Add --analyze-stacks option

That using `git rev-base`, prints total number of stacks, and its
average, mean and max depth

At the time of submission here is top 10 ghstack uses of pytorch:
```
ezyang has 462 stacks max depth is 15 avg depth is 1.70 mean is 1
awgu has 240 stacks max depth is 28 avg depth is 4.30 mean is 1
peterbell10 has 146 stacks max depth is 7 avg depth is 1.84 mean is 1
zou3519 has 128 stacks max depth is 7 avg depth is 1.98 mean is 1
jerryzh168 has 113 stacks max depth is 16 avg depth is 1.45 mean is 1
bdhirsh has 111 stacks max depth is 7 avg depth is 1.85 mean is 2
wconstab has 108 stacks max depth is 7 avg depth is 2.15 mean is 1
SherlockNoMad has 99 stacks max depth is 4 avg depth is 1.24 mean is 1
zasdfgbnm has 80 stacks max depth is 11 avg depth is 2.52 mean is 6
desertfire has 73 stacks max depth is 3 avg depth is 1.14 mean is 1
```

analytics/github_analyze.py

@@ -161,9 +161,12 @@ def __init__(self, path, remote='upstream'):
         self.repo_dir = path
         self.remote = remote
 
+    def _run_git_cmd(self, *args) -> str:
+        return _check_output(['git', '-C', self.repo_dir] + list(args))
+
     def _run_git_log(self, revision_range) -> List[GitCommit]:
-        log = _check_output(['git', '-C', self.repo_dir, 'log',
-                             '--format=fuller', '--date=unix', revision_range, '--', '.']).split("\n")
+        log = self._run_git_cmd('log', '--format=fuller',
+                             '--date=unix', revision_range, '--', '.').split("\n")
         rc: List[GitCommit] = []
         cur_msg: List[str] = []
         for line in log:
@@ -179,6 +182,18 @@ def _run_git_log(self, revision_range) -> List[GitCommit]:
     def get_commit_list(self, from_ref, to_ref) -> List[GitCommit]:
         return self._run_git_log(f"{self.remote}/{from_ref}..{self.remote}/{to_ref}")
 
+    def get_ghstack_orig_branches(self) -> List[str]:
+        return [x.strip() for x in self._run_git_cmd("branch", "--remotes", "--list", self.remote + "/gh/*/orig").strip().split("\n")]
+
+    def show_ref(self, ref) -> str:
+        return self._run_git_cmd("show-ref", ref).split(" ")[0]
+
+    def merge_base(self, ref1, ref2) -> str:
+        return self._run_git_cmd("merge-base", ref1, ref2).strip()
+
+    def rev_list(self, ref):
+        return self._run_git_cmd("rev-list", f"{self.remote}/master..{ref}").strip().split()
+
 
 def build_commit_dict(commits: List[GitCommit]) -> Dict[str, GitCommit]:
     rc = {}
@@ -358,6 +373,22 @@ def get_commits_dict(x, y):
         print(f'{html_url};{issue["title"]};{state}')
 
 
+def analyze_stacks(repo: GitRepo) -> None:
+    from tqdm.contrib.concurrent import thread_map
+    branches = repo.get_ghstack_orig_branches()
+    stacks_by_author: Dict[str, List[int]] = {}
+    for branch,rv_commits in thread_map(lambda x: (x, repo.rev_list(x)), branches, max_workers=10):
+        author = branch.split("/")[2]
+        if author not in stacks_by_author:
+            stacks_by_author[author]=[]
+        stacks_by_author[author].append(len(rv_commits))
+    for author, slen in sorted(stacks_by_author.items(), key=lambda x:len(x[1]), reverse=True):
+        if len(slen) == 1:
+            print(f"{author} has 1 stack of depth {slen[0]}")
+            continue
+        print(f"{author} has {len(slen)} stacks max depth is {max(slen)} avg depth is {sum(slen)/len(slen):.2f} mean is {slen[len(slen)//2]}")
+
+
 def parse_arguments():
     from argparse import ArgumentParser
     parser = ArgumentParser(description="Print GitHub repo stats")
@@ -375,6 +406,7 @@ def parse_arguments():
     parser.add_argument("--print-reverts", action="store_true")
     parser.add_argument("--contributor-stats", action="store_true")
     parser.add_argument("--missing-in-branch", action="store_true")
+    parser.add_argument("--analyze-stacks", action="store_true")
     return parser.parse_args()
 
 
@@ -392,6 +424,10 @@ def main():
 
     repo = GitRepo(args.repo_path, remote)
 
+    if args.analyze_stacks:
+        analyze_stacks(repo)
+        return
+
     if args.missing_in_branch:
         # Use milestone idx or search it along milestone titles
         try: