Generator yield of a call expression lowers to unsupported IR

• Type: bug (compiler / IR lowering)
• Status: done
• Owner: Track A
• Opened: 2026-06-21
• Relation: current examples/chess blocker; belongs to the generator / record-yield family but is narrower than the old demo-gap ticket.

Symptom

examples/chess/chess.pas fails in the move generator:

Unsupported linear node in IR codegen! Kind=10 node=120 IRA=8 IRB=107 IRC=-1 IRIVal=90
pascal26:629: error: Unsupported linear node in IR codegen ()

The source reported at line 629 is the closing end of GenMoves, but the IR dump shows unsupported nodes immediately under IR_YIELD. The first offending source construct is:

if RankOf(dest) = promoRank then
begin
  yield MkMove(from, dest, pkQueen,  [mfPromo]);
  yield MkMove(from, dest, pkRook,   [mfPromo]);
  yield MkMove(from, dest, pkBishop, [mfPromo]);
  yield MkMove(from, dest, pkKnight, [mfPromo]);
end

MkMove(...) returns a TMove record. The same shape appears throughout GenMoves:

yield MkMove(from, dest, pkNone, [mfCapture]);
yield MkMove(4, 6, pkNone, [mfCastleK]);

--dump-ir shows:

unsupported a=8 ... ival=90 ...
yield a=<unsupported-node> ...

where IR_UNSUPPORTED carries a=8, i.e. AN_CALL.

Root Cause

IR lowering for stackful generator yield can handle record-yield storage once it has a lowered value/address, but AN_YIELD does not lower a record-returning call expression used directly as the yielded value. The call expression falls through to IR_UNSUPPORTED, then x86-64 codegen reports the generic unsupported linear node.

Using a local temporary is expected to sidestep the issue:

tmp := MkMove(from, dest, pkQueen, [mfPromo]);
yield tmp;

but the direct expression is legal source and should compile.

Direction

• Fix AN_YIELD / record-yield lowering so a call expression can be materialized before yielding.
• Prefer a general solution: any yield expression that returns an aggregate should lower through the same temporary/address path as assignment of a record-returning call.
• Add a small regression test with a generator yielding a record returned by a helper function.
• Keep the chess source as-is; do not require manual temporaries in the demo.

Acceptance

• Minimal yield MakeRecord(...) generator test compiles and runs.
• examples/chess/chess.pas gets past the current IR_UNSUPPORTED failure.
• Existing generator record-yield tests remain green.

Log

• 2026-06-21 - Opened from pinned v26 chess discovery failure. The failing source is direct yield MkMove(...) in GenMoves; the diagnostic lands on the generator's closing end because the unsupported call expression is discovered during IR codegen.
• 2026-06-21 - DONE (Track A). Fixed at parse time in the yield builtin dispatch (ParseStatementAST): when the yielded value is a tyRecord that is not an addressable lvalue (not AN_IDENT/AN_FIELD/AN_INDEX/AN_DEREF, i.e. a record-returning call), materialise it into a generator-frame local (AllocVar + InferSymTypeFromNode to carry RecName from ProcRetRecId + AllocateSymOffset), emit tmp := <call> before the yield, and yield the temp. The stackful frame keeps the temp alive until the next resume, so the existing AN_YIELD→IRLowerAddress record path (which previously fell through to IR_UNSUPPORTED on AN_CALL) now sees an AN_IDENT. Source stays manual-temp-free. Regression test test/test_generator_yield_call.pas. make test green; self-host + threadsafe fixedpoint byte-identical.

Resolved-in: 085be11 (finalizing commit)