Allow to change (or disable) the default driver name for registration

A link variable now allows to change or disable the name of the driver
that is automatically registered with database/sql:

Change:
    go build "-ldflags=-X github.com/go-sql-driver/mysql.driverName=custom"

Disable:
    go build "-ldflags=-X github.com/go-sql-driver/mysql.driverName="

In the same way, a variable overridable at link time is also provided to
override the driver name used in the test suite. This allows to run our
test suite on another driver.

    go build "-ldflags=-X github.com/go-sql-driver/mysql.driverNameTest=custom"

benchmark_test.go

@@ -48,7 +48,7 @@ func (tb *TB) checkStmt(stmt *sql.Stmt, err error) *sql.Stmt {
 
 func initDB(b *testing.B, queries ...string) *sql.DB {
 	tb := (*TB)(b)
-	db := tb.checkDB(sql.Open("mysql", dsn))
+	db := tb.checkDB(sql.Open(driverNameTest, dsn))
 	for _, query := range queries {
 		if _, err := db.Exec(query); err != nil {
 			b.Fatalf("error on %q: %v", query, err)
@@ -105,7 +105,7 @@ func BenchmarkExec(b *testing.B) {
 	tb := (*TB)(b)
 	b.StopTimer()
 	b.ReportAllocs()
-	db := tb.checkDB(sql.Open("mysql", dsn))
+	db := tb.checkDB(sql.Open(driverNameTest, dsn))
 	db.SetMaxIdleConns(concurrencyLevel)
 	defer db.Close()
 
@@ -151,7 +151,7 @@ func BenchmarkRoundtripTxt(b *testing.B) {
 	sampleString := string(sample)
 	b.ReportAllocs()
 	tb := (*TB)(b)
-	db := tb.checkDB(sql.Open("mysql", dsn))
+	db := tb.checkDB(sql.Open(driverNameTest, dsn))
 	defer db.Close()
 	b.StartTimer()
 	var result string
@@ -184,7 +184,7 @@ func BenchmarkRoundtripBin(b *testing.B) {
 	sample, min, max := initRoundtripBenchmarks()
 	b.ReportAllocs()
 	tb := (*TB)(b)
-	db := tb.checkDB(sql.Open("mysql", dsn))
+	db := tb.checkDB(sql.Open(driverNameTest, dsn))
 	defer db.Close()
 	stmt := tb.checkStmt(db.Prepare("SELECT ?"))
 	defer stmt.Close()

driver.go

@@ -90,8 +90,14 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 	return c.Connect(context.Background())
 }
 
+// This variable can be replaced with -ldflags like below:
+// go build "-ldflags=-X github.com/go-sql-driver/mysql.driverName=custom"
+var driverName = "mysql"
+
 func init() {
-	sql.Register("mysql", &MySQLDriver{})
+	if driverName != "" {
+		sql.Register(driverName, &MySQLDriver{})
+	}
 }
 
 // NewConnector returns new driver.Connector.

driver_test.go

@@ -31,6 +31,16 @@ import (
 	"time"
 )
 
+// This variable can be replaced with -ldflags like below:
+// go test "-ldflags=-X github.com/go-sql-driver/mysql_test.driverNameTest=custom"
+var driverNameTest string
+
+func init() {
+	if driverNameTest == "" {
+		driverNameTest = driverName
+	}
+}
+
 // Ensure that all the driver interfaces are implemented
 var (
 	_ driver.Rows = &binaryRows{}
@@ -111,7 +121,7 @@ func runTestsWithMultiStatement(t *testing.T, dsn string, tests ...func(dbt *DBT
 	dsn += "&multiStatements=true"
 	var db *sql.DB
 	if _, err := ParseDSN(dsn); err != errInvalidDSNUnsafeCollation {
-		db, err = sql.Open("mysql", dsn)
+		db, err = sql.Open(driverNameTest, dsn)
 		if err != nil {
 			t.Fatalf("error connecting: %s", err.Error())
 		}
@@ -130,7 +140,7 @@ func runTests(t *testing.T, dsn string, tests ...func(dbt *DBTest)) {
 		t.Skipf("MySQL server not running on %s", netAddr)
 	}
 
-	db, err := sql.Open("mysql", dsn)
+	db, err := sql.Open(driverNameTest, dsn)
 	if err != nil {
 		t.Fatalf("error connecting: %s", err.Error())
 	}
@@ -141,7 +151,7 @@ func runTests(t *testing.T, dsn string, tests ...func(dbt *DBTest)) {
 	dsn2 := dsn + "&interpolateParams=true"
 	var db2 *sql.DB
 	if _, err := ParseDSN(dsn2); err != errInvalidDSNUnsafeCollation {
-		db2, err = sql.Open("mysql", dsn2)
+		db2, err = sql.Open(driverNameTest, dsn2)
 		if err != nil {
 			t.Fatalf("error connecting: %s", err.Error())
 		}
@@ -1917,7 +1927,7 @@ func testDialError(t *testing.T, dialErr error, expectErr error) {
 		return nil, dialErr
 	})
 
-	db, err := sql.Open("mysql", fmt.Sprintf("%s:%s@mydial(%s)/%s?timeout=30s", user, pass, addr, dbname))
+	db, err := sql.Open(driverNameTest, fmt.Sprintf("%s:%s@mydial(%s)/%s?timeout=30s", user, pass, addr, dbname))
 	if err != nil {
 		t.Fatalf("error connecting: %s", err.Error())
 	}
@@ -1956,7 +1966,7 @@ func TestCustomDial(t *testing.T) {
 		return d.DialContext(ctx, prot, addr)
 	})
 
-	db, err := sql.Open("mysql", fmt.Sprintf("%s:%s@mydial(%s)/%s?timeout=30s", user, pass, addr, dbname))
+	db, err := sql.Open(driverNameTest, fmt.Sprintf("%s:%s@mydial(%s)/%s?timeout=30s", user, pass, addr, dbname))
 	if err != nil {
 		t.Fatalf("error connecting: %s", err.Error())
 	}
@@ -2054,7 +2064,7 @@ func TestUnixSocketAuthFail(t *testing.T) {
 		}
 		t.Logf("socket: %s", socket)
 		badDSN := fmt.Sprintf("%s:%s@unix(%s)/%s?timeout=30s", user, badPass, socket, dbname)
-		db, err := sql.Open("mysql", badDSN)
+		db, err := sql.Open(driverNameTest, badDSN)
 		if err != nil {
 			t.Fatalf("error connecting: %s", err.Error())
 		}
@@ -2243,7 +2253,7 @@ func TestEmptyPassword(t *testing.T) {
 	}
 
 	dsn := fmt.Sprintf("%s:%s@%s/%s?timeout=30s", user, "", netAddr, dbname)
-	db, err := sql.Open("mysql", dsn)
+	db, err := sql.Open(driverNameTest, dsn)
 	if err == nil {
 		defer db.Close()
 		err = db.Ping()
@@ -3210,7 +3220,7 @@ func TestConnectorObeysDialTimeouts(t *testing.T) {
 		return d.DialContext(ctx, prot, addr)
 	})
 
-	db, err := sql.Open("mysql", fmt.Sprintf("%s:%s@dialctxtest(%s)/%s?timeout=30s", user, pass, addr, dbname))
+	db, err := sql.Open(driverNameTest, fmt.Sprintf("%s:%s@dialctxtest(%s)/%s?timeout=30s", user, pass, addr, dbname))
 	if err != nil {
 		t.Fatalf("error connecting: %s", err.Error())
 	}
@@ -3375,7 +3385,7 @@ func TestConnectionAttributes(t *testing.T) {
 
 	var db *sql.DB
 	if _, err := ParseDSN(dsn); err != errInvalidDSNUnsafeCollation {
-		db, err = sql.Open("mysql", dsn)
+		db, err = sql.Open(driverNameTest, dsn)
 		if err != nil {
 			t.Fatalf("error connecting: %s", err.Error())
 		}