Merge branch 'master' into implement-smart-pipeline-in-parser

* master: (222 commits)
  Set correct methods name
  Use toPropertyKey in the "decorate" helper
  Allow function types in type params within arrow return types (#8954)
  Fix message when plugin of a wrong type is passed (#8950)
  rename colliding let bindings with for loop init (#8937)
  edge incomplete support for arrow destructuring (babel #8349) (#8926)
  fix single-arg async arrows when retainLines=true (#8868)
  [flow] Explicit inexact objects with `...` (#8884)
  Update preset-env data (#8898)
  Treat break inside block inside loop (#8914)
  fixed "source map" formatting in comment (#8878) [skip ci]
  fix typo in contributing guidelines (#8901) [skip ci]
  fix: Expression x === 'y' && '' should not evaluate to undefined. (#8880)
  fixed an extra word
  Fixes #8865 (#8866)
  v7.1.4
  v7.1.3
  Bump Babel deps (#8770)
  flow-bin@0.82.0 (#8832)
  Insertafter jsx fix (#8833)
  ...

# Conflicts:
#	packages/babel-parser/src/tokenizer/index.js
#	packages/babel-parser/test/fixtures/experimental/class-private-properties/failure-numeric-literal/options.json
#	packages/babel-parser/test/fixtures/experimental/pipeline-operator/invalid-proposal/options.json

packages/babel-parser/src/plugin-utils.js

@@ -41,13 +41,28 @@ export function getPluginOption(
 const PIPELINE_PROPOSALS = ["minimal", "smart"];
 
 export function validatePlugins(plugins: PluginList) {
-  if (
-    hasPlugin(plugins, "decorators") &&
-    hasPlugin(plugins, "decorators-legacy")
-  ) {
-    throw new Error(
-      "Cannot use the decorators and decorators-legacy plugin together",
+  if (hasPlugin(plugins, "decorators")) {
+    if (hasPlugin(plugins, "decorators-legacy")) {
+      throw new Error(
+        "Cannot use the decorators and decorators-legacy plugin together",
+      );
+    }
+
+    const decoratorsBeforeExport = getPluginOption(
+      plugins,
+      "decorators",
+      "decoratorsBeforeExport",
     );
+    if (decoratorsBeforeExport == null) {
+      throw new Error(
+        "The 'decorators' plugin requires a 'decoratorsBeforeExport' option," +
+          " whose value must be a boolean. If you are migrating from" +
+          " Babylon/Babel 6 or want to use the old decorators proposal, you" +
+          " should use the 'decorators-legacy' plugin instead of 'decorators'.",
+      );
+    } else if (typeof decoratorsBeforeExport !== "boolean") {
+      throw new Error("'decoratorsBeforeExport' must be a boolean.");
+    }
   }
 
   if (hasPlugin(plugins, "flow") && hasPlugin(plugins, "typescript")) {