parser: restore outer variable in index exprs

compiler/fn.v

@@ -53,7 +53,7 @@ fn (f mut Fn) close_scope() {
 	f.defer_text = f.defer_text.left(f.scope_level + 1)
 }
 
-fn (f &Fn) mark_var_used(v Var) {
+fn (f mut Fn) mark_var_used(v Var) {
 	for i, vv in f.local_vars {
 		if vv.name == v.name {
 			//mut ptr := &f.local_vars[i]
@@ -64,7 +64,7 @@ fn (f &Fn) mark_var_used(v Var) {
 	}
 }
 
-fn (f &Fn) mark_var_changed(v Var) {
+fn (f mut Fn) mark_var_changed(v Var) {
 	for i, vv in f.local_vars {
 		if vv.name == v.name {
 			//mut ptr := &f.local_vars[i]
@@ -75,7 +75,7 @@ fn (f &Fn) mark_var_changed(v Var) {
 	}
 }
 
-fn (f &Fn) known_var(name string) bool {
+fn (f mut Fn) known_var(name string) bool {
 	v := f.find_var(name)
 	return v.name.len > 0
 }

compiler/parser.v

@@ -1946,6 +1946,7 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 		if close_bracket {
 			p.gen(']/*r$typ $v.is_mut*/')
 		}
+		p.expr_var = v
 	}
 	// TODO move this from index_expr()
 	// TODO if p.tok in ...

compiler/tests/mut_test.v

@@ -1,3 +1,13 @@
+struct A {
+pub mut:
+	v []int
+}
+
+struct B {
+pub mut:
+	a []A
+}
+
 fn foo(b int, a mut []int) {
 	a[0] = 7 
 	a << 4 
@@ -17,4 +27,26 @@ fn test_mut() {
 
 	//mut b := mut a
 	//b = 10 
+}
+
+fn test_mut_2() {
+	zero := 0
+
+	mut b := B{}
+	b.a << A{}
+
+	b.a[0].v = [9, 8, 7]
+
+	b.a[0].v << 6
+	b.a[zero].v << 5
+
+	b.a[0].v[zero] = 3
+	b.a[0].v[b.a[zero].v[zero]] += 1b.a[0].v[b.a[0].v[zero]] += 1
+
+	assert b.a[0].v.len == 5
+	assert b.a[0].v[0] == 3
+	assert b.a[0].v[1] == 8
+	assert b.a[0].v[2] == 7
+	assert b.a[0].v[3] == 8
+	assert b.a[0].v[4] == 5
 } 

examples/nbody.v

@@ -32,7 +32,7 @@ pub mut:
       s []Position
 }
 
-fn advance(sys System, dt f64) {
+fn advance(sys mut System, dt f64) {
     for i := 0; i < N - 1; i++ {
         mut _vx := sys.v[i].x
         mut _vy := sys.v[i].y
@@ -125,7 +125,7 @@ offsetmomentum(mut sys)
 
 println('${energy(sys):.9f}')  //-0.169075164
 for i := 0; i < 50000000; i++ {
-    advance(sys, 0.01)
+    advance(mut sys, 0.01)
 }
 println('${energy(sys):.9f}') //-0.169059907