From e8ec820d2e127c98b1b4032368ddec72e38affec Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Wed, 16 Feb 2022 18:43:12 +0300
Subject: [PATCH] vm: add `unload` command

When execution fails it's the only way to change the prompt showing the
last executed instruction. Example:

```
NEO-GO-VM > loadgo examples/engine/engine.go
READY: loaded 117 instructions
NEO-GO-VM 0 > run
Error: at instruction 3 (SYSCALL): failed to invoke syscall 805851437: syscall not found
NEO-GO-VM 8 > parse
Error: missing argument
NEO-GO-VM 8 > parse 123
Integer to Hex			7b
Integer to Base64		ew==
String to Hex			313233
String to Base64		MTIz

NEO-GO-VM 8 > unload
NEO-GO-VM > exit

```
---
 pkg/vm/cli/cli.go      | 16 ++++++++++++++++
 pkg/vm/cli/cli_test.go | 16 ++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/pkg/vm/cli/cli.go b/pkg/vm/cli/cli.go
index a7fb9f60f..3e696aaf0 100644
--- a/pkg/vm/cli/cli.go
+++ b/pkg/vm/cli/cli.go
@@ -136,6 +136,11 @@ both parameters are mandatory, example:
 > loadgo /path/to/file.go`,
 		Action: handleLoadGo,
 	},
+	{
+		Name:   "reset",
+		Usage:  "Unload compiled script from the VM",
+		Action: handleReset,
+	},
 	{
 		Name:      "parse",
 		Usage:     "Parse provided argument and convert it into other possible formats",
@@ -288,6 +293,11 @@ func getVMFromContext(app *cli.App) *vm.VM {
 	return app.Metadata[vmKey].(*vm.VM)
 }
 
+func setVMInContext(app *cli.App, v *vm.VM) {
+	old := getVMFromContext(app)
+	*old = *v
+}
+
 func getManifestFromContext(app *cli.App) *manifest.Manifest {
 	return app.Metadata[manifestKey].(*manifest.Manifest)
 }
@@ -466,6 +476,12 @@ func handleLoadGo(c *cli.Context) error {
 	return nil
 }
 
+func handleReset(c *cli.Context) error {
+	setVMInContext(c.App, vm.New())
+	changePrompt(c.App)
+	return nil
+}
+
 func getManifestFromFile(name string) (*manifest.Manifest, error) {
 	bs, err := ioutil.ReadFile(name)
 	if err != nil {
diff --git a/pkg/vm/cli/cli_test.go b/pkg/vm/cli/cli_test.go
index de6525a47..7ee2a6333 100644
--- a/pkg/vm/cli/cli_test.go
+++ b/pkg/vm/cli/cli_test.go
@@ -641,3 +641,19 @@ func TestExit(t *testing.T) {
 	e.runProg(t, "exit")
 	require.True(t, e.exit.Load())
 }
+
+func TestReset(t *testing.T) {
+	script := []byte{byte(opcode.PUSH1)}
+	e := newTestVMCLI(t)
+	e.runProg(t,
+		"loadhex "+hex.EncodeToString(script),
+		"ops",
+		"reset",
+		"ops")
+
+	e.checkNextLine(t, "READY: loaded 1 instructions")
+	e.checkNextLine(t, "INDEX.*OPCODE.*PARAMETER")
+	e.checkNextLine(t, "0.*PUSH1.*")
+	e.checkNextLine(t, "")
+	e.checkError(t, fmt.Errorf("VM is not ready: no program loaded"))
+}