Add "floating comments" to the AST

[matthewmueller]

Problem

In the Prisma Schema, we have two different kinds of comments, attached comments and floating comments.

Attached Comment

// This is attached to the model
model User {

  // This is attached to 
  // the field
  id Int @id

  title String // This is a side comment
}

These are comments that are above or to the side of field or model.

Floating Comment

// I float!

model User {

  // I float!
	
  title String
  // I float

}

Floating comments are comments that are not above or to the side of a field or model.

Currently floating comments aren't added to the AST. This means they are lost when we write tools that operate on the Prisma Schema. Today, we're running into this with re-introspect, but this is a general problem.

Note: we have another dimension to this with triple comments ///. In this specific context, they would behave the same way as //. They can be ignored for this issue.

Suggested solution

My preference would be to fix the AST with a distinct Comment node for floating comments. Since our Schema language is rather simple, we'd need Comment nodes in only two places: outside the blocks and inside.

Alternatives

Warning about free-floating comments has also been suggested. prisma/language-tools#446

I'd prefer we didn't go this way because 1. it's surprising and 2. there are valid use cases for floating comments.

// This datamodel powers our recommendation engine.
// 
// Owners: 
//   Mark <mark@prisma.io>
//   Alice <alice@prisma.io>
//   Nicole <nicole@prisma.io>

model User {

}