support generating notes of merged PRs with rebase (MystenLabs#18458)

## Description 

When merging a PR, we can either use `squashed` or `rebase`.
Before, our release note script supports `squashed` commit only, this
change will add support to `rebase` PR as well.
The downside of this is it might take a bit longer to run given that
we'll need to send a HTTP request to Github API if it's not a squashed
commit. But given this script won't be run more than once a week, it's a
good tradeoff.

## Test plan 

`GITHUB_TOKEN=<my_PAT> python ./scripts/release_notes.py generate
9e2be6a
1428c71`
(all the release notes from `releases/sui-v1.27.0-release` to
`releases/sui-v1.28.0-release` branch) now shows @bmwill 's
MystenLabs#18099

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

scripts/release_notes.py

@@ -10,6 +10,7 @@
 import subprocess
 import sys
 from typing import NamedTuple
+import urllib.request
 
 RE_NUM = re.compile("[0-9_]+")
 
@@ -60,10 +61,12 @@
     "Rust SDK",
 ]
 
+
 class Note(NamedTuple):
     checked: bool
     note: str
 
+
 def parse_args():
     """Parse command line arguments."""
 
@@ -116,7 +119,24 @@ def git(*args):
     return subprocess.check_output(["git"] + list(args)).decode().strip()
 
 
-def extract_notes(commit):
+def extract_notes_from_rebase_commit(commit):
+    # we'll need to go one level deeper to find the PR number
+    url = f"https://api.github.com/repos/MystenLabs/sui/commits/{commit}/pulls"
+    headers = {
+        "Accept": "application/vnd.github.v3+json",
+        "Authorization": f"token {os.environ['GITHUB_TOKEN']}",
+    }
+    req = urllib.request.Request(url, headers=headers)
+    with urllib.request.urlopen(req) as response:
+        data = json.load(response)
+        if len(data) == 0:
+            return None, ""
+        pr_number = data[0]["number"]
+        pr_notes = data[0]["body"] if data[0]["body"] else ""
+        return pr_number, pr_notes
+
+
+def extract_notes(commit, seen):
     """Get release notes from a commit message.
 
     Find the 'Release notes' section in the commit message, and
@@ -130,19 +150,29 @@ def extract_notes(commit):
     """
     message = git("show", "-s", "--format=%B", commit)
 
-    # Extract PR number
+    # Extract PR number from squashed commits
     match = RE_PR.match(message)
     pr = match.group(1) if match else None
+
     result = {}
 
-    # Find the release notes section
-    match = RE_HEADING.search(message)
-    if not match:
+    notes = ""
+    if pr is None:
+        # Extract PR number from rebase commits if it's not a squashed commit
+        pr, notes = extract_notes_from_rebase_commit(commit)
+    else:
+        # Otherwise, find the release notes section from the squashed commit message
+        match = RE_HEADING.search(message)
+        if not match:
+            return pr, result
+        notes = match.group(1)
+
+    if pr in seen:
+        # a PR can be in multiple commits if it's from a rebase,
+        # so we only want to process it once
         return pr, result
 
     start = 0
-    notes = match.group(1)
-
     while True:
         # Find the next possible release note
         match = RE_NOTE.search(notes, start)
@@ -158,8 +188,8 @@ def extract_notes(commit):
         end = match.start() if match else len(notes)
 
         result[impacted] = Note(
-            checked = checked in 'xX',
-            note = notes[begin:end].strip(),
+            checked=checked in "xX",
+            note=notes[begin:end].strip(),
         )
         start = end
 
@@ -170,7 +200,9 @@ def extract_protocol_version(commit):
     """Find the max protocol version at this commit.
 
     Assumes that it is being called from the root of the sui repository."""
-    for line in git("show", f"{commit}:crates/sui-protocol-config/src/lib.rs").splitlines():
+    for line in git(
+        "show", f"{commit}:crates/sui-protocol-config/src/lib.rs"
+    ).splitlines():
         if "const MAX_PROTOCOL_VERSION" not in line:
             continue
 
@@ -200,7 +232,7 @@ def do_check(commit):
 
     """
 
-    _, notes = extract_notes(commit)
+    _, notes = extract_notes(commit, set())
     issues = []
     for impacted, note in notes.items():
         if impacted not in NOTE_ORDER:
@@ -210,7 +242,9 @@ def do_check(commit):
             issues.append(f" - '{impacted}' is checked but has no release note.")
 
         if not note.checked and note.note:
-            issues.append(f" - '{impacted}' has a release note but is not checked: {note.note}")
+            issues.append(
+                f" - '{impacted}' has a release note but is not checked: {note.note}"
+            )
 
     if not issues:
         return
@@ -243,16 +277,20 @@ def do_generate(from_, to):
     protocol_version = extract_protocol_version(to) or "XX"
 
     commits = git(
-        "log", "--pretty=format:%H",
+        "log",
+        "--pretty=format:%H",
         f"{from_}..{to}",
-        "--", *INTERESTING_DIRECTORIES,
-    ).strip();
+        "--",
+        *INTERESTING_DIRECTORIES,
+    ).strip()
 
     if not commits:
         return
 
+    seen_prs = set()
     for commit in commits.split("\n"):
-        pr, notes = extract_notes(commit)
+        pr, notes = extract_notes(commit, seen_prs)
+        seen_prs.add(pr)
         for impacted, note in notes.items():
             if note.checked:
                 results[impacted].append((pr, note.note))
@@ -282,7 +320,7 @@ def do_generate(from_, to):
 
 
 args = parse_args()
-if args["command"]== "generate":
+if args["command"] == "generate":
     do_generate(args["from"], args["to"])
 elif args["command"] == "check":
     do_check(args["commit"])