High(Type)/Low(Type) not accepted in constant expressions / array bounds

• Type: bug (Pascal frontend — const-eval) — Track P (edits the shared parser/const-eval, so it runs under A's gate + no-concurrent-edit rule)
• Status: done
• Opened: 2026-07-11, first blocker of the New-ZenGL Pascal ladder ([[feature-game-library-candidate-suite]] slice C).

Symptom

High(T) (and presumably Low(T)) works as a runtime expression (project memory: "High/Low of type" landed) but is rejected by the constant evaluator, so it cannot appear in an array bound or const declaration:

type
  TSmall = array[0..High(Byte)] of Byte;              { minimal repro }
  TByteArray = array[0..High(LongWord) shr 1 - 1] of Byte;   { ZenGL zgl_types.pas:105 }

ConstEval error at SrcLine 3: SVal = High Kind = 1 TokPos = 11

Also note the diagnostic itself: ConstEval error reports a raw token dump instead of a file:line error like the parser's other messages — worth folding into the normal error path while in there.

FPC accepts both forms; High(LongWord) = 4294967295 must evaluate as an unsigned value in const context (the ZenGL bound is High(LongWord) shr 1 - 1 = $7FFFFFFE).

Where hit

library_candidates/zengl/Zengl_SRC/src/zgl_types.pas:105 — blocks the whole New-ZenGL Pascal ladder (every zgl unit pulls zgl_types via uses).

Acceptance

• High(T)/Low(T) for ordinal types (incl. LongWord, Int64, enums, subranges, Char, Boolean) evaluate in const expressions: array bounds, const x = High(...), case labels.
• Compose with const operators (shr, -, ...) as in the ZenGL bound.
• Self-host byte-identical; a compile-run test covers the forms above.

Log

• 2026-07-12 — resolved, commit HEAD.