Fix rails-ujs auto start() in bundled environments

An issue was recently raised that users were seeing an error when
upgrading `@rails/ujs` to 7.1.0+:

```
Uncaught Error: rails-ujs has already been loaded!
```

Generally this issue appears due to the difference in how rails-ujs is
expected to behave in a pure sprockets environment (js appending) vs a
bundled environment (webpack, esbuild, etc.). The sprockets environment
is supposed to call start() automatically, while the bundled environment
is supposed to require users to import and call start() themselves.

As part of the transition from coffeescript to javascript, a condition
was added that was intended to detect whether the current environment
was a bundler so that it would only call start() when in sprockets.
However, this condition is not working as expected, and I was able to
reproduce the error appearing when using rails-ujs with importmaps and
esbuild. Interestingly, the issue did not appear when using Webpack as a
bundler.

I believe the best fix here is to make the condition very explicit.
Since sprockets users should not be using the esm version of rails-ujs,
we can use the rollup replace plugin to explicitly opt the esm bundle
out of _ever_ calling start() automatically. This works because terser
will run after the replace plugin and remove the whole condition as dead
code (since it sees true == false).

Co-authored-by: Ryunosuke Sato <[email protected]>

Author: skipkayhil

actionview/.eslintrc

@@ -1,5 +1,8 @@
 {
   "extends": "eslint:recommended",
+  "globals": {
+    "__esm": "readonly"
+  },
   "rules": {
     "semi": ["error", "never"],
     "quotes": ["error", "double"],

actionview/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Fix `@rails/ujs` calling `start()` an extra time when using bundlers
+
+    *Hartley McGuire*, *Ryunosuke Sato*
+
 *   Fix the `capture` view helper compatibility with HAML and Slim
 
     When a blank string was captured in HAML or Slim (and possibly other template engines)

actionview/app/assets/javascripts/rails-ujs.esm.js

@@ -683,11 +683,4 @@ if (typeof jQuery !== "undefined" && jQuery && jQuery.ajax) {
   }));
 }
 
-if (typeof exports !== "object" && typeof module === "undefined") {
-  window.Rails = Rails;
-  if (fire(document, "rails:attachBindings")) {
-    start();
-  }
-}
-
 export { Rails as default };

actionview/app/javascript/rails-ujs/index.js

@@ -149,7 +149,7 @@ if (typeof jQuery !== "undefined" && jQuery && jQuery.ajax) {
 // difference between what happens in a bundler and what happens using a
 // sprockets compiler. In the sprockets case, Rails.start() is called
 // automatically, but it is not in the ESModule case.
-if (typeof exports !== "object" && typeof module === "undefined") {
+if (__esm == false && typeof exports !== "object" && typeof module === "undefined") {
   // The coffeescript bundle would set this at the very top. The Rollup bundle
   // doesn't set this until the entire bundle has finished running, so we need
   // to make sure its set before firing the rails:attachBindings event for

actionview/package.json

@@ -34,6 +34,7 @@
   "devDependencies": {
     "@rollup/plugin-commonjs": "^19.0.1",
     "@rollup/plugin-node-resolve": "^11.0.1",
+    "@rollup/plugin-replace": "^5.0.4",
     "eslint": "^4.19.1",
     "eslint-plugin-import": "^2.23.4",
     "jquery": "^2.2.0",

actionview/rollup.config.js

@@ -1,4 +1,5 @@
 import { terser } from "rollup-plugin-terser"
+import replace from "@rollup/plugin-replace"
 
 const banner = `
 /*
@@ -33,7 +34,11 @@ export default [
       banner,
     },
     plugins: [
-      terser(terserOptions)
+      replace({
+        preventAssignment: true,
+        values: { __esm: false },
+      }),
+      terser(terserOptions),
     ]
   },
 
@@ -45,7 +50,11 @@ export default [
       banner,
     },
     plugins: [
-      terser(terserOptions)
+      replace({
+        preventAssignment: true,
+        values: { __esm: true },
+      }),
+      terser(terserOptions),
     ]
   }
 ]

actionview/rollup.config.test.js

@@ -1,6 +1,7 @@
 // Rollup configuration for compiling the UJS tests
 
 import commonjs from "@rollup/plugin-commonjs"
+import replace from "@rollup/plugin-replace"
 import resolve from "@rollup/plugin-node-resolve"
 
 export default {
@@ -12,6 +13,10 @@ export default {
   },
 
   plugins: [
+    replace({
+      preventAssignment: true,
+      values: { __esm: false }, // false because the tests expects start() to be called automatically
+    }),
     resolve(),
     commonjs()
   ]

yarn.lock

@@ -28,6 +28,11 @@
   resolved "https://registry.npmjs.org/@jridgewell/source-map/-/source-map-0.3.4.tgz"
   integrity sha512-KE/SxsDqNs3rrWwFHcRh15ZLVFrI0YoZtgAdIyIq9k5hUNmiWRXXThPomIxHuL20sLdgzbDFyvkUMna14bvtrw==
 
+"@jridgewell/sourcemap-codec@^1.4.15":
+  version "1.4.15"
+  resolved "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.4.15.tgz"
+  integrity sha512-eF2rxCRulEKXHTRiDrDy6erMYWqNw4LPdQ8UQA4huuxaQsVeRPFl2oM8oDGxMFhJUWZf9McpLtJasDDZb/Bpeg==
+
 "@rails/activestorage@>= 7.1.0-alpha":
   version "7.1.0-beta1"
   resolved "https://registry.npmjs.org/@rails/activestorage/-/activestorage-7.1.0-beta1.tgz"
@@ -60,6 +65,14 @@
     is-module "^1.0.0"
     resolve "^1.19.0"
 
+"@rollup/plugin-replace@^5.0.4":
+  version "5.0.4"
+  resolved "https://registry.yarnpkg.com/@rollup/plugin-replace/-/plugin-replace-5.0.4.tgz#fef548dc751d06747e8dca5b0e8e1fbf647ac7e1"
+  integrity sha512-E2hmRnlh09K8HGT0rOnnri9OTh+BILGr7NVJGB30S4E3cLRn3J0xjdiyOZ74adPs4NiAMgrjUMGAZNJDBgsdmQ==
+  dependencies:
+    "@rollup/pluginutils" "^5.0.1"
+    magic-string "^0.30.3"
+
 "@rollup/pluginutils@^3.1.0":
   version "3.1.0"
   resolved "https://registry.npmjs.org/@rollup/pluginutils/-/pluginutils-3.1.0.tgz"
@@ -69,11 +82,25 @@
     estree-walker "^1.0.1"
     picomatch "^2.2.2"
 
+"@rollup/pluginutils@^5.0.1":
+  version "5.0.5"
+  resolved "https://registry.yarnpkg.com/@rollup/pluginutils/-/pluginutils-5.0.5.tgz#bbb4c175e19ebfeeb8c132c2eea0ecb89941a66c"
+  integrity sha512-6aEYR910NyP73oHiJglti74iRyOwgFU4x3meH/H8OJx6Ry0j6cOVZ5X/wTvub7G7Ao6qaHBEaNsV3GLJkSsF+Q==
+  dependencies:
+    "@types/estree" "^1.0.0"
+    estree-walker "^2.0.2"
+    picomatch "^2.3.1"
+
 "@types/estree@*", "@types/[email protected]":
   version "0.0.39"
   resolved "https://registry.npmjs.org/@types/estree/-/estree-0.0.39.tgz"
   integrity sha512-EYNwp3bU+98cpU4lAWYYL7Zz+2gryWH1qbdDTidVd6hkiR6weksdbMadyXKXNPEkQFhXM+hVO9ZygomHXp+AIw==
 
+"@types/estree@^1.0.0":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/@types/estree/-/estree-1.0.1.tgz#aa22750962f3bf0e79d753d3cc067f010c95f194"
+  integrity sha512-LG4opVs2ANWZ1TJoKc937iMmNstM/d0ae1vNbnBvBhqCSezgVUOzcLCqbI5elV8Vy6WKwKjaqR+zO9VKirBBCA==
+
 "@types/json5@^0.0.29":
   version "0.0.29"
   resolved "https://registry.npmjs.org/@types/json5/-/json5-0.0.29.tgz"
@@ -1786,7 +1813,7 @@ estree-walker@^1.0.1:
   resolved "https://registry.npmjs.org/estree-walker/-/estree-walker-1.0.1.tgz"
   integrity sha512-1fMXF3YP4pZZVozF8j/ZLfvnR8NSIljt56UhbZ5PeeDmmGHpgpdwQt7ITlGvYaQukCvuBRMLEiKiYC+oeIg4cg==
 
-estree-walker@^2.0.1:
+estree-walker@^2.0.1, estree-walker@^2.0.2:
   version "2.0.2"
   resolved "https://registry.npmjs.org/estree-walker/-/estree-walker-2.0.2.tgz"
   integrity sha512-Rfkk/Mp/DL7JVje3u18FxFujQlTNR2q6QfMSMB7AvCBx91NGj/ba3kCfza0f6dVDbw7YlRf/nDrn7pQrCCyQ/w==
@@ -3045,6 +3072,13 @@ magic-string@^0.25.7:
   dependencies:
     sourcemap-codec "^1.4.8"
 
+magic-string@^0.30.3:
+  version "0.30.5"
+  resolved "https://registry.yarnpkg.com/magic-string/-/magic-string-0.30.5.tgz#1994d980bd1c8835dc6e78db7cbd4ae4f24746f9"
+  integrity sha512-7xlpfBaQaP/T6Vh8MO/EqXSW5En6INHEvEXQiuff7Gku0PWjU3uf6w/j9o7O+SpB5fOAkrI5HeoNgwjEO0pFsA==
+  dependencies:
+    "@jridgewell/sourcemap-codec" "^1.4.15"
+
 make-dir@^2.0.0:
   version "2.1.0"
   resolved "https://registry.npmjs.org/make-dir/-/make-dir-2.1.0.tgz"
@@ -3573,7 +3607,7 @@ performance-now@^2.1.0:
   resolved "https://registry.npmjs.org/performance-now/-/performance-now-2.1.0.tgz"
   integrity sha512-7EAHlyLHI56VEIdK57uwHdHKIaAGbnXPiw0yWbarQZOKaKpvUIgW0jWRVLiatnM+XXlSwsanIBH/hzGMJulMow==
 
-picomatch@^2.0.4, picomatch@^2.2.1, picomatch@^2.2.2:
+picomatch@^2.0.4, picomatch@^2.2.1, picomatch@^2.2.2, picomatch@^2.3.1:
   version "2.3.1"
   resolved "https://registry.npmjs.org/picomatch/-/picomatch-2.3.1.tgz"
   integrity sha512-JU3teHTNjmE2VCGFzuY8EXzCDVwEqB2a8fsIvwaStHhAWJEeVd1o1QD80CU6+ZdEXXSLbSsuLwJjkCBWqRQUVA==