Add Tabular Diff for CSV files (#14661)

Implements request #14320 The rendering of CSV files does match the diff style.

* Moved CSV logic into base package.

* Added method to create a tabular diff.

* Added CSV compare context.

* Added CSV diff template.

* Use new table style in CSV markup.

* Added file size limit for CSV rendering.

* Display CSV parser errors in diff.

* Lazy read single file.

* Lazy read rows for full diff.

* Added unit tests for various CSV changes.

services/gitdiff/csv_test.go

@@ -0,0 +1,119 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitdiff
+
+import (
+	"encoding/csv"
+	"strings"
+	"testing"
+
+	csv_module "code.gitea.io/gitea/modules/csv"
+	"code.gitea.io/gitea/modules/setting"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCSVDiff(t *testing.T) {
+	var cases = []struct {
+		diff  string
+		base  string
+		head  string
+		cells [][2]TableDiffCellType
+	}{
+		// case 0
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
++++ b/unittest.csv
+@@ -0,0 +1,2 @@
++col1,col2
++a,a`,
+			base:  "",
+			head:  "col1,col2\na,a",
+			cells: [][2]TableDiffCellType{{TableDiffCellAdd, TableDiffCellAdd}, {TableDiffCellAdd, TableDiffCellAdd}},
+		},
+		// case 1
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
++++ b/unittest.csv
+@@ -1,2 +1,3 @@
+ col1,col2
+-a,a
++a,a
++b,b`,
+			base:  "col1,col2\na,a",
+			head:  "col1,col2\na,a\nb,b",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellAdd, TableDiffCellAdd}},
+		},
+		// case 2
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
++++ b/unittest.csv
+@@ -1,3 +1,2 @@
+ col1,col2
+-a,a
+ b,b`,
+			base:  "col1,col2\na,a\nb,b",
+			head:  "col1,col2\nb,b",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellDel, TableDiffCellDel}, {TableDiffCellEqual, TableDiffCellEqual}},
+		},
+		// case 3
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
++++ b/unittest.csv
+@@ -1,2 +1,2 @@
+ col1,col2
+-b,b
++b,c`,
+			base:  "col1,col2\nb,b",
+			head:  "col1,col2\nb,c",
+			cells: [][2]TableDiffCellType{{TableDiffCellEqual, TableDiffCellEqual}, {TableDiffCellEqual, TableDiffCellChanged}},
+		},
+		// case 4
+		{
+			diff: `diff --git a/unittest.csv b/unittest.csv
+--- a/unittest.csv
++++ b/unittest.csv
+@@ -1,2 +0,0 @@
+-col1,col2
+-b,c`,
+			base:  "col1,col2\nb,c",
+			head:  "",
+			cells: [][2]TableDiffCellType{{TableDiffCellDel, TableDiffCellDel}, {TableDiffCellDel, TableDiffCellDel}},
+		},
+	}
+
+	for n, c := range cases {
+		diff, err := ParsePatch(setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffLineCharacters, setting.Git.MaxGitDiffFiles, strings.NewReader(c.diff))
+		if err != nil {
+			t.Errorf("ParsePatch failed: %s", err)
+		}
+
+		var baseReader *csv.Reader
+		if len(c.base) > 0 {
+			baseReader = csv_module.CreateReaderAndGuessDelimiter([]byte(c.base))
+		}
+		var headReader *csv.Reader
+		if len(c.head) > 0 {
+			headReader = csv_module.CreateReaderAndGuessDelimiter([]byte(c.head))
+		}
+
+		result, err := CreateCsvDiff(diff.Files[0], baseReader, headReader)
+		assert.NoError(t, err)
+		assert.Equal(t, 1, len(result), "case %d: should be one section", n)
+
+		section := result[0]
+		assert.Equal(t, len(c.cells), len(section.Rows), "case %d: should be %d rows", n, len(c.cells))
+
+		for i, row := range section.Rows {
+			assert.Equal(t, 2, len(row.Cells), "case %d: row %d should have two cells", n, i)
+			for j, cell := range row.Cells {
+				assert.Equal(t, c.cells[i][j], cell.Type, "case %d: row %d cell %d should be equal", n, i, j)
+			}
+		}
+	}
+}