Hardening: Remove or at least warn about sections.url

[jkrems]

Index maps in the spec support putting each section into a separate resource, linking via the url field. In practice, few (if any) tools actually support this. If that's the case, it may be less confusing to remove it from the spec.

[mitsuhiko]

I would go even further and advocate against the use of indexed source maps. It's not much harder for a tool to rewrite source maps properly today.

[littledan]

Do any tools support this [edit: specifically, the url field]? Do browsers support it?

If this feature doesn't match implementations, we should remove it.

[jkrems]

@mitsuhiko We're actively using index maps in general (no sections[].url though) and it would be non-trivial to replace them. We assemble JS in production dynamically and do the same for the source maps for those responses. Parsing and merging the source map fragments would be fairly (and very likely too) expensive.

[littledan]

@mitsuhiko Let's break out the discussion about indexed source maps into a separate issue then?

Here, let's focus on the url field. Does anyone have information compiled about the implementation reality?

[bmeurer]

Chromium DevTools supports index maps (and has always supported them), but does not support the url field in the sections.

Regarding tools: @sokra recently filed an issue regarding performance of index maps in Chrome DevTools, which might indicate that webpack and/or turbopack might be using them as well soon(ish)? 😄

[mitsuhiko]

I separated out the wider discussion about the index maps.

[bomsy]

I can confirm the same for https://github.com/mozilla/source-map which is used by Firefor DevTools ( and maybe used by other tools) that indexed sourcemaps are supported but not the url field.