lean4-htt/tests/lean/multiConstantError.lean
Robert J. Simmons 08c87b2ad3
feat: focused error messages for named examples (#11714)
This PR gives a focused error message when a user tries to name an
example, and tweaks error messages for attempts to define multiple
opaque names at once.

## Example errors

```
example x : 1 == 1 := by grind
```

Current message:
```
Failed to infer type of binder `x`

Note: Because this declaration's type has been explicitly provided, all parameter types and holes (e.g., `_`) in its header are resolved before its body is processed; information from the declaration body cannot be used to infer what these values should be
```

New message:
```
Failed to infer type of binder `x`

Note: Examples don't have names. The identifier `x` is being interpreted as a parameter `(x : _)`.
```

## Plural-aware identifier lists

Both the example errors and opaque errors understand pluralization and
use oxford commas.

```
opaque a b c : Nat
```

Current message:
```
Failed to infer type of binder `c`

Note: Multiple constants cannot be declared in a single declaration. The identifier(s) `b`, `c` are being interpreted as parameters `(b : _)`, `(c : _)`.
```

New message:
```
Failed to infer type of binder `c`

Note: Multiple constants cannot be declared in a single declaration. The identifiers `b` and `c` are being interpreted as parameters `(b : _)` and `(c : _)`.```
2025-12-17 14:54:41 +00:00

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opaque a b : Nat
opaque a b c : Nat
opaque a b c d : Nat
opaque a b c d e: Nat
opaque a b (c : _) : Nat
opaque a α β : β → Bool
set_option pp.rawOnError true
example x : True := sorry
example x y : True := sorry
example x y z : True := sorry
example α β γ : β → True := sorry
example x y (c : True) : True := sorry