Description of problem:

ResolveExpressionHandler deliberately does not make use of the full range of expression resolutions sources, because by design the intent is not to support vault resolution.
However, the way it implements that limitation is by simply calling ModelNode.resolve(). That is overly restrictive, as DMR alone does not support other valid resolution features, i.e. nested expressions and recursive resolution.
Fix is to switch the handler to use an ExpressionResolver impl, just one that doesn't plug in the vault resolver.

Version-Release number of selected component (if applicable):

6.4.0.DR12, although similar issues exist in 6.3, just not reproducible using the nested expression example below, as nested expressions aren't supported there.

How reproducible:

Always.

Steps to Reproduce:
1. Add 3 system properties:

[standalone@localhost:9999 /] /system-property=A:add(value=a)
{"outcome" => "success"}
[standalone@localhost:9999 /] /system-property=B:add(value=b){"outcome" => "success"}
[standalone@localhost:9999 /] /system-property=ab:add(value=asd)
{"outcome" => "success"}

2.

Use the "resolve-expressions" op to try and resolve a nested expression:

[standalone@localhost:9999 /] :resolve-expression(expression=${${A}b})


Actual results:

{
"outcome" => "failed",
"failure-description" => "JBAS014802: Cannot resolve expression '${${A}b}'",
"rolled-back" => true
}

Expected results:

{ "outcome" => "success", "result" => "asd" }