compiler: fix initialization of struct fields, fix #1164

Make `s{}` initializers work. Deduplicate code a bit along the way. The test
added follows bf6aa02dcf test.

pkg/compiler/codegen.go

@@ -1310,41 +1310,32 @@ func (c *codegen) convertStruct(lit *ast.CompositeLit) {
 	// We will initialize all fields to their "zero" value.
 	for i := 0; i < strct.NumFields(); i++ {
 		sField := strct.Field(i)
-		fieldAdded := false
+		var initialized bool
 
-		if !keyedLit {
 		emit.Opcode(c.prog.BinWriter, opcode.DUP)
 		emit.Int(c.prog.BinWriter, int64(i))
-			ast.Walk(c, lit.Elts[i])
-			emit.Opcode(c.prog.BinWriter, opcode.SETITEM)
-			continue
-		}
 
+		if !keyedLit {
+			if len(lit.Elts) > i {
+				ast.Walk(c, lit.Elts[i])
+				initialized = true
+			}
+		} else {
 			// Fields initialized by the program.
 			for _, field := range lit.Elts {
 				f := field.(*ast.KeyValueExpr)
 				fieldName := f.Key.(*ast.Ident).Name
 
 				if sField.Name() == fieldName {
-				emit.Opcode(c.prog.BinWriter, opcode.DUP)
-
-				pos := indexOfStruct(strct, fieldName)
-				emit.Int(c.prog.BinWriter, int64(pos))
-
 					ast.Walk(c, f.Value)
-
-				emit.Opcode(c.prog.BinWriter, opcode.SETITEM)
-				fieldAdded = true
+					initialized = true
 					break
 				}
 			}
-		if fieldAdded {
-			continue
 		}
-
-		emit.Opcode(c.prog.BinWriter, opcode.DUP)
-		emit.Int(c.prog.BinWriter, int64(i))
+		if !initialized {
 			c.emitDefault(sField.Type())
+		}
 		emit.Opcode(c.prog.BinWriter, opcode.SETITEM)
 	}
 }

pkg/compiler/struct_test.go

@@ -405,6 +405,29 @@ var structTestCases = []testCase{
 		}`,
 		big.NewInt(12),
 	},
+	{
+		"uninitialized struct fields",
+		`package foo
+               type Foo struct {
+                       i int
+                       m map[string]int
+                       b []byte
+                       a []int
+                       s struct { ii int }
+               }
+               func NewFoo() Foo { return Foo{} }
+               func Main() int {
+                       foo := NewFoo()
+                       if foo.i != 0 { return 1 }
+                       if len(foo.m) != 0 { return 1 }
+                       if len(foo.b) != 0 { return 1 }
+                       if len(foo.a) != 0 { return 1 }
+                       s := foo.s
+                       if s.ii != 0 { return 1 }
+                       return 2
+               }`,
+		big.NewInt(2),
+	},
 }
 
 func TestStructs(t *testing.T) {