transform-sdk/js: fix asan violations for assignment operators

Author: rockwotj

src/transform-sdk/cpp/BUILD

@@ -1,10 +1,11 @@
 cc_library(
-    name = "transform-sdk",
+    name = "transform_sdk",
     srcs = ["src/transform_sdk.cc"],
     hdrs = ["include/redpanda/transform_sdk.h"],
     copts = [
         "-std=c++23",
         "-fno-exceptions",
     ],
     includes = ["include"],
+    visibility = ["//visibility:public"],
 )

src/transform-sdk/js/BUILD

@@ -22,3 +22,16 @@ cc_test(
         "@googletest//:gtest_main",
     ],
 )
+
+cc_binary(
+    name = "main",
+    srcs = ["main.cc"],
+    copts = [
+        "-std=c++23",
+        "-fno-exceptions",
+    ],
+    deps = [
+        ":js_vm",
+        "//src/transform-sdk/cpp:transform_sdk",
+    ],
+)

src/transform-sdk/js/js_vm.cc

@@ -48,7 +48,9 @@ value& value::operator=(value&& other) noexcept {
     if (this == &other) {
         return *this;
     }
-    JS_FreeValue(_ctx, _underlying);
+    if (_ctx != nullptr) {
+        JS_FreeValue(_ctx, _underlying);
+    }
     _ctx = std::exchange(other._ctx, nullptr);
     _underlying = std::exchange(other._underlying, JS_UNINITIALIZED);
     return *this;
@@ -62,7 +64,9 @@ value& value::operator=(const value& other) noexcept {
     if (this == &other) {
         return *this;
     }
-    JS_FreeValue(_ctx, _underlying);
+    if (_ctx != nullptr) {
+        JS_FreeValue(_ctx, _underlying);
+    }
     _ctx = other._ctx;
     _underlying = other.raw_dup();
     return *this;