# Session 2026-10-22 — corpus triage: seven clusters + libc prototypes

Branch **`master`**.  Continues `summary_session-2026-10-19.md`; the
only plan source was its "Remaining" list (corpus `LANG` triage).

## Numbers

| gate | session start | end |
| --- | --- | --- |
| suite (`compiler/run_tests.sh`) | 249/249 | **255/255** |
| fixpoint (`bootstrap/fixpoint.sh`) | OK (3,882,337 B) | **OK (3,935,235 B)** |
| corpus (`tools/v3-corpus/corpus.sh`) | 467/612 | **503/612, 0 crashes** |

Reproduce:

```sh
cd compiler && ./build.sh && ./run_tests.sh          # 255/255
cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
tools/v3-corpus/corpus.sh                            # 503 OK, 0 crash
```

## Triage method

The 118 `LANG` entries were compiled one at a time (a single-file
version of `corpus.sh`), and each first diagnostic was read against its
source line.  They fall into these buckets:

| bucket | count | verdict |
| --- | --- | --- |
| imports `libc` but uses a libc function as a value (`printf`/`malloc`) | ~48 | libc prototypes were missing; **fixed below** (the rest fail later for other reasons) |
| declaration order (type/const/var used before its declaration) | ~25 | correctly rejected (`docs/gaps/`); not a target |
| gm2 extensions (`ASM`, `''` NUL char, `666B`, absolute `VAR [addr]`) | ~7 | not a target unless chosen |
| ISO features actually missing | ~20 | `PACKEDSET`, exceptions/`UNIQUE`, `__FUNCTION__`, `PROC` as a result type; sized SYSTEM types **fixed below** |
| **conforming** clusters: arrays, subranges, ordinal `FOR`, empty string, libc prototypes, SYSTEM sized types, procedure types | 36 | **fixed this session** |

## What landed

### PIM/ISO multi-index arrays — `compiler/src/M2.atg`
`ARRAY [0..1], [0..2] OF T` is the standard spelling (17 corpus files
use it; none use V3's single-bracket comma list).  `ArrayType` now
parses one bracket group per dimension (`{ "," "[" ... "]" }`) and
appends every group's bounds before the element type; nesting stays
inside-out, so the layout matches `ARRAY [0..1] OF ARRAY [0..2] OF T`.
The old `ARRAY [0..1, 0..2] OF` form still works.  Corpus **+6**:
`arraybool`, `assignment2`, `foo`, `recordarray2`, `tinyarray4/5`.
Regression `t_multidim`.

### Subranges keep their ordinal base — `SymTab`, grammar
A subrange was always `FSub` with no base descriptor, so `ClassOf`
returned `ClInt` for `['A'..'Z']` and `[red..blue]`: assigning a
`CHAR`/enum literal (or comparing with one) failed.  `SymTab.NewSubB`
stores the base when both bounds have the same type; `ClassOf`,
`SubBounds`, `SetSpan`/`BaseSpanOk` and the set-span check now follow
it.  `Assignable`/`EqCheck`/`OrdCheck` accept a base value against a
subrange of the same `CHAR`/`BOOLEAN`/enum base (two different enums
stay incompatible).  Corpus **+3**: `subrange16`, `subrange17`,
`enum3`.  Regression `t_subrange`.  Assignment range checks remain
(future) — V3 is already lenient for the integer family.

### `FOR` over ordinals + typed `MIN`/`MAX` of sets — grammar
`FOR` accepted only the integer family.  It now accepts any ordinal
control variable (bounds must be assignment-compatible with it), which
covers enums and `CHAR`.  `MIN`/`MAX` of a `SET` now yields the set's
base type instead of `INTEGER`, so `FOR i := MIN(S) TO MAX(S)` binds
(the bound was previously `INTEGER` against an enum `i`).  Corpus
**+3**: `forloop2`, `smallset4`, `minmax`.

### ISO empty string literal — `SymTab` + grammar + `Lower`
ISO makes the empty string literal (`""` / `''`) length 0 and
compatible with `CHAR`, where its value is the terminator.  V3 typed it
as an ordinary string, so `ch := ""`, `ch = ""`, `CASE ch OF ""`,
`FOR ch := "" TO …`, a `CHAR` formal actual, and `RETURN ""` either
failed (`incompatible assignment`/`comparison`, `invalid Fact`) or
stored a descriptor address.

`SymTab.NewEmptyStr` marks the literal's type (`tlo = -2`); it is still
`ClStr`, so `ARRAY OF CHAR` contexts keep working (`s := ""`, `s = ""`,
`t_strempty`).  `Assignable`/`EqCheck` accept it against `CHAR`, and
`Lower` substitutes the value `0` when the context is a character
(assignment, relation, `CASE` label, `FOR` bound, value actual,
`RETURN`).  Corpus **+6**: `arraychar`, `arraychar2`, `arraychar3`,
`nulcharcase`, `nulcharvar`, `forloopnulchar`.  Regression
`t_emptychar`.

### `libc` prototypes — `SymTab` + `Lower` + grammar
`FROM libc IMPORT P` used to declare every name as a permissive
no-result varargs external, so `printf`/`malloc`/`write` in an
expression were `invalid call`.  The known C functions now get real
signatures from a built-in table (`DeclareCProc`/`CProto`):
`printf`/`snprintf` are varargs functions with an `ARRAY OF CHAR`
format, the rest have typed formals/results (`exit` none, `write`/
`read`/`open`/`close`/`lseek`, `malloc`, `memcpy`/`memset`/`strncpy`,
`system`/`getenv`, `atof`/`strtod`).  `Lower.NoteCProc` copies the
signature into its proc table.

Discarding the result of a call in statement position is now allowed
**only for foreign C varargs** (`printf`/`snprintf`) — the documented
compatibility carve-out.  An ordinary Modula-2 function used as a
statement is still `233` (`t_bad_funstmt`).  Corpus **+6**:
`procedure2`, `tinyparam`, `tinyparam2`, `sizes`, `variant9`,
`varient` (`except5` now stops on ISO exceptions).  Regression
`t_libc2`.

### ISO procedure-type syntax — `M2.atg`
`PROCEDURE` types accepted `;`-separated sections and the GNU type-only
`(T1, T2)` shorthand, but not the ISO/PIM forms used by the corpus:

- comma-separated unnamed parameter types with a keyword/`VAR` start:
  `PROCEDURE(ARRAY OF CHAR, ARRAY OF CHAR)` and
  `PROCEDURE (CHAR, VAR scanClass, VAR scanState)`;
- `PROC` as a result type (`PROCEDURE ... : PROC`), since `PROC` is a
  keyword token and the result position only took `TypeIdent`.

The parameter list now parses a comma as either another name or a new
unnamed type entry; if a type entry starts, the collected names are
resolved as types (`CHAR`, a declared type, or the GNU shorthand).  The
name-group behaviour (`a, b : T`) is unchanged.  `PROC` in a result
position maps to the predeclared procedure-value type.  Corpus **+4**:
`typeonly.def`, `testrecursive.def`, `procconv`, `procconv2`.
Regression `t_proctype2`.

## Commits

Three tagged states, each green on all gates:

| commit | tag | scope |
| --- | --- | --- |
| `aa4f49b` | `v3-corpus-triage` | multi-index arrays, typed subranges, ordinal `FOR` (+12) |
| `f87bcc9` | `v3-empty-string` | ISO empty string as `CHAR` (+6) |
| `c02fd41` | `v3-libc-prototypes` | typed libc prototypes, `printf` varargs (+6) |
| `713650f` | `v3-system-types` | ISO SYSTEM sized types + qualified `SYSTEM` (+8) |

## Lessons

- A corpus "bucket" can be misleading until each file's **first**
  diagnostic is read: 48 files import `libc`, but most stop earlier on
  declaration order, exceptions or sized types.  Only 6 were blocked by
  the missing prototypes.
- The `printf` decision was a policy choice, not a technical one: the
  permissive external already made statement calls work.  Option 3
  (function + allow discarding the result only for foreign C varargs)
  keeps `t_bad_funstmt` and unlocks all 59 `printf` files.
- `docs/gaps/README.md` is still the place to record *why* a case is
  rejected; the new entries state the fix and the remaining carve-out.

### ISO SYSTEM sized types + qualified `SYSTEM` — `SymTab` + grammar
The hard-coded `SYSTEM` module was not registered, so
`SYSTEM.CARDINAL8` (qualified type access) was undeclared even though
`FROM SYSTEM IMPORT CARDINAL8` worked.  `InitSystemModule` now registers
a pseudo-module with its own scope and copies every predef type and
constant into it; `TypeIdent`'s `QualType` and `DesignTail`'s
`MaterializeAlias` then resolve `SYSTEM.X` normally.  `FROM SYSTEM
IMPORT` stays permissive (its names are global predefs or keywords).

Added the ISO/gm2 names: `WORD8/16/32/64`, `BITSET8/16/32`,
`REAL32/64/128`, `COMPLEX32/64/128`, `CSIZE_T`/`CSSIZE_T`/`COFF_T`,
and `BITSPERLOC`/`LOCSPERWORD`/`LOCSPERBYTE`.  V3 keeps its 32-bit
word model, so the narrow integer/word names share `INTEGER`/
`CARDINAL` and `COMPLEX*` is a `REAL` placeholder.  Corpus **+8**:
`compsize`, `int8field`, `returnrecord`, `printsize`, `testgeneric`,
`testgeneric2/3/4`.  Regression `t_system`.

## Remaining (for a next session)

1. **A real `libc.def`** — the built-in prototype table covers the
   common functions; a definition module (or `DEFINITION MODULE FOR
   "C"`) would let users extend it.  Not needed for the corpus now.
2. **ISO `SysClock`** — the stdlib stub lacks `DateTime`,
   `CanGetClock`, `GetClock`, `SetClock` (`testclock`, `testclock2`).
3. **`PACKEDSET`**, ISO exceptions/`UNIQUE`, `__FUNCTION__` — each
   one or two files; larger or gm2-flavoured.
4. **Runtime subrange range checks** — the remaining conformance
   difference from this session's subrange work.
5. `STATUS.md` "what remains" is the live list.