compiler: initialize struct fields explicitly

By default VM initializes every field of a new struct to a Boolean.
If field contains another struct, we need to initialize it to default
value explicitly. This commit sets default values for uninitialized
field.

pkg/compiler/analysis.go

@@ -2,9 +2,7 @@ package compiler
 
 import (
 	"errors"
-	"fmt"
 	"go/ast"
-	"go/constant"
 	"go/types"
 
 	"github.com/nspcc-dev/neo-go/pkg/vm/emit"
@@ -23,33 +21,6 @@ var (
 	}
 )
 
-// typeAndValueForField returns a zero initialized typeAndValue for the given type.Var.
-func typeAndValueForField(fld *types.Var) (types.TypeAndValue, error) {
-	switch t := fld.Type().(type) {
-	case *types.Basic:
-		switch t.Kind() {
-		case types.Int:
-			return types.TypeAndValue{
-				Type:  t,
-				Value: constant.MakeInt64(0),
-			}, nil
-		case types.String:
-			return types.TypeAndValue{
-				Type:  t,
-				Value: constant.MakeString(""),
-			}, nil
-		case types.Bool, types.UntypedBool:
-			return types.TypeAndValue{
-				Type:  t,
-				Value: constant.MakeBool(false),
-			}, nil
-		default:
-			return types.TypeAndValue{}, fmt.Errorf("could not initialize struct field %s to zero, type: %s", fld.Name(), t)
-		}
-	}
-	return types.TypeAndValue{}, nil
-}
-
 // newGlobal creates new global variable.
 func (c *codegen) newGlobal(name string) {
 	c.globals[name] = len(c.globals)

pkg/compiler/codegen.go

@@ -239,8 +239,15 @@ func (c *codegen) emitDefault(t types.Type) {
 			emit.Opcode(c.prog.BinWriter, opcode.NEWBUFFER)
 		}
 	case *types.Struct:
-		emit.Int(c.prog.BinWriter, int64(t.NumFields()))
+		num := t.NumFields()
+		emit.Int(c.prog.BinWriter, int64(num))
 		emit.Opcode(c.prog.BinWriter, opcode.NEWSTRUCT)
+		for i := 0; i < num; i++ {
+			emit.Opcode(c.prog.BinWriter, opcode.DUP)
+			emit.Int(c.prog.BinWriter, int64(i))
+			c.emitDefault(t.Field(i).Type())
+			emit.Opcode(c.prog.BinWriter, opcode.SETITEM)
+		}
 	default:
 		emit.Opcode(c.prog.BinWriter, opcode.PUSHNULL)
 	}
@@ -1211,15 +1218,9 @@ func (c *codegen) convertStruct(lit *ast.CompositeLit) {
 			continue
 		}
 
-		typeAndVal, err := typeAndValueForField(sField)
-		if err != nil {
-			c.prog.Err = err
-			return
-		}
-
 		emit.Opcode(c.prog.BinWriter, opcode.DUP)
 		emit.Int(c.prog.BinWriter, int64(i))
-		c.emitLoadConst(typeAndVal)
+		c.emitDefault(sField.Type())
 		emit.Opcode(c.prog.BinWriter, opcode.SETITEM)
 	}
 }

pkg/compiler/struct_test.go

@@ -368,6 +368,32 @@ var structTestCases = []testCase{
 		}`,
 		big.NewInt(11),
 	},
+	{
+		"complex struct default value",
+		`package foo
+		type S1 struct { x S2 }
+		type S2 struct { y S3 }
+		type S3 struct { a int }
+		func Main() int {
+			var s1 S1
+			s1.x.y.a = 11
+			return s1.x.y.a
+		}`,
+		big.NewInt(11),
+	},
+	{
+		"nested selectors (complex write)",
+		`package foo
+		type S1 struct { x S2 }
+		type S2 struct { y, z S3 }
+		type S3 struct { a int }
+		func Main() int {
+			var s1 S1
+			s1.x.y.a, s1.x.z.a = 11, 31
+			return s1.x.y.a + s1.x.z.a
+		}`,
+		big.NewInt(42),
+	},
 }
 
 func TestStructs(t *testing.T) {