Java method lookup for arity-1 method with inexact argument fails in the presence of arity-2 method with same name

[ikaronen-relex]

Test case:

Create the following Java class:

package foobar;

public class JRubyArityTest {
    public JRubyArityTest() {}

    public String foo(String s) {
        return "foo(" + s + ")";
    }

    public String bar(String s) {
        return "bar(" + s + ")";
    }

    public String bar(String s, boolean b) {
        return "NOT EXPECTED TO BE CALLED";
    }
}

and run the following JRuby code:

obj = Java::Foobar::JRubyArityTest.new
puts obj.foo('string')
puts obj.foo(:symbol)
puts obj.bar('string')
puts obj.bar(:symbol)

Expected output:

foo(string)
foo(symbol)
bar(string)
bar(symbol)

Observed output:

foo(string)
foo(symbol)
bar(string)
NameError: no method 'bar' for arguments (org.jruby.RubySymbol) on Java::Foobar::JRubyArityTest

Tested on JRuby 9.3.11.0 and 9.4.5.0. However, this appears to be a longstanding issue, since our codebase apparently has old workarounds for this bug dating from 2018.

[ikaronen-relex]

Note that there are (at least) two possible ways to fix the specific unexpected behavior in the test case:

1. Make RubyToJavaInvoker#findCallableArityOne (and friends) skip the argument matching logic and return immediately if only one candidate method with the correct name and arity is found.
2. Make the argument matching logic in CallableSelector recognize RubySymbol as assignable to String.

In my opinion, while option 2 might be nice to have, option 1 fixes the real problem of non-varargs Java methods with different arities affecting each other's behavior when called from JRuby.