3fc99eef10
This PR adds two validation checks to `addInstance` that provide early feedback for common mistakes in instance declarations: 1. **Non-class instance check**: errors when an instance target type is not a type class. This catches the common mistake of writing `instance` for a plain structure. Previously handled by the `nonClassInstance` linter in Batteries (`Batteries.Tactic.Lint.TypeClass`), this is now checked directly at declaration time. 2. **Impossible argument check**: errors when an instance has arguments that cannot be inferred by instance synthesis. Specifically, it flags arguments that are not instance-implicit and do not appear in any subsequent instance-implicit argument or in the return type. Previously such instances would be silently accepted but could never be synthesised. Supersedes #13237 and #13333.
22 lines
830 B
Text
22 lines
830 B
Text
class MyClass (α : Type u) where
|
||
point : α
|
||
|
||
/--
|
||
error: Instance @bad1 has arguments n : Nat that are impossible to infer. Those arguments are not instance-implicit and do not appear in another instance-implicit argument or the return type.
|
||
---
|
||
warning: declaration uses `sorry`
|
||
-/
|
||
#guard_msgs in
|
||
instance bad1 {α : Type} [Inhabited α] (n : Nat) : MyClass α := sorry
|
||
|
||
/--
|
||
error: Instance @bad2 has arguments n : Nat, m : Nat that are impossible to infer. Those arguments are not instance-implicit and do not appear in another instance-implicit argument or the return type.
|
||
---
|
||
warning: declaration uses `sorry`
|
||
-/
|
||
#guard_msgs in
|
||
instance bad2 {α : Type} [Inhabited α] (n m : Nat) : MyClass α := sorry
|
||
|
||
/-- warning: declaration uses `sorry` -/
|
||
#guard_msgs in
|
||
instance good {α : Type} [Inhabited α] : MyClass α := sorry
|