cgen: fix multiple assign array index (#10926)

vlib/v/gen/c/cgen.v

@@ -2230,6 +2230,7 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 	}
 	mut return_type := ast.void_type
 	is_decl := assign_stmt.op == .decl_assign
+	g.assign_op = assign_stmt.op
 	op := if is_decl { token.Kind.assign } else { assign_stmt.op }
 	right_expr := assign_stmt.right[0]
 	match right_expr {
@@ -2359,6 +2360,22 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 				}
 				g.expr(lx)
 				noscan := if is_auto_heap { g.check_noscan(return_type) } else { '' }
+				if g.is_arraymap_set {
+					if is_opt {
+						mr_base_styp := g.base_type(return_type)
+						if is_auto_heap {
+							g.writeln('HEAP${noscan}($mr_base_styp, *($mr_base_styp*)${mr_var_name}.data).arg$i) });')
+						} else {
+							g.writeln('(*($mr_base_styp*)${mr_var_name}.data).arg$i });')
+						}
+					} else {
+						if is_auto_heap {
+							g.writeln('HEAP${noscan}($styp, ${mr_var_name}.arg$i) });')
+						} else {
+							g.writeln('${mr_var_name}.arg$i });')
+						}
+					}
+				} else {
 					if is_opt {
 						mr_base_styp := g.base_type(return_type)
 						if is_auto_heap {
@@ -2374,6 +2391,10 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 						}
 					}
 				}
+			}
+			if g.is_arraymap_set {
+				g.is_arraymap_set = false
+			}
 			return
 		}
 	}

vlib/v/tests/multiple_assign_array_index_test.v

@@ -0,0 +1,24 @@
+fn round(a int, b int, c int) (int, int, int) {
+	mut ax := a
+	mut bx := b
+	mut cx := c
+
+	ax += bx
+	bx ^= cx
+	cx -= 1
+
+	return ax, bx, cx
+}
+
+fn round_assignment(mut res []int) {
+	_ = res[2]
+	res[0], res[1], res[2] = round(res[0], res[1], res[2])
+}
+
+fn test_multiple_assign_array_index() {
+	mut a := []int{len: 3}
+	round_assignment(mut a)
+
+	println(a)
+	assert a == [0, 0, -1]
+}