NewDialect panics if an unknown dialect is passed

The former behavior (returning the default dialect) may return the
default dialect when we actually want an existing dialect but
forgot to import it. This situation should be caught as early as
possible, hence the panic.

dialect.go

@@ -6,7 +6,7 @@ func NewDialect(driver string) Dialect {
 	if ok {
 		return factory()
 	}
-	return &DefaultDialect{false}
+	panic("No such dialect: " + driver)
 }
 
 // A DialectFactory is a Dialect Factory

dialect_default.go

@@ -7,6 +7,11 @@ type DefaultDialect struct {
 	escaping bool
 }
 
+// NewDefaultDialect instanciate a DefaultDialect
+func NewDefaultDialect() Dialect {
+	return &DefaultDialect{false}
+}
+
 // CompileType compiles a type into its DDL
 func (d *DefaultDialect) CompileType(t TypeElem) string {
 	return DefaultCompileType(t, d.SupportsUnsigned())
@@ -62,3 +67,8 @@ func (d *DefaultDialect) GetCompiler() Compiler {
 func (d *DefaultDialect) WrapError(err error) Error {
 	return Error{Orig: err}
 }
+
+func init() {
+	RegisterDialect("default", NewDefaultDialect)
+	RegisterDialect("", NewDefaultDialect)
+}

dialect_test.go

@@ -27,3 +27,9 @@ func TestDefaultDialect(t *testing.T) {
 	qbErr := dialect.WrapError(err)
 	assert.Equal(t, err, qbErr.Orig)
 }
+
+func TestGetDialect(t *testing.T) {
+	assert.Panics(t, func() {
+		NewDialect("unknown")
+	})
+}