From 5dd10d115fb1b55f4e8420cd36ced13009c39f02 Mon Sep 17 00:00:00 2001
From: Roger Chapman <rogchap@gmail.com>
Date: Tue, 23 Mar 2021 17:38:37 +1100
Subject: [PATCH] Allow setting/unsetting of V8 feature flags

---
 v8go.cc      |  6 +++++-
 v8go.go      | 15 +++++++++++++++
 v8go.h       |  1 +
 v8go_test.go | 16 ++++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/v8go.cc b/v8go.cc
index 19f09058..1a44c3df 100644
--- a/v8go.cc
+++ b/v8go.cc
@@ -1148,9 +1148,13 @@ ValuePtr ExceptionTypeError(IsolatePtr iso_ptr, const char* message) {
   return static_cast<ValuePtr>(val);
 }
 
-/********** Version **********/
+/********** v8::V8 **********/
 
 const char* Version() {
   return V8::GetVersion();
 }
+
+void SetFlags(const char* flags) {
+  V8::SetFlagsFromString(flags);
+}
 }
diff --git a/v8go.go b/v8go.go
index aa36d2fd..32990558 100644
--- a/v8go.go
+++ b/v8go.go
@@ -8,9 +8,24 @@ Package v8go provides an API to execute JavaScript.
 package v8go
 
 // #include "v8go.h"
+// #include <stdlib.h>
 import "C"
+import (
+	"strings"
+	"unsafe"
+)
 
 // Version returns the version of the V8 Engine with the -v8go suffix
 func Version() string {
 	return C.GoString(C.Version())
 }
+
+// SetFlags sets flags for V8. For possible flags: https://github.com/v8/v8/blob/master/src/flags/flag-definitions.h
+// Flags are expected to be prefixed with `--`, for example: `--harmony`.
+// Flags can be reverted using the `--no` prefix equivalent, for example: `--use_strict` vs `--nouse_strict`.
+// Flags will affect all Isolates created, even after creation.
+func SetFlags(flags ...string) {
+	cflags := C.CString(strings.Join(flags, " "))
+	C.SetFlags(cflags)
+	C.free(unsafe.Pointer(cflags))
+}
diff --git a/v8go.h b/v8go.h
index f7677476..68fb52fe 100644
--- a/v8go.h
+++ b/v8go.h
@@ -181,6 +181,7 @@ extern ValuePtr ExceptionSyntaxError(IsolatePtr iso_ptr, const char* message);
 extern ValuePtr ExceptionTypeError(IsolatePtr iso_ptr, const char* message);
 
 const char* Version();
+extern void SetFlags(const char* flags);
 
 #ifdef __cplusplus
 }  // extern "C"
diff --git a/v8go_test.go b/v8go_test.go
index 89d04d63..8d9df283 100644
--- a/v8go_test.go
+++ b/v8go_test.go
@@ -19,3 +19,19 @@ func TestVersion(t *testing.T) {
 		t.Errorf("version string is in the incorrect format: %s", v)
 	}
 }
+
+func TestSetFlag(t *testing.T) {
+	t.Parallel()
+	ctx, _ := v8go.NewContext()
+	if _, err := ctx.RunScript("a = 1", "default.js"); err != nil {
+		t.Errorf("expected <nil> error, but got: %v", err)
+	}
+	v8go.SetFlags("--use_strict")
+	if _, err := ctx.RunScript("b = 1", "use_strict.js"); err == nil {
+		t.Error("expected error but got <nil>")
+	}
+	v8go.SetFlags("--nouse_strict")
+	if _, err := ctx.RunScript("c = 1", "nouse_strict.js"); err != nil {
+		t.Errorf("expected <nil> error, but got: %v", err)
+	}
+}