This PR closes#3791, making sure that the Syntax formatter inserts
whitespace before and after comments in the leading and trailing text of
Syntax to avoid having comments comment out any following syntax, and to
avoid comments' lexical syntax from being interpreted as being part of
another syntax. If the text contains newlines before or after any
comments, they are formatted as hard newlines rather than soft newlines.
For example, `--` comments will have a hard newline after them. Note:
metaprograms generating Syntax with comments should be sure to include
newlines at the ends of `--` comments.
This PR implements signature help support. When typing a function
application, editors with support for signature help will now display a
popup that designates the current (remaining) function type. This
removes the need to remember the function signature while typing the
function application, or having to constantly cycle between hovering
over the function identifier and typing the application. In VS Code, the
signature help can be triggered manually using `Ctrl+Shift+Space`.

### Other changes
- In order to support signature help for the partial syntax `f a <|` or
`f a $`, these notations now elaborate as `f a`, not `f a .missing`.
- The logic in `delabConstWithSignature` that delaborates parameters is
factored out into a function `delabForallParamsWithSignature` so that it
can be used for arbitrary `forall`s, not just constants.
- The `InfoTree` formatter is adjusted to produce output where it is
easier to identify the kind of `Info` in the `InfoTree`.
- A bug in `InfoTree.smallestInfo?` is fixed so that it doesn't panic
anymore when its predicate `p` does not ensure that both `pos?` and
`tailPos?` of the `Info` are present.
This PR ensures info tree users such as linters and request handlers
have access to info subtrees created by async elab task by introducing
API to leave holes filled by such tasks.
**Breaking change**: other metaprogramming users of
`Command.State.infoState` may need to call `InfoState.substituteLazy` on
it manually to fill all holes.
This fixes an issue where the completion would use info nodes before the
cursor for computing completions.
Fixes https://github.com/leanprover/lean4/issues/3462.
ToDo:
- [x] Fix test failures for completions that previously worked by
accident (cc: @Kha)
- [x] stage0 update
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Co-authored-by: Sebastian Ullrich <sebasti@nullri.ch>
This upstreams NatCast and IntCast alone independent of norm_cast in
#3322.
This will allow more efficiently upstreaming parts of Std.Data.Int
relevant for omega.
---------
Co-authored-by: Scott Morrison <scott.morrison@gmail.com>