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 server-side support for dedicated 'unsolved goals' and
'goals accomplished' diagnostics that will have special support in the
Lean 4 VS Code extension. The special 'unsolved goals' diagnostic is
adapted from the 'unsolved goals' error diagnostic, while the 'goals
accomplished' diagnostic is issued when a `theorem` or `Prop`-typed
`example` has no errors or `sorry`s. The Lean 4 VS Code extension
companion PR is at leanprover/vscode-lean4#585.
Specifically, this PR extends the diagnostics served by the language
server with the following fields:
- `leanTags`: Custom tags that denote the kind of diagnostic that is
being served. As opposed to the `code`, `leanTags` should never be
displayed in the UI. Examples introduced by this PR are a tag to
distinguish 'unsolved goals' errors from other diagnostics, as well as a
tag to distinguish the new 'goals accomplished' diagnostic from other
diagnostics.
- `isSilent`: Whether a diagnostic should not be displayed as a regular
diagnostic in the editor. In VS Code, this means that the diagnostic is
displayed in the InfoView under 'Messages', but that it will not be
displayed under 'All Messages' and that it will also not be displayed
with a squiggly line.
The `isSilent` field is also implemented for `Message` so that silent
diagnostics can be logged in the elaborator. All code paths except for
the language server that display diagnostics to users are adjusted to
filter `Message`s with `isSilent := true`.
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.
Adds a mechanism where when an autoparam tactic fails to synthesize a
parameter, the associated parameter name or field name for the autoparam
is reported in an error.
Examples:
```text
could not synthesize default value for parameter 'h' using tactics
could not synthesize default value for field 'inv' of 'S' using tactics
```
Notes:
* Autoparams now run their tactics without any error recovery or
error-to-sorry enabled. This enables catching the error and reporting
the contextual information. This is justified on the grounds that
autoparams are not interactive.
* Autoparams for applications now cleanup the autoParam annotation,
bringing it in line with autoparams for structure fields.
* This preserves the old behavior that autoparams leave terminfo, but we
will revisit this after some imminent improvements to the unused
variable linter.
Closes#2950
Autoparam tactic scripts have no source positions, which until recently
made it so that any errors or messages would be logged at the current
ref, which was the application or structure instance being elaborated.
However, with the new incrementality features the ref is now carefully
managed to avoid leakage of outside data. This inhibits the elaborator's
ref from being used for the tactic's ref, causing messages to be placed
at the beginning of the file rather than on the syntax that triggered
the autoparam.
To fix this, now the elaborators insert the ref's source position
everywhere into the autoparam tactic script.
If in the future messages for synthetic tactics appear at the tops of
files in other contexts, we should consider an approach where
`Lean.Elab.Term.withReuseContext` uses something like `replaceRef` to
set the ref while disabling incrementality when the tactic does not
contain source position information.
Closes#4880
