compiler: correctly handle defer in functions without return values

Fix #2253.

pkg/compiler/codegen.go

@@ -499,6 +499,7 @@ func (c *codegen) convertFuncDecl(file ast.Node, decl *ast.FuncDecl, pkg *types.
 	// we should clean alt.stack manually.
 	// This can be the case with void and named-return functions.
 	if !isInit && !isDeploy && !lastStmtIsReturn(decl.Body) {
+		c.processDefers()
 		c.saveSequencePoint(decl.Body)
 		emit.Opcodes(c.prog.BinWriter, opcode.RET)
 	}
@@ -1329,10 +1330,13 @@ func (c *codegen) processDefers() {
 		c.emitStoreByIndex(varLocal, finalIndex)
 		ast.Walk(c, stmt.expr)
 		if i == 0 {
-			// After panic, default values must be returns, except for named returns,
-			// which we don't support here for now.
-			for i := len(c.scope.decl.Type.Results.List) - 1; i >= 0; i-- {
-				c.emitDefault(c.typeOf(c.scope.decl.Type.Results.List[i].Type))
+			results := c.scope.decl.Type.Results
+			if results.NumFields() != 0 {
+				// After panic, default values must be returns, except for named returns,
+				// which we don't support here for now.
+				for i := len(results.List) - 1; i >= 0; i-- {
+					c.emitDefault(c.typeOf(results.List[i].Type))
+				}
 			}
 		}
 		emit.Jmp(c.prog.BinWriter, opcode.ENDTRYL, after)

pkg/compiler/defer_test.go

@@ -3,6 +3,8 @@ package compiler_test
 import (
 	"math/big"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestDefer(t *testing.T) {
@@ -79,6 +81,33 @@ func TestDefer(t *testing.T) {
 		}`
 		eval(t, src, big.NewInt(13))
 	})
+	t.Run("NoReturnReturn", func(t *testing.T) {
+		src := `package main
+		var i int
+		func Main() {
+			defer func() {
+				i++
+			}()
+			return
+		}`
+		vm := vmAndCompile(t, src)
+		err := vm.Run()
+		require.NoError(t, err)
+		require.Equal(t, 0, vm.Estack().Len(), "stack contains unexpected items")
+	})
+	t.Run("NoReturnNoReturn", func(t *testing.T) {
+		src := `package main
+		var i int
+		func Main() {
+			defer func() {
+				i++
+			}()
+		}`
+		vm := vmAndCompile(t, src)
+		err := vm.Run()
+		require.NoError(t, err)
+		require.Equal(t, 0, vm.Estack().Len(), "stack contains unexpected items")
+	})
 }
 
 func TestRecover(t *testing.T) {