4913: Remove debugging code for incremental sync r=matklad a=lnicola
4915: Inspect markdown code fences to determine whether to apply syntax highlighting r=matklad a=ltentrup
Fixes#4904
4916: Warnings as hint or info r=matklad a=GabbeV
Fixes#4229
This PR is my second attempt at providing a solution to the above issue. My last PR(#4721) had to be rolled back(#4862) due to it overriding behavior many users expected. This PR solves a broader problem while trying to minimize surprises for the users.
### Problem description
The underlying problem this PR tries to solve is the mismatch between [Rustc lint levels](https://doc.rust-lang.org/rustc/lints/levels.html) and [LSP diagnostic severity](https://microsoft.github.io/language-server-protocol/specification#diagnostic). Rustc currently doesn't have a lint level less severe than warning forcing the user to disable warnings if they think they get to noisy. LSP however provides two severitys below warning, information and hint. This allows editors like VSCode to provide more fine grained control over how prominently to show different diagnostics.
Info severity shows a blue squiggly underline in code and can be filtered separately from errors and warnings in the problems panel.
Hint severity doesn't show up in the problems panel at all and only show three dots under the affected code or just faded text if the diagnostic also has the unnecessary tag.
### Solution
The solution provided by this PR allows the user to configure lists of of warnings to report as info severity and hint severity respectively. I purposefully only convert warnings and not errors as i believe it's a good idea to have the editor show the same severity as the compiler as much as possible.
### Open questions
#### Discoverability
How do we teach this to new and existing users? Should a section be added to the user manual? If so where and what should it say?
#### Defaults
Other languages such as TypeScript report unused code as hint by default. Should rust-analyzer similarly report some problems as hint/info by default?
Co-authored-by: Laurențiu Nicola <lnicola@dend.ro>
Co-authored-by: Leander Tentrup <leander.tentrup@gmail.com>
Co-authored-by: Gabriel Valfridsson <gabriel.valfridsson@gmail.com>
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