[BUG] Predicates on named function references are ignored

[joewiz]

Describe the bug

As noted by @alanpaxton in https://github.com/eXist-db/exist/pull/4405, eXist ignores predicates on named function references:

eXist-db at present has no support for predicates on Function References (NamedFunctionReference.java) and as such completely ignores the Predicate.

This is likely related to https://github.com/eXist-db/exist/issues/3695.

Expected behavior

eXist should evaluate predicates on function references.

To Reproduce

The expression current-date#0[false()] should evaluate to an empty sequence. BaseX and Saxon return this result, but eXist unexpectedly returns the function reference.

xquery version "3.1";

module namespace t="http://exist-db.org/xquery/test";

declare namespace test="http://exist-db.org/xquery/xqsuite";

declare
    %test:assertEmpty
function t:test() {
    current-date#0[false()]
};

Screenshots

n/a

Context (please always complete the following information):

• OS: macOS 12.4
• eXist-db version: eXist 6.1.0-SNAPSHOT 5086400a7798dcaf6af849ecc7adbb837412c0b8 20220704154708
• Java Version:

  openjdk version "1.8.0_332" OpenJDK Runtime Environment (Temurin)(build 1.8.0_332-b09) OpenJDK 64-Bit Server VM (Temurin)(build 25.332-b09, mixed mode)

Additional context

• How is eXist-db installed? [e.g. JAR installer, DMG, … ] built from source
• Any custom changes in e.g. conf.xml? none

[joewiz]

Note that current-date#0[false()] => serialize() triggers an AST bug:

Cannot compile xquery: exerr:ERROR <AST>:0:0: unexpected AST node: Pred [at line 1, column 25]