ARROW-8097: [Dev] Comment bot's crossbow command acts on the master b…

…ranch

It changes the previous behavior to clone the repository and branch referenced by the pull request as arrow and execute its crossbow command with its configuration files.

Closes #6599 from kszucs/ARROW-8097 and squashes the following commits:

1947547 <Krisztián Szűcs> use the crossbow.py from the PR
7868d39 <Krisztián Szűcs> move into the context mngr
7cbb683 <Krisztián Szűcs> use clone_url instead of the url referencing the api endpoint
b08caee <Krisztián Szűcs> clone arrow again with the PR's reference

Authored-by: Krisztián Szűcs <szucs.krisztian@gmail.com>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>

.github/workflows/comment_bot.yml

@@ -26,19 +26,14 @@ on:
 
 jobs:
 
-  debug:
-    name: Debug
+  listen:
+    name: Listen!
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Arrow
         uses: actions/checkout@v2
         with:
           path: arrow
-      # in order to generate version number based on git we need the tags
-      # fetched but checkout@v2 doesn't do that by default
-      - name: Featch Arrow tags
-        working-directory: arrow
-        run: git fetch --depth=1 origin +refs/tags/*:refs/tags/*
       # because libgit2 is a dependency of crossbow so prefer conda
       - name: Setup Conda
         uses: s-weigand/setup-conda@v1

dev/archery/archery/bot.py

@@ -19,6 +19,7 @@
 import shlex
 from pathlib import Path
 from functools import partial
+import tempfile
 
 import click
 import github
@@ -258,20 +259,34 @@ def submit(obj, task, group, dry_run):
 
     See groups defined in arrow/dev/tasks/tests.yml
     """
+    git = Git()
+
+    # construct crossbow arguments
     args = []
     for g in group:
         args.extend(['-g', g])
     for t in task:
         args.append(t)
 
-    # clone crossbow
-    git = Git()
-    git.clone('https://github.com/{}'.format(obj['crossbow_repo']), 'crossbow')
+    # pygithub pull request object
+    pr = obj['pull']
+    crossbow_url = 'https://github.com/{}'.format(obj['crossbow_repo'])
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        tmpdir = Path(tmpdir)
+        arrow = tmpdir / 'arrow'
+        queue = tmpdir / 'crossbow'
+
+        # clone arrow, crossbow and checkout the pull request's branch
+        git.clone('--branch', pr.head.ref, pr.head.repo.clone_url, str(arrow))
+        git.clone(crossbow_url, str(queue))
 
-    # submit the crossbow tasks
-    result = Path('result.yml').resolve()
-    xbow = Crossbow('arrow/dev/tasks/crossbow.py')
-    xbow.run('--output-file', str(result), 'submit', *args)
+        # submit the crossbow tasks
+        result = Path('result.yml').resolve()
+        xbow = Crossbow(str(arrow / 'dev' / 'tasks' / 'crossbow.py'))
+        xbow.run('--queue-path', str(queue),
+                 '--output-file', str(result),
+                 'submit', *args)
 
     # parse the result yml describing the submitted job
     yaml = YAML()
@@ -283,4 +298,4 @@ def submit(obj, task, group, dry_run):
     response = formatter.render(job)
 
     # send the response
-    obj['pull'].create_issue_comment(response)
+    pr.create_issue_comment(response)