StringScanner#scan does not accept a String argument as a pattern

[postmodern]

In strscan 1.0.2 Strings can be given as a literal pattern to scan:

require 'strscan'
scanner = StringScanner.new("foo bar baz")
scanner.scan("foo")
# => "foo"
scanner.scan(/\s+/)
# => " "

truffleruby-21.2.0.1 claims to ship with strscan-1.0.3, however it does not accept a String as a pattern argument.

$ truffleruby -v
truffleruby 21.2.0.1, like ruby 2.7.3, GraalVM CE Native [x86_64-linux]
$ gem list strscan

*** LOCAL GEMS ***

strscan (default: 1.0.3)

scanner.scan("foo")
Traceback (most recent call last):
	from /opt/rubies/truffleruby-21.2.0.1/bin/irb:42:in `<main>'
	from <internal:core> core/kernel.rb:400:in `load'
	from <internal:core> core/kernel.rb:400:in `load'
	from /opt/rubies/truffleruby-21.2.0.1/lib/gems/gems/irb-1.3.3/exe/irb:11:in `<top (required)>'
	from <internal:core> core/throw_catch.rb:36:in `catch'
	from <internal:core> core/throw_catch.rb:36:in `catch'
	from <internal:core> core/kernel.rb:437:in `loop'
	from <internal:core> core/kernel.rb:325:in `eval'
	from (irb):3:in `<top (required)>'
	from /opt/rubies/truffleruby-21.2.0.1/lib/truffle/strscan.rb:243:in `scan'
/opt/rubies/truffleruby-21.2.0.1/lib/truffle/strscan.rb:313:in `scan_internal': bad pattern argument: "foo" (TypeError)

[eregon]

Thanks for the report.

TruffleRuby has its own implementation of strscan in Ruby code for efficiency.
It needs to declare the default gem too, so it uses the same gemspec.

As part of the import from MRI, we already have the strscan tests in https://github.com/oracle/truffleruby/blob/master/test/mri/tests/strscan/test_stringscanner.rb.
So we just need to implement this new case and untag the corresponding MRI test.
The feature was added in ruby/strscan#4, it's only for headonly so we can use String#start_with? to implement it.

[aardvark179]

This was fixed in commit 15bb22a