Bug report

Many tests that expect RecursionError from C stack exhaustion misbehave when the stack limit is very large (DragonFly BSD's default is 512 MiB; ulimit -s can be raised up to unlimited). Tests with a fixed recursion depth fail:

$ ulimit -s 524288
$ ./python -m test test_dict -m test_repr_deep
AssertionError: RecursionError not raised by repr

or run for minutes (deep repr() is quadratic). Tests with unbounded recursion take time proportional to the stack limit (test_ast.test_recursion_direct: 66 ms with 8 MiB, 43 s with 16 GiB), crash with a segmentation fault, or consume all memory. This breaks the default test suite run on DragonFly BSD and on Linux with a raised stack limit.

@support.skip_if_unlimited_stack_size (gh-143460) only covers a truly unlimited stack, and some of its client tests also break or slow down with a large finite limit.

Add a @support.skip_if_huge_c_stack(depth) decorator which skips a test if _testinternalcapi.get_c_recursion_remaining() reports that recursion to the given depth cannot trigger the protection (including a negative result from integer overflow with an unlimited stack), falling back to the unlimited-stack check if _testinternalcapi is not available. Use it in the affected tests, and remove @skip_if_unlimited_stack_size where it becomes redundant.

Linked PRs

• gh-154211: Skip C-stack exhaustion tests when the C stack is huge #154212
• [3.15] gh-154211: Skip C-stack exhaustion tests when the C stack is huge (GH-154212) #154216
• [3.14] gh-154211: Skip C-stack exhaustion tests when the C stack is huge (GH-154212) #154231