empty source-map files incorrectly considered invalid

[stefanpenner]

It seems that valid, but empty source-map files are considered invalid. sourcemaps.io appears to agree they are valid, just empty.

https://sourcemaps.io/validate?url=https%3A%2F%2Fgist.githubusercontent.com%2FTurbo87%2Fe39b740c872227698227d3fc7005ad36%2Fraw%2Fdc5f1ca29a8bb98030f63773cc2c4561026711ea%2Fnothing.js

related: broccolijs/broccoli-concat#51 (comment)

I can submit a PR you agree. If not, would love to here your thoughts on this.

[ben-ng]

I vaguely remember making empty sourcemaps fail because they're usually a sign of programmer error... similar to how compilers will warn if you have dead code, and how git doesn't let you make empty commits (without the --allow-empty option).

Rather than make them valid, maybe we should have the error be something like "Warning: The sourcemap appears to be empty. You can set allowEmpty=true to suppress this warning." and then add the option to the validator.

What are your thoughts?

[stefanpenner]

I vaguely remember making empty sourcemaps fail because they're usually a sign of programmer error... similar to how compilers will warn if you have dead code, and how git doesn't let you make empty commits (without the --allow-empty option).

The assertion "is this the right source-map" is different from "is this a valid source-map". Today this module only tests "is this a valid source-map", the exception to this is the assumption "empty map" is invalid.

Now, I do see the value in this case. So let me propose:

1. by default, continue to disallow empty maps
2. the assertion for empty maps become as follows "did not expect and empty map, if this is expected please provide allowBlank: true" or something..

[ben-ng]

I think the proposal is a good one, and is consistent with the behavior of similar tools.