From 89cc7c646deea10666fd7dc09c485e7910675cce Mon Sep 17 00:00:00 2001
From: zeripath <art27@cantab.net>
Date: Tue, 9 Apr 2019 21:45:58 +0100
Subject: [PATCH] Prevent server 500 on compare branches with no common history
 (#6555)

* Prevent 500 if there is no common mergebase
* Prevent creation of PR with no history
---
 modules/git/repo_pull.go          | 27 ++++++++++++++++-----------
 options/locale/locale_en-US.ini   |  1 +
 templates/repo/commits_table.tmpl | 12 ++++++++----
 templates/repo/pulls/compare.tmpl |  3 +++
 4 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/modules/git/repo_pull.go b/modules/git/repo_pull.go
index c6d97a6fd1..65c5414551 100644
--- a/modules/git/repo_pull.go
+++ b/modules/git/repo_pull.go
@@ -48,17 +48,22 @@ func (repo *Repository) GetPullRequestInfo(basePath, baseBranch, headBranch stri
 
 	prInfo := new(PullRequestInfo)
 	prInfo.MergeBase, err = repo.GetMergeBase(remoteBranch, headBranch)
-	if err != nil {
-		return nil, fmt.Errorf("GetMergeBase: %v", err)
-	}
-
-	logs, err := NewCommand("log", prInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
-	if err != nil {
-		return nil, err
-	}
-	prInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
-	if err != nil {
-		return nil, fmt.Errorf("parsePrettyFormatLogToList: %v", err)
+	if err == nil {
+		// We have a common base
+		logs, err := NewCommand("log", prInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
+		if err != nil {
+			return nil, err
+		}
+		prInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
+		if err != nil {
+			return nil, fmt.Errorf("parsePrettyFormatLogToList: %v", err)
+		}
+	} else {
+		prInfo.Commits = list.New()
+		prInfo.MergeBase, err = GetFullCommitID(repo.Path, remoteBranch)
+		if err != nil {
+			prInfo.MergeBase = remoteBranch
+		}
 	}
 
 	// Count number of changed files.
diff --git a/options/locale/locale_en-US.ini b/options/locale/locale_en-US.ini
index abcb89767d..2c764f1706 100644
--- a/options/locale/locale_en-US.ini
+++ b/options/locale/locale_en-US.ini
@@ -684,6 +684,7 @@ editor.cannot_commit_to_protected_branch = Cannot commit to protected branch '%s
 
 commits.desc = Browse source code change history.
 commits.commits = Commits
+commits.no_commits = No commits in common. '%s' and '%s' have entirely different histories.
 commits.search = Search commits…
 commits.find = Search
 commits.search_all = All Branches
diff --git a/templates/repo/commits_table.tmpl b/templates/repo/commits_table.tmpl
index 53c2f98f4d..55c550ae95 100644
--- a/templates/repo/commits_table.tmpl
+++ b/templates/repo/commits_table.tmpl
@@ -1,9 +1,13 @@
 <h4 class="ui top attached header">
 	<div class="ui stackable grid">
-		<div class="six wide column">
-			{{.CommitCount}} {{.i18n.Tr "repo.commits.commits"}} {{if .Branch}}({{.Branch}}){{end}}
+		<div class="ten wide column">
+			{{if or .PageIsCommits (gt .CommitCount 0)}}
+				{{.CommitCount}} {{.i18n.Tr "repo.commits.commits"}} {{if .Branch}}({{.Branch}}){{end}}
+			{{else}}
+				{{.i18n.Tr "repo.commits.no_commits" $.BaseBranch $.HeadBranch }} {{if .Branch}}({{.Branch}}){{end}}
+			{{end}}
 		</div>
-		<div class="ten wide right aligned column">
+		<div class="six wide right aligned column">
 			{{if .PageIsCommits}}
 				<form class="ignore-dirty" action="{{.RepoLink}}/commits/{{.BranchNameSubURL | EscapePound}}/search">
 					<div class="ui tiny search input">
@@ -23,7 +27,7 @@
 	</div>
 </h4>
 
-{{if .Commits}}
+{{if and .Commits (gt .CommitCount 0)}}
 	<div class="ui attached table segment">
 		<table class="ui very basic striped fixed table single line" id="commits-table">
 			<thead>
diff --git a/templates/repo/pulls/compare.tmpl b/templates/repo/pulls/compare.tmpl
index d2e00ace36..2296acf1df 100644
--- a/templates/repo/pulls/compare.tmpl
+++ b/templates/repo/pulls/compare.tmpl
@@ -54,6 +54,9 @@
 				<div class="ui segment">
 					{{.i18n.Tr "repo.pulls.has_pull_request" $.RepoLink $.RepoRelPath .PullRequest.Index | Safe}}
 				</div>
+			{{else if eq .CommitCount 0 }}
+				{{template "repo/commits_table" .}}
+				{{template "repo/diff/box" .}}
 			{{else}}
 				{{template "repo/issue/new_form" .}}
 				{{template "repo/commits_table" .}}