"Hit an error we didn't make a nice message for yet" minimal reproducible

[kylegoetz]

Describe and demonstrate the bug

ability Deprecated where
  wrap: '{g} a -> {Deprecated} a

Deprecated.warn p = handle p() with cases
  { k } -> k
  { wrap fn -> k } ->
    Debug.trace "WARNING: This function is deprecated." ()
    res = fn()
    go do k res

When I save the scratch file, I get an error:

deprecated/main> 

  Loading changes detected in ~/Documents/workspace/unison-code/oauth2.u.


  Sorry, you hit an error we didn't make a nice message for yet.
  
  Here is a summary of the Note:
  
    simple cause:
      TypeMismatch
    context:
    Γ
      |start1|
      |𝕩2|
      'User "p"-4
      'Inference Ability-5
      'Inference Output-6
      p3 : p4
      'Inference PatternPureV-17
      'Inference Ability-20
      '𝕖21 = Deprecated
      '𝕦19 = 𝕖20, Deprecated
      '𝕗18 = Request
      '𝕗16 = Request {𝕖20, Deprecated}
      'gs589pqna818 = Request {𝕖20, Deprecated} 𝕧17
      'Inference Ability-60
      'User "g"-61
      '𝕖9 = 𝕖60, g61
      '𝕣10 = 𝕧17
      gs589pqna817 : Request {𝕖20, Deprecated} 𝕧17
      'User "a"-11
      'User "g"-12
      '𝕖14 = 𝕖20
      '𝕧13 = 𝕧17
      'Inference Ability-15
      'User "a"-58
      'User "g"-59

• ucm --version release/0.5.39
• OS/Architecture: macOS 15.0.1 silicon

Additional context
This shows up sometimes but I'm not sure I've been able to share such a simple example before. This is done immediately after project.create with only base as a dependency.

[kylegoetz]

The issue is with the line res = fn()

[kylegoetz]

If I update the code to have explicit types (plus delete the ability in order to change the name from wrap to deprecate:

delete Deprecated

ability Deprecated a where
  deprecate: 'a -> {Deprecated a} a

Deprecated.warn : '{Deprecated, g} a ->{g} a
Deprecated.warn p =
  go : '{Deprecated, g} a ->{g} a
  go p =
    handle p() with cases
      { k } -> k
      { wrap fn -> k } ->
        Debug.trace "WARNING: This function is deprecated." ()
        res = fn()
        go do k res
  go p

the error becomes this, and I do not know what this ability is that it's apparently requiring:

Edit Apparently when I view #.... it's an old Deprecated ability that I deleted (because I couldn't rename an ability function from wrap to deprecate, I deleted the ability and added one with the updated name).

So now I've put --- below the ability and tried update:

ability Deprecated a where
  deprecate: 'a -> {Deprecated a} a
---

stuff here

and I get:

deprecated/main> update

  Sorry, I wasn't able to perform the update, because I need all constructor names to be nested
  somewhere beneath the corresponding type name.
  
  The constructor Deprecated.wrap is not nested beneath the corresponding type name. Please either
  use `move` to move it, or if it's an extra copy, you can simply `delete` it. Then try the update
  again.

But I'd deleted it. Now:

deprecated/main> find wrap

  1. Deprecated.wrap : '{g} a ->{#58da40bc9m} a

[aryairani]

First of all, thanks for the report. There's definitely supposed to be a "nice message" for all type errors.

In the initial report, where is go defined? Is that a copy/paste error, or is it defined elsewhere, or is the missing definition part of the problem?