Handle null names field when parsing source map files

[todbachman-wf]

Problem:

If names doesn't exist in a source map file, parsing it fails with the following exception:

  NoSuchMethodError: The getter 'iterator' was called on null.
  Receiver: null
  Tried calling: iterator
  dart:core                               new List.from
  package:source_maps/parser.dart 345:15  new SingleMapping.fromJson
  package:source_maps/parser.dart 72:24   parseJson
  package:source_maps/parser.dart 27:5    parse
  test/parser_test.dart 134:9             main.<fn>

Source maps created by Dart tooling don't seem to omit this field. However, you will encounter this exception if you use this library to parse a source map that was created by tooling that omits the names field when the list is empty. For example, the Go package used by gopherjs to generate source maps omits fields when they are empty. We could update that package so it doesn't omit empty fields when encoding them to json, but it's certainly possible this could be an issue with source maps generated by other toolchains as well.

Solution:

Added a null-aware operator to treat a missing names field as an empty list.

[robbecker-wf]

@kevmoo @sigmundch This fixes some sourcemapping errors we're getting. Mind taking a look?

[sigmundch]

LGTM

Technically this is a mandatory field according to the source-map v3 specification, but I'm not opposed to making the parser a bit more resilient here. It might not be a bad idea to send a fix to the Go package as well.

[todbachman-wf]

@sigmundch I agree this ought to be fixed at the source too. I just put up a PR to the Go package to do just that. It looks like there haven't been any commits in over 4 years, so I'm not sure if this will get merged or not. 🤞

[todbachman-wf]

Thanks for the merge y'all! Would you mind cutting a release for us? Thanks!

[natebosch]

published as 0.10.9