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"Is this node a whole array?" is answered in four places with four lists

The four

site predicate
AssignSideKind, ident arm Syms[].IsArray
AssignSideKind, field arm (as of 12af8ef60) NodeDynDepth
the fixed→dynamic sibling NodeDynDepth plus Syms[].Kind <> skParam
the lowering ASTNodeIsWholeArray

Measured disagreement: for a static array FIELD, ASTNodeIsWholeArray answers True and NodeDynDepth answers 0. c.SA := b on an array[0..2] of TR field matches fpc today, whole-assignment and per-element, so nothing is broken — the field-arm fix is complete for dynamic arrays and silent about static ones, and frankD wrote that down rather than leaving it to be found.

Why it ranks with the shape readers rather than with the funnel

Three of Group 28's rows are "the reader could not ask the question it actually had". This is the fourth form: four readers ask, and get four answers.

frankS's classification, which is the reason this is a separate row: a partially-consulted record is found by a set difference — is that column consulted where the cases are distinguished — while four predicates that agree on all but one shape cannot be found that way, because every consumer exists and every one compiles. Agreeing on all but one shape is worse than disagreeing visibly: four obviously different answers get reconciled the first time anyone looks at them together, and four that agree in every probed case do not.

Compare the sibling already closed in this group, [[bug-p-low-and-high-of-a-nested-static-array-row-answer-the-outer-arrays-bounds]]: there, NDRowSourceInfo answers a different question off the same data and both its callers are right. That one is found by noticing two correct callers want different numbers. This one is found by asking four readers the same question. Neither is found by grepping for an absence.

Availability

Deliberately ownerless in the parent, for stated reasons: frankD is at rung 7 (pparser.pp next) and offered a handover of the per-side half with the two arms and the measured disagreement; frankS declined on scheduling, not interest, because their instance sits in the pairwise half. frankD's handover offer is live. Take the handover before starting.

What would settle it

One predicate, node-shape-independent, that every one of the four consults — and, before that, a probe per shape (ident, field, param, deref, index) crossed with static and dynamic, recording what each of the four answers today. The disagreement above is one cell of that table and it is the only cell anyone has filled in.

Do not collapse the pairwise checks into it. Enum identity and fixed-to-dynamic are facts about two sides TOGETHER; a per-side predicate cannot express them, and putting one in a per-side slot is the specific mistake the parent's axis split exists to prevent.

The census, and it corrects this ticket's own framing — 2026-09-06 (frankB), compiler aa8f3c3b4b68

There are not four answers to one question. There are THREE questions and one duplicated predicate, and once they are named the "measured disagreement" in this ticket stops being one.

# question who asks it
1 is this lvalue a whole array, of any kind? ASTNodeIsWholeArray; and AssignSideKind's AN_IDENT arm, which spelled the same test inline as Syms[].IsArray
2 how many dynamic array of levels remain? NodeDynDepth; AssignSideKind's element/field/deref arm asks > 0
3 is this a fixed-length, non-parameter array symbol? the fixed→dynamic guard's four conjuncts

frankD's cell — a static array FIELD answers True to ASTNodeIsWholeArray and 0 to NodeDynDepth — is question 1 and question 2 each answering correctly. Neither is wrong; they are different questions. Question 3 is a third: its own comment records that ArrLen > 0 does NOT mean fixed-length, because AllocParam stamps 1000 on every array parameter, so Kind <> skParam is the property that separates them. A single predicate cannot serve all three, and merging them is the mistake, not the fix.

What IS wrong at that site, and it is not what this ticket predicted

AssignSideKind's AN_IDENT arm asks question 1 and its element/field/deref arm asks question 2, at the same decision point. But a bail there means "I cannot type this side", and the check then STANDS DOWN — so the arms do not disagree about the outcome, they agree on it:

type TSA = array[0..2] of AnsiString;
var sa: TSA; s: AnsiString; c: TC;  { c.SA: TSA; c.DA: array of AnsiString }
  sa   := s;    pxx ACCEPTED, SIGSEGV     fpc: Incompatible types
  c.SA := s;    pxx ACCEPTED, SIGSEGV     fpc: Incompatible types
  p^   := s;    pxx ACCEPTED, exit 0      fpc: Incompatible types
  c.DA := s;    pxx ACCEPTED, exit 0      fpc: Incompatible types

Every whole-array destination is unchecked, in every spelling, and two of the four segfault. Filed as [[bug-p-a-whole-array-assignment-destination-is-never-type-checked]] — it is a NARROWING (the funnel would start refusing programs it accepts today) and it needs its own evidence, not a refactor's.

What landed here

  1. AssignSideKind's AN_IDENT arm asks ASTNodeIsWholeArray(node) instead of spelling Syms[si].IsArray inline. Byte-identical answer for AN_IDENT; one name for question 1.
  2. ASTNodeIsWholeArray gained the AN_DEREF arm via DerefPtrArrayShape (Group 28's own generalisation). Its opening sentence says "this lvalue node" and p^ on ^array[0..2] of T or ^TDyn is a whole array — the element is p^[i], an AN_INDEX, which already falls out.

MEASURED INERT, AND RECORDED AS INERT RATHER THAN CREDITED. The sole caller is the X := nil lowering, and p^ := nil through a pointer to a dynamic array of records answers len=0 byte-for-byte with fpc 3.2.2 with a live handle AND with an already-nil one — the two shapes that produced the SIGSEGV that function was written for. Another arm catches it. The arm is here because the QUESTION has a right answer for a deref and this reader owns the question, not because a row moved.

The cell that is still empty, and it is not empty by accident

Nothing here measured a parameter. Question 3's whole existence is that a parameter's recorded length is untrustworthy in both directions (AllocParam stamps ArrLen := 1000), so a param row would be the most informative cell of all — and the fixed→dynamic guard already excludes it by name for that reason. Whoever picks up the narrowing above should start there.

Gate

make compiler/pascal26 converged; --tier quick GREEN; run_fgl_corpus.sh 7/7; the four := nil deref/field probes byte-identical to fpc 3.2.2 before and after.

frankD's handover, and it settles the shape rather than adding detail

Asked for it before starting, per this ticket's own instruction. Three answers, and the second is the one that decides what NOT to do:

NodeDynDepth in the field arm was CHOSEN, and the reason is in the code rather than in this ticket — ir.inc, immediately above the bail: "it already types AN_FIELD, AN_INDEX and AN_DEREF (and calls, and Copy, and array constructors), and a second derivation here would be a second answer to a question already answered." So the constraint on any unification is not "agree with ASTNodeIsWholeArray" — it is be the walk that already types calls, Copy and array constructors. Merging that arm toward ASTNodeIsWholeArray would narrow it from six node classes to two and lose shapes it never had a bug in. It was left exactly as it is, and the AN_IDENT arm is the only one that changed.

Two predicates, not one, independently reached from both ends: frankD's cell is the proof rather than an example, because both answers are correct. Merging four readers into one has to pick one of the two and would silently hand the wrong one to two of the four callers.

A suspected FIFTH reader, unfilled and flagged as unfilled: the field arm bails on NodeDynDepth > 0 before asking RecIsReferenceShaped(rec), which is a neighbouring question about the same node, and whether the two can disagree was never probed. Treat it as an empty cell, not a checked one.

The naming trap is live in this very function and is the coordinator's SymBlockId shape one file over: ASTNodeIsWholeArray promises the general question and answered it for AN_IDENT only until this morning, then AN_IDENT and AN_FIELD, and reads as the general one at every call site regardless. The AN_DEREF arm added here closes the third of five node classes; AN_INDEX is correctly False, and a CALL returning an array is the one still unanswered.

And frankD's own cell is a weak green, by their own account: c.SA := b matches fpc both ways, measured as an OUTPUT comparison on x86-64. Anything here whose answer is a width or a layout is invisible to that — the structurally native-only blind spot CLAUDE.md names.

Log