[wmadden-electric]

After this work, a lossy type change is answered like this:

$ prisma migration plan --name age-to-int
✖ [CLI.CONSENT_REQUIRED] 1 subject needs a statement, and the session is not interactive.
  why: Change type of column "User"."age" would lose the data of field "User.age".
→ Pass --convert User.age
→ Pass --delete User.age

This PR plans the rest of the project that makes prisma migration plan and prisma db update refuse to lose data until the user says what each change means. It specifies the next two pieces. It changes no code.

The plan

Slice	What it delivers	State
1, 2	--rename; the refusal with --delete and --allow	Merged
3a	--convert and --backfill on Postgres and SQLite	Specified here
4a	Renames and deletes on MongoDB	Specified here
3b	The remaining SQL renames and deletes	Later
4b	--convert, --backfill and value object renames on MongoDB	Later

3a and 4a can be built at the same time. Slices 3 and 4 were split because each was too large to review as one pull request.

Read these

• plan.md
• Slice 3a spec
• Slice 4a spec

Each spec opens with an example, a table of what changes for users, and the decisions to check.

Decisions to check

3a

1. Without --backfill, migration plan fills a new required field with a temporary value ('', 0) in existing rows.
2. alterColumnType options in migration.ts change shape. Hand-written migrations need the upgrade instructions.

4a

1. Removing a MongoDB field is now asked about. --delete removes it from every document.
2. MongoDB statements name fields as stored (User._id).
3. The document rewrites are classed widening or destructive, not data, so db update can run them. This amends ADR 188.

Alternatives considered

• Keep slices 3 and 4 whole. Neither would fit one review.
• All of MongoDB first. Its --convert and --backfill would design those flags before the SQL slice that owns them.
• Name MongoDB fields as written in the schema. The contract doesn't keep that name, so this would change the contract, its hashes and the client.

Agent: gauss-84

[coderabbitai]

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[wmadden]

specs look good