Recognize PR# at end of commit title for github_pull_request_* templates

Summary:
On GitHub, commits that are squash/merged from pull requests
such as facebook/dotslash@4c0563c
commonly have the pull request number at the end of
the first line of the commit message like so:

```
Document experimental `fetch` subcommand (facebook#24)
```

This updates the logic for the various `github_pull_request_*`
templates to match this pattern.

Note this required adding `repo` as an argument to
`_parse_github_pull_request_url()` so that it could produce
a complete `PullRequestId` object even if it only had
the commit number in the commit message.

Test Plan:

Added a `FakeGitHubRepo` to `testutil.py` to make it easier
to write doctests against this new logic.

```
./tests/run-tests.py ./tests/test-doctest.py
```

I also looked for a repo that doesn't use Meta's tooling
(so it doesn't have the `Pull Request resolved` line in its commits)
and decided to test with https://github.com/google/generative-ai-docs as follows:

```
$ sl clone https://github.com/google/generative-ai-docs
$ cd generative-ai-docs
$ /home/mbolin/src/sapling/eden/scm/sl log -T '{node} {github_pull_request_number}\n' --limit 10
d216731f8ab1f2e46da37b62ada121848f1be9e9 375
bc112742515b93e718d9c417203de12fd8786f6a 374
9c91576af5a7b45885ef89858fd3b904501fbb8e 370
45cac496b9a93f4c2251dbe42b0eff71b2a47bc7 360
650a2a48c12ac09a8fe03640f257da6cfac68976 363
576a808e5110dee0d3a9b4456ab8d572c29a8905 359
35e3ae486b2dec7a09952153dda62819a5f4abf2 358
71f9451edc19de37c311906b7f3a689bcacb2bc6 352
da44a67beb8a85bda0e27eb38d5bb8ecec5b26dd 342
955e2842f720fdddb0164d168bc1379470b9b8e9 340
$ /home/mbolin/src/sapling/eden/scm/sl log -T '{node} {github_pull_request_url}\n' --limit 10
d216731f8ab1f2e46da37b62ada121848f1be9e9 https://reviewstack.dev/google/generative-ai-docs/pull/375
bc112742515b93e718d9c417203de12fd8786f6a https://reviewstack.dev/google/generative-ai-docs/pull/374
9c91576af5a7b45885ef89858fd3b904501fbb8e https://reviewstack.dev/google/generative-ai-docs/pull/370
45cac496b9a93f4c2251dbe42b0eff71b2a47bc7 https://reviewstack.dev/google/generative-ai-docs/pull/360
650a2a48c12ac09a8fe03640f257da6cfac68976 https://reviewstack.dev/google/generative-ai-docs/pull/363
576a808e5110dee0d3a9b4456ab8d572c29a8905 https://reviewstack.dev/google/generative-ai-docs/pull/359
35e3ae486b2dec7a09952153dda62819a5f4abf2 https://reviewstack.dev/google/generative-ai-docs/pull/358
71f9451edc19de37c311906b7f3a689bcacb2bc6 https://reviewstack.dev/google/generative-ai-docs/pull/352
da44a67beb8a85bda0e27eb38d5bb8ecec5b26dd https://reviewstack.dev/google/generative-ai-docs/pull/342
955e2842f720fdddb0164d168bc1379470b9b8e9 https://reviewstack.dev/google/generative-ai-docs/pull/340
```

eden/scm/sapling/ext/github/github_repo_util.py

@@ -86,6 +86,8 @@ def find_github_repo(repo) -> Result[GitHubRepo, NotGitHubRepoError]:
         test_url = os.environ.get("SL_TEST_GH_URL")
         if test_url:
             url = util.url(test_url)
+        elif hasattr(repo, "get_github_url"):
+            url = util.url(repo.get_github_url())
         else:
             url = repo.ui.paths.get("default", "default-push").url
     except AttributeError:  # ex. paths.default is not set

eden/scm/sapling/ext/github/pr_marker.py

@@ -91,7 +91,7 @@ def _get_draft_commits(repo) -> t.Dict[PullRequestId, t.Set[Node]]:
 
 def _get_pr_for_context(repo, ctx) -> t.Optional[PullRequestId]:
     store = PullRequestStore(repo)
-    return get_pull_request_for_context(store, ctx)
+    return get_pull_request_for_context(store, repo, ctx)
 
 
 def _get_landed_commits(

eden/scm/sapling/ext/github/pr_parser.py

@@ -6,12 +6,14 @@
 import re
 from typing import Optional
 
+from .github_repo_util import find_github_repo
 from .pullrequest import PullRequestId
 from .pullrequeststore import PullRequestStore
 
 
 def get_pull_request_for_context(
     store: PullRequestStore,
+    repo,
     ctx,
 ) -> Optional[PullRequestId]:
     """Returns a pull request associated with a commit context, if any. Checks
@@ -20,20 +22,55 @@ def get_pull_request_for_context(
     """
     node = ctx.node()
     pr = store.find_pull_request(node)
-    return pr if pr else _parse_github_pull_request_url(ctx.description())
+    return pr if pr else _parse_github_pull_request_url(ctx.description(), repo)
 
 
-def _parse_github_pull_request_url(descr: str) -> Optional[PullRequestId]:
+def _parse_github_pull_request_url(descr: str, repo) -> Optional[PullRequestId]:
     r"""If the commit message has a comment in a special format that indicates
     it is associated with a GitHub pull request, returns the corresponding
     PullRequestId.
 
+    Match the number at the end of the title.
+    >>> from .testutil import FakeGitHubRepo
+    >>> gh_repo = FakeGitHubRepo(name="dotslash")
+    >>> commit_msg = 'Document experimental `fetch` subcommand (#24)\nSummary:\nDocument...'
+    >>> _parse_github_pull_request_url(commit_msg, gh_repo)
+    PullRequestId(hostname='github.com', owner='facebook', name='dotslash', number=24)
+
+    Should work with a single line title.
+    >>> commit_msg = 'Document experimental `fetch` subcommand (#24)'
+    >>> _parse_github_pull_request_url(commit_msg, gh_repo)
+    PullRequestId(hostname='github.com', owner='facebook', name='dotslash', number=24)
+
+    Does not match if the pattern appears after the first line.
+    >>> commit_msg = 'TITLE\nDocument experimental `fetch` subcommand (#24)\nSummary:\nDocument...'
+    >>> _parse_github_pull_request_url(commit_msg, gh_repo) is None
+    True
+
+    Match the "Pull Request resolved" text.
     >>> descr = 'foo\nPull Request resolved: https://github.com/bolinfest/ghstack-testing/pull/71\nbar'
-    >>> _parse_github_pull_request_url(descr)
+    >>> _parse_github_pull_request_url(descr, gh_repo)
     PullRequestId(hostname='github.com', owner='bolinfest', name='ghstack-testing', number=71)
-    >>> _parse_github_pull_request_url('') is None
+
+    Test a trivial "no match" case.
+    >>> _parse_github_pull_request_url('', gh_repo) is None
     True
     """
+    # The default for "squash and merge" in the GitHub pull request flow appears
+    # to put the pull request number at the end of the first line of the commit
+    # message, so check that first.
+    match = re.search(r'^.*\(#([1-9][0-9]*)\)\r?(\n|$)', descr)
+    if match:
+        result = find_github_repo(repo)
+        if result.is_ok():
+            github_repo = result.unwrap()
+            return PullRequestId(
+                hostname=github_repo.hostname,
+                owner=github_repo.owner,
+                name=github_repo.name,
+                number=int(match.group(1)),
+            )
+
     # This is the format used by ghstack, though other variants may be supported
     # in the future.
     match = re.search(

eden/scm/sapling/ext/github/pr_status.py

@@ -44,7 +44,7 @@ def _prefetch(repo, ctx_iter):
     pr_store = PullRequestStore(repo)
     for batch in util.eachslice(ctx_iter, peek_ahead):
         cached = getattr(repo, _PR_STATUS_CACHE, {})
-        pr_list = {get_pull_request_for_context(pr_store, ctx) for ctx in batch}
+        pr_list = {get_pull_request_for_context(pr_store, repo, ctx) for ctx in batch}
 
         pr_list = [pr for pr in pr_list if pr and pr not in cached]
         if pr_list:

eden/scm/sapling/ext/github/submit.py

@@ -710,7 +710,7 @@ async def get_repo(hostname: str, owner: str, name: str) -> Repository:
 
 async def derive_commit_data(node: bytes, repo, store: PullRequestStore) -> CommitData:
     ctx = repo[node]
-    pr_id = get_pull_request_for_context(store, ctx)
+    pr_id = get_pull_request_for_context(store, repo, ctx)
     pr = await get_pull_request_details_or_throw(pr_id) if pr_id else None
     msg = None
     if pr:

eden/scm/sapling/ext/github/templates.py

@@ -69,7 +69,7 @@ def get_pull_request_url_for_rev(repo, ctx, **args) -> Optional[PullRequestId]:
         return pull_request_url
 
     store = get_pull_request_store(repo, args["cache"])
-    pull_request_url = get_pull_request_for_context(store, ctx)
+    pull_request_url = get_pull_request_for_context(store, repo, ctx)
 
     revcache[_GITHUB_PULL_REQUEST_URL_REVCACHE_KEY] = (
         pull_request_url if pull_request_url is not None else _NO_ENTRY

eden/scm/sapling/ext/github/testutil.py

@@ -6,11 +6,29 @@
 """test utilities for doctests in this folder
 """
 
+from sapling import git
+
 
 class FakeRepo:
     pass
 
 
+"""Designed to be compatible with find_github_repo()."""
+class FakeGitHubRepo:
+    def __init__(
+        self,
+        hostname: str = "github.com",
+        owner: str = "facebook",
+        name: str = "sapling",
+    ) -> None:
+        # This should be sufficient to satisfy git.isgitpeer().
+        self.storerequirements = {git.GIT_STORE_REQUIREMENT}
+        self.github_url = f"https://{hostname}/{owner}/{name}"
+
+    def get_github_url(self) -> str:
+        return self.github_url
+
+
 class FakePullRequestStore:
     def find_pull_request(self, node: bytes):
         return None