feat(psl): add validation + warning on missing indexes for relationMode = "prisma"

[jkomyno]

Context: internal Notion doc.

This new validation is disabled when one of the following holds:

• relationMode = "foreignKeys" (or similarly, when no relationMode is specified)
• provider = "mongodb"

Contributes to prisma/language-tools#1296.
Closes prisma/language-tools#992.

TODOs (which do not block this PR):

• agree on a warning message
• create a https://pris.ly/d/relation-mode-prisma-indexes link in https://github.com/prisma/pris.ly
• remove previewFeatures = ["referentialIntegrity"] from newly added tests when chore: make referentialIntegrity preview feature GA #3428 is merged.

Warning message:
"""
With relationMode = \"prisma\", no foreign keys are used, so relation fields will not benefit from the index usually created by the relational database under the hood.
This can lead to poor performance when querying these fields. We recommend adding an index manually.
Learn more at https://pris.ly/d/relation-mode#indexes"
"""

[tomhoule]

Just a few things.

I also think we're missing a test for the case where fields in the relation is a prefix of an indexe's fields.

Also we're missing code that wolud consider the primary key (which is also an index), but let's make that a separate issue/PR.

[tomhoule]

The highlighting is going to be on the field type, so only the OtherModel part in other OtherModel @relation(...). I think it would be more readable for users if we highlighted the whole field. So relation_field.ast_field().span.

[jkomyno]

Yeah I had a doubt about this span here. I think we mentioned elsewhere in the Notion doc that we wanted to highlight the @relation attribute.
Hence, I'd propose the following

let span = ast_field
  .span_for_attribute("relation")
  .unwrap_or_else(|| ast_field.span());

which falls back to your solution

[janpio]

Waiting for updated warning message.

[jkomyno]

About @tomhoule's comment:

Also we're missing code that would consider the primary key (which is also an index), but let's make that a separate issue/PR.

Do you mean something like

model SomeUser {
  id            Int       @id
  successor     SomeUser? @relation("UserHistory")
  predecessorId Int?      @unique
  predecessor   SomeUser? @relation("UserHistory", fields: [id], references: [id])
}

?

[jkomyno]

This is also useful for https://github.com/prisma/prisma-private/issues/198 and for #3435

[pimeys]

A few small things. Ping me when done, and I'll approve!

[pimeys]

Uh, didn't mean to press approve yet

[Jolg42]

Note: we can do changes in a follow-up PR, we really need to merge this asap

[janpio]

Error msg feedback was ignored, left 2 comments.

[jkomyno]

Github Actions is green, Buildkite is all green except CockroachDB, which is in progress. I'm merging