A stdlib call backed by a Pascal procedure is not None as a value

import random
print(random.seed(1) is None)   # v451: False (CPython True)
x = random.seed(2)              # v451: x == 2

Cause

PyParseStdlibCall typed the call node with the procedure's RetType. A procedure has none, so a value use read a stale register.

Fix (compiler/pyparser.inc)

When the shim is not a function, the call becomes (call, None): an AN_COMMA whose value is PyMakeNone. A class method with no result already works this way.

Census

Of the 76 entries of PyStdlibCallProc, 4 are Pascal procedures: sys.exit, sys.setswitchinterval, random.seed and random.shuffle. The census grepped procedure <name> in compiler/ and lib/. sys.exit never returns, so it has no value to see. The fixture covers the other three, both as values and as statements.

Rows

test/test_nilpy_stdlib_procedure_call_is_none.npy, with its .expected taken from CPython. Rows: x64 (procnone26), wasm32 and i386. All three are red on the compiler before the fix.