Missing FPC surface found by the differential probe (Eoln, TSeekOrigin, Sorted, IncMonth)

• Type: feature gap — Track B (library), tag compat
• Status: backlog
• Opened: 2026-08-04
• Found by: tools/fpc_diff_probe.sh after widening it into file I/O, streams, containers and date arithmetic.
• prio: 35

Each is a hard "undefined"/"no such member" error, so none can miscompile — they are missing surface, not wrong behaviour. Grouped because they were found in one sweep and each is small.

The items

1. Eoln(f) — undefined variable (Eoln). Eof exists. Eoln is how character-at-a-time reading finds the end of a line, so its absence forces a readln-and-index workaround.

2. TSeekOrigin constants — undefined variable (soFromBeginning). TStream.Seek itself exists; the origin constants (soFromBeginning / soFromCurrent / soFromEnd, and the modern soBeginning / soCurrent / soEnd) do not, so Seek cannot be called portably.

3. TStringList.Sorted — no such member. Sort (the one-shot method) exists; the Sorted property, which keeps the list ordered across subsequent Adds and switches IndexOf to a binary search, does not. Note the semantic difference from Sort when taking this on: setting Sorted := True changes where later Adds land, and FPC raises on Insert into a sorted list. Also missing alongside it: Duplicates (dupIgnore/dupError/dupAccept), which only has meaning when sorted.

4. IncMonth — undefined variable. The end-of-month clamp is the whole point and the part worth reading off FPC rather than deriving: IncMonth(EncodeDate(2026,1,31), 1) is 2026-02-28, not an overflow into March.

Append, FileExists, DeleteFile and IsLeapYear were suspected in the same sweep and all exist and behave correctly — the probe cases that seemed to implicate them were actually failing on bug-p-writeln-text-rejects-char. Checked individually before filing.

Method note

Each has a probe case waiting in tools/fpc_diff_probe.sh, tagged known. Whoever implements one should read the expectations off an FPC build rather than from the documentation — IncMonth's clamp and Sorted's effect on Add are both the kind of rule that is easy to state slightly wrong.