wcc/ww: round-trip @symbol in the .wwi producer (#47)

The M2 .wwi producer rendered an exported fn carrying @symbol("...")
as a bare prototype, dropping the FFI link-symbol binding. A
sep-compiled consumer reading the .wwi then emitted `CALL malloc`
instead of `CALL rt_malloc` for `@symbol("rt_malloc") export fn
malloc`, breaking the bodies-vs-.wwi byte-id and the link. Affects
every package whose closure reaches rt/os.

Emit codegen/link-relevant attributes through a single named
predicate (wwi_attr_relevant / wwiattrrelevant), today true iff the
name is "symbol" — the only such attribute that exists. @align/@offset
are NOT field attributes in ww (the parser parses no field attrs, the
N_TFIELD node has no attr slot); the predicate is named for the class
so they slot in if ww ever grows them (#51). attr is assigned at
exactly one site per stage (parse.c:1351 / decl.ww:168), both inside
parsefn, so only N_FNDECL carries attrs and the fn-decl render path
covers the whole class.

Both stages, byte-identical (rule 10). 989_m2wwi_run synth gate gains
an @symbol fn + a content assertion that the .wwi carries it verbatim.

cmd/w6c/wwi.c

@@ -310,11 +310,45 @@ wwi_expr(FILE *of, Node *e)
 	}
 }
 
+/* Only codegen/link-relevant attributes round-trip into the `.wwi`. Today
+ * that is exactly @symbol (the FFI link-symbol override, read back at cgen
+ * fficollect — dropping it makes sep-compile emit `CALL malloc` for a
+ * `@symbol("rt_malloc")` fn). Named for the class so @align/@offset would
+ * slot in here IF ww ever grows field-layout attributes — it has none
+ * today (task #47 report). @test never reaches a `.wwi` (test fns are not
+ * export-marked), so it needs no exclusion arm. */
+static int
+wwi_attr_relevant(const char *nm)
+{
+	return nm && strcmp(nm, "symbol") == 0;
+}
+
+static void
+wwi_attrs(FILE *of, Node *d)
+{
+	for (Node *a = d->attr; a; a = a->next) {
+		if (a->kind != N_ATTR || !wwi_attr_relevant(a->str))
+			continue;
+		fputc('@', of);
+		fputs(a->str, of);
+		if (a->list) {
+			fputc('(', of);
+			for (Node *arg = a->list; arg; arg = arg->next) {
+				if (arg != a->list) fputs(", ", of);
+				wwi_expr(of, arg);
+			}
+			fputc(')', of);
+		}
+		fputc(' ', of);
+	}
+}
+
 static void
 wwi_decl(FILE *of, Node *d)
 {
 	switch (d->kind) {
 	case N_FNDECL:
+		wwi_attrs(of, d);
 		fputs("export fn ", of);
 		fputs(d->str, of);
 		fputc('(', of);

selfhost/cmd/w6c/main.combined.ww

@@ -45676,8 +45676,42 @@ fn wwitype(fd: i32, t: *node) void = {
 	};};};};};};};};};};};
 };
 
+// Only codegen/link-relevant attributes round-trip into the `.wwi`. Today
+// that is exactly @symbol (the FFI link-symbol override, read back at cgen
+// fficollect — dropping it makes sep-compile emit `CALL malloc` for a
+// `@symbol("rt_malloc")` fn). Named for the class so @align/@offset would
+// slot in here IF ww ever grows field-layout attributes — it has none
+// today (task #47 report). @test never reaches a `.wwi` (test fns are not
+// export-marked), so it needs no exclusion arm.
+fn wwiattrrelevant(nm: str) bool = {
+	return streq(nm, "symbol");
+};
+
+fn wwiattrs(fd: i32, d: *node) void = {
+	let a: *node = d.attr;
+	for (a != nil) {
+		if (a.kind == nkind.N_ATTR && wwiattrrelevant(a.str)) {
+			wputb(fd, '@');
+			wputs(fd, a.str);
+			if (a.list != nil) {
+				wputb(fd, '(');
+				let arg: *node = a.list;
+				for (arg != nil) {
+					if (arg != a.list) { wputs(fd, ", "); };
+					wwiexpr(fd, arg);
+					arg = arg.next;
+				};
+				wputb(fd, ')');
+			};
+			wputb(fd, 32u8);
+		};
+		a = a.next;
+	};
+};
+
 fn wwidecl(fd: i32, d: *node) void = {
 	if (d.kind == nkind.N_FNDECL) {
+		wwiattrs(fd, d);
 		wputs(fd, "export fn ");
 		wputs(fd, d.str);
 		wputb(fd, '(');

selfhost/cmd/wcc/wwi.ww

@@ -349,8 +349,42 @@ fn wwitype(fd: i32, t: *node) void = {
 	};};};};};};};};};};};
 };
 
+// Only codegen/link-relevant attributes round-trip into the `.wwi`. Today
+// that is exactly @symbol (the FFI link-symbol override, read back at cgen
+// fficollect — dropping it makes sep-compile emit `CALL malloc` for a
+// `@symbol("rt_malloc")` fn). Named for the class so @align/@offset would
+// slot in here IF ww ever grows field-layout attributes — it has none
+// today (task #47 report). @test never reaches a `.wwi` (test fns are not
+// export-marked), so it needs no exclusion arm.
+fn wwiattrrelevant(nm: str) bool = {
+	return streq(nm, "symbol");
+};
+
+fn wwiattrs(fd: i32, d: *node) void = {
+	let a: *node = d.attr;
+	for (a != nil) {
+		if (a.kind == nkind.N_ATTR && wwiattrrelevant(a.str)) {
+			wputb(fd, '@');
+			wputs(fd, a.str);
+			if (a.list != nil) {
+				wputb(fd, '(');
+				let arg: *node = a.list;
+				for (arg != nil) {
+					if (arg != a.list) { wputs(fd, ", "); };
+					wwiexpr(fd, arg);
+					arg = arg.next;
+				};
+				wputb(fd, ')');
+			};
+			wputb(fd, 32u8);
+		};
+		a = a.next;
+	};
+};
+
 fn wwidecl(fd: i32, d: *node) void = {
 	if (d.kind == nkind.N_FNDECL) {
+		wwiattrs(fd, d);
 		wputs(fd, "export fn ");
 		wputs(fd, d.str);
 		wputb(fd, '(');

test/wcc/989_m2wwi_run.c

@@ -77,6 +77,17 @@ slurp(const char *path, char **outbuf, size_t *outlen)
 	return 0;
 }
 
+static int
+file_contains(const char *path, const char *needle)
+{
+	char *b = NULL;
+	size_t n = 0;
+	if (slurp(path, &b, &n) < 0) return -1;
+	int found = (strstr(b, needle) != NULL);
+	free(b);
+	return found ? 0 : 1;
+}
+
 static int
 files_eq(const char *a, const char *b)
 {
@@ -246,7 +257,11 @@ static const char *synth_src =
 	"export fn risky() !i32;\n"
 	"export fn matrix() [LIMIT]u8;\n"
 	"export fn pair() (i32, i32);\n"
-	"export fn opt(p: *color, b: []u8) (i32 | void);\n";
+	"export fn opt(p: *color, b: []u8) (i32 | void);\n"
+	/* #47: a codegen/link-relevant attribute (@symbol — the FFI link-
+	 * symbol override) MUST round-trip into the `.wwi`; dropping it makes
+	 * sep-compile emit `CALL ext` for a `@symbol("rt_ext")` fn. */
+	"@symbol(\"rt_ext\") export fn ext(n: i32) i32;\n";
 
 static int
 synth(const char *bin)
@@ -288,6 +303,12 @@ synth(const char *bin)
 		    "/ decl-kind unparse diverges across stages)\n");
 		goto out;
 	}
+	/* #47: the @symbol attribute must survive the round-trip verbatim. */
+	if (file_contains(cs, "@symbol(\"rt_ext\") export fn ext") != 0) {
+		fprintf(stderr, "m2wwi FAIL: synth — .wwi dropped @symbol "
+		    "(sep-compile would emit the wrong link symbol)\n");
+		goto out;
+	}
 	snprintf(cmd, sizeof cmd,
 	    "timeout 180 %s/wwdump -a %s >/dev/null 2>&1", bin, cs);
 	if (runwait(cmd) != 0) {