Make babel-node a standalone package (#6023)

* Make babel-node a standalone package

* New package `babel-node` previously `babel-cli/bin/babel-node`

* updates

packages/babel-node/src/babel-node.js

@@ -0,0 +1,98 @@
+/**
+ * This tiny wrapper file checks for known node flags and appends them
+ * when found, before invoking the "real" _babel-node(1) executable.
+ */
+
+import getV8Flags from "v8flags";
+import path from "path";
+
+let args = [path.join(__dirname, "_babel-node")];
+
+let babelArgs = process.argv.slice(2);
+let userArgs;
+
+// separate node arguments from script arguments
+const argSeparator = babelArgs.indexOf("--");
+if (argSeparator > -1) {
+  userArgs = babelArgs.slice(argSeparator); // including the  --
+  babelArgs = babelArgs.slice(0, argSeparator);
+}
+
+/**
+ * Replace dashes with underscores in the v8Flag name
+ * Also ensure that if the arg contains a value (e.g. --arg=true)
+ * that only the flag is returned.
+ */
+function getNormalizedV8Flag(arg) {
+  const matches = arg.match(/--(.+)/);
+
+  if (matches) {
+    return `--${matches[1].replace(/-/g, "_")}`;
+  }
+
+  return arg;
+}
+
+getV8Flags(function(err, v8Flags) {
+  babelArgs.forEach(function(arg) {
+    const flag = arg.split("=")[0];
+
+    switch (flag) {
+      case "-d":
+        args.unshift("--debug");
+        break;
+
+      case "debug":
+      case "--debug":
+      case "--debug-brk":
+      case "--inspect":
+        args.unshift(arg);
+        break;
+
+      case "-gc":
+        args.unshift("--expose-gc");
+        break;
+
+      case "--nolazy":
+        args.unshift(flag);
+        break;
+
+      default:
+        if (
+          v8Flags.indexOf(getNormalizedV8Flag(flag)) >= 0 ||
+          arg.indexOf("--trace") === 0
+        ) {
+          args.unshift(arg);
+        } else {
+          args.push(arg);
+        }
+        break;
+    }
+  });
+
+  // append arguments passed after --
+  if (argSeparator > -1) {
+    args = args.concat(userArgs);
+  }
+
+  try {
+    const kexec = require("kexec");
+    kexec(process.argv[0], args);
+  } catch (err) {
+    if (err.code !== "MODULE_NOT_FOUND") throw err;
+
+    const child_process = require("child_process");
+    const proc = child_process.spawn(process.argv[0], args, {
+      stdio: "inherit",
+    });
+    proc.on("exit", function(code, signal) {
+      process.on("exit", function() {
+        if (signal) {
+          process.kill(process.pid, signal);
+        } else {
+          process.exit(code);
+        }
+      });
+    });
+  }
+});