge commit.
+        """

src/lando/main/scm/git.py

@@ -716,3 +716,14 @@ def tag(self, name: str, target: str | None):
 
             # If the tag did not already exist, bubble up the exception.
             raise exc
+
+    def merge_remote(
+        self, commit_message: str, remote: str, commit: str, allow_unrelated: bool
+    ) -> str:
+        self._git_run("fetch", remote, commit, cwd=self.path)
+        merge_args = ["--no-ff", "-m", commit_message]
+        if allow_unrelated:
+            merge_args.append("--allow-unrelated-histories")
+        self._git_run("merge", *merge_args, commit, cwd=self.path)
+
+        return self.head_ref()

src/lando/main/scm/hg.py

@@ -813,3 +813,8 @@ def tag(self, name: str, target: str | None):
             tag_command.append(target)
 
         self.run_hg(tag_command)
+
+    def merge_remote(
+        self, commit_message: str, remote: str, commit: str, allow_unrelated: bool
+    ) -> str:
+        raise NotImplementedError("`merge_remote` not implemented for hg.")