Instead of implementing pasls.inactiveRegions why not textDocument/publishDiagnostics?

[oisanjaya]

inactiveRegions is custom LSP extension originally created for clangd.

Why don't we use textDocument/publishDiagnostics with Unnecessary tag which is standard LSP message.

Or maybe we do both?

I made test case hacking TCheckInactiveRegions.Execute to also send textDocument/publishDiagnostics with Unnecessary tag, and I feel that inactive regions marking could be handled. Maybe I'll make PR once i done with that.

I read that clangd decide to use custom message because Vscode render unnecessary tag without syntax highlighting. Also i heard their parser don't produce AST nodes for inactive regions so they create their own system to let Vscode render correctly.

I don't use Vscode personally, I use Zed. In Zed, they are able to render regions with Unecessary tag correctly, i.e. dimmed but sytax highlighting still intact.

[genericptr]

Inactive regions in the editors I've used are dimmed text in the editor where as diagnostics are displayed in some states bar or are popups. They're not similar at all so I don't understand what you're proposing.

[oisanjaya]

Diagnostics has tags property which meant to mark section of code Unnecessary (dimmed text) and/or Deprecated (striked through).

The thing is, JSON-RPC method "inactiveRegions" never mentioned in LSP specifications, it was custom message created by clangd and to be processed by clangd client. I think official MS c_cpp Vscode extension also support this. I think that's why upon receiving this notification your editor dimmed that range.

So my proposal is: Support standard "inactive regions" mechanism via Diagnostics message instead of (or maybe alongside of) current inactiveRegions notification.

[genericptr]

Ok that sounds legit to me but are you sure this is how other servers are doing it? I can see the inactive regions in VSCode but not SublimeText so maybe this is what you're seeing other editors too? Maybe @mvancanneyt can explain his reasoning behind doing it like he did and if we should keep both.

[oisanjaya]

I asked AI to sumarize what vscode extensions using textDocument/publishDiagnostics and how.

TypeScript / JavaScript (Built-in tsserver): Fades out unused variables, unused imports, and unreachable code after return statements.
Python (Pylance / Pyright): Dims unused imports and unreferenced function parameters.
Rust (rust-analyzer): Fades out unused variables (like those not prefixed with _), unused struct fields, and unused modules.
C# (C# Dev Kit / OmniSharp): Dims unnecessary using directives and unreferenced source code.
Go (vscode-go / gopls): Greys out unreferenced packages and unused variables.
C/C++ (clangd): While clangd relies on inactiveRegions for preprocessor macros, it strictly uses DiagnosticTag.Unnecessary for standard unused variables.
COBOL (COBOL Quality): Identifies unreferenced variables and shows them as greyed-out text.

Maybe that message not really intended for inactive region of code because semanitcally 'unused' code still compiles. I don't know, maybe there are actually no official LSP spec to specifically mark code regions as inactive (i.e. not compiled)

[genericptr]

It looks like @mvancanneyt implemented this in extension.ts for VSCode too and maybe that's not why we're seeing it in other editors. Maybe this is something you just need to try first and then we can see how it works and if it's good solution?