decl: Allow union specifiers to contain structs/unions with flexible array members

Thanks to Thorsten Glaser for reporting this issue.

Fixes #91.

Author: michaelforney

decl.c

@@ -744,19 +744,22 @@ addmember(struct structbuilder *b, struct qualtype mt, char *name, int align, un
 	struct member *m;
 	size_t end;
 
-	if (t->flexible)
+	if (t->kind == TYPESTRUCT && t->flexible)
 		error(&tok.loc, "struct has member '%s' after flexible array member", name);
 	if (mt.type->incomplete) {
 		if (mt.type->kind != TYPEARRAY)
 			error(&tok.loc, "struct member '%s' has incomplete type", name);
 		t->flexible = true;
 	}
+	if (mt.type->flexible) {
+		if (t->kind == TYPESTRUCT)
+			error(&tok.loc, "struct member '%s' contains flexible array member", name);
+		t->flexible = true;
+	}
 	if (mt.type->kind == TYPEFUNC)
 		error(&tok.loc, "struct member '%s' has function type", name);
 	if (mt.type->prop & PROPVM)
 		error(&tok.loc, "struct member '%s' has variably modified type", name);
-	if (mt.type->flexible)
-		error(&tok.loc, "struct member '%s' contains flexible array member", name);
 	assert(mt.type->align > 0);
 	if (name || width == -1) {
 		m = xmalloc(sizeof(*m));

test/union-struct-flexible-array.c

@@ -0,0 +1,13 @@
+union u {
+	struct {
+		int a;
+		short b[];
+	} s;
+	unsigned char storage[32];
+};
+
+int x = sizeof(union u);
+
+int f(union u *u) {
+	return u->s.b[2] + u->storage[0];
+}

test/union-struct-flexible-array.qbe

@@ -0,0 +1,25 @@
+export data $x = align 4 { w 32, }
+export
+function w $f(l %.1) {
+@start.1
+	%.2 =l alloc8 8
+	storel %.1, %.2
+@body.2
+	%.3 =l loadl %.2
+	%.4 =l add %.3, 0
+	%.5 =l add %.4, 4
+	%.6 =l extsw 2
+	%.7 =l mul %.6, 2
+	%.8 =l add %.5, %.7
+	%.9 =w loadsh %.8
+	%.10 =w extsh %.9
+	%.11 =l loadl %.2
+	%.12 =l add %.11, 0
+	%.13 =l extsw 0
+	%.14 =l mul %.13, 1
+	%.15 =l add %.12, %.14
+	%.16 =w loadub %.15
+	%.17 =w extub %.16
+	%.18 =w add %.10, %.17
+	ret %.18
+}