fix: credit co-authors of a PR in the generated changelog

dev/release/generate-changelog.py

@@ -17,6 +17,7 @@
 
 import argparse
 import sys
+from collections import Counter
 from github import Github
 import os
 import re
@@ -26,12 +27,43 @@ def print_pulls(repo_name, title, pulls):
     if len(pulls)  > 0:
         print("**{}:**".format(title))
         print()
-        for (pull, commit) in pulls:
+        for (pull, authors) in pulls:
             url = "https://github.com/{}/pull/{}".format(repo_name, pull.number)
-            print("- {} [#{}]({}) ({})".format(pull.title, pull.number, url, commit.author.login))
+            print("- {} [#{}]({}) ({})".format(pull.title, pull.number, url, ", ".join(authors)))
         print()
 
 
+def pull_authors(repo, pull, commit, participants):
+    """
+    Return {login: name} for the GitHub users who authored commits in a PR, starting with the
+    author of the commit that merged it.
+    """
+    authors = {commit.author.login: commit.commit.author.name}
+
+    # a squash merge has a Co-authored-by trailer for each other author in the PR, so the PR's
+    # commits only need fetching when there is one
+    if not re.search(r"^co-authored-by:", commit.commit.message, re.IGNORECASE | re.MULTILINE):
+        return authors
+
+    for c in pull.get_commits():
+        # skip merges of the base branch into the PR, and commits whose email is not linked to a
+        # GitHub account
+        if len(c.parents) == 1 and c.author is not None:
+            authors.setdefault(c.author.login, c.commit.author.name)
+
+    # GitHub links a commit to whichever account has its email address, so a placeholder identity
+    # or an AI agent can map to an account that has nothing to do with the project. Only credit
+    # accounts that have opened an issue or PR here.
+    for login in list(authors)[1:]:
+        if login not in participants:
+            # not totalCount, which is 0 when GitHub pages the results with a cursor
+            participants[login] = len(repo.get_issues(creator=login, state="all").get_page(0)) > 0
+        if not participants[login]:
+            print(f"Not crediting {login} ({authors.pop(login)}) on #{pull.number}: they have not opened "
+                  f"an issue or PR in {repo.full_name}", file=sys.stderr)
+    return authors
+
+
 def generate_changelog(repo, repo_name, tag1, tag2, version):
 
     # get a list of commits between two tags
@@ -42,14 +74,20 @@ def generate_changelog(repo, repo_name, tag1, tag2, version):
     print("Fetching pull requests", file=sys.stderr)
     unique_pulls = []
     all_pulls = []
+    # the name git shortlog credits each commit author under
+    names = {}
+    # whether each co-author has opened an issue or PR in the repository
+    participants = {}
     for commit in comparison.commits:
+        if commit.author is not None:
+            names.setdefault(commit.author.login, commit.commit.author.name)
         pulls = commit.get_pulls()
         for pull in pulls:
             # there can be multiple commits per PR if squash merge is not being used and
             # in this case we should get all the author names, but for now just pick one
             if pull.number not in unique_pulls:
                 unique_pulls.append(pull.number)
-                all_pulls.append((pull, commit))
+                all_pulls.append((pull, pull_authors(repo, pull, commit, participants)))
 
     # we split the pulls into categories
     breaking = []
@@ -61,7 +99,7 @@ def generate_changelog(repo, repo_name, tag1, tag2, version):
 
     # categorize the pull requests based on GitHub labels
     print("Categorizing pull requests", file=sys.stderr)
-    for (pull, commit) in all_pulls:
+    for (pull, authors) in all_pulls:
 
         # see if PR title uses Conventional Commits
         cc_type = ''
@@ -76,17 +114,17 @@ def generate_changelog(repo, repo_name, tag1, tag2, version):
 
         labels = [label.name for label in pull.labels]
         if 'api change' in labels or cc_breaking:
-            breaking.append((pull, commit))
+            breaking.append((pull, authors))
         elif 'performance' in labels or cc_type == 'perf':
-            performance.append((pull, commit))
+            performance.append((pull, authors))
         elif 'bug' in labels or cc_type == 'fix':
-            bugs.append((pull, commit))
+            bugs.append((pull, authors))
         elif 'enhancement' in labels or cc_type == 'feat':
-            enhancements.append((pull, commit))
+            enhancements.append((pull, authors))
         elif 'documentation' in labels or cc_type == 'docs' or cc_type == 'doc':
-            docs.append((pull, commit))
+            docs.append((pull, authors))
         else:
-            other.append((pull, commit))
+            other.append((pull, authors))
 
     # produce the changelog content
     print("Generating changelog content", file=sys.stderr)
@@ -116,10 +154,20 @@ def generate_changelog(repo, repo_name, tag1, tag2, version):
     # get the number of commits
     commit_count = subprocess.check_output(f"git log --pretty=oneline {tag1}..{tag2} | wc -l", shell=True, text=True).strip()
 
-    # get number of contributors
-    contributor_count = subprocess.check_output(f"git shortlog -sn {tag1}..{tag2} | wc -l", shell=True, text=True).strip()
-
-    print(f"This release consists of {commit_count} commits from {contributor_count} contributors. "
+    # credit each person once for every commit they authored, and once for every PR by someone
+    # else that has commits of theirs
+    credits = Counter()
+    for line in subprocess.check_output(f"git shortlog -sn {tag1}..{tag2}", shell=True, text=True).splitlines():
+        count, name = line.split("\t", 1)
+        credits[name] += int(count)
+    for (pull, authors) in all_pulls:
+        # git shortlog has already counted the merge commit's author, who comes first. Count each
+        # name once, as git shortlog does, so that someone with two accounts is not counted twice.
+        (merge_author, *others) = [names.get(login, name) for (login, name) in authors.items()]
+        for name in set(others) - {merge_author}:
+            credits[name] += 1
+
+    print(f"This release consists of {commit_count} commits from {len(credits)} contributors. "
           f"See credits at the end of this changelog for more information.\n")
 
     print_pulls(repo_name, "Breaking changes", breaking)
@@ -130,13 +178,12 @@ def generate_changelog(repo, repo_name, tag1, tag2, version):
     print_pulls(repo_name, "Other", other)
 
     # show code contributions
-    credits = subprocess.check_output(f"git shortlog -sn {tag1}..{tag2}", shell=True, text=True).rstrip()
-
     print("## Credits\n")
     print("Thank you to everyone who contributed to this release. Here is a breakdown of commits (PRs merged) "
-          "per contributor.\n")
+          "per contributor. A PR with commits from more than one person counts for each of them.\n")
     print("```")
-    print(credits)
+    for (name, count) in sorted(credits.items(), key=lambda item: (-item[1], item[0])):
+        print(f"{count:6d}\t{name}")
     print("```\n")
 
     print("Thank you also to everyone who contributed in other ways such as filing issues, reviewing "