Rachel Greenham created GROOVY-10099:
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Summary: A single null argument to a varargs parameter is received
as null
Key: GROOVY-10099
URL: https://issues.apache.org/jira/browse/GROOVY-10099
Project: Groovy
Issue Type: Bug
Environment: Observed on Groovy 3.0.8 on macOS Big Sur (Intel), but I
don't think that's relevant; it'll be everywhere.
Reporter: Rachel Greenham
Attachments: VarArgsTest.groovy, VarArgsTest.jsh
(NB: I would set the priority to P2 default to be triaged, but I seem not to
have that option, so I left it at the default I was presented with.)
When calling a method with a varargs parameter with a single value, that value
is wrapped into an array of length 1. This is the behaviour in Java, and is the
expected behaviour, and _most_ of the time is the behaviour in Groovy too.
But when that single value is null, Groovy will instead just pass the null into
the method. Java will not do this: You'll get an array with a single null in
it. Because Groovy's behaviour is unexpected, especially when interfacing with
Java code, NullPointerExceptions can often ensue.
Adding to the inconsistencies, if the Groovy code calling the method is in a
{{@CompileStatic}} context, it behaves just like Java, and the method (whether
or not _it_ is statically compiled or a dynamic Groovy method) receives an
array with a null in it.
So the behaviour in Groovy is inconsistent, both with itself in a
{{@CompileStatic}} situation, and with Java, and is requiring workarounds in
Java code to handle this normally-impossible eventuality. (Even if no varargs
parameter is given you get an empty array, as in fact you do in Groovy too.)
This may be an "early instalment weirdness": There's an ancient ticket, from
not long after varargs were introduced into Java, which appears to have argued
- successfully at the time - that the normal behaviour is a bug:
https://issues.apache.org/jira/browse/GROOVY-1026
Further adding to the confusion may be that Groovy usually elides the
difference between an {{Object[]}} parameter and an {{Object...}} parameter:
They both behave the same.
The offending code appears to be in
org.codehaus.groovy.reflection.ParameterTypes.java in method fitToVars, lines
200-215 in master at the time of writing, which even includes a comment that
"if the last argument is null, then we don't have to do anything", with which I
respectfully disagree. :) That behaviour should be to return an array with a
single null in it (Handily, MetaClassHelper.ARRAY_WITH_NULL saves having to
make a new one.)
In principle it's an easy fix (although I've left tagging to others as this is
my first issue here), but there'd be an obvious nervousness about changing
behaviour like this when there might be a lot of old code out there depending
on it behaving the way it does now. OTOH the way it behaves now is breaking the
expectations of those of us coming to Groovy from a lifetime of Java...
Attachments:
VarArgsTest.groovy - a script saved from, and runnable in, groovyConsole,
demonstrating the behaviour. The behaviour is the same regardless of whether
the console is launched with the --indy option. (The issue was initially
observed in indy.) The dynamic portion of the test, when run, ends in a
NullPointerException as Arrays.asList is not expecting a null varargs
parameter. Output seen (--indy or not):
{code:java}
name: the static name 1
params is null? false
params length is 1
[blah]
name: the static name 2
params is null? false
params length is 2[blah, blue]
name: the static name 3 with blah=null
params is null? false
params length is 1
[null]
Arrays.asList(blah)? [null]
name: the dynamic name 1
params is null? false
params length is 1
[blah]
name: the dynamic name 2
params is null? false
params length is 2[blah, blue]
name: the dynamic name 3 with blah=null
params is null? true
Exception thrown
java.lang.NullPointerException
...{code}
(etc. stack trace not shown for formatting reasons.)
VarArgsTest.jsh - a jshell script demonstrating Java's behaviour, very similar
to the groovy test, but omitting the dynamic portion of the test for obvious
reasons. (The statements in the Groovy script ending in semicolons are left
that way precisely to mark that they're identical to the Java test.) Runnable
with
{code:java}
jshell PRINTING VarArgsTest.jsh
{code}
Output seen:
{code:java}
name: the static name 1
params is null? false
params length is 1
[blah]
name: the static name 2
params is null? false
params length is 2
[blah, blue]
name: the static name 3 with blah=null
params is null? false
params length is 1
[null]
Arrays.asList(blah)? [null]
{code}
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