dialect/entsql: supports setting SQL column comments (#3191)

* feat: Add column comment in SQL DDL, using EntSQL annotations to achieve it.

* Update annotation.go

* fix lint

* Add table primary key column comment

* entsql.Comment(string)  is unnecessary

* entc/gen: minor changes to entsql.WithComments + add tests

Co-authored-by: chenghonour <wantto@outlook.com>

dialect/entsql/annotation.go

@@ -89,6 +89,16 @@ type Annotation struct {
 	//
 	Size int64 `json:"size,omitempty"`
 
+	// WithComments specifies whether fields' comments should
+	// be stored in the database schema as column comments.
+	//
+	//  withCommentsEnabled := true
+	//	entsql.WithComments{
+	//		WithComments: &withCommentsEnabled,
+	//	}
+	//
+	WithComments *bool `json:"with_comments,omitempty"`
+
 	// Incremental defines the auto-incremental behavior of a column. For example:
 	//
 	//  incrementalEnabled := true
@@ -205,6 +215,20 @@ func DefaultExprs(exprs map[string]string) *Annotation {
 	}
 }
 
+// WithComments specifies whether fields' comments should
+// be stored in the database schema as column comments.
+//
+//	func (T) Annotations() []schema.Annotation {
+//		return []schema.Annotation{
+//			entsql.WithComments(true),
+//		}
+//	}
+func WithComments(b bool) *Annotation {
+	return &Annotation{
+		WithComments: &b,
+	}
+}
+
 // Merge implements the schema.Merger interface.
 func (a Annotation) Merge(other schema.Annotation) schema.Annotation {
 	var ant Annotation
@@ -247,6 +271,9 @@ func (a Annotation) Merge(other schema.Annotation) schema.Annotation {
 	if s := ant.Size; s != 0 {
 		a.Size = s
 	}
+	if b := ant.WithComments; b != nil {
+		a.WithComments = b
+	}
 	if i := ant.Incremental; i != nil {
 		a.Incremental = i
 	}

dialect/sql/schema/atlas.go

@@ -912,6 +912,9 @@ func (a *Atlas) aColumns(et *Table, at *schema.Table) error {
 		if c1.Collation != "" {
 			c2.SetCollation(c1.Collation)
 		}
+		if c1.Comment != "" {
+			c2.SetComment(c1.Comment)
+		}
 		if err := a.sqlDialect.atTypeC(c1, c2); err != nil {
 			return err
 		}

dialect/sql/schema/schema.go

@@ -295,6 +295,7 @@ 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.
 }
 
 // Expr represents a raw expression. It is used to distinguish between