[ylluminate]

py2v crashed with V panic: stack overflow on files that nest deeply: about 70 nested blocks, an if/elif chain of 70 branches (Python nests each elif inside the else before it), or one expression about 200 levels deep, such as a sum of 196 terms. The transpiler walks the tree by recursion on the main thread's stack. The crash can't be caught, so in --package it ends the whole run.

The work now runs on a thread with a 64 MiB stack, set with #flag -DV_THREAD_STACK_SIZE=67108864, which V's generated C reads when it creates a thread (@[spawn_stack] had no effect when I tried it). The translation itself isn't touched.

64 MiB is twice the smallest stack size I tested successfully. V's json2 rejects JSON deeper than 512 nested levels. For an elif chain that means 250 branches translate (with 32 MiB; 16 overflows) and 256 exit 1 with Invalid json: Syntax: exceeded the maximum nesting depth. Other shapes have other limits: a sum of 1001 terms exits 1 with a RecursionError from the frontend, which this doesn't change, as does sympy's polys/numberfields/resolvent_lookup.py (569 levels). The macro applies to every thread V starts, so the --check workers get 64 MiB stacks too; on Windows, where a thread's stack size is committed up front, that is about 576 MiB with the default eight workers. I measured on macOS arm64 only.

Separately, V refuses an expression nested more than 100 levels when it compiles the output (expr level > 100), so a sum of 401 terms now translates to V that doesn't build.

I ran into it on sympy, where polys/polyquinticconst.py (230 levels) crashes on master and translates with this.

Test plan

• Two new checks in tests/run_tests.vsh: an elif chain of 120 branches and a sum of 401 terms must translate. Master's py2v exits 139 on both.
• The translated elif chain builds and prints 5, as Python does.
• The 184 Python files under tests/ give the same output and exit status with master's py2v and with this change.
• v tests/run_tests.vsh: 180 passed, 0 failed (178 before, plus the two checks).