Delegate to local installs of wrangler when possible (#1270)

Delegate to a local install of `wrangler` if one exists.

Users will frequently install `wrangler` globally to run commands like
`wrangler init`, but we also recommend pinning a specific version of
`wrangler` in a project's `package.json`. Now, when a user invokes a
global install of `wrangler`, we'll check to see if they also have a
local installation. If they do, we'll delegate to that version.

This requires that we define a `main` (maybe `module` would work too?)
field in `package.json` so that `require.resolve` can find `"wrangler"`,
but it's something of an implementation detail.

.changeset/lovely-toys-happen.md

@@ -0,0 +1,7 @@
+---
+"wrangler": patch
+---
+
+Delegate to a local install of `wrangler` if one exists.
+
+Users will frequently install `wrangler` globally to run commands like `wrangler init`, but we also recommend pinning a specific version of `wrangler` in a project's `package.json`. Now, when a user invokes a global install of `wrangler`, we'll check to see if they also have a local installation. If they do, we'll delegate to that version.

packages/wrangler/bin/wrangler.js

@@ -9,7 +9,10 @@ const MIN_NODE_VERSION = "16.7.0";
 
 let wranglerProcess;
 
-async function main() {
+/**
+ * Executes ../wrangler-dist/cli.js
+ */
+function runWrangler() {
   if (semiver(process.versions.node, MIN_NODE_VERSION) < 0) {
     // Note Volta and nvm are also recommended in the official docs:
     // https://developers.cloudflare.com/workers/get-started/guide#2-install-the-workers-cli
@@ -46,7 +49,7 @@ Consider using a Node.js version manager such as https://volta.sh/ or https://gi
     pathToCACerts = certPath;
   }
 
-  wranglerProcess = spawn(
+  return spawn(
     process.execPath,
     [
       ...(semiver(process.versions.node, "18.0.0") >= 0
@@ -70,11 +73,65 @@ Consider using a Node.js version manager such as https://volta.sh/ or https://gi
   );
 }
 
+/**
+ * Runs a locally-installed version of wrangler, delegating from this version.
+ * @throws {MODULE_NOT_FOUND} if there isn't a locally installed version of wrangler.
+ */
+function runDelegatedWrangler() {
+  const packageJsonPath = require.resolve("wrangler/package.json", {
+    paths: [process.cwd()],
+  });
+  const {
+    bin: { wrangler: binaryPath },
+    version,
+  } = JSON.parse(fs.readFileSync(packageJsonPath));
+  const resolvedBinaryPath = path.resolve(packageJsonPath, "..", binaryPath);
+
+  console.log(
+    `Delegating to locally-installed version of wrangler @ v${version}`
+  );
+  // this call to `spawn` is simpler because the delegated version will do all
+  // of the other work.
+  return spawn(
+    process.execPath,
+    [resolvedBinaryPath, ...process.argv.slice(2)],
+    {
+      stdio: "inherit",
+    }
+  ).on("exit", (code) =>
+    process.exit(code === undefined || code === null ? 0 : code)
+  );
+}
+
+/**
+ * Indicates if this invocation of `wrangler` should delegate
+ * to a locally-installed version.
+ */
+function shouldDelegate() {
+  try {
+    // `require.resolve` will throw if it can't find
+    // a locally-installed version of `wrangler`
+    const delegatedPackageJson = require.resolve("wrangler/package.json", {
+      paths: [process.cwd()],
+    });
+    const thisPackageJson = path.resolve(__dirname, "..", "package.json");
+    // if it's the same path, then we're already a local install -- no need to delegate
+    return thisPackageJson !== delegatedPackageJson;
+  } catch (e) {
+    // there's no local version to delegate to -- `require.resolve` threw
+    return false;
+  }
+}
+
+async function main() {
+  wranglerProcess = shouldDelegate() ? runDelegatedWrangler() : runWrangler();
+}
+
 process.on("SIGINT", () => {
-  wranglerProcess.kill();
+  wranglerProcess?.kill();
 });
 process.on("SIGTERM", () => {
-  wranglerProcess.kill();
+  wranglerProcess?.kill();
 });
 
 void main();