Improve "incompatible dimension" errors

[triallax]

Fixes #104.

TODO:

• Clean up
• Add tests
• Deduplicate code
• 
• Never suggest changing the parameter type instead of the argument type (probably won't be done in this PR)
• Use https://docs.rs/unicode-width/latest/unicode_width/ to get the actual display width

[sharkdp]

Minor: I think we should offset the physical dimension hint a bit more and maybe not use (…) parens, because this looks confusing:

  = specified dimension: Length × Mass / (Current × Time³) (ElectricFieldStrength)

Maybe:

  = specified dimension: Length × Mass / (Current × Time³)    [= ElectricFieldStrength]

[sharkdp]

Concerning the suggestions, I think we should only show them in a limited set of cases. For example: this suggestion is correct — but not very helpful:

>>> (20 km/h) / 2km -> hours
error: while type checking
  ┌─ <input>:1:2
  │
1 │ (20 km/h) / 2km -> hours
  │  ^^^^^^^^^^^^^^ -- ^^^^^ Time
  │  │              │   
  │  │              incompatible dimensions in unit conversion
  │  Time⁻¹
  │
  =  left hand side: Time⁻¹    [=Frequency, Activity, Rate]
    right hand side: Time  
     Suggested fix: multiply left hand side by Time²

those 1/x vs x errors are common, I believe. And typically they are not resolved by multiplying with [x]^2, but rather by inverting one side.

Another thing: it would be great to also see the [= …] abbreviated names for the suggested types:

Suggested fix: multiply left hand side by Length² × Mass / Time²    [= Torque, Energy]

[triallax]

Another thing: it would be great to also see the [= …] abbreviated names for the suggested types:

I'm not sure how to go about doing that, because the fmt method for IncompatibleDimensionsError doesn't have access to the registry to get those dimension names. Any suggestions?

[sharkdp]

Another thing: it would be great to also see the [= …] abbreviated names for the suggested types:

I'm not sure how to go about doing that, because the fmt method for IncompatibleDimensionsError doesn't have access to the registry to get those dimension names. Any suggestions?

let's skip it for now

[triallax]

@sharkdp please squash when you merge, I don't want my horrible commit messages forever in the commit log (also, please remove the commit titles from the squashed commit's description).

[sharkdp]

Thank you very much. Great work 👍