From 83bb93dc5e2e907c939af41fbd03d30eca6c9fe9 Mon Sep 17 00:00:00 2001
From: Pierre-Yves Chibon <pingou@pingoured.fr>
Date: Jul 19 2018 08:48:29 +0000
Subject: Fix diff a non-empty repo against an empty one


Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

---

diff --git a/pagure/lib/git.py b/pagure/lib/git.py
index 5df021c..aa54fcf 100644
--- a/pagure/lib/git.py
+++ b/pagure/lib/git.py
@@ -1528,7 +1528,7 @@ def get_diff_info(repo_obj, orig_repo, branch_from, branch_to, prid=None):
         repo_obj = orig_repo
 
     if not repo_obj.is_empty and not orig_repo.is_empty:
-        _log.info('Pulling into an non-empty repo')
+        _log.info('pagure.lib.get_diff_info: Pulling into a non-empty repo')
         if branch:
             orig_commit = orig_repo[branch.get_object().hex]
             main_walker = orig_repo.walk(
@@ -1583,11 +1583,13 @@ def get_diff_info(repo_obj, orig_repo, branch_from, branch_to, prid=None):
                     repo_obj.revparse_single(diff_commits[0].oid.hex)
                 )
             elif first_commit.oid.hex == diff_commits[0].oid.hex:
-                _log.info('First commit is also the last commit')
+                _log.info(
+                    'pagure.lib.get_diff_info: First commit is also the last '
+                    'commit')
                 diff = diff_commits[0].tree.diff_to_tree(swap=True)
 
     elif orig_repo.is_empty and not repo_obj.is_empty:
-        _log.info('Pulling into an empty repo')
+        _log.info('pagure.lib.get_diff_info: Pulling into an empty repo')
         if 'master' in repo_obj.listall_branches():
             repo_commit = repo_obj[repo_obj.head.target]
         else:
@@ -1606,6 +1608,10 @@ def get_diff_info(repo_obj, orig_repo, branch_from, branch_to, prid=None):
             'request with'
         )
 
+    _log.info(
+        'pagure.lib.get_diff_info: diff_commits length: %s', len(diff_commits))
+    _log.info('pagure.lib.get_diff_info: original commit: %s', orig_commit)
+
     return(diff, diff_commits, orig_commit)
 
 
diff --git a/pagure/ui/fork.py b/pagure/ui/fork.py
index 5cd6be6..84ab6d4 100644
--- a/pagure/ui/fork.py
+++ b/pagure/ui/fork.py
@@ -250,10 +250,22 @@ def request_pull(repo, requestid, username=None, namespace=None):
             pass
 
         if diff_commits:
-            diff = repo_obj.diff(
-                repo_obj.revparse_single(diff_commits[-1].parents[0].oid.hex),
-                repo_obj.revparse_single(diff_commits[0].oid.hex)
-            )
+            # Ensure the first commit in the PR as a parent, otherwise
+            # point to it
+            start = diff_commits[-1].oid.hex
+            if diff_commits[-1].parents:
+                start = diff_commits[-1].parents[0].oid.hex
+
+            # If the start and the end commits are the same, it means we are,
+            # dealing with one commit that has no parent, so just diff that
+            # one commit
+            if start == diff_commits[0].oid.hex:
+                diff = diff_commits[0].tree.diff_to_tree(swap=True)
+            else:
+                diff = repo_obj.diff(
+                    repo_obj.revparse_single(start),
+                    repo_obj.revparse_single(diff_commits[0].oid.hex)
+                )
     else:
         try:
             diff_commits, diff = pagure.lib.git.diff_pull_request(