dialect/sql/schema: add support for pg arrays in migration

dialect/sql/schema/migrate.go

@@ -354,7 +354,7 @@ func (m *Migrate) changeSet(curr, new *Table) (*changes, error) {
 			}
 			change.index.drop.append(idx)
 		// Extending column types.
-		case m.cType(c1) != m.cType(c2):
+		case m.needsConversion(c2, c1):
 			if !c2.ConvertibleTo(c1) {
 				return nil, fmt.Errorf("changing column type for %q is invalid (%s != %s)", c1.Name, m.cType(c1), m.cType(c2))
 			}
@@ -645,6 +645,7 @@ type sqlDialect interface {
 	tBuilder(*Table) *sql.TableBuilder
 	addIndex(*Index, string) *sql.IndexBuilder
 	alterColumns(table string, add, modify, drop []*Column) sql.Queries
+	needsConversion(*Column, *Column) bool
 }
 
 type preparer interface {

dialect/sql/schema/mysql.go

@@ -677,3 +677,9 @@ func (d *MySQL) defaultSize(c *Column) int64 {
 	}
 	return size
 }
+
+// needsConversion reports if column "old" needs to be converted
+// (by table altering) to column "new".
+func (d *MySQL) needsConversion(old, new *Column) bool {
+	return d.cType(old) != d.cType(new)
+}

dialect/sql/schema/postgres.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"fmt"
 	"strings"
+	"unicode"
 
 	"entgo.io/ent/dialect"
 	"entgo.io/ent/dialect/sql"
@@ -262,6 +263,17 @@ func (d *Postgres) scanColumn(c *Column, rows *sql.Rows) error {
 		c.Type = field.TypeUUID
 	case "cidr", "inet", "macaddr", "macaddr8":
 		c.Type = field.TypeOther
+	case "ARRAY":
+		c.Type = field.TypeOther
+		if !udt.Valid {
+			return fmt.Errorf("missing array type for column %q", c.Name)
+		}
+		// Note that for ARRAY types, the 'udt_name' column holds the array type
+		// prefixed with '_'. For example, for 'integer[]' the result is '_int',
+		// and for 'text[N][M]' the result is also '_text'. That's because, the
+		// database ignores any size or multi-dimensions constraints.
+		c.SchemaType = map[string]string{dialect.Postgres: "ARRAY"}
+		c.typ = udt.String
 	case "USER-DEFINED":
 		c.Type = field.TypeOther
 		if !udt.Valid {
@@ -484,6 +496,13 @@ func (d *Postgres) alterColumns(table string, add, modify, drop []*Column) sql.Q
 	return sql.Queries{b}
 }
 
+// needsConversion reports if column "old" needs to be converted
+// (by table altering) to column "new".
+func (d *Postgres) needsConversion(old, new *Column) bool {
+	oldT, newT := d.cType(old), d.cType(new)
+	return oldT != newT && (oldT != "ARRAY" || !arrayType(newT))
+}
+
 // seqfunc reports if the given string is a sequence function.
 func seqfunc(defaults string) bool {
 	for _, fn := range [...]string{"currval", "lastval", "setval", "nextval"} {
@@ -493,3 +512,17 @@ func seqfunc(defaults string) bool {
 	}
 	return false
 }
+
+// arrayType reports if the given string is an array type (e.g. int[], text[2]).
+func arrayType(t string) bool {
+	i, j := strings.LastIndexByte(t, '['), strings.LastIndexByte(t, ']')
+	if i == -1 || j == -1 {
+		return false
+	}
+	for _, r := range t[i+1 : j] {
+		if !unicode.IsDigit(r) {
+			return false
+		}
+	}
+	return true
+}

dialect/sql/schema/sqlite.go

@@ -328,3 +328,9 @@ func (d *SQLite) tables() sql.Querier {
 		From(sql.Table("sqlite_schema")).
 		Where(sql.EQ("type", "table"))
 }
+
+// needsConversion reports if column "old" needs to be converted
+// (by table altering) to column "new".
+func (d *SQLite) needsConversion(old, new *Column) bool {
+	return d.cType(old) != d.cType(new)
+}