PChar(s)^ / cast-derefs rejected as var/untyped method-call arguments

• Type: bug (Pascal frontend — call-argument lvalue path) — Track P (shared parser, A's gate)
• Status: done
• Opened: 2026-07-12, next Synapse wall after the untyped-Pointer-deref expression fix ([[feature-synapse-compile-check]]).

Symptom

Passing a deref-of-cast as a by-ref (var/out/untyped) argument fails with undefined variable (PChar) — the by-ref argument path resolves a bare IDENT (CompileLValueAddress-style) instead of parsing a full lvalue expression:

uses classes;
var st: TMemoryStream; s: AnsiString; x: Integer;
begin
  st := TMemoryStream.Create;
  s := 'abc';
  st.Write(PChar(s)^, Length(s));    { undefined variable (PChar) }
  x := st.Read(PChar(s)^, 3);        { same }
end.

PAnsiChar spelled out fails identically. Note the EXPRESSION-level form is fine since the untyped-deref fix (Pointer(p)^ / PChar(s)^ as plain-proc untyped args work — see test/test_ptr_untyped_deref.pas); the gap is the METHOD-call by-ref argument route.

Where hit

external/synapse/synautil.pas:1867/1884 — Stream.read(PAnsiChar(Result)^, Len) / Stream.Write(PAnsiChar(Value)^, Length(Value)). This is the current wall of the whole Synapse compile.

Acceptance

• A cast-deref (PChar(s)^, Pointer(p)^, PByte(x)^) is accepted wherever a var/out/untyped argument lvalue is expected, in BOTH the plain-proc and the method-call argument paths (the address of the deref is passed).
• The repro above compiles and round-trips 'abc' through the stream.
• Self-host byte-identical; test covers method + plain forms.

Log

• 2026-07-12 — resolved, commit 541f8fda.