upload: Split populate reviews into 2 phases

This sets the function up to allow arbitrary topic
order in the future.

The first pass handles finding the relative topic, but
does not assume it's already populated. The second pass
needs to assume that the relative is already populated
since it uses it, so it needs to be done in topological
order (which is a followup pr).

revup/topic_stack.py

@@ -513,13 +513,43 @@ async def populate_reviews(
 
             if relative_topic:
                 topic.relative_topic = self.topics[relative_topic]
+
+            if labels is not None:
+                topic.tags[TAG_LABEL].update([label.lower() for label in labels.split(",")])
+
+            if user_aliases is not None:
+                for mapping in user_aliases.split(","):
+                    # Map usernames from alias -> user_target
+                    alias, _, user_target = mapping.partition(":")
+                    for tag in [TAG_REVIEWER, TAG_ASSIGNEE]:
+                        if alias in topic.tags[tag]:
+                            topic.tags[tag].remove(alias)
+                            topic.tags[tag].add(user_target)
+
+            if auto_add_users in ("r2a", "both"):
+                topic.tags[TAG_ASSIGNEE].update(topic.tags[TAG_REVIEWER])
+            if auto_add_users in ("a2r", "both"):
+                topic.tags[TAG_REVIEWER].update(topic.tags[TAG_ASSIGNEE])
+
+            seen_topics[name] = topic
+
+        if limit_topics:
+            for name in limit_topics:
+                if name not in self.topics:
+                    logging.warning(f"Couldn't find any topic named {name}")
+
+        await self.populate_relative_reviews(uploader)
+
+    async def populate_relative_reviews(self, uploader: str) -> None:
+        for name, topic in list(self.topics.items()):
+            if topic.relative_topic:
                 if len(topic.tags[TAG_BRANCH]) == 0:
                     topic.tags[TAG_BRANCH].update(topic.relative_topic.tags[TAG_BRANCH])
                 elif not topic.tags[TAG_BRANCH].issubset(topic.relative_topic.tags[TAG_BRANCH]):
                     raise RevupUsageException(
                         f"Topic {name} has branches"
                         f" {topic.tags[TAG_BRANCH] - topic.relative_topic.tags[TAG_BRANCH]} not in"
-                        f" relative topic {relative_topic}"
+                        f" relative topic {topic.relative_topic.name}"
                     )
 
                 if len(topic.tags[TAG_RELATIVE_BRANCH]) == 0:
@@ -531,8 +561,8 @@ async def populate_reviews(
                     != topic.relative_topic.tags[TAG_RELATIVE_BRANCH]
                 ):
                     raise RevupUsageException(
-                        f"Topic {name} and relative topic {relative_topic} have differing relative "
-                        f"branches, {topic.tags[TAG_RELATIVE_BRANCH]} vs "
+                        f"Topic {name} and relative topic {topic.relative_topic.name} have "
+                        f"differing relative branches, {topic.tags[TAG_RELATIVE_BRANCH]} vs "
                         f"{topic.relative_topic.tags[TAG_RELATIVE_BRANCH]}"
                     )
             else:
@@ -571,7 +601,7 @@ async def populate_reviews(
             ):
                 raise RevupUsageException(
                     f"Topic {name} has uploader '{topic.tags[TAG_UPLOADER]}' while relative topic"
-                    f" {relative_topic} has uploader"
+                    f" {topic.relative_topic.name} has uploader"
                     f" {topic.relative_topic.tags[TAG_UPLOADER] or '{}'}"
                 )
             topic_uploader = min(topic.tags[TAG_UPLOADER]) if topic.tags[TAG_UPLOADER] else uploader
@@ -583,18 +613,6 @@ async def populate_reviews(
                     if extra_label:
                         topic.tags[TAG_LABEL].add(extra_label.lower())
 
-            if labels is not None:
-                topic.tags[TAG_LABEL].update([label.lower() for label in labels.split(",")])
-
-            if user_aliases is not None:
-                for mapping in user_aliases.split(","):
-                    # Map usernames from alias -> user_target
-                    alias, _, user_target = mapping.partition(":")
-                    for tag in [TAG_REVIEWER, TAG_ASSIGNEE]:
-                        if alias in topic.tags[tag]:
-                            topic.tags[tag].remove(alias)
-                            topic.tags[tag].add(user_target)
-
             for branch in topic.tags[TAG_BRANCH]:
                 review = Review(topic)
                 # Track whether we need to query for the relative pr
@@ -628,18 +646,6 @@ async def populate_reviews(
             # Don't add draft as a label since its instead used to mark a pr as a draft
             topic.tags[TAG_LABEL].discard("draft")
 
-            if auto_add_users in ("r2a", "both"):
-                topic.tags[TAG_ASSIGNEE].update(topic.tags[TAG_REVIEWER])
-            if auto_add_users in ("a2r", "both"):
-                topic.tags[TAG_REVIEWER].update(topic.tags[TAG_ASSIGNEE])
-
-            seen_topics[name] = topic
-
-        if limit_topics:
-            for name in limit_topics:
-                if name not in self.topics:
-                    logging.warning(f"Couldn't find any topic named {name}")
-
     async def mark_rebases(self, skip_rebase: bool) -> None:
         """
         Scan all topics and compare patch-ids to remote patch-ids. Appropriately mark any