Use beforeCommit instead of baseCommit (#22949)

Replaces: https://github.com/go-gitea/gitea/pull/22947
Fixes https://github.com/go-gitea/gitea/issues/22946
Probably related to https://github.com/go-gitea/gitea/issues/19530

Basically, many of the diffs were broken because they were comparing to
the base commit, where a 3-dot diff should be comparing to the [last
common
ancestor](https://matthew-brett.github.io/pydagogue/git_diff_dots.html).

This should have an integration test so that we don’t run into this
issue again.

---------

Co-authored-by: Jonathan Tran <jonnytran@gmail.com>

1 files changed, 78 insertions, 0 deletions

diff --git a/tests/integration/compare_test.go b/tests/integration/compare_test.go
index dc2bff89fd..509524ca56 100644
--- a/tests/integration/compare_test.go
+++ b/tests/integration/compare_test.go
@@ -4,6 +4,7 @@
 package integration
 
 import (
+	"fmt"
 	"net/http"
 	"strings"
 	"testing"
@@ -40,3 +41,80 @@ func TestCompareDefault(t *testing.T) {
 	selection := htmlDoc.doc.Find(".choose.branch .filter.dropdown")
 	assert.Lenf(t, selection.Nodes, 2, "The template has changed")
 }
+
+// Ensure the comparison matches what we expect
+func inspectCompare(t *testing.T, htmlDoc *HTMLDoc, diffCount int, diffChanges []string) {
+	selection := htmlDoc.doc.Find("#diff-file-boxes").Children()
+
+	assert.Lenf(t, selection.Nodes, diffCount, "Expected %v diffed files, found: %v", diffCount, len(selection.Nodes))
+
+	for _, diffChange := range diffChanges {
+		selection = htmlDoc.doc.Find(fmt.Sprintf("[data-new-filename=\"%s\"]", diffChange))
+		assert.Lenf(t, selection.Nodes, 1, "Expected 1 match for [data-new-filename=\"%s\"], found: %v", diffChange, len(selection.Nodes))
+	}
+}
+
+// Git commit graph for repo20
+// * 8babce9 (origin/remove-files-b) Add a dummy file
+// * b67e43a Delete test.csv and link_hi
+// | * cfe3b3c (origin/remove-files-a) Delete test.csv and link_hi
+// |/
+// * c8e31bc (origin/add-csv) Add test csv file
+// * 808038d (HEAD -> master, origin/master, origin/HEAD) Added test links
+
+func TestCompareBranches(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	session := loginUser(t, "user2")
+
+	// Inderect compare remove-files-b (head) with add-csv (base) branch
+	//
+	//	'link_hi' and 'test.csv' are deleted, 'test.txt' is added
+	req := NewRequest(t, "GET", "/user2/repo20/compare/add-csv...remove-files-b")
+	resp := session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc := NewHTMLParser(t, resp.Body)
+
+	diffCount := 3
+	diffChanges := []string{"link_hi", "test.csv", "test.txt"}
+
+	inspectCompare(t, htmlDoc, diffCount, diffChanges)
+
+	// Inderect compare remove-files-b (head) with remove-files-a (base) branch
+	//
+	//	'link_hi' and 'test.csv' are deleted, 'test.txt' is added
+
+	req = NewRequest(t, "GET", "/user2/repo20/compare/remove-files-a...remove-files-b")
+	resp = session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc = NewHTMLParser(t, resp.Body)
+
+	diffCount = 3
+	diffChanges = []string{"link_hi", "test.csv", "test.txt"}
+
+	inspectCompare(t, htmlDoc, diffCount, diffChanges)
+
+	// Inderect compare remove-files-a (head) with remove-files-b (base) branch
+	//
+	//	'link_hi' and 'test.csv' are deleted
+
+	req = NewRequest(t, "GET", "/user2/repo20/compare/remove-files-b...remove-files-a")
+	resp = session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc = NewHTMLParser(t, resp.Body)
+
+	diffCount = 2
+	diffChanges = []string{"link_hi", "test.csv"}
+
+	inspectCompare(t, htmlDoc, diffCount, diffChanges)
+
+	// Direct compare remove-files-b (head) with remove-files-a (base) branch
+	//
+	//	'test.txt' is deleted
+
+	req = NewRequest(t, "GET", "/user2/repo20/compare/remove-files-b..remove-files-a")
+	resp = session.MakeRequest(t, req, http.StatusOK)
+	htmlDoc = NewHTMLParser(t, resp.Body)
+
+	diffCount = 1
+	diffChanges = []string{"test.txt"}
+
+	inspectCompare(t, htmlDoc, diffCount, diffChanges)
+}