Prisma re-generates and drops default on `migrate dev`

[casey-chow]

Bug description

When running prisma migrate dev, the generated schema drops the default value for a complex default value, and its corresponding sequence.

How to reproduce

1. Use the below schema.
2. Generate a schema using prisma migrate dev, modify to look like the SQL migration below.
3. Generate another schema using prisma migrate dev.

(Note that the default in Postgres is also the outputted value from Postgres when examining generated DDL.)

Expected behavior

The second invocation of migrate dev shouldn't generate another migration.

Prisma information

Schema Used

model User {
    id         Int @id @default(autoincrement())
    externalId Int @default(dbgenerated("pseudo_encrypt((nextval('user_eid_seq'::regclass))::integer)"))
}

SQL Migration

... pseudo-encrypt function from https://wiki.postgresql.org/wiki/Pseudo_encrypt ...
CREATE SEQUENCE user_eid_seq MAXVALUE 2147483647;
CREATE TABLE "user" (
      id SERIAL NOT NULL,
      eid integer DEFAULT pseudo_encrypt((nextval('user_eid_seq'::regclass))::integer) NOT NULL
);

Environment & setup

• OS: macOS Big Sur
• Database: Postgres 13
• Node.js version: 14.16.1

Prisma Version

prisma               : 2.27.0
@prisma/client       : 2.27.0
Current platform     : darwin
Query Engine         : query-engine cdba6ec525e0213cce26f8e4bb23cf556d1479bb (at node_modules/@prisma/engines/query-engine-darwin)
Migration Engine     : migration-engine-cli cdba6ec525e0213cce26f8e4bb23cf556d1479bb (at node_modules/@prisma/engines/migration-engine-darwin)
Introspection Engine : introspection-core cdba6ec525e0213cce26f8e4bb23cf556d1479bb (at node_modules/@prisma/engines/introspection-engine-darwin)
Format Binary        : prisma-fmt cdba6ec525e0213cce26f8e4bb23cf556d1479bb (at node_modules/@prisma/engines/prisma-fmt-darwin)
Default Engines Hash : cdba6ec525e0213cce26f8e4bb23cf556d1479bb
Studio               : 0.410.0

[thebiglabasky]

We'll need to table this until there's more capacity.

[sibeliuz]

Bug still exists.

[adamlong5]

I'm seeing this same behavior with a different @default(dbgenerated()) value. Also on Postgres on Prisma 2.23.0. Every new migration I make, it tries to add an ALTER line to set the column's default value.