chore: support modernAst flag on repl

[baseballyama]

I added modernAst option for REPL.
Sometimes I need to use this now, so this is convenient at least for me.

Simple demo:

Screen.Recording.2024-06-29.at.14.26.09-1.mov

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[Rich-Harris]

Thank you — agree this would be useful, but UI-wise it really belongs on the 'AST Output' tab rather than 'JS Output' (and in both cases, the draggable pane divider makes no real sense; it should be either visible or not). And ideally it would preserve the expanded/collapsed state when toggling.

The big wrinkle is that all this code is currently being rewritten for the new site, and work done here will have to be redone (but against a subtly different codebase) on the other side. So my inclination is to hold off on this for the time being.

[baseballyama]

Yes, we can optimize the UI for the new site.

IMO, Regarding “compiler options,” it would be better if the settings were not spread across several tabs. When users want to change behavior, they need to modify the compiler options in their actual code. It would be good if the REPL had the same structure. It might be better to have a configuration area/tab, similar to the Rollup REPL.

[Rich-Harris]

I'm not sure that's really what people want from this — in the playground, they want to see the effect of those changes, in order to understand the difference between SSR and CSR, or prod mode and dev mode. That only works if the options are visible at the same time as the output.

Also, the compiler options only affect the JS Output and AST Output tabs, not the code that's actually bundled and executed in the iframe, and scoping the UI appropriately helps avoid confusion there.

[Rich-Harris]

I opened an issue on the omnisite repo so that we don't lose sight of this, but for now I'll close this — thanks