Errors due to lack of kind checking

[evancz]

The Elm compiler does not do any special checking for kind mismatches during type inference. So if you are extending a record with a non-record (or a record with overlapping fields) you can get weird things. Fortunately, these bad cases overlap with programs that would be disallowed anyway.

Active reports:

• errors when extending records in invalid ways #1661 - extending records with non-records
• Shadowing in extensible records #1660 - extending records with overlapping fields

If you have other examples that seem related, please open a new issue and make a nice http://sscce.org about it. More examples from more perspectives is always helpful! It will be collected here if it is definitely related.

Old Reports:

• There were many reports (No kind checking #1146, Missing type arguments are not detected #1505, Leaving type parameters out of type annotation compiles when it shouldn't #1542, Make it possible to refer to (* -> *) types #1598, List without any type compiles in Union Type #1645) about trying to use a Type -> Type as a Type, and they almost all used List and Dict with missing type arguments. This was fixed by making sure that types have the right number of arguments during canonicalization.
• We also had No kind checking - subrecords can be non-records #917 about extending non-record values. This was "fixed" because there is no value-level extension anymore.

To summarize, the kind issues have been narrowed down by syntactic restrictions so far, but you can still get kind errors for record extension in types.