Fix error in diff html rendering (go-gitea#13191)

* Fix error in diff html rendering

Was missing an optional whitespace check in regex. Also noticed a rare case where diff.Type == Equal would be empty and thus get a newline attached. Fixed that too.

Fixes go-gitea#13177

* Update services/gitdiff/gitdiff.go

Co-authored-by: zeripath <art27@cantab.net>

* Update gitdiff_test.go

* fmt

Co-authored-by: zeripath <art27@cantab.net>

Author: mrsdizzie

services/gitdiff/gitdiff.go

@@ -181,7 +181,7 @@ var (
 	removedCodePrefix = []byte(`<span class="removed-code">`)
 	codeTagSuffix     = []byte(`</span>`)
 )
-var addSpanRegex = regexp.MustCompile(`<span [class="[a-z]*]*$`)
+var addSpanRegex = regexp.MustCompile(`<span\s*[a-z="]*$`)
 
 func diffToHTML(fileName string, diffs []diffmatchpatch.Diff, lineType DiffLineType) template.HTML {
 	buf := bytes.NewBuffer(nil)
@@ -221,7 +221,7 @@ func diffToHTML(fileName string, diffs []diffmatchpatch.Diff, lineType DiffLineT
 				diffs[i].Text = strings.TrimSuffix(diffs[i].Text, addSpan)
 			}
 			buf.Write(addedCodePrefix)
-			buf.WriteString(getLineContent(diffs[i].Text))
+			buf.WriteString(diffs[i].Text)
 			buf.Write(codeTagSuffix)
 		case diffs[i].Type == diffmatchpatch.DiffDelete && lineType == DiffLineDel:
 			if len(addSpan) > 0 {
@@ -238,7 +238,7 @@ func diffToHTML(fileName string, diffs []diffmatchpatch.Diff, lineType DiffLineT
 				diffs[i].Text = strings.TrimSuffix(diffs[i].Text, addSpan)
 			}
 			buf.Write(removedCodePrefix)
-			buf.WriteString(getLineContent(diffs[i].Text))
+			buf.WriteString(diffs[i].Text)
 			buf.Write(codeTagSuffix)
 		}
 	}

services/gitdiff/gitdiff_test.go

@@ -74,6 +74,15 @@ func TestDiffToHTML(t *testing.T) {
 		{Type: dmp.DiffInsert, Text: "lass=\"p\">,</span> <span class=\"kc\">true</span><span class=\"p\">,</span> <span class=\"nx\">attrs"},
 		{Type: dmp.DiffEqual, Text: "</span><span class=\"p\">,</span> <span class=\"kc\">false</span><span class=\"p\">)</span>"},
 	}, DiffLineAdd))
+
+	assertEqual(t, "<span class=\"k\">print</span><span class=\"added-code\"></span><span class=\"added-code\"><span class=\"p\">(</span></span><span class=\"sa\"></span><span class=\"s2\">&#34;</span><span class=\"s2\">// </span><span class=\"s2\">&#34;</span><span class=\"p\">,</span> <span class=\"n\">sys</span><span class=\"o\">.</span><span class=\"n\">argv</span><span class=\"added-code\"><span class=\"p\">)</span></span>", diffToHTML("", []dmp.Diff{
+		{Type: dmp.DiffEqual, Text: "<span class=\"k\">print</span>"},
+		{Type: dmp.DiffInsert, Text: "<span"},
+		{Type: dmp.DiffEqual, Text: " "},
+		{Type: dmp.DiffInsert, Text: "class=\"p\">(</span>"},
+		{Type: dmp.DiffEqual, Text: "<span class=\"sa\"></span><span class=\"s2\">&#34;</span><span class=\"s2\">// </span><span class=\"s2\">&#34;</span><span class=\"p\">,</span> <span class=\"n\">sys</span><span class=\"o\">.</span><span class=\"n\">argv</span>"},
+		{Type: dmp.DiffInsert, Text: "<span class=\"p\">)</span>"},
+	}, DiffLineAdd))
 }
 
 func TestParsePatch_singlefile(t *testing.T) {