# Unsupported / non-standard cases

One minimal source per known V3 gap (2026-10-18).  Each file's header
comment carries its **tag**, its **Modula-2 status**, and the gm2 corpus
file(s) it stands for.  These are *not* part of the test suite (they are
expected to fail); they exist so each case has a runnable example.

Verify one with:

```sh
cd compiler && ./build.sh
./M2 ../docs/gaps/gap07_convert.mod     # prints the diagnostic on stdout
```

## Policy: follow Modula-2, not degraded gm2

The corpus is **gcc's gm2 testsuite**, so "compiles on the corpus" mixes
conforming Modula-2 with **gm2 leniencies and extensions**.  This
project follows the language:

> Standard Modula-2 (PIM and ISO) requires **declaration before use**;
> the declaration part is ordered `CONST`, `TYPE`, `VAR`.  The only
> forward reference the language allows is a **`POINTER`'s base type**
> (for recursive/self-referential types).

V3 therefore *intentionally rejects* use-before-declaration; that is
conforming behaviour, not a gap.  gm2 accepts such programs because it
resolves the whole declaration part before checking — a **leniency**.

The `class` column says what a change would mean:

- `decl-order` — **not legal Modula-2**; gm2 leniency.  V3 rejects it
  correctly.  *Not a target.*
- `gm2-ext` — **not standard**; a gm2/PIM extension or leniency.
  *Not a target unless we choose gm2 compatibility.*
- `iso/system` — a standard ISO Modula-2 / SYSTEM facility V3 lacks.
  *A genuine gap.*
- `v3-deviation` — V3 is **stricter than the standard** (a V3 bug to
  fix).
- `impl-limit` — the language allows it; V3 has a fixed implementation
  limit.

## Index

| tag | file | class | diagnostic | corpus exemplars |
| --- | --- | --- | --- | --- |
| `gap01-fwd-type-const-conv` | `gap01_fwd_type_const_conv.mod` | `decl-order` | `undeclared identifier` | `subrange4`, `subrange7` |
| `gap02-fwd-type-var` | `gap02_fwd_type_var.mod` | `decl-order` | `undeclared identifier` | `subrange11`, `arrayptr`, `arrayptr6`, `constructor1`, `constructor3`, `param3` |
| `gap03-fwd-type-heading` | `gap03_fwd_type_heading.mod` | `decl-order` | `undeclared identifier` | `shift3`, `shift4` |
| `gap04-fwd-const-bound` | `gap04_fwd_const_bound.mod` | `decl-order` | `undeclared identifier` | `setconst3` |
| `gap05-fwd-type-size` | `gap05_fwd_type_size.mod` | `decl-order` | `undeclared identifier` | `constsize2` |
| `gap06-fwd-setconst` | `gap06_fwd_setconst.mod` | `decl-order` | `undeclared identifier` | `setoverflow` |
| `gap09-scalar-to-bytearray` | `gap09_scalar_to_bytearray.mod` | `gm2-ext` | `invalid call` | `aochar`, `arrayofbyte`, `bytearray` |
| `gap10-var-param-type` | `gap10_var_param_type.mod` | `gm2-ext` | `invalid call` | `testparam2`, `testparam3` |
| `gap11-bare-proc-stmt` | `gap11_bare_proc_stmt.mod` | `gm2-ext` | `invalid call` | `tinyproc2`, `tinyproc4` |
| `gap12-variant-empty-arms` | `gap12_variant_empty_arms.mod` | `gm2-ext` | `invalid VarLabel` | `varient2`, `varient3`, `varient8`, `tsize`, `tsize2` |
| `gap14-builtin-pragma` | `gap14_builtin_pragma.def` | `gm2-ext` | `ident expected` | `builtin.def`, `builtin.mod` |
| `gap16-wide-set` | `gap16_wide_set.mod` | `impl-limit` | `not supported yet` | `settest1` |
| `gap17-set-of-cardinal` | `gap17_set_of_cardinal.mod` | `impl-limit` | `not supported yet` | `settest3` |
| `gap18-set-case-labels` | `gap18_set_case_labels.mod` | `gm2-ext` | `not supported yet` | `bitset5` |
| `gap19-fwd-array-index` | `gap19_fwd_array_index.mod` | `decl-order` | `not supported yet` | `record7`, `complextypes` |
| `gap20-fwd-set-of-type` | `gap20_fwd_set_of_type.mod` | `decl-order` | `undeclared identifier` | `tinyset6`, `tinyset7` |
| `gap21-fwd-record-field` | `gap21_fwd_record_field.mod` | `decl-order` | `undeclared identifier` | `record14.def`, `record15.def`, `record16.def` |
| `gap22-file-line` | `gap22_file_line.mod` | `gm2-ext` | `invalid Fact` | `packed` |

First diagnostic (message) per file at commit time (line:col varies as
comments change):

```
gap01_fwd_type_const_conv.mod   undeclared identifier   (ind0)
gap02_fwd_type_var.mod          undeclared identifier   (arr)
gap03_fwd_type_heading.mod      undeclared identifier   (large)
gap04_fwd_const_bound.mod       undeclared identifier   (n)
gap05_fwd_type_size.mod         undeclared identifier   (t)
gap06_fwd_setconst.mod          undeclared identifier   (CharSet / tab)
gap09_scalar_to_bytearray.mod   invalid call            (scalar -> ARRAY OF BYTE)
gap10_var_param_type.mod        invalid call            (VAR actual type)
gap11_bare_proc_stmt.mod        invalid call            (bare proc value)
gap12_variant_empty_arms.mod    invalid VarLabel
gap14_builtin_pragma.def        ident expected          (__BUILTIN__)
gap16_wide_set.mod              not supported yet       (span > 65536)
gap17_set_of_cardinal.mod       not supported yet       (unbounded base)
gap18_set_case_labels.mod       not supported yet       (set as CASE selector)
gap19_fwd_array_index.mod       not supported yet       (array index declared later)
gap20_fwd_set_of_type.mod       undeclared identifier   (SET OF base declared later)
gap21_fwd_record_field.mod      undeclared identifier   (record field type declared later)
gap22_file_line.mod             invalid Fact            (__LINE__)
```

## Genuine gaps (worth fixing, standard Modula-2)

- **`gap07` CONVERT — fixed** (2026-10-18): `CONVERT(T, x)` is accepted as
  a `VAL` sibling (`procconv2` passes).
- **`gap08` set↔word `CAST`/`VAL` — fixed** (2026-10-18): `VAL`/`CAST`
  between a set and its machine word (`constset`, `constset2`,
  `constset3` pass).  `packed` still needs `gap22` (`__FILE__`/`__LINE__`).
- **`gap13` builtins as identifiers — the corpus case is fixed**
  (2026-10-18): `ORDL` (a gm2/FileIO helper, not a Modula-2 built-in) is
  no longer reserved, so `PROCEDURE ORDL` is accepted (`fileio.def/mod`,
  `baseimport` pass; the scanner frame now imports `FileIO.ORDL`).  The
  *standard* built-ins (`ORD`, `CHR`, `VAL`, …) are still keyword-style —
  de-reserving them is a larger parser refactor.
- **`gap15` enumeration literals with an imported type — fixed**
  (2026-10-18): literals now travel with the type through re-export,
  FROM-import and qualified access; also fixed the qualified-const value
  (`LoadDesignator` returned 0 for enum consts).  `imp*` pass.
- Foreign modules `FOR "C"` / `EXPORT UNQUALIFIED` — already fixed
  (§ STATUS).

`gap16`/`gap17` are implementation limits (raising the set span cap).

## Not represented by a source

- **Size-sensitive V3 miscompile** — a *latent* codegen bug that only
  manifests at the compiler's own scale (the historical "removing
  `ASTDUMP` breaks the fixpoint"); see `docs/summary_l3_selfhost_fix.md`.
  No small standalone source triggers it.