Stop fallback to XPath.match in FunctionsClass#send

[tompng]

Related to #342, I found one more contamination path.

Return value of xpath function should be either number, string, boolean or nodeset. But the fallback path returns XPath.match(unregistered_function_name) which may return number/string/boolean wrapped in an array. (#353)
Instead of rejecting these invalid value types or unwrapping the array, simply removing the XPath-
noncompliant behavior is better.

The TODO comment below is kept because falling back to [] instead of raising error may be still not XPath spec behavior.

# TODO: Maybe, this is not XPath spec behavior.
# This behavior must be reconsidered.

Related bugs/glitch (though it's probably a combination of bug in REXML::Parsers::XPathParser)

REXML::XPath::match(REXML::Document.new('<root/>'), "/foo[1-2()]")
#=> []
REXML::XPath::match(REXML::Document.new('<root/>'), "/root[1-2()]")
#=> Garbage component exists at the end: <_2>: <1_2> (REXML::ParseException)

# Invalid type contamination
REXML::XPath::match(REXML::Document.new('<root/>'), "41()/a")
#=> undefined method 'node_type' for an instance of Integer (NoMethodError)

REXML::XPath::match(REXML::Document.new('<local-namae/>'), "local-namae()")
# => []
REXML::XPath::match(REXML::Document.new('<local_namae/>'), "local-namae()")
# => [<local_namae/>]

[Copilot]

Pull request overview

This pull request removes the non-standard fallback behavior where an unregistered XPath function call could implicitly be treated as an element lookup via XPath.match, which could also contaminate return types (e.g., arrays wrapping scalars). The change aligns function evaluation more closely with XPath expectations by returning an empty nodeset for unknown functions.

Changes:

• Update FunctionsClass#send to return [] for unregistered functions instead of falling back to XPath.match(...).
• Adjust function tests to assert nil/empty results for unknown functions and add coverage for previously problematic cases (e.g., "42()").

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/rexml/functions.rb	Removes XPath.match fallback for unknown functions and returns an empty nodeset instead.
test/functions/test_base.rb	Updates expectations for unknown functions and adds assertions preventing invalid return type contamination.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[naitoh]

Thanks!