Syntax Tree Trivia

[nojaf]

Is your feature request related to a problem? Please describe.

In order to have better results in Fantomas, we require more information in the syntax tree about certain specifics.
Examples are locations of certain tokens or keywords.

Describe the solution you'd like

In the past, we added this information directly to the syntax tree nodes.
However, this can lead to a lot of overhead as discussed in #12400.

As a compromise, we could instantiate a new object/record/structure per syntax tree node to bundle these.
The proposal would be to have them as the last item in a DU case.

Example:

SyntaxTrivia.fs:

namespace FSharp.Compiler.Syntax.Trivia // or SyntaxTrivia ?

type SynTryWithTrivia =
    { TryKeyword: Range
      WithKeyword: Range }

SyntaxTree.fs:

type SynExpr =
    | TryWith of
        tryExpr: SynExpr *
        tryRange: range *
        withCases: SynMatchClause list *
        withRange: range *
        tryDebugPoint: DebugPointAtTry *
        withDebugPoint: DebugPointAtWith
        range: range *
        trivia: SynTryWithTrivia 

Describe alternatives you've considered

The alternative is to have all extra information unbundled in the Syntax tree.

Additional context

related: #11481

I'm not really fixed on the appendix name, I would like to avoid using any trivia terminology.
Trivia is used as a concept in Fantomas to add additional information found in the tokens to the tree.

In this case, we really are enriching the tree. So to avoid any confusion I would go with a different name.
Let me know what you think.

//cc @dsyme @auduchinok @baronfel

[dsyme]

Looks fine to me. In your example are tryRange and withRange then in the appendix, rather than the node as you've shown?

TBH I'd kind of like to use trivia, even if it conflicts with Fantomas

[dsyme]

The name should be SynExprTryWithAppendix (or SynExprTryWithTrivia). All the types in SyntaxTree get Syn, and in some cases we will need to disambiguate from SynPat.

[nojaf]

In your example are tryRange and withRange then in the appendix, rather than the node as you've shown?

This is from the original code that is already there, so I left that unchanged.
I'm fine with moving those, either way, I don't really know what is being done with those.

[dsyme]

I see. Yes, they should really be renamed to tryToWithRange and withToEndRange. Looks like they are used for error reporting and to choose whether to look inside for syntax tree traversal I guess they should go into trivia.

If we could use the name Trivia I've be grateful, it is the standard terminology for what all this is.

[nojaf]

If we could use the name Trivia I've be grateful, it is the standard terminology for what all this is.

Sure thing, I'll get over it in the morning 😅.

[dsyme]

This has largely been addressed by @nojaf's PRs linked above