Reject underscored XPath function names

[sjh9714]

Summary

Fixes #352.

Reject XPath function names containing underscores instead of treating them as
aliases for hyphenated standard functions. Standard names such as
local-name() continue to parse normally.

Changes

• Stop underscored names from being parsed as XPath function calls.
• Update XPath fixtures to use standard hyphenated names and add regression
  coverage.

Testing

• ruby -Itest -Ilib test/parser/test_xpath.rb --name=test_function_with_underscore
• rake test

[kou]

I want to keep backward compatibility as much as possible.

How about rejecting _ only when a user specify an option explicitly?

[sjh9714]

Updated this so underscored function names remain accepted by default and are rejected only when the existing strict: true option is passed. The low-level XPath parser now receives that option, and the tests cover both default compatibility and strict rejection.

Ran:

• ruby -Ilib:test test/parser/test_xpath.rb
• ruby -Ilib:test test/functions/test_base.rb
• ruby -Ilib:test test/run.rb

[tompng]

The mechanism that this return path rejects the xpath, is complicated. (See LocationPath → RelativeLocationPath → NodeTest called when 'local_name()' is passed)

I think underscored function names are invalid not because it has underscore, but because it's not registered as a function in XPath 1.0 spec.
Both examples in the code below is in the same situation: using unknown function, so the result (return value or raised error) should be the same.

REXML::XPath.match(REXML::Document.new('<root/>'), 'local_name()')
REXML::XPath.match(REXML::Document.new('<root/>'), 'localname()')

From a viewpoint of module's responsibility, I personally think this check shouldn't be done in REXML::Parsers:XPathParser, but in one of:

• REXML::XPathParser: layer that converts '-' to '_', function name to a method name
• REXML::FunctionsClass: layer that knows all available functions, checks if a method name is registered as a function