wcc: Hare-style struct embedding (anon + bare-name)

Struct members can be `struct { ... }` (anonymous nested) or a bare
named type, in addition to `name: type`. The inner struct's fields
are promoted to the outer scope with offsets shifted by the embed
base; codegen already keys off Tfield.offset so cgen needs no change.
Errors on non-struct embed or name collision.

cmd/wcc/check.c

@@ -167,16 +167,56 @@ resolve_type(Checker *c, Node *n)
 		Tfield *head = NULL, *tail = NULL;
 		u64 off = 0, maxalign = 1;
 		for (Node *f = n->list; f; f = f->next) {
-			Tfield *tf = amalloc(c->a, sizeof *tf);
-			tf->name = f->str;
-			tf->type = resolve_type(c, f->lhs);
-			if (tf->type->align > maxalign) maxalign = tf->type->align;
-			off = (off + tf->type->align - 1) & ~(tf->type->align - 1);
-			tf->offset = off;
-			off += tf->type->size;
-			if (head == NULL) head = tf;
-			else tail->next = tf;
-			tail = tf;
+			Type *ft = resolve_type(c, f->lhs);
+			if (ft->align > maxalign) maxalign = ft->align;
+			off = (off + ft->align - 1) & ~(ft->align - 1);
+			if (f->str != NULL) {
+				/* regular named field */
+				for (Tfield *e = head; e; e = e->next)
+					if (e->name && strcmp(e->name, f->str) == 0) {
+						err(c, f->pos, "duplicate field '%s'",
+						    f->str);
+						break;
+					}
+				Tfield *tf = amalloc(c->a, sizeof *tf);
+				tf->name = f->str;
+				tf->type = ft;
+				tf->offset = off;
+				off += ft->size;
+				if (head == NULL) head = tf;
+				else tail->next = tf;
+				tail = tf;
+				continue;
+			}
+			/* embed (anonymous struct or bare-name): the inner type
+			 * must be a struct; its fields are promoted to the outer
+			 * scope with offsets shifted by the embed base. */
+			Type *inner = (ft && ft->kind == TY_NAMED) ? ft->under : ft;
+			if (inner == NULL || inner->kind != TY_STRUCT) {
+				err(c, f->pos, "embedded type must be a struct");
+				off += ft ? ft->size : 0;
+				continue;
+			}
+			u64 base = off;
+			for (Tfield *src = inner->fields; src; src = src->next) {
+				for (Tfield *e = head; e; e = e->next)
+					if (e->name && src->name &&
+					    strcmp(e->name, src->name) == 0) {
+						err(c, f->pos,
+						    "embedded field '%s' "
+						    "collides with existing field",
+						    src->name);
+						break;
+					}
+				Tfield *tf = amalloc(c->a, sizeof *tf);
+				tf->name = src->name;
+				tf->type = src->type;
+				tf->offset = base + src->offset;
+				if (head == NULL) head = tf;
+				else tail->next = tf;
+				tail = tf;
+			}
+			off = base + inner->size;
 		}
 		t->fields = head;
 		t->align = maxalign;

cmd/wcc/parse.c

@@ -191,9 +191,21 @@ parsetype(Parser *p)
 		while (p->cur.kind != TK_RBRACE && p->cur.kind != TK_EOF) {
 			Pos fp = p->cur.pos;
 			Node *f = newnode(p->a, N_TFIELD, fp);
-			f->str = expectident(p);
-			expect(p, TK_COLON);
-			f->lhs = parsetype(p);
+			/* Three member forms:
+			 *   name: type       — regular field
+			 *   struct { ... }   — anonymous embedded struct
+			 *   Identifier       — bare-name embedded type
+			 * Embeds carry f->str == NULL and the type in f->lhs. */
+			if (p->cur.kind == TK_STRUCT) {
+				f->lhs = parsetype(p);
+			} else if (p->cur.kind == TK_IDENT
+			    && peek(p).kind != TK_COLON) {
+				f->lhs = parsetype(p);
+			} else {
+				f->str = expectident(p);
+				expect(p, TK_COLON);
+				f->lhs = parsetype(p);
+			}
 			if (head == NULL) head = f;
 			else tail->next = f;
 			tail = f;

test/wcc/700_e2e.c

@@ -344,6 +344,20 @@ static const struct row rows[] = {
 	  "  os.assert(r == 42, \"sum mismatch\\n\");\n"
 	  "  return r: i32;\n"
 	  "};", 42 },
+	/* Hare-style struct embedding: bare-name embed + anonymous
+	 * nested struct, fields promoted to the outer scope. Both
+	 * field-by-field assignment and flat struct-literal init must
+	 * see promoted fields. */
+	{ "type point = struct { x: i32, y: i32 };\n"
+	  "type vec = struct {\n"
+	  "  point,\n"
+	  "  struct { z: i32 },\n"
+	  "  w: i32,\n"
+	  "};\n"
+	  "fn main() i32 = {\n"
+	  "  let v: vec = vec { x = 1, y = 2, z = 3, w = 36 };\n"
+	  "  return v.x + v.y + v.z + v.w;\n"
+	  "};", 42 },
 	/* 3-field tuple destructure in for-range */
 	{ "fn main() i32 = {\n"
 	  "  let buf: [3]i64;\n"