Do we support Multi-level mapping source map lookups for final source map consumption

[littledan]

For multilevel source maps, This solution is proposed in the v3 source map spec, in the "Multi-level Mapping Notes" section for maps between languages which don't have built-in syntactic support (which is just JS and CSS, now with Wasm added). Should we do this?

[tromey]

This bug is referring to the text here: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit#heading=h.e8hx254xu4sa

[jridgewell]

I maintain @ampproject/remapping, which traces multi-level source maps to generate a flattened output. It has a (bad) test suite of fixture outputs from build tools, and a few unit tests.

There are a few complexities when remapping, eg:

• What happens if the output map points to an unmapped region in the transitive map?
• What happens if the output map points to a "generated" mapping in the transitive map?
• What happens if the output map has a named mapping, but the transitive map doesn't?
• What happens if the output map has a source mapping, but the transitive map has a named mapping?

[petebacondarwin]

I also spent some time building a similar tool for Angular.

https://github.com/angular/angular/tree/1eda1bdfccc09426ea8d8dd8cfbd8f521cc15f14/packages/compiler-cli/src/ngtsc/sourcemaps

I wrote a doc on what we found and built.

https://docs.google.com/document/d/1x1laiDVFgJtpiw49ozwr91LG7hqohytWDiptJ93nJcE/edit#heading=h.9gb628qxj3gl

In case this is useful here.

[Jack-Works]

Is a multi-level source map ever supported in any debugger? e.g. Chrome doesn't support it (https://bugs.chromium.org/p/chromium/issues/detail?id=1086380)

I think this feature is useful when there is multiple-level transformation of the code.