From a370bb224595cac049fe3c04e53e516ee0994520 Mon Sep 17 00:00:00 2001
From: Pierre-Yves Chibon <pingou@pingoured.fr>
Date: Mar 20 2017 17:17:19 +0000
Subject: Optimize diffing two branches


Instead of building the list of all the commits of one and then iterating
through the other to see if it has commits shared with the first, we now
go through the commits on both branches one step at a time and check if
they have overlapping commits at each steps.

---

diff --git a/pagure/internal/__init__.py b/pagure/internal/__init__.py
index 44ba017..9e4733b 100644
--- a/pagure/internal/__init__.py
+++ b/pagure/internal/__init__.py
@@ -270,12 +270,6 @@ def get_pull_request_ready_branch():
         if not repo_obj.head_is_unborn:
             compare_branch = repo_obj.lookup_branch(
                 repo_obj.head.shorthand)
-            compare_commits = [
-                commit.oid.hex
-                for commit in repo_obj.walk(
-                    compare_branch.get_object().hex,
-                    pygit2.GIT_SORT_TIME)
-            ]
         else:
             compare_branch = None
 
@@ -290,18 +284,35 @@ def get_pull_request_ready_branch():
                     and compare_branch.branch_name == branch.branch_name:
                 continue
 
-            diff_commits = []
-
             repo_commit = repo_obj[branch.get_object().hex]
 
-            for commit in repo_obj.walk(
-                    repo_commit.oid.hex, pygit2.GIT_SORT_TIME):
-                if commit.oid.hex in compare_commits:
+            if compare_branch:
+                main_walker = repo_obj.walk(
+                    compare_branch.get_object().hex,
+                    pygit2.GIT_SORT_TIME)
+            branch_walker = repo_obj.walk(
+                    repo_commit.oid.hex,
+                    pygit2.GIT_SORT_TIME)
+            main_commits = set()
+            branch_commits = list()
+            while 1:
+                if compare_branch:
+                    try:
+                        com = main_walker.next()
+                        main_commits.add(com.hex)
+                    except StopIteration:
+                        pass
+                try:
+                    com = branch_walker.next()
+                    branch_commits.append(com.hex)
+                except StopIteration:
+                    break
+
+                if main_commits.intersection(set(branch_commits)):
                     break
-                diff_commits.append(commit.oid.hex)
 
-            if diff_commits:
-                branches[branchname] = diff_commits
+            if branch_commits:
+                branches[branchname] = branch_commits
 
     prs = pagure.lib.search_pull_requests(
         pagure.SESSION,