Feature request: prettyPrint

[mjmahone]

Request: Add a Pretty-Printing function to go from AST => well-formatted string

This is a utility I've wanted to exist as part of the core library for a long time. @adek05 began a simple implementation of this in #1557. The Prettier library has even implemented a version of this: https://github.com/prettier/prettier/tree/master/src/language-graphql

Ideal API (I think)

• Should take in a "max-width" as configuration (default to 80 chars?)
• Should preserve comments from the original source
• Should be extensible in the future to support prettier-like configs

Why not re-use print?

• Ideally, print is as high-performance as possible. I imagine calculating line-width will be a non-trivial performance regression, as would preserving comments.
• print currently does not preserve comments, and it would potentially break tooling that depends on this comment-stripping feature.
• This would likely be experimental. We should make sure the output is "ideal" before making the default print functionality be "pretty".

What are potential use cases?

• Codemod tooling that wants to do a one-time insertion of an AST node into existing GraphQL source files. The current print re-formats and strips comments, and leads to super-long lines if, for instance, your query has more than 4 variable definitions.
• Test output snapshots would be easier to read, and easier to see how they change over time
• Prettier and prettier-like tooling could consume this new print function directly

[imolorhe]

Was just about to create an issue for this. 😄 👍