compiler: support named returns

pkg/compiler/codegen.go

@@ -421,10 +421,23 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		}
 		c.dropItems(cnt)
 
+		if len(n.Results) == 0 {
+			results := c.scope.decl.Type.Results
+			if results.NumFields() != 0 {
+				// function with named returns
+				for i := len(results.List) - 1; i >= 0; i-- {
+					names := results.List[i].Names
+					for j := len(names) - 1; j >= 0; j-- {
+						c.emitLoadLocal(names[j].Name)
+					}
+				}
+			}
+		} else {
 			// first result should be on top of the stack
 			for i := len(n.Results) - 1; i >= 0; i-- {
 				ast.Walk(c, n.Results[i])
 			}
+		}
 
 		c.saveSequencePoint(n)
 		emit.Opcode(c.prog.BinWriter, opcode.FROMALTSTACK)

pkg/compiler/func_scope.go

@@ -84,6 +84,11 @@ func (c *funcScope) stackSize() int64 {
 	size := 0
 	ast.Inspect(c.decl, func(n ast.Node) bool {
 		switch n := n.(type) {
+		case *ast.FuncType:
+			num := n.Results.NumFields()
+			if num != 0 && len(n.Results.List[0].Names) != 0 {
+				size += num
+			}
 		case *ast.AssignStmt:
 			if n.Tok == token.DEFINE {
 				size += len(n.Rhs)

pkg/compiler/return_test.go

@@ -1,8 +1,12 @@
 package compiler_test
 
 import (
+	"fmt"
 	"math/big"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestReturnInt64(t *testing.T) {
@@ -92,3 +96,30 @@ func TestSingleReturn(t *testing.T) {
 	`
 	eval(t, src, big.NewInt(9))
 }
+
+func TestNamedReturn(t *testing.T) {
+	src := `package foo
+	func Main() (a int, b int) {
+		a = 1
+		b = 2
+		c := 3
+		_ = c
+		return %s
+	}`
+
+	runCase := func(ret string, result ...interface{}) func(t *testing.T) {
+		return func(t *testing.T) {
+			src := fmt.Sprintf(src, ret)
+			v := vmAndCompile(t, src)
+			require.NoError(t, v.Run())
+			require.Equal(t, len(result), v.Estack().Len())
+			for i := range result {
+				assert.EqualValues(t, result[i], v.Estack().Pop().Value())
+			}
+		}
+	}
+
+	t.Run("NormalReturn", runCase("a, b", big.NewInt(1), big.NewInt(2)))
+	t.Run("EmptyReturn", runCase("", big.NewInt(1), big.NewInt(2)))
+	t.Run("AnotherVariable", runCase("b, c", big.NewInt(2), big.NewInt(3)))
+}