From 1e40f9dac055b4a399e6b2810b027635bb8ee8ba Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Wed, 20 May 2020 11:05:01 +0300
Subject: [PATCH] compiler: support nested struct reading

---
 pkg/compiler/codegen.go     | 15 ++++++---------
 pkg/compiler/struct_test.go | 14 ++++++++++++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/pkg/compiler/codegen.go b/pkg/compiler/codegen.go
index 9dadbeff9..e5a558ce4 100644
--- a/pkg/compiler/codegen.go
+++ b/pkg/compiler/codegen.go
@@ -753,17 +753,14 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		return nil
 
 	case *ast.SelectorExpr:
-		switch t := n.X.(type) {
-		case *ast.Ident:
-			if strct, ok := c.typeOf(t).Underlying().(*types.Struct); ok {
-				c.emitLoadVar(t.Name) // load the struct
-				i := indexOfStruct(strct, n.Sel.Name)
-				c.emitLoadField(i) // load the field
-			}
-		default:
-			c.prog.Err = fmt.Errorf("nested selectors not supported yet")
+		strct, ok := c.typeOf(n.X).Underlying().(*types.Struct)
+		if !ok {
+			c.prog.Err = fmt.Errorf("selectors are supported only on structs")
 			return nil
 		}
+		ast.Walk(c, n.X) // load the struct
+		i := indexOfStruct(strct, n.Sel.Name)
+		c.emitLoadField(i) // load the field
 		return nil
 
 	case *ast.UnaryExpr:
diff --git a/pkg/compiler/struct_test.go b/pkg/compiler/struct_test.go
index f50390899..cffb8c335 100644
--- a/pkg/compiler/struct_test.go
+++ b/pkg/compiler/struct_test.go
@@ -338,6 +338,20 @@ var structTestCases = []testCase{
 		}`,
 		big.NewInt(2),
 	},
+	{
+		"nested selectors (simple read)",
+		`package foo
+		type S1 struct { x, y S2 }
+		type S2 struct { a, b int }
+		func Main() int {
+			var s1 S1
+			var s2 S2
+			s2.a = 3
+			s1.y = s2
+			return s1.y.a
+		}`,
+		big.NewInt(3),
+	},
 }
 
 func TestStructs(t *testing.T) {