1-element tuple rendered incorrectly

[rowan-stein]

1-element tuple rendered incorrectly

User request:

Describe the bug
This is a followup to sphinx-doc#7964 which has been addressed in sphinx-doc#8265.

However the special case of a 1-element tuple is still not handled correctly.

(1,) is rendered as (1), but should keep the trailing comma.

To Reproduce
Add a testcase

    ("(1,)", "(1,)"),                           # Tuple (single element)

at tests/test_pycode_ast.py around the tuple cases.

Researcher specification:

• Root cause:
  • In sphinx/pycode/ast.py, _UnparseVisitor.visit_Tuple joins elements with ", ".join(...) for non-empty tuples, which drops the trailing comma for single-element tuples.
• Proposed fix:
  • Special-case single-element tuples:
    • If len(node.elts) == 1, return "(" + self.visit(node.elts[0]) + ",)".
    • If not node.elts, return "()".
    • Else, keep current behavior for multi-element tuples.
• Files/functions to modify:
  • sphinx/pycode/ast.py: class _UnparseVisitor, method visit_Tuple.
• Tests to add:
  • In tests/test_pycode_ast.py add:
    • ("(1,)", "(1,)") # single-element tuple
    • Optionally ( "((1,),)", "((1,),)" ) # nested single-element tuple
• Reproduction & expected failure before fix:
  • Run: pytest -q tests/test_pycode_ast.py -k test_unparse
  • Failure snippet for the new case:
    • Expected: (1,)
    • Actual: (1)
    • Assertion diff:
      • (1) != (1,)