This PR adds an addition newline before the "Additional diagnostic
information may be available using the `set_option ... true` command."
messages, to provide better visual separation from the main error
message.
This message is often incorporated into source files via `#guard_msgs`.
This change ensures it won't go over the 100 character ruler, and I
think is equally grammatical. :-)
It is confusing that the message suggesting to use the `diagnostics`
option is given even when the option is already set. This PR makes use
of lazy message data to make the message contingent on the option being
false.
It also tones down the promise that there is any diagonostic information
available, since sometimes there is nothing to report.
Suggested by Johan Commelin.
Summary:
- Take `synthPendingDepth` into account when caching TC results
- Add `maxSynthPendingDepth` option with default := 2.
- Add support for tracking `synthPending` failures when using
`set_option diagnostics true`
closes#2522closes#3313closes#3927
Identical to #4114 but with `maxSynthPendingDepth := 1`
closes#4114
cc @semorrison
@Kha We will probably have to refine the heuristic for hiding the
inaccessible names, but the first version is already useful.
Here is the error message for a `_` before this commit
```
error: don't know how to synthesize placeholder
context:
x✝⁴ : List Nat
x✝³ : Nat
x✝² : x✝⁴ ≠ []
a b x✝¹ : Nat
x✝ : [a, b] ≠ []
⊢ Nat
```
After
```
error: don't know how to synthesize placeholder
a b : Nat
: [a, b] ≠ []
⊢ Nat
```
