Parser::SourceParser#convert_encoding - fixup BOM encoding

[MSP-Greg]

Description

Ruby 3.3 may change handling of BOM encoded files. Change code to work with 3.3 and earlier versions.

Closes #1509

Note that Ruby 2.7 added IO##set_encoding_by_bom

Completed Tasks

• I have read the Contributing Guide.
• The pull request is complete (implemented / written).
• Git commits have been cleaned up (squash WIP / revert commits).
• I wrote tests and ran bundle exec rake locally (if code is attached to PR).

[lsegal]

I think this would be good if it retained the initial equality check.

[lsegal]

Not sure there's a good enough reason to switch to this more restrictive (newer) API given the simplicity of the existing line.

[MSP-Greg]

I changed it for two reasons, first, content[0, bom.size] creates a string, second, both content and bom are both forced to binary encoding, so there won't be any encoding issues with a character based test, which also happens with the existing check. Not sure why you're calling it 'more restrictive'?

Regardless, I can revert that change if you'd like...

[lsegal]

I remember start_with? being added in Ruby 2.5+, but it seems like it was added much earlier-- in which case this is fine.

[MSP-Greg]

I remember start_with? being added in Ruby 2.5+

My memory isn't good for that sort of thing. CI did pass... I remember a starts_with? a very long time ago. Thanks.

[lsegal]

Thanks for the quick fix on #1509!