feat: include trailers in PR body (#526)

* feat: include trailers in PR body

for the two trailers we expect merge-on-green bot to consume.

* fix: update golden log

* chore: trailers arg defaults to empty

autosynth/change_pusher.py

@@ -22,6 +22,7 @@
 
 from autosynth import git, github
 from autosynth.log import logger
+import re
 
 
 class AbstractPullRequest(ABC):
@@ -82,12 +83,13 @@ def push_changes(
         self, commit_count: int, branch: str, pr_title: str, synth_log: str = ""
     ) -> AbstractPullRequest:
         git.push_changes(branch)
+        trailers = _collect_trailers(commit_count)
 
         pr = self._gh.create_pull_request(
             self._repository,
             branch=branch,
             title=pr_title,
-            body=build_pr_body(synth_log),
+            body=build_pr_body(synth_log, trailers),
         )
 
         # args.synth_path (and api: * labels) only exist in monorepos
@@ -129,6 +131,8 @@ def push_changes(
         subprocess.check_call(["git", "checkout", branch])  # Probably redundant.
         with tempfile.NamedTemporaryFile() as message_file:
             # Collect the commit messages into a temporary file.
+            message_file.write("changes triggered by multiple versions\n\n".encode())
+            message_file.flush()
             subprocess.run(
                 ["git", "log", f"-{commit_count}", "--format=* %s%n%b"],
                 stdout=message_file,
@@ -148,7 +152,7 @@ def check_if_pr_already_exists(self, branch) -> bool:
         return self.inner_change_pusher.check_if_pr_already_exists(branch)
 
 
-def build_pr_body(synth_log: str):
+def build_pr_body(synth_log: str, trailers: str = ""):
     """Composes the pull request body with the synth_log.
 
     If synth_log is empty, then creates link to kokoro build log.
@@ -171,4 +175,43 @@ def build_pr_body(synth_log: str):
 This PR was generated using Autosynth. :rainbow:
 
 {build_log_text}
+
+{trailers}
 """.strip()
+
+
+def _collect_trailers(commit_count: int, git_dir: typing.Optional[str] = None) -> str:
+    """Collects the trailers from recent commits in the repo.
+
+    Only collects the two trailers we're interested in.
+    Arguments:
+        commit_count {int} -- Number of commits to collect trailers from.
+
+    Keyword Arguments:
+        git_dir {typing.Optional[str]} -- directory of git repo (default: {None})
+
+    Returns:
+        str -- The trailer lines from the recent commits.
+    """
+    text = subprocess.run(
+        ["git", "log", f"-{commit_count}", "--pretty=%b"],
+        universal_newlines=True,
+        check=True,
+        stdout=subprocess.PIPE,
+        cwd=git_dir,
+    ).stdout
+    return _parse_trailers(text)
+
+
+def _parse_trailers(text: str) -> str:
+    """Parses and returns trailers in the text.
+
+    Arguments:
+        text {str} -- commit body text with trailers
+
+    Returns:
+        str -- the trailer lines.
+    """
+    lines = text.splitlines()
+    trailer = re.compile(r"\s*(Source-Link:|PiperOrigin-RevId:).*")
+    return "\n".join([line for line in lines if trailer.match(line)])

tests/test_change_pusher.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from autosynth.change_pusher import build_pr_body
+from autosynth.change_pusher import build_pr_body, _parse_trailers
 from integration_tests import util
 
 
@@ -39,3 +39,36 @@ def test_build_pr_body_with_synth_log_and_kokoro_build_id():
             pr_body.find("https://source.cloud.google.com/results/invocations/42") == -1
         )
         assert pr_body.find(synth_log) > -1
+
+
+def test_build_pr_body_with_synth_trailers():
+    synth_log = "synth log"
+    pr_body = build_pr_body(synth_log, "a: b\nc: d")
+    assert pr_body.find("a: b") > -1
+    assert pr_body.find("c: d") > -1
+
+
+def test_parse_trailers():
+    text = """
+Source-Author: Google APIs <noreply@google.com>
+Source-Date: Mon Apr 13 12:05:23 2020 -0700
+Source-Repo: googleapis/googleapis
+Source-Sha: 4d61e1cb40184a7ad63ef37b1813f6608718674a
+Source-Link: https://github.com/googleapis/googleapis/commit/4d61e1cb40184a7ad63ef37b1813f6608718674a
+
+* Removing erroneous comment, a la https://github.com/googleapis/java-speech/pull/103
+PiperOrigin-RevId: 296332968
+
+Source-Author: Google APIs <noreply@google.com>
+Source-Date: Thu Feb 20 17:19:15 2020 -0800
+Source-Repo: googleapis/googleapis
+Source-Sha: 17567c4a1ef0a9b50faa87024d66f8acbb561089
+Source-Link: https://github.com/googleapis/googleapis/commit/17567c4a1ef0a9b50faa87024d66f8acbb561089
+
+* changes without context
+        autosynth cannot find the source of changes triggered by earlier changes in this
+        repository, or by version upgrades to tools such as linters.
+""".strip()
+    trailers = _parse_trailers(text)
+    golden_trailers = "Source-Link: https://github.com/googleapis/googleapis/commit/4d61e1cb40184a7ad63ef37b1813f6608718674a\nPiperOrigin-RevId: 296332968\nSource-Link: https://github.com/googleapis/googleapis/commit/17567c4a1ef0a9b50faa87024d66f8acbb561089"
+    assert trailers == golden_trailers

tests/testdata/mock-synth-golden-squash-prs.log

@@ -1,7 +1,9 @@
-commit 3c25ad4bca383a3248d5f05abc87e0e33e9dbd6d
+commit b2feb453f021a09e486919dfe79980c38125a22e
 Author: Jeffrey Rennie <rennie@google.com>
-Date:   Wed Apr 22 12:37:51 2020 -0700
+Date:   Wed May 6 09:15:08 2020 -0700
 
+    changes triggered by multiple versions
+
     * Wrote c-more to c.txt.
 
     * Wrote c to c.txt.
@@ -27,9 +29,9 @@ index 0000000..0794b8a
 +c-more
 \ No newline at end of file
 
-commit ec0d8367aa2e53f951625078ac87d432bbebd057
+commit 3a3e7a2e74a010875449e9d0df16d2a1a9d1e612
 Author: Jeffrey Rennie <rennie@google.com>
-Date:   Wed Apr 22 12:37:47 2020 -0700
+Date:   Wed May 6 09:15:04 2020 -0700
 
     Added Readme