Some floating-point numbers are changed

[ErikSchierboom]

Issue created from fantomas-ui

The value of some floating-point numbers will change when formatting the code. It appears to only apply to negative floating-point numbers:

Code

module Numbers

let x = -3.213f
let y = 1.621f
let z = -1.5f
let a = 3.213f

Result

module Numbers

let x = -3.213000059f
let y = 1.621f
let z = -1.5f
let a = 3.213f

Options

Fantomas 3.2.0

Name	Value
IndentOnTryWith	false
IndentSpaceNum	4
KeepNewlineAfter	false
MaxIfThenElseShortWidth	40
PageWidth	120
ReorderOpenDeclaration	false
SemicolonAtEndOfLine	false
SpaceAfterComma	true
SpaceAfterSemicolon	true
SpaceAroundDelimiter	true
SpaceBeforeArgument	true
SpaceBeforeColon	false
StrictMode	false

[ErikSchierboom]

I've dug into this a bit more, and it looks like this is not Fantomas' doing but FSC: https://fsprojects.github.io/fantomas-tools/#/ast?data=N4KABGBEAmCmBmBLAdrAzpAXFSAacUiaAYmolmPAIYA2as%2BEkAxgPZwWQ2wAuYAHmAC8YALQBmAHQAmAIzj4kEAF8gA

[nojaf]

Yes, there seems to be a problem in the FCS indeed, however, there is also a Fantomas one here I believe.

Numbers can't be trusted from the AST anyways, so we use trivia to set the correct number, which in this case also didn't happen correctly.

[nojaf]

We detected the number, the problem is somewhere around the assignment of the trivia to a trivia node.

Given this insight @ErikSchierboom, could I persuade you to tackle this issue yourself?

[nojaf]

I believe the problem is located in here.
The minus sign is part of the SynConst range and that is why the match is not found.

Proposed solution:
extend TokenParser to have a case of MINUS + NUMBER TOKEN.

Something along the lines:

| minus::head::rest when (minus.TokenInfo.TokenName = "MINUS" && isNumber head) ->
...

[ErikSchierboom]

Yeah sure! It will be my pleasure :) I'll work on this tomorrow.

[nojaf]

Great to hear! I recommend you watch https://www.youtube.com/watch?v=FCrkUqCCzgI&list=PLvw_J2kfZCX3Mf6tEbIPZXbzJOD1VGl4K first to have some understanding of what all this trivia fuzz is about.

If you were to have any questions, please reach out over here or on the F# foundation slack.

[ErikSchierboom]

Will do! Thanks for the links.

[ErikSchierboom]

@nojaf I've submitted a PR to fix this. I have one question about how to best implement it, which I've left as a comment in the PR.