[wgsl-in] Subtraction without spaces

[munrocket]

This code gives an error

fn sub() -> f32 {
  return 4.-2.;
}

the same code with spaces or another operation +*/ is ok

fn sub() -> f32 {
  return 4.- 2.;
}

this bug little bit annoying for users because it is not easy to find it. I am used metal as an output but probably this kind of bug occur on other platforms, because it is related to parser.

[hcsch]

I believe this is currently how the spec intends it to be, based on the discussion in gpuweb/gpuweb#775. The spec considers the - as part of the number literals and those are greedily parsed, at least with the current version of the spec.
That means that as long as the spec doesn't change and naga wants to maintain its compliance, this is likely not actionable.

See also https://www.w3.org/TR/2021/WD-WGSL-20210823/#literals (the current version at the time of writing), which specifically mentions this issue in a note.

gpuweb/gpuweb#775 does show that this might change in the (perhaps even near) future, at least from what I'm reading in the more recent comments.

[munrocket]

O_o

[munrocket]

Chrome didn't follow this greedy parser rule. WGSL shaders works as expected.
@hcsch we just can fix it in naga and improve specification (specially when it with TODO addition).

[jimblandy]

This is per spec, but considered a bug in the spec. I explained the current plans to fix the spec over here. When the spec is fixed, we'll create a new issue for that work.