dialect/sql/schema: allow setting table comments (#3365)

dialect/sql/schema/atlas.go

@@ -872,6 +872,9 @@ func (a *Atlas) tables(tables []*Table) ([]*schema.Table, error) {
 	ts := make([]*schema.Table, len(tables))
 	for i, et := range tables {
 		at := schema.NewTable(et.Name)
+		if et.Comment != "" {
+			at.SetComment(et.Comment)
+		}
 		a.sqlDialect.atTable(et, at)
 		if a.universalID && et.Name != TypeTable && len(et.PrimaryKey) == 1 {
 			r, err := a.pkRange(et)

dialect/sql/schema/schema.go

@@ -36,6 +36,7 @@ type Table struct {
 	PrimaryKey  []*Column
 	ForeignKeys []*ForeignKey
 	Annotation  *entsql.Annotation
+	Comment     string
 }
 
 // NewTable returns a new table with the given name.
@@ -46,6 +47,12 @@ func NewTable(name string) *Table {
 	}
 }
 
+// SetComment sets the table comment.
+func (t *Table) SetComment(c string) *Table {
+	t.Comment = c
+	return t
+}
+
 // AddPrimary adds a new primary key to the table.
 func (t *Table) AddPrimary(c *Column) *Table {
 	c.Key = PrimaryKey
@@ -295,7 +302,7 @@ type Column struct {
 	typ        string            // row column type (used for Rows.Scan).
 	indexes    Indexes           // linked indexes.
 	foreign    *ForeignKey       // linked foreign-key.
-	Comment    string            // column comment.
+	Comment    string            // optional column comment.
 }
 
 // Expr represents a raw expression. It is used to distinguish between