feat: generate JSDoc from column comments

README.md

@@ -168,6 +168,19 @@ const rows = await database.selectFrom("User").selectAll().execute()
 
 Fully type-safe queries derived from your actual database schema.
 
+### Column comments
+
+Column comments (`COMMENT ON COLUMN` in PostgreSQL, `COMMENT '...'` in MySQL) are emitted as JSDoc above the column, so they show up in your editor on hover:
+
+```ts
+export interface Users {
+  /** Contact email address. */
+  email: string | null
+}
+```
+
+SQLite has no column comments, so none are generated.
+
 ## Extending to other database dialects
 
 `kysely-typegen` ships with `KyselyTypegenPostgresDialect`, `KyselyTypegenMySQLDialect`, and `KyselyTypegenSQLiteDialect`, but you can add support for any database by extending the abstract `KyselyTypegenDialect` class.

src/_test/__snapshots__/mysql.test.ts.snapshot

@@ -62,10 +62,16 @@ exports[`typegen MySQL > generate types matching snapshot 1`] = `
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<\\"EUR\\" | \\"GBP\\" | \\"USD\\">",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<\\"cancelled\\" | \\"paid\\" | \\"pending\\" | \\"shipped\\">",
     "  userId: number",
@@ -73,6 +79,7 @@ exports[`typegen MySQL > generate types matching snapshot 1`] = `
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<number>",
     "  isActive: Generated<number>",

src/_test/__snapshots__/postgres.test.ts.snapshot

@@ -79,10 +79,16 @@ exports[`typegen PostgreSQL > generate types matching snapshot (kysely-postgres-
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<Currency>",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<OrderStatus>",
     "  userId: string",
@@ -90,6 +96,7 @@ exports[`typegen PostgreSQL > generate types matching snapshot (kysely-postgres-
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<string>",
     "  isActive: Generated<boolean>",
@@ -190,10 +197,16 @@ exports[`typegen PostgreSQL > generate types matching snapshot (pg) 1`] = `
     "}",
     "",
     "export interface Orders {",
+    "  /**",
+    "   * Total amount in cents.",
+    "   *",
+    "   * Excludes taxes.",
+    "   */",
     "  amountCents: number",
     "  createdAt: Generated<Timestamp>",
     "  currency: Generated<Currency>",
     "  id: Generated<Int8>",
+    "  /** Free text, may contain *\\\\/ characters. */",
     "  note: string | null",
     "  status: Generated<OrderStatus>",
     "  userId: string",
@@ -201,6 +214,7 @@ exports[`typegen PostgreSQL > generate types matching snapshot (pg) 1`] = `
     "",
     "export interface Users {",
     "  createdAt: Generated<Timestamp>",
+    "  /** Contact email address. */",
     "  email: string | null",
     "  id: Generated<string>",
     "  isActive: Generated<boolean>",

src/_test/mysql.test.ts

@@ -117,7 +117,9 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
     .addColumn("username", "varchar(50)", (column) => {
       return column.notNull().unique()
     })
-    .addColumn("email", "text")
+    .addColumn("email", "text", (column) => {
+      return column.modifyEnd(sql`comment ${sql.lit("Contact email address.")}`)
+    })
     .addColumn("role", sql`enum('admin','member','guest')`, (column) => {
       return column.notNull().defaultTo("member")
     })
@@ -144,9 +146,13 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
       return column.notNull().defaultTo("EUR")
     })
     .addColumn("amountCents", "integer", (column) => {
-      return column.notNull()
+      return column
+        .notNull()
+        .modifyEnd(sql`comment ${sql.lit("Total amount in cents.\n\nExcludes taxes.")}`)
+    })
+    .addColumn("note", "text", (column) => {
+      return column.modifyEnd(sql`comment ${sql.lit("Free text, may contain */ characters.")}`)
     })
-    .addColumn("note", "text")
     .addColumn("createdAt", "timestamp", (column) => {
       return column.notNull().defaultTo(sql`current_timestamp`)
     })

src/_test/postgres.test.ts

@@ -195,6 +195,16 @@ const createSchema = async (database: Kysely<any>): Promise<void> => {
       return column.notNull().defaultTo(sql`now()`)
     })
     .execute()
+
+  await sql`comment on column ${sql.ref("Users.email")} is ${sql.lit("Contact email address.")}`.execute(
+    database,
+  )
+  await sql`comment on column ${sql.ref("Orders.amountCents")} is ${sql.lit("Total amount in cents.\n\nExcludes taxes.")}`.execute(
+    database,
+  )
+  await sql`comment on column ${sql.ref("Orders.note")} is ${sql.lit("Free text, may contain */ characters.")}`.execute(
+    database,
+  )
 }
 
 describe("typegen PostgreSQL", () => {

src/index.ts

@@ -73,6 +73,24 @@ export abstract class KyselyTypegenDialect {
     return scalars[dataType] ?? "unknown"
   }
 
+  protected formatColumnComment(comment: string): string[] {
+    const trimmedComment = comment.trim()
+    if (trimmedComment.length === 0) {
+      return []
+    }
+    const lines = trimmedComment.replaceAll("*/", "*\\/").split(/\r?\n/u)
+    if (lines.length === 1) {
+      return [`  /** ${lines[0]} */`]
+    }
+    return [
+      "  /**",
+      ...lines.map((line) => {
+        return line.length === 0 ? "   *" : `   * ${line}`
+      }),
+      "   */",
+    ]
+  }
+
   public getTablesTypegen(
     tables: TableMetadata[],
     enums: EnumMetadata[],
@@ -94,6 +112,9 @@ export abstract class KyselyTypegenDialect {
         if (column.hasDefaultValue || column.isAutoIncrementing) {
           columnType = `Generated<${columnType}>`
         }
+        if (column.comment != null) {
+          result.push(...this.formatColumnComment(column.comment))
+        }
         result.push(`  ${column.name}: ${columnType}`)
       }
       result.push("}", "")