A migration of `@default(cuid())` inserts `null` values to the DB

[AviBueno]

Bug description

Adding a new column with @default(cuid()) ends up with null values in the new column after migration.

How to reproduce

Add a new column to an existing table, e.g.:

model Folder {
  ...
  uid String? @default(cuid())
  ...
}

Run prisma migrate save --experimental followed by prisma migrate up --experimental

Notes:

1. Tried with and without @unique and the result is the same
2. String? type is required as String crashes the migration. Not sure why. It would be preferred that the column would be mandatory.

---

Edit:

With String as the type, the migration fails on the following error, which is also described in #527:

Added the required column X to the Y table without a default value. There are N rows in this table, it is not possible to execute this migration.

---

Expected behavior

The Folder table should contain a new uid column with generated cuid values.

Prisma information

N/A

Environment & setup

• OS: Mac OS
• Database: PostgreSQL
• Node.js version: v12.18.3
• Prisma version:

@prisma/cli          : 2.5.1
Current platform     : darwin
Query Engine         : query-engine c88925ce44a9b89b4351aec85ba6a28979d2658e (at node_modules/@prisma/cli/query-engine-darwin)
Migration Engine     : migration-engine-cli c88925ce44a9b89b4351aec85ba6a28979d2658e (at node_modules/@prisma/cli/migration-engine-darwin)
Introspection Engine : introspection-core c88925ce44a9b89b4351aec85ba6a28979d2658e (at node_modules/@prisma/cli/introspection-engine-darwin)
Format Binary        : prisma-fmt c88925ce44a9b89b4351aec85ba6a28979d2658e (at node_modules/@prisma/cli/prisma-fmt-darwin)
Studio               : 0.261.0

[Jolg42]

Looks like a duplicate of https://github.com/prisma/migrate/issues/527 (to confirm)

[albertoperdomo]

Closing as duplicate of #527. Please follow that one to track progress.