feat: mark generated and identity columns across writers and DBML

- bun: scanonly+generated for GENERATED columns; scanonly+identity for ALWAYS identity (PK gets identity only)
- gorm: <-:false+generated / identity, same primary key rule
- dbml: write GENERATED/IDENTITY column notes and read them back into the model
- pgsql: emit generation/identity clauses in migration create-table and add-column, no DEFAULT
- readmes updated

pkg/writers/dbml/generated_columns_test.go

@@ -0,0 +1,77 @@
+package dbml
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/readers"
+	dbmlreader "git.warky.dev/wdevs/relspecgo/pkg/readers/dbml"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+)
+
+func TestGeneratedAndIdentityColumnsRoundTrip(t *testing.T) {
+	table := models.InitTable("people", "public")
+
+	id := models.InitColumn("id", "people", "public")
+	id.Type = "bigint"
+	id.IsPrimaryKey = true
+	id.AutoIncrement = true
+	id.Identity = true
+	id.IdentityGeneration = "ALWAYS"
+	table.Columns["id"] = id
+
+	seq := models.InitColumn("seq", "people", "public")
+	seq.Type = "integer"
+	seq.Identity = true
+	seq.IdentityGeneration = "BY DEFAULT"
+	table.Columns["seq"] = seq
+
+	full := models.InitColumn("full_name", "people", "public")
+	full.Type = "text"
+	full.Generated = true
+	full.GenerationExpression = "first || ' ' || last"
+	table.Columns["full_name"] = full
+
+	plain := models.InitColumn("first", "people", "public")
+	plain.Type = "text"
+	plain.Comment = "given name"
+	table.Columns["first"] = plain
+
+	schema := models.InitSchema("public")
+	schema.Tables = append(schema.Tables, table)
+	db := models.InitDatabase("testdb")
+	db.Schemas = append(db.Schemas, schema)
+
+	out := filepath.Join(t.TempDir(), "people.dbml")
+	require.NoError(t, NewWriter(&writers.WriterOptions{OutputPath: out}).WriteDatabase(db))
+
+	content, err := os.ReadFile(out)
+	require.NoError(t, err)
+	assert.Contains(t, string(content), "GENERATED ALWAYS AS (first || \\' \\' || last) STORED")
+	assert.Contains(t, string(content), "GENERATED ALWAYS AS IDENTITY")
+	assert.Contains(t, string(content), "GENERATED BY DEFAULT AS IDENTITY")
+
+	got, err := dbmlreader.NewReader(&readers.ReaderOptions{FilePath: out}).ReadDatabase()
+	require.NoError(t, err)
+	cols := got.Schemas[0].Tables[0].Columns
+
+	assert.True(t, cols["id"].Identity)
+	assert.Equal(t, "ALWAYS", cols["id"].IdentityGeneration)
+	assert.Empty(t, cols["id"].Comment, "marker note must not become a comment")
+
+	assert.True(t, cols["seq"].Identity)
+	assert.Equal(t, "BY DEFAULT", cols["seq"].IdentityGeneration)
+
+	assert.True(t, cols["full_name"].Generated)
+	assert.Equal(t, "first || ' ' || last", cols["full_name"].GenerationExpression)
+	assert.Empty(t, cols["full_name"].Comment)
+
+	assert.False(t, cols["first"].Generated)
+	assert.False(t, cols["first"].Identity)
+	assert.Equal(t, "given name", cols["first"].Comment)
+}