Add change ident patcher test

Author: antonmedv

test/patch/change_ident_test.go

@@ -0,0 +1,61 @@
+package patch_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/ast"
+	"github.com/expr-lang/expr/vm"
+	"github.com/expr-lang/expr/vm/runtime"
+)
+
+func TestPatch_change_ident(t *testing.T) {
+	program, err := expr.Compile(
+		`foo`,
+		expr.Env(Env{}),
+		expr.Patch(changeIdent{}),
+	)
+	require.NoError(t, err)
+
+	expected := &vm.Program{
+		Bytecode: []vm.Opcode{
+			vm.OpLoadField,
+		},
+		Arguments: []int{
+			0,
+		},
+		Constants: []any{
+			&runtime.Field{
+				Path:  []string{"bar"},
+				Index: []int{1},
+			},
+		},
+	}
+
+	require.Equal(t, expected.Disassemble(), program.Disassemble())
+}
+
+type Env struct {
+	Foo int `expr:"foo"`
+	Bar int `expr:"bar"`
+}
+
+type changeIdent struct{}
+
+func (changeIdent) Visit(node *ast.Node) {
+	id, ok := (*node).(*ast.IdentifierNode)
+	if !ok {
+		return
+	}
+	if id.Value == "foo" {
+		// A correct way to patch the node:
+		//
+		//	newNode := &ast.IdentifierNode{Value: "bar"}
+		//	ast.Patch(node, newNode)
+		//
+		// But we can do it in a wrong way:
+		id.Value = "bar"
+	}
+}