From 75f085d0b22ec4110982fae2fe9728bc44a57f96 Mon Sep 17 00:00:00 2001
From: Tristan Cartledge <tristan@speakeasyapi.dev>
Date: Tue, 3 Jun 2025 09:22:10 +1000
Subject: [PATCH 1/2] fix: add the ability to provide a random source

---
 engine.go              | 11 ++++++++++-
 internal/vm/vm.go      | 10 +++++++++-
 internal/vm/vm_test.go | 24 +++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/engine.go b/engine.go
index f1b89c9..86a1ffa 100644
--- a/engine.go
+++ b/engine.go
@@ -113,6 +113,13 @@ func WithDebug() Opt {
 	}
 }
 
+// WithRandSource sets the random source to use in the engine.
+func WithRandSource(randSource func() float64) Opt {
+	return func(e *Engine) {
+		e.randSource = randSource
+	}
+}
+
 // Engine provides the templating engine.
 type Engine struct {
 	searchLocations []string
@@ -125,6 +132,8 @@ type Engine struct {
 
 	tracer trace.Tracer
 
+	randSource vm.RandSource
+
 	vm *vm.VM
 }
 
@@ -248,7 +257,7 @@ func (e *Engine) init(ctx context.Context, data any) (*vm.VM, error) {
 		return nil, ErrAlreadyInitialized
 	}
 
-	v, err := vm.New()
+	v, err := vm.New(e.randSource)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create vm: %w", err)
 	}
diff --git a/internal/vm/vm.go b/internal/vm/vm.go
index 136ecac..fe12d6c 100644
--- a/internal/vm/vm.go
+++ b/internal/vm/vm.go
@@ -50,6 +50,8 @@ type Options struct {
 // Option represents an option for running a script.
 type Option func(*Options)
 
+type RandSource func() float64
+
 // WithStartingLineNumber sets the starting line number for the script.
 func WithStartingLineNumber(lineNumber int) Option {
 	return func(o *Options) {
@@ -63,7 +65,7 @@ type program struct {
 }
 
 // New creates a new VM.
-func New() (*VM, error) {
+func New(randSource RandSource) (*VM, error) {
 	g := goja.New()
 	_, err := g.RunString(underscore.JS)
 	if err != nil {
@@ -73,6 +75,12 @@ func New() (*VM, error) {
 	new(require.Registry).Enable(g)
 	console.Enable(g)
 
+	if randSource != nil {
+		g.SetRandSource(func() float64 {
+			return randSource()
+		})
+	}
+
 	return &VM{Runtime: g, globalSourceMapCache: make(map[string]*sourcemap.Consumer)}, nil
 }
 
diff --git a/internal/vm/vm_test.go b/internal/vm/vm_test.go
index d3e41ab..d1819bf 100644
--- a/internal/vm/vm_test.go
+++ b/internal/vm/vm_test.go
@@ -9,8 +9,30 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestVM_Run_Runtime_Success(t *testing.T) {
+	v, err := vm.New(nil)
+	require.NoError(t, err)
+
+	typeScript := `console.log("hello world");`
+
+	_, err = v.Run(context.Background(), "test", typeScript)
+	assert.NoError(t, err)
+}
+
+func TestVM_Run_Runtime_WithRandSource_Success(t *testing.T) {
+	v, err := vm.New(func() float64 {
+		return 0
+	})
+	require.NoError(t, err)
+
+	typeScript := `console.log("hello world");`
+
+	_, err = v.Run(context.Background(), "test", typeScript)
+	assert.NoError(t, err)
+}
+
 func TestVM_Run_Runtime_Errors(t *testing.T) {
-	v, err := vm.New()
+	v, err := vm.New(nil)
 	require.NoError(t, err)
 
 	typeScript := `type Test = {

From cc2f8d93b75fad80a634affe90bf862d3d9ab515 Mon Sep 17 00:00:00 2001
From: Tristan Cartledge <tristan@speakeasyapi.dev>
Date: Tue, 3 Jun 2025 09:29:26 +1000
Subject: [PATCH 2/2] fix

---
 internal/vm/vm.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/internal/vm/vm.go b/internal/vm/vm.go
index fe12d6c..7f2f027 100644
--- a/internal/vm/vm.go
+++ b/internal/vm/vm.go
@@ -50,6 +50,7 @@ type Options struct {
 // Option represents an option for running a script.
 type Option func(*Options)
 
+// RandSource is a function that returns a seeded float64 value.
 type RandSource func() float64
 
 // WithStartingLineNumber sets the starting line number for the script.