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A keyword argument through a callable value is undefined variable

RE-RANKED 65 -> 72 on 2026-08-19 (coordinator). This is now the sole remaining wall on the 12-file corpus group, and it inherited that position by measurement, not by argument.

frank2 fixed the shadowing bug (5fc7dc358) that produced the corpus's decode has no parameter named 'final'. webencodings/__init__.py now reports undefined variable (final) — i.e. exactly this ticket. The 12 files moved one wall further along and still do not compile.

Read that as the expected result, not a failed fix. A ladder run whose decode row is replaced by a final row rather than shrinking is what success looks like at this stage; conflating "moved past a wall" with "cleared" misreads the campaign in both directions.

Scope note from frank2, who built the PySig record and went looking: this is a design increment on p88, not a fifth caller to teach the same trick. It needs something the record does not carry at all — parameter NAMES — plus a call-site lowering that can hand a keyword name to the runtime. Today final=True is parsed as an expression and dies on the bare name. Recommended order: (1) extend PySig with parameter names, (2) lower a keyword argument at a callable-value call site into a name/value pair the dispatcher can match. Step (3), consolidating the carriers, is deliberately split out as [[refactor-a-one-signature-record-for-every-callable-carrier]] and must not be done inside this ticket — that kind of absorption is what grew p88 to four increments.

Filed 2026-08-19 by frank3-etree (Track B) out of the corpus-ladder investigation. Track N owns the fix; this is a report, not a claim on the lane.

Repro — measured on pinned v357 (ebcf15ccb1046b29353b3b85091a8cdc)

class D:
    def decode(self, a, final=False):
        return "d:" + str(a) + ":" + str(final)
d = D()
f = d.decode
print(d.decode("x", final=True))   # direct call: fine, prints d:x:True
print(f("y", final=True))          # through a callable value: FAILS



pascal26:7: error: undefined variable (final)
  near:  f  y  final >>>

CPython prints d:x:True / d:y:True.

Not name-specific. The same file with decode->mymeth and final->flag fails identically (undefined variable (flag)), so nothing about builtin method names is involved.

No collision required. There is no module-level def decode anywhere in the repro — which is what separates this from the shadowing bug below.

What it is NOT — and this distinction is the point of the ticket

It is not the 12-file corpus wall. That one produces decode has no parameter named 'final' and is [[bug-nilpy-a-callable-in-a-variable-loses-to-a-def-of-the-same-name]] (frank2, unfinished/): a local decode = decoder.decode loses to a module-level def decode, the call binds to the module function, and that function genuinely has no final. The diagnostic there is correct about the wrong callee, which is exactly why it reads as a signature bug and is not one.

The two were conflated for most of a day. What separated them was refusing to treat a near-miss repro as the bug: the minimal case produced a different diagnostic from the corpus, and different diagnostics mean a neighbour, not the thing. Two bugs, not one confused one.

Likely mechanism, and the request that goes with it

Sibling of [[bug-n-a-call-through-a-callable-value-drops-the-callees-defaults]], whose summary already names the shared carrier: "the box carries a code address and no signature." Defaults are one missing field; parameter names are another, and a keyword argument needs the names.

frank2's request, recorded here so it reaches whoever picks this up: extend the PySig record rather than start a fifth mechanism. Per normalise-dont-special-case.md, a second path for "call through a value" is the one that stays broken.

Not merged with the defaults ticket — frank2's call, on the grounds that it is the same carrier but a different missing field and that ticket is nearly closed. Cross-referenced instead.

FIXED. The signature record was extended, not duplicated.

Three pieces, in the order frank2 recommended when it declined to merge this with the defaults ticket.

1. PYSIG grows a NAMES field (PYSIG_OFF_NAMES = 40, PYSIG_SIZE 40 → 48). EmitPySignatures emits TotN pointers followed by the NUL-terminated names themselves, in the SAME record as the defaults rather than beside it — one carrier answers every signature question. A proc with no user parameters leaves the field nil, which the dispatcher reads as "no names known" and treats exactly as it did before names existed.

2. The call site sends the name to run time. There is no callee to resolve final against at compile time — that is the entire difficulty, and it is why this failed as undefined variable (final): the name was parsed as an ordinary expression because nothing had told the parser it was a parameter. PyMakeDynCall now recognises ident = in a dynamic call's argument list and appends the name (as a string) and its value to two parallel TPyLists, exactly the way the existing *args arm builds its list.

3. The dispatcher matches them. pyvar_callv_kw → pybound_pair_call_kw, which reads Names and binds each keyword to a position, THEN fills the remaining holes from the defaults — that order is what makes a supplied keyword win over a default, which is the only reason a caller writes one. PySigNameEq compares in place rather than converting to an AnsiString: putting the names in .data was pointless if answering a question about one allocated.

Errors are Python's, not silence: unknown keyword, multiple values for one argument, and missing required arguments each raise TypeError, and the required-argument count is recomputed after keyword binding rather than trusting the positional count — a keyword can supply a required parameter.

A shape that does NOT carry names gets a named refusal, not a wrong answer. Only the tag-8 pair has a signature today; a keyword through any other callable carrier raises rather than silently dropping the keyword and binding the default, which would return something plausible. That is the failure mode most worth avoiding, and the refusal names why.

Verified

test/test_nilpy_keyword_arg_through_a_callable_value.npy, wired into test-nilpy, expectation generated from CPython, byte-identical. Covers the ticket's own repro, keywords out of declaration order, all-defaulted callees, a keyword supplying a REQUIRED parameter, and all three TypeError cases.

The corpus

webencodings/__init__.py COMPILES — the file behind all 12. Sampled dependents move past the decode wall too: tinycss2/__init__.py and tinycss2/parser.py both go from decode has no parameter named 'final' to undefined variable (MULTILINE) (re.MULTILINE), a new and unrelated wall.

So the decode row is cleared from the ladder. Whether the 12 files now COMPILE is per-file and is the ladder's to report — the ones sampled advance rather than finish, which is the ordinary shape of corpus progress and should be read as such.

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