Recommend/convert to use case-sensitive collation for MySQL/MSSQL (#28662)

Mainly for MySQL/MSSQL.

It is important for Gitea to use case-sensitive database charset
collation. If the database is using a case-insensitive collation, Gitea
will show startup error/warning messages, and show the errors/warnings
on the admin panel's Self-Check page.

Make `gitea doctor convert` work for MySQL to convert the collations of
database & tables & columns.

* Fix #28131

## ⚠️ BREAKING ⚠️

It is not quite breaking, but it's highly recommended to convert the
database&table&column to a consistent and case-sensitive collation.

tests/integration/db_collation_test.go

@@ -0,0 +1,123 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+	"xorm.io/xorm"
+)
+
+type TestCollationTbl struct {
+	ID  int64
+	Txt string `xorm:"VARCHAR(10) UNIQUE"`
+}
+
+func TestDatabaseCollation(t *testing.T) {
+	x := db.GetEngine(db.DefaultContext).(*xorm.Engine)
+
+	// there are blockers for MSSQL to use case-sensitive collation, see the comments in db/collation.go
+	if setting.Database.Type.IsMSSQL() {
+		t.Skip("there are blockers for MSSQL to use case-sensitive collation")
+		return
+	}
+
+	// all created tables should use case-sensitive collation by default
+	_, _ = x.Exec("DROP TABLE IF EXISTS test_collation_tbl")
+	err := x.Sync(&TestCollationTbl{})
+	assert.NoError(t, err)
+	_, _ = x.Exec("INSERT INTO test_collation_tbl (txt) VALUES ('main')")
+	_, _ = x.Exec("INSERT INTO test_collation_tbl (txt) VALUES ('Main')") // case-sensitive, so it inserts a new row
+	_, _ = x.Exec("INSERT INTO test_collation_tbl (txt) VALUES ('main')") // duplicate, so it doesn't insert
+	cnt, err := x.Count(&TestCollationTbl{})
+	assert.NoError(t, err)
+	assert.EqualValues(t, 2, cnt)
+	_, _ = x.Exec("DROP TABLE IF EXISTS test_collation_tbl")
+
+	// by default, SQLite3 and PostgreSQL are using case-sensitive collations, but MySQL and MSSQL are not
+	// the following tests are only for MySQL and MSSQL
+	if !setting.Database.Type.IsMySQL() && !setting.Database.Type.IsMSSQL() {
+		t.Skip("only MySQL and MSSQL requires the case-sensitive collation check at the moment")
+		return
+	}
+
+	t.Run("Default startup makes database collation case-sensitive", func(t *testing.T) {
+		r, err := db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.True(t, r.IsCollationCaseSensitive(r.DatabaseCollation))
+		assert.True(t, r.CollationEquals(r.ExpectedCollation, r.DatabaseCollation))
+		assert.NotEmpty(t, r.AvailableCollation)
+		assert.Empty(t, r.InconsistentCollationColumns)
+
+		// and by the way test the helper functions
+		if setting.Database.Type.IsMySQL() {
+			assert.True(t, r.IsCollationCaseSensitive("utf8mb4_bin"))
+			assert.True(t, r.IsCollationCaseSensitive("utf8mb4_xxx_as_cs"))
+			assert.False(t, r.IsCollationCaseSensitive("utf8mb4_general_ci"))
+			assert.True(t, r.CollationEquals("abc", "abc"))
+			assert.True(t, r.CollationEquals("abc", "utf8mb4_abc"))
+			assert.False(t, r.CollationEquals("utf8mb4_general_ci", "utf8mb4_unicode_ci"))
+		} else if setting.Database.Type.IsMSSQL() {
+			assert.True(t, r.IsCollationCaseSensitive("Latin1_General_CS_AS"))
+			assert.False(t, r.IsCollationCaseSensitive("Latin1_General_CI_AS"))
+			assert.True(t, r.CollationEquals("abc", "abc"))
+			assert.False(t, r.CollationEquals("Latin1_General_CS_AS", "SQL_Latin1_General_CP1_CS_AS"))
+		} else {
+			assert.Fail(t, "unexpected database type")
+		}
+	})
+
+	if setting.Database.Type.IsMSSQL() {
+		return // skip table converting tests because MSSQL doesn't have a simple solution at the moment
+	}
+
+	t.Run("Convert tables to utf8mb4_bin", func(t *testing.T) {
+		defer test.MockVariableValue(&setting.Database.CharsetCollation, "utf8mb4_bin")()
+		assert.NoError(t, db.ConvertDatabaseTable())
+		r, err := db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.Equal(t, "utf8mb4_bin", r.DatabaseCollation)
+		assert.True(t, r.CollationEquals(r.ExpectedCollation, r.DatabaseCollation))
+		assert.Empty(t, r.InconsistentCollationColumns)
+
+		_, _ = x.Exec("DROP TABLE IF EXISTS test_tbl")
+		_, err = x.Exec("CREATE TABLE test_tbl (txt varchar(10) COLLATE utf8mb4_unicode_ci NOT NULL)")
+		assert.NoError(t, err)
+		r, err = db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.Contains(t, r.InconsistentCollationColumns, "test_tbl.txt")
+	})
+
+	t.Run("Convert tables to utf8mb4_general_ci", func(t *testing.T) {
+		defer test.MockVariableValue(&setting.Database.CharsetCollation, "utf8mb4_general_ci")()
+		assert.NoError(t, db.ConvertDatabaseTable())
+		r, err := db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.Equal(t, "utf8mb4_general_ci", r.DatabaseCollation)
+		assert.True(t, r.CollationEquals(r.ExpectedCollation, r.DatabaseCollation))
+		assert.Empty(t, r.InconsistentCollationColumns)
+
+		_, _ = x.Exec("DROP TABLE IF EXISTS test_tbl")
+		_, err = x.Exec("CREATE TABLE test_tbl (txt varchar(10) COLLATE utf8mb4_bin NOT NULL)")
+		assert.NoError(t, err)
+		r, err = db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.Contains(t, r.InconsistentCollationColumns, "test_tbl.txt")
+	})
+
+	t.Run("Convert tables to default case-sensitive collation", func(t *testing.T) {
+		defer test.MockVariableValue(&setting.Database.CharsetCollation, "")()
+		assert.NoError(t, db.ConvertDatabaseTable())
+		r, err := db.CheckCollations(x)
+		assert.NoError(t, err)
+		assert.True(t, r.IsCollationCaseSensitive(r.DatabaseCollation))
+		assert.True(t, r.CollationEquals(r.ExpectedCollation, r.DatabaseCollation))
+		assert.Empty(t, r.InconsistentCollationColumns)
+	})
+}