Wasm source maps

[mason-lgtm]

Add support for "inlines" and "compileunits" sources for Wasm using source maps.

Adds a new option "--source-map" which can be specified to map a URL to source map file:

--source-map=http://myurl/output.wasm.map=output.wasm.map

The source map URL is found in the Wasm binary in the sourceMappingURL section.

We also support specifying the source map by file name, which is useful for specifying multiple source maps in diff mode where the sourceMappingURL might be identical between the binaries.

--source-map=path/to/output.wasm=output.wasm.map

[haberman]

I think this would be simpler and safer to write as id.assign(source_mapping_url).

[mason-lgtm]

Thanks! done

[gkdn]

Hi. Wanted to quickly check if there is additional work needed for PR or if it is ready to go?

[haberman]

Please add documentation for this flag to the usage string and into the user guide.

[mason-lgtm]

Done - added usage notes to using.md and added the option to the usage string

[haberman]

Thanks so much for adding yaml2obj tests. Could we add one for diff mode, so we can test our design for distinguishing between different versions of the same file?

[mason-lgtm]

Thanks. I think the simplest way to do this would be to make a copy of the Wasm binary generated by yaml2obj, then create 2 different source maps for each of these. Made the change. PTAL

[jordo]

I'm trying to use this with an emscripten build, and using the generated source map file:

Example:

godot.web.template_release.wasm32.nothreads.wasm
godot.web.template_release.wasm32.nothreads.wasm.map

Passing the map file as an argument doesn't seem to work:

bloaty godot.web.template_release.wasm32.nothreads.wasm -d compileunits --source-map ./godot.web.template_release.wasm32.nothreads.wasm.map
bloaty: Source map filename './godot.web.template_release.wasm32.nothreads.wasm.map' must have a build id and file name separated by '='

It's not clear to me what the cmd line help actually means:

  --source-map=ID=FILE
                     Use this source map file for the binary. The ID can be
                     the build ID (or Wasm sourceMappingURL) or the file path
                     as specified in the command line.
                     Currently only supported for Wasm.

[haberman]

There is a bit more documentation here: https://github.com/google/bloaty/blob/main/doc/using.md#source-maps