Default standard units: System + textfile

• Type: feature (compiler / RTL loading)
• Status: done
• Track: A
• Owner: —
• Opened: 2026-06-21
• Relation: follows feature-textfile-keyword-io-dispatch and bug-implicit-textfile-unit-method-local; needed by examples/adventure. Also sets the expected home for System helpers such as Inc.

Problem

The current implicit textfile import is a token-scan special case. It works for a simple program with a program-level var f: Text, but it misses method-local Text declarations inside units:

procedure TGame.SaveTo(const path: AnsiString);
var f: Text;
begin
  Assign(f, path); Rewrite(f);

pascal26:563: error: undefined variable (Assign)

This is the wrong shape long-term. Classic Pascal expects a standard surface: System is always in scope, and text-file I/O is close enough to that surface that making users write uses textfile everywhere is awkward. At the same time, the compiler must still be buildable by FPC, and the self-host compiler should not be forced through unstable RTL while that surface is still moving.

Direction

• Introduce a default standard unit set, initially System and textfile.
• Load default standard units uniformly for programs and units before user declarations are resolved.
• Keep implementations in RTL units. Do not move Text/Assign/Inc into compiler builtins just to make them visible.
• Preserve zero-cost unused code: a trivial program that does not use text-file I/O must not emit textfile routines or pull platform file I/O into the binary.
• Keep textfile parse-safe on all targets: platform/PAL calls must stay inside referenced routines, with no mandatory unit initialization.
• Add an escape hatch for bootstrap and constrained targets while the default RTL surface stabilizes. Prefer a command-line switch for build scripts, such as --no-default-rtl or --no-implicit-system; a source directive such as {$PXXDEFAULTUNITS OFF} can be added if source-level control is useful.
• When the escape hatch is active, code must explicitly import the units it needs, or rely only on true compiler builtins.

Acceptance

• A minimal program can use Inc from System without an explicit uses.
• A unit method with local var f: Text can call Assign/Rewrite/ WriteLn(f, ...) without explicit uses textfile.
• examples/adventure gets past engine.pas:563 without adding an explicit uses textfile workaround.
• make bootstrap / compiler self-build has a documented opt-out path until System and textfile are stable enough to compile the compiler itself under default units.
• test/hello.pas remains the same size as the current baseline, 29,086 bytes, or any size increase is explained and tracked as a dead-code/lazy-emission follow-up before this broadens further.
• Existing explicit uses textfile tests continue to pass.

Log

• 2026-06-21 - Opened after confirming the implicit textfile scanner catches a simple program but misses Text in a unit method-local var section. Design preference: default-load System and textfile, with an opt-out for compiler self-build while RTL stability catches up.
• 2026-06-21 - Baseline guard: test/hello.pas compiles to 29,086 bytes with both pinned v26 and rebuilt live compiler/pascal26; use this as the first check that unused default units stay free.
• 2026-06-21 - DONE (commit d5c7498, Track A). textfile (+ its builtin numeric-format backing) is now loaded by default on every non-ESP target, uniformly for programs and units, replacing the : Text token scan. The posix PAL backend dir is auto-added to the unit search path (ExeDir-anchored + CWD-relative) so pxx foo.pas resolves platform_backend with no -Fu. Opt-out: --no-default-rtl flag or {$define PXX_NODEFAULTRTL} in source; the compiler defines the latter so every self-build path (bootstrap, cross-bootstrap, stabilize) opts out with no per-site Makefile flag, and the self-host fixedpoint stays byte-identical. Acceptance: unit method-local var f: Text resolves Assign/Rewrite/WriteLn with no uses/-Fu; examples/adventure clears the engine.pas:563 blocker (now stops at :604, the separate nested-proc bug). Inc/System part: Inc was already a true compiler builtin (works with no uses), so no System RTL unit was needed for the acceptance — left as a no-op; revisit if/when real System helpers land. Two latent compiler bugs surfaced and fixed in the same commit (would crash any program that pulled a >8-byte managed record): (1) whole array-of-record idents mis-routed through the record-by-value temp path in IRLowerCallArg → corrupted SetLength target; (2) managed value-records leaked into the __rttireg class registry via EmitLayoutRTTI's UClsRTTIOff. Size guard NOT met / accepted tradeoff: test/hello.pas grows 29,086 → ~42,661 bytes (textfile+builtin in every program, no DCE). User chose the simpler "always include" over chasing the token scan. Tracked as feature-lazy-standard-unit-emission (dead-code / routine-level lazy emission) before the default surface broadens further.