Add BranchParameter for Force Build dialog

[slydiman]

Summary

Note urllib3 is already present in Zorg requirements.
Note GitHub has the rate limit (60 per hour) for unauthenticated API requests, so the last branch is cached for 15 minutes.

[gkistanova]

LGTM.

buildbot/osuosl/master/config/schedulers.py

 # TODO: Reconsile builders with explicitly set schedulers detection.
 
 from twisted.python import log
 
 from buildbot.plugins import schedulers, util
 
+import datetime
+import json
+import urllib3
 
 # Each scheduler listens only for those projects it is interested in.
 # Every change comes with a comms-separated list of projects it
 # affects, and we want to schedule a build if one of them is
 # at interest.
 def isProjectOfInterest(cp, projects_of_interest):
     if cp:
         changed_projects = frozenset(cp.split(','))
if builders_with_automatic_schedulers:
             log.msg(
                 "Generated release SingleBranchScheduler: {{ name='{}'".format(automatic_scheduler_name),
                 ", builderNames=", release_builders,
                 ", change_filter=", projects, " (branch: {release/*})",
                 ", treeStableTimer={}".format(treeStableTimer),
                 "}")
     return automatic_schedulers
 
+
+class BranchParameter(util.StringParameter):
+
+    def __init__(self, default=None, **kwargs):
+        super().__init__(**kwargs)
+        self._default = default
+        self._last_branch = None
+        self._timestamp = None
+
+    @property
+    def default(self):
+        if self._default:
+            return self._default
+        now = datetime.datetime.now()
+        if (self._last_branch is None or self._timestamp is None or
+            (now - self._timestamp).total_seconds() > 15*60): # 15 minutes
+            self._timestamp = now
+            http = urllib3.PoolManager(1)
+            per_page = 100 # 100 is max
+            page = 1
+            self._last_branch = "release" # default in case of the empty list
+            while True:
+                try:
+                    # https://docs.github.com/en/rest/branches/branches?apiVersion=2022-11-28#list-branches
+                    # Note GitHub has the rate limit (60 per hour) for unauthenticated API requests.
+                    resp = http.request("GET",
+                               f"https://api.github.com/repos/llvm/llvm-project/branches?per_page={per_page}&page={page}",
+                               headers={"User-Agent": "Buildbot"})
+                    if resp.status != 200:
+                        self._last_branch = "Error requesting llvm-project branches. " \
+                                            f"Got HTTP status {resp.status}, {resp.reason}"
+                    else:
+                        branches = json.loads(resp.data)
+                        if len(branches) > 0:
+                            self._last_branch = branches[-1]["name"]
+                            if len(branches) == per_page:
+                                page += 1
+                                continue
+                except Exception as e:
+                    self._last_branch = "Error requesting llvm-project branches. " + str(e)
+                break
+        return self._last_branch
+
+
 def getForceSchedulers(builders):
     # TODO: Move these settings to the configuration file.
     _repourl = "https://github.com/llvm/llvm-project"
     _branch = "main"
 
     # Walk over all builders and collect their names.
+    release_builders = [
+        builder.name for builder in builders
+        if 'release' in getattr(builder, 'tags', [])
+    ]
+
     scheduler_builders = [
         builder.name for builder in builders
+        if builder.name not in release_builders
     ]
 
     # Create the force schedulers.
+    name = ["force-build-scheduler", "force-release-build-scheduler"]
+    builderNames = [scheduler_builders, release_builders]
+    defaultBranch = [_branch, None]
     return [ schedulers.ForceScheduler(
-                name            = "force-build-scheduler",
+                name            = name[i],
                 label           = "Force Build",
                 buttonName      = "Force Build",
                 reason = util.ChoiceStringParameter(
                             name        = "reason",
                             label       = "reason:",
                             required    = True,
                             choices     = [
                                 "Build a particular revision",
                                 "Force clean build",
                                 "Narrow down blamelist",
                             ],
                             default     = "Build a particular revision"
                 ),
-                builderNames    = scheduler_builders,
+                builderNames    = builderNames[i],
                 codebases       = [
                     util.CodebaseParameter(
                         codebase    = "",
-                        branch      = util.StringParameter(
+                        branch      = BranchParameter(
                             name        = "branch",
                             label       = "branch:",
                             size        = 64,
-                            default     = _branch
+                            default     = defaultBranch[i]
                         ),
                         revision    = util.StringParameter(
                             name        = "revision",
                             label       = "revision:",
                             size        = 45,
                             default     = ''
                         ),
                         repository  = util.FixedParameter(
return [ schedulers.ForceScheduler(
                         default     = False
                     ),
                     util.BooleanParameter(
                         name        = "clean_obj",
                         label       = "Clean build directory",
                         default     = False
                     )
                 ]
-            )
+            ) for i in range(2)
         ]
 
 # TODO: Abstract this kind of scheduler better.
 def getLntSchedulers():
     _project = "lnt"
     _branch = 'master'
     _repourl = "https://github.com/llvm/llvm-lnt"
     _lnt_builders = [