jrubyc-compiled code with an array pattern fails to load (NullPointerException reading persisted IR) #9834

A file compiled with jrubyc that uses an array pattern can't be loaded. Loading the .class file fails while reading the persisted IR:

# arr.rb
p([1] in [1])

$ jrubyc arr.rb
$ mkdir only && mv arr.class only/
$ jruby -e 'load "only/arr.class"'
Unhandled Java exception: java.lang.NullPointerException: Cannot invoke "org.jruby.ir.operands.OperandType.ordinal()" because "type" is null

The same file without the pattern, or with a hash pattern like {a: 1} in {a: 1}, loads and prints true. It fails the same way on 9.4.15.0, 10.1.2.0 and master. These all fail:

• [1] in [1] and [1] in [Integer]
• [1, 2] in [_, 2] and [1, *] in [1, *]
• case [1]; in [x] then p x; end

With -Xir.reading.debug=true, the last operand read before the failure is a temporary variable that decodes to null, after which the reader is out of step with the data:

INSTR<copy
OP<temporary_variable
Decoding operand temporary_variable
>OP = null
OP<null

Array patterns use TemporaryIntVariables for the array's length, the rest count and element indexes (IRBuilder#intTemp). It's written with type INT, but TemporaryLocalVariable.decode has no case for INT, so it falls through to return null:

switch(type) {
    case CLOSURE: return TemporaryClosureVariable.decode(d);
    case CURRENT_MODULE: return TemporaryCurrentModuleVariable.decode(d);
    case FLOAT: return TemporaryFloatVariable.decode(d);
    case FIXNUM: return TemporaryFixnumVariable.decode(d);
    case BOOLEAN: return TemporaryBooleanVariable.decode(d);
    case LOCAL: return d.getCurrentScope().getManager().newTemporaryLocalVariable(d.decodeInt());
}
return null; // Should not reach here.

TemporaryIntVariable.decode already exists, so adding case INT: return TemporaryIntVariable.decode(d); should fix it.

I ran into this while writing a spec for #9831, where the persistence mode of spec/compiler/general_spec.rb fails the same way on [1] in [1].