Default parameter values on class/interface methods (works on free routines)

Type: feature (parser — method declarations, Track A)
Status: done
Owner: —
Opened: 2026-07-04 (bisecting the fgl wall; see [[fpc-lcl-compile-probe]])

Problem

Default parameter values work on free routines but not on methods:

function F(a: Integer; b: Integer = 10): Integer;          { OK }

type TFoo = class
  procedure M(n: Integer = 5);                             { pascal26: unexpected token }
  constructor Create(AItemSize: Integer = sizeof(Pointer));{ unexpected token }
end;

Any = <default> in a class/interface method parameter list errors — it is not sizeof-specific (even = 10 fails), so the method param parser simply has no default-value clause. fgl.pp's TFPSList.Create(AItemSize: Integer = sizeof(Pointer)) hits this (one of several fgl walls; see the probe doc).

Root cause

The free-routine param parser (ParseSubroutine, ~parser.inc:13893) handles the default:

if CurTok.Kind = tkEq then begin Next; defaultVal := ConstEval; hasDefault := True; end;

The method param parsers do not:

class-method params (in ParseTypeSection's class body) — the param loop that ends at if not Eat(tkSemicolon) then mDoneArgs := True (~parser.inc:12234).
interface-method params — the analogous loop (~parser.inc:11974).

Both parse the param type then expect ;/), so = is unexpected. They also do not populate ProcParamDefaultVal/pdefault for the registered method proc, so even if parsed, a call omitting the arg would not substitute it.

Fix (Track A, parser.inc)

Mirror ParseSubroutine's default-value clause into the two method param loops: after the param type, accept = ConstEval, set the per-param default flag/value, and record them into ProcParamDefaultVal for the method's proc index (the call site already substitutes defaults from there — see the .Create (parameter … has no default) path at ~parser.inc:5613). Depends on / pairs with [[feature-sizeof-const-intrinsic-in-const-eval]] so = sizeof(Pointer) folds.

Acceptance

procedure M(n: Integer = 5) and constructor Create(n: Integer = sizeof(Pointer)) compile; a call omitting the arg uses the default; a call supplying it overrides.
Self-host byte-identical; make test green; regression .pas.

Resolution (2026-07-04)

DONE (commit 54b20c0e). Mirrored ParseSubroutine default clause into the class-method and interface-method param loops; defaults stored at class-decl registration (Self-shifted). All nine method-call arg-parse loops accept a shorter call and fill trailing defaults (FillDefaultArgs helper, mirroring the ctor arity fill); body impls that repeat params without defaults no longer clear them. Covers ctor sizeof(Pointer) default, virtual-through-base, class-static, interface dispatch, paren-less calls. Regression test/test_default_params_methods.pas (12/12) in test-core. Self-host byte-identical, make test green.