A kind is a stable id per error, so a test can assert which error this is
without matching on prose and a message can be reworded without breaking
anything. The reader's fourteen refusals all have one; in the checker they
go on the errors a test names and the handful that are common enough to be
worth classifying. Not a hundred of them, because jank has a hundred from
being mature and the number is not the feature.
The notes are the part that could not be said before. A duplicate definition
now points at the second and notes the first; a duplicate parameter and a
duplicate field do the same; an unknown field, an unknown struct and a
non-exhaustive match all note the declaration and list what is actually
there, so the reader's next move arrives with the question instead of after
it. The reader's unclosed bracket is the clearest case — the error sits on
the bracket, because that is where the fix goes, and the note sits where the
file ran out, because that is the surprise.
No message text changed, so every existing needle still means what it meant.
The new assertions are on kinds and on note positions, which is the house
rule about asserting the reason, made stable.
Joseph Ferano
17892852f8