workflows: Add a simple pull request subscription workflow

This new workflows will make it possible for people to subscribe to
pull requests based on the files that are being modified.  Whenever
a pull request is created, this action will look through all of
the teams whose name begins with pr-subscribers- and it will try
to match the files changed in the pull request to a comma separated
list of globs in the team's description.

One limitation of this workflow is that it only runs when a pull
request is created, so any files added in subsequent updates will
not create notifications for the appropriate teams.  This is planned
to be fixed in a future update.

Author: tstellar

.github/workflows/pr-subscriber.yml

@@ -0,0 +1,27 @@
+name: PR Subscriber
+
+on:
+  pull_request:
+    types:
+      - opened
+
+permissions:
+  contents: read
+
+jobs:
+  auto-subscribe:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup Automation Script
+        run: |
+          curl -O -L https://raw.githubusercontent.com/$GITHUB_REPOSITORY/$GITHUB_SHA/llvm/utils/git/github-automation.py
+          curl -O -L https://raw.githubusercontent.com/$GITHUB_REPOSITORY/$GITHUB_SHA/llvm/utils/git/requirements.txt
+          chmod a+x github-automation.py
+          pip install -r requirements.txt
+
+      - name: Update watchers
+        run: |
+          ./github-automation.py \
+          --token '${{ secrets.ISSUE_SUBSCRIBER_TOKEN }}' \
+          pr-subscriber \
+          --issue-number '${{ github.event.pull_request.number }}'

llvm/utils/git/github-automation.py

@@ -9,6 +9,7 @@
 # ==-------------------------------------------------------------------------==#
 
 import argparse
+import fnmatch
 from git import Repo  # type: ignore
 import github
 import os
@@ -65,6 +66,43 @@ def run(self) -> bool:
         return False
 
 
+class PRSubscriber:
+
+    class PRTeam:
+        def __init__(self, slug: str, description: str):
+            self.slug = slug
+            self.globs = [x.strip() for x in description.split(",")]
+
+    def __init__(self, token: str, repo: str, pr_number: int):
+        self.repo = github.Github(token).get_repo(repo)
+        self.org = github.Github(token).get_organization(self.repo.organization.login)
+        self.pr = self.repo.get_issue(pr_number).as_pull_request()
+        self.teams = []
+        for team in self.org.get_teams():
+            if not team.name.startswith("pr-subscribers-"):
+                continue
+            self.teams.append(PRSubscriber.PRTeam(team.slug, team.description))
+
+    def run(self) -> bool:
+        mentions = []
+        for c in self.pr.get_commits():
+            for f in c.files:
+                print(f.filename)
+            for t in self.teams:
+                for g in t.globs:
+                    if len(fnmatch.filter([f.filename for f in c.files], g)):
+                        print('Matches {} for {}'.format(g, t.slug))
+                        mentions.append(t.slug)
+                        break
+
+        if not len(mentions):
+            return False
+
+        comment = "\n".join(['@llvm/{}'.format(m) for m in mentions])
+        self.pr.as_issue().create_comment(comment)
+        return True
+
+
 def setup_llvmbot_git(git_dir="."):
     """
     Configure the git repo in `git_dir` with the llvmbot account so
@@ -506,6 +544,9 @@ def execute_command(self) -> bool:
 issue_subscriber_parser.add_argument("--label-name", type=str, required=True)
 issue_subscriber_parser.add_argument("--issue-number", type=int, required=True)
 
+pr_subscriber_parser = subparsers.add_parser("pr-subscriber")
+pr_subscriber_parser.add_argument("--issue-number", type=int, required=True)
+
 release_workflow_parser = subparsers.add_parser("release-workflow")
 release_workflow_parser.add_argument(
     "--llvm-project-dir",
@@ -551,6 +592,11 @@ def execute_command(self) -> bool:
         args.token, args.repo, args.issue_number, args.label_name
     )
     issue_subscriber.run()
+elif args.command == "pr-subscriber":
+    pr_subscriber = PRSubscriber(
+        args.token, args.repo, args.issue_number
+    )
+    pr_subscriber.run()
 elif args.command == "release-workflow":
     release_workflow = ReleaseWorkflow(
         args.token,