Bug: IndexError instead of SolveFailure when using tuple syntax in rangelist with unsolvable constraints

[BanuAdrian]

Description

When using vsc.rangelist() with tuple syntax to specify a range constraint that conflicts with other constraints, PyVSC throws an IndexError instead of the expected SolveFailure exception. The same constraint using multi-argument syntax correctly throws SolveFailure.

Minimal Reproducible Example

import vsc  
  
@vsc.randobj  
class C():  
    def __init__(self):  
        self.a = vsc.rand_uint8_t()  
      
    @vsc.constraint  
    def constr(self):  
        self.a > 128  
  
# Case 1: Tuple syntax - throws IndexError (BUG)  
c = C()  
try:  
    with c.randomize_with() as it:  
        it.a in vsc.rangelist((0, 50))  
except Exception as e:  
    print("Exception:", type(e), e)  
    # Output: 
    # Exception: <class 'IndexError'> list index out of range  
  
# Case 2: Multi-argument syntax - correctly throws SolveFailure  
c = C()  
try:  
    with c.randomize_with() as it:  
        it.a in vsc.rangelist(0, 50)  
except Exception as e:  
    print("Exception:", type(e), e)  
    # Output: 
    # Solve failure: set 'solve_fail_debug=1' for more details
    # Exception: <class 'vsc.model.solve_failure.SolveFailure'> solve failure

Expected Behavior

Both cases should throw SolveFailure since the constraints are unsolvable:

• Class constraint: self.a > 128
• Inline constraint: self.a must be in range [0, 50] (tuple case) or equal to 0 or 50 (multi-arg case)

These constraints cannot be satisfied simultaneously, so both should result in SolveFailure.

Actual Behavior

• Tuple syntax vsc.rangelist((0, 50)) throws IndexError: list index out of range
• Multi-argument syntax vsc.rangelist(0, 50) correctly throws SolveFailure

Impact

This bug makes debugging constraint issues more difficult since:

• The error message is misleading (IndexError instead of constraint-related error)
• Users cannot rely on consistent exception types for the same type of constraint conflict
• It may mask the actual constraint solving problem