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/api_branch_test.go

@@ -139,6 +139,8 @@ func testAPICreateBranches(t *testing.T, giteaURL *url.URL) {
 			ExpectedHTTPStatus: http.StatusConflict,
 		},
 		// Trying to create from other branch (not default branch)
+		// ps: it can't test the case-sensitive behavior here: the "BRANCH_2" can't be created by git on a case-insensitive filesystem, it makes the test fail quickly before the database code.
+		// Suppose some users are running Gitea on a case-insensitive filesystem, it seems that it's unable to support case-sensitive branch names.
 		{
 			OldBranch:          "new_branch_from_master_1",
 			NewBranch:          "branch_2",
@@ -150,10 +152,18 @@ func testAPICreateBranches(t *testing.T, giteaURL *url.URL) {
 			NewBranch:          "new_branch_from_non_existent",
 			ExpectedHTTPStatus: http.StatusNotFound,
 		},
+		// Trying to create a branch with UTF8
+		{
+			OldBranch:          "master",
+			NewBranch:          "test-👀",
+			ExpectedHTTPStatus: http.StatusCreated,
+		},
 	}
 	for _, test := range testCases {
 		session := ctx.Session
-		testAPICreateBranch(t, session, "user2", "my-noo-repo", test.OldBranch, test.NewBranch, test.ExpectedHTTPStatus)
+		t.Run(test.NewBranch, func(t *testing.T) {
+			testAPICreateBranch(t, session, "user2", "my-noo-repo", test.OldBranch, test.NewBranch, test.ExpectedHTTPStatus)
+		})
 	}
 }
 
@@ -168,7 +178,7 @@ func testAPICreateBranch(t testing.TB, session *TestSession, user, repo, oldBran
 	var branch api.Branch
 	DecodeJSON(t, resp, &branch)
 
-	if status == http.StatusCreated {
+	if resp.Result().StatusCode == http.StatusCreated {
 		assert.EqualValues(t, newBranch, branch.Name)
 	}
 

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)
+	})
+}