which web editor to use?

[nikomatsakis]

Currently we are using ace.js. It was painless to setup and I've always found play.rust-lang.org quite pleasant to use. But there are some shortcomings, and thinking forward there are some features I would like that I it may not support:

• Squiggly underlines for errors, warnings, breakpoints etc
• Ability to overlay complex messages with arrows and things? (I want flow-based errors to look more like this., but for "borrow checker" errors.) Actually, probably nobody supports this very well natively, so I suppose I want mostly the ability to overlay things.
• Ability to insert "hints" like rust-analyzer does. For example I want to rewrite vec.push(22) to vec.leased.push(22) or show the inferred types for things.

JS editors I'm aware of:

• ace.js -- current choice, seems to support 2, and I think I could fake 1 in the same way we are doing breakpoints now, but I didn't see anything for 3, if I'm not mistaken
• https://microsoft.github.io/monaco-editor/ -- presumably supports 1 and 3 above
• https://codemirror.net/ -- I don't know what it supports!
• other things?

[nikomatsakis]

Given that we expect to have a VSCode extension, I wonder if using monaco will make it easier to get syntax coloring and other sorts of support?

[brson]

I needed a code editor recently and tried monaco and codemirror 6. monaco was difficult to build but codemirror 6 was effortless.

[vemoo]

I have used monaco and its api is close to vscode but not exactly the same, but there's https://github.com/TypeFox/monaco-languageclient that would make it easier to reuse the lsp server.

It does support 3: https://microsoft.github.io/monaco-editor/api/interfaces/monaco.languages.InlayHintsProvider.html

And for 2 it seems it's quite flexible: https://microsoft.github.io/monaco-editor/playground.html#interacting-with-the-editor-listening-to-mouse-events

Another point in favor may be that the editing experience is familiar it you come from vscode.

Also I think it's what a lot of web ide like projects are based on, like Compiler Explorer, CodeSandbox, StackBlitz, Theia