ArrayIndexOutOfBoundsException in STR0a with AllDifferent and a variable whose domain has a single value #11

The following instance (generated by PyCSP3) has a unique solution (x[0]=0, x[1]=1, x[2]=2):

<instance format="XCSP3" type="CSP">
  <variables>
    <array id="x" size="[3]">
      <domain for="x[0]"> 0 </domain>
      <domain for="x[1]"> 0 1 </domain>
      <domain for="x[2]"> 0..2 </domain>
    </array>
  </variables>
  <constraints>
    <allDifferent> x[] </allDifferent>
  </constraints>
</instance>

but ACE 2.6 fails (java -jar ACE-2.6.jar model.xml -ev):

! ERROR (use -ev for more details)
java.lang.ArrayIndexOutOfBoundsException: Index -1 out of bounds for length 2
	at sets.SetLinkedBinary.contains(SetLinkedBinary.java:80)
	at constraints.extension.STR0$STR0a.isValidTuple(STR0.java:178)
	at constraints.extension.STR0$STR0a.runPropagator(STR0.java:194)
	at constraints.ConstraintExtension$ConstraintExtensionSpecific.launchFiltering(ConstraintExtension.java:192)
	...
s UNKNOWN

The model in PyCSP3:

from pycsp3 import *

x = VarArray(size=3, dom=lambda i: range(i + 1))

satisfy(
    AllDifferent(x)
)

This looks like xcsp3team/pycsp3#50 (AllEqual with a single-value domain).

Tests

Found by the unit tests of PyCSP3 (branch unit-tests, xcsp3team/pycsp3#66), where the following tests are marked as expected failures until this bug is fixed:

• test_variables.py: test_vararray_domain_depending_on_index_solutions[ACE]

Results of the other solvers

with (ACE 2.6 and CHOCO (choco-parsers-4.10.15-beta), embedded in PyCSP3, and cosoco 2.6.1, from pip: the versions used by PyCSP3):

• CHOCO: java -cp choco-parsers-4.10.15-beta.jar org.chocosolver.parser.xcsp.ChocoXCSP model.xml -a -f -flt
• cosoco: cosoco model.xml -model=2 -nbsols=0

This issue was found by the unit tests of PyCSP3: xcsp3team/pycsp3#66