parse,check,type,wwi: @packed struct attribute, both stages (#51)

Hare/harec @packed struct layout: no inter-field or trailing padding, align =
max field align (NOT forced to 1) — matches harec type_store.c + types.c:621
(packed{u8,u64}=size 9/align 8). Parser consumes inline @packed (loud-rejects
unknown struct attrs, both stages); layout gates padding on !packed; cstage
type_eq enforces packed type-distinctness; the .wwi producer round-trips
"struct @packed {". wwstage sets slotsize=size for packed so its composite-ABI
copy matches cstage byte-for-byte. cstage identity is faithful; wwstage identity
rides the deferred #224 nominal-resolvealias arc (#108). Both stages byte-id;
447 tests pass.

cmd/w6c/wwi.c

@@ -252,7 +252,9 @@ wwi_type(FILE *of, Node *t)
 		wwi_type(of, t->lhs);
 		break;
 	case N_TSTRUCT:
-		fputs("struct { ", of);
+		/* re-emit the `@packed` attr so the flag round-trips
+		 * through sep-compile (harec unparse/type.ha:122-126). */
+		fputs(t->packed ? "struct @packed { " : "struct { ", of);
 		for (Node *f = t->list; f; f = f->next) {
 			if (f != t->list) fputs(", ", of);
 			if (f->str && f->str[0]) {

cmd/wcc/check.c

@@ -935,7 +935,11 @@ resolve_type(Checker *c, Node *n)
 			if (!require_sized(c, ft, f->pos, "a struct field"))
 				continue;
 			if (ft->align > maxalign) maxalign = ft->align;
-			off = (off + ft->align - 1) & ~(ft->align - 1);
+			/* packed: no inter-field padding (harec
+			 * type_store.c:206-213); align still tracks the
+			 * max field align below. */
+			if (!n->packed)
+				off = (off + ft->align - 1) & ~(ft->align - 1);
 			if (f->str != NULL) {
 				/* regular named field */
 				for (Tfield *e = head; e; e = e->next)
@@ -985,8 +989,12 @@ resolve_type(Checker *c, Node *n)
 			off = base + inner->size;
 		}
 		t->fields = head;
+		t->packed = n->packed;
 		t->align = maxalign;
-		t->size = (off + maxalign - 1) & ~(maxalign - 1);
+		/* packed: skip the trailing pad-to-align (harec
+		 * type_store.c:886 `!packed`); align value unchanged. */
+		t->size = n->packed ? off
+		    : ((off + maxalign - 1) & ~(maxalign - 1));
 		return t;
 	}
 	case N_TENUM: {

cmd/wcc/parse.c

@@ -204,8 +204,25 @@ parsetype(Parser *p)
 	}
 	case TK_STRUCT: {
 		advance(p);
-		expect(p, TK_LBRACE);
 		Node *n = newnode(p->a, N_TSTRUCT, pp);
+		/* `@packed` is an inline struct TYPE attribute (harec
+		 * ast.h:95 `bool packed`), sitting after `struct` and
+		 * before `{` — NOT a fn-decl attr, so it does not route
+		 * through parseattrs. */
+		if (p->cur.kind == TK_AT) {
+			advance(p);
+			const char *an = expectident(p);
+			/* p->errs gates the build (cmd/w6c/main.c:82);
+			 * nerrors is advisory-only, so an errorf on a
+			 * clean-recovery path must bump p->errs itself. */
+			if (strcmp(an, "packed") != 0) {
+				errorf(p->cur.pos,
+				    "unknown struct attribute '@%s'", an);
+				p->errs++;
+			} else
+				n->packed = 1;
+		}
+		expect(p, TK_LBRACE);
 		Node *head = NULL, *tail = NULL;
 		while (p->cur.kind != TK_RBRACE && p->cur.kind != TK_EOF) {
 			Pos fp = p->cur.pos;

cmd/wcc/type.c

@@ -267,6 +267,9 @@ type_eq(Type *a, Type *b)
 		return pa == NULL && pb == NULL;
 	}
 	case TY_STRUCT: {
+		/* packed is part of struct identity: a packed struct is
+		 * not equal to its unpacked twin (harec types.c:621). */
+		if (a->packed != b->packed) return 0;
 		Tfield *fa = a->fields, *fb = b->fields;
 		while (fa && fb) {
 			if (strcmp(fa->name, fb->name) != 0) return 0;

cmd/wcc/ww.h

@@ -345,6 +345,8 @@ struct Node {
 	Node		*next;	/* sibling link inside `list` */
 	Node		*attr;	/* @attribute chain (N_ATTR list) */
 	int		export;
+	int		packed;	/* N_TSTRUCT: `struct @packed` — no field/
+				 * trailing padding (harec ast.h:95). */
 	Type		*type;	/* filled in by checker */
 	const char	*tsuffix;	/* typed numeric literal suffix */
 	const char	*module;	/* `// MODULE: foo` directive at the
@@ -487,6 +489,8 @@ struct Type {
 				 * stored as a single 8-byte pointer; null
 				 * is the void variant. Mirrors Hare's
 				 * `(*T | null)` folding. */
+	int		packed;	/* TY_STRUCT laid out with no padding; part
+				 * of type identity (harec types.c:517/621). */
 };
 
 extern Type	*ty_void, *ty_bool, *ty_rune;