This PR improves the error message encountered in the case of a type
class instance resolution failure, and adds an error explanation that
discusses the common new-user case of binary operation overloading and
points to the `trace.Meta.synthInstance` option for advanced debugging.
## Example
```lean4
def f (x : String) := x + x
```
Before:
```
failed to synthesize
HAdd String String ?m.5
Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command.
```
After:
```
failed to synthesize instance of type class
HAdd String String ?m.5
Hint: Type class instance resolution failures can be inspected with the `set_option trace.Meta.synthInstance true` command.
Error code: lean.failedToSynthesizeTypeclassInstance
[View explanation](https://lean-lang.org/doc/reference/latest/find/?domain=Manual.errorExplanation&name=lean.failedToSynthesizeTypeclassInstance)
```
The error message is changed in three important ways:
* Explains *what* failed to synthesize, using the "type class"
terminology that's more likely to be recognized than the "instance"
terminology
* Points to the `trace.Meta.synthInstance` option which is otherwise
nearly undiscoverable but is quite powerful (see also
leanprover/reference-manual#663 which is adding commentary on this
option)
* Gives an error explanation link (which won't actually work until the
next release after this is merged) which prioritizes the common-case
explanation of using the wrong binary operation
This PR adds a `warn.sorry` option (default true) that logs the
"declaration uses 'sorry'" warning when declarations contain `sorryAx`.
When false, the warning is not logged.
Closes#8611 (assuming that one would set `warn.sorry` as an extra flag
when building).
Other change: Uses `warn.sorry` when creating auxiliary declarations in
`structure` elaborator, to suppress irrelevant 'sorry' warnings.
We could include the sorries themselves in the message if they are
labeled, letting users "go to definition" to see where the sorries are
coming from.
In an earlier version, added additional information to the warning when
it is a synthetic sorry, since these can be caused by elaboration bugs
and they can also be caused by elaboration failures in previous
declarations. This idea needs some more work, so it's not included.
This PR translates `lean::mk_projections` into Lean, adding
`Lean.Meta.mkProjections`. It also puts `hasLooseBVarInExplicitDomain`
back in sync with the kernel version. Deletes
`src/library/constructions/projection.{h,cpp}`.
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.
this is the simplest of the constructions to be ported from C++ to Lean,
so I’ll PR this one first.
This begins to put each construction into its own file, as it was the
case with C++.
For validation I developed this in a separate repository at
https://github.com/nomeata/lean-constructions/tree/fad715e
and checked that all `.recOn` declarations found in Lean and Mathlib are
identical (per `==`) to the ones produced by the C code.
