Add an option to Babylon to have decorators before export (#7869)

* Add support for plugin options in Babylon

They work similarly to how they work in Babel. e.g.
  babylon.parse({
    options: [
      "plugin1",
      ["plugin2", { option: true }]
    ]
  });

The inernal api to get an option is
  this.getPluginOption("pluginName", "option")
If the plugin isn't defined, it returns undefined.

* Add Babylon option decorators.secoratorsBeforeExport

* Nit

packages/babylon/src/index.js

@@ -67,39 +67,39 @@ function getParserClass(
   pluginsFromOptions: $ReadOnlyArray<string>,
 ): Class<Parser> {
   if (
-    pluginsFromOptions.indexOf("decorators-legacy") >= 0 &&
-    pluginsFromOptions.indexOf("decorators") >= 0
+    hasPlugin(pluginsFromOptions, "decorators") &&
+    hasPlugin(pluginsFromOptions, "decorators-legacy")
   ) {
-    throw new Error("Cannot use decorators and decorators2 plugin together");
+    throw new Error(
+      "Cannot use the decorators and decorators-legacy plugin together",
+    );
   }
 
   // Filter out just the plugins that have an actual mixin associated with them.
-  let pluginList = pluginsFromOptions.filter(
-    p => p === "estree" || p === "flow" || p === "jsx" || p === "typescript",
-  );
+  let pluginList = pluginsFromOptions.filter(plugin => {
+    const p = getPluginName(plugin);
+    return p === "estree" || p === "flow" || p === "jsx" || p === "typescript";
+  });
 
-  if (pluginList.indexOf("flow") >= 0) {
+  if (hasPlugin(pluginList, "flow")) {
     // ensure flow plugin loads last
-    pluginList = pluginList.filter(plugin => plugin !== "flow");
+    pluginList = pluginList.filter(p => getPluginName(p) !== "flow");
     pluginList.push("flow");
   }
 
-  if (
-    pluginList.indexOf("flow") >= 0 &&
-    pluginList.indexOf("typescript") >= 0
-  ) {
+  if (hasPlugin(pluginList, "flow") && hasPlugin(pluginList, "typescript")) {
     throw new Error("Cannot combine flow and typescript plugins.");
   }
 
-  if (pluginList.indexOf("typescript") >= 0) {
+  if (hasPlugin(pluginList, "typescript")) {
     // ensure typescript plugin loads last
-    pluginList = pluginList.filter(plugin => plugin !== "typescript");
+    pluginList = pluginList.filter(p => getPluginName(p) !== "typescript");
     pluginList.push("typescript");
   }
 
-  if (pluginList.indexOf("estree") >= 0) {
+  if (hasPlugin(pluginList, "estree")) {
     // ensure estree plugin loads first
-    pluginList = pluginList.filter(plugin => plugin !== "estree");
+    pluginList = pluginList.filter(p => getPluginName(p) !== "estree");
     pluginList.unshift("estree");
   }
 
@@ -114,3 +114,11 @@ function getParserClass(
   }
   return cls;
 }
+
+function getPluginName(plugin) {
+  return Array.isArray(plugin) ? plugin[0] : plugin;
+}
+
+function hasPlugin(pluginsList, name) {
+  return pluginsList.some(plugin => getPluginName(plugin) === name);
+}

packages/babylon/src/parser/base.js

@@ -26,6 +26,10 @@ export default class BaseParser {
   }
 
   hasPlugin(name: string): boolean {
-    return !!this.plugins[name];
+    return Object.hasOwnProperty.call(this.plugins, name);
+  }
+
+  getPluginOption(plugin: string, name: string) {
+    if (this.hasPlugin(plugin)) return this.plugins[plugin][name];
   }
 }

packages/babylon/src/parser/index.js

@@ -41,9 +41,10 @@ export default class Parser extends StatementParser {
 function pluginsMap(
   pluginList: $ReadOnlyArray<string>,
 ): { [key: string]: boolean } {
-  const pluginMap = {};
-  for (const name of pluginList) {
-    pluginMap[name] = true;
+  const pluginMap = Object.create(null);
+  for (const plugin of pluginList) {
+    const [name, options = {}] = Array.isArray(plugin) ? plugin : [plugin];
+    pluginMap[name] = options;
   }
   return pluginMap;
 }

packages/babylon/src/parser/statement.js

@@ -230,7 +230,10 @@ export default class StatementParser extends ExpressionParser {
   }
 
   parseDecorators(allowExport?: boolean): void {
-    if (this.hasPlugin("decorators")) {
+    if (
+      this.hasPlugin("decorators") &&
+      !this.getPluginOption("decorators", "decoratorsBeforeExport")
+    ) {
       allowExport = false;
     }
 
@@ -1422,6 +1425,12 @@ export default class StatementParser extends ExpressionParser {
     } else if (this.match(tt._class)) {
       return this.parseClass(expr, true, true);
     } else if (this.match(tt.at)) {
+      if (
+        this.hasPlugin("decorators") &&
+        this.getPluginOption("decorators", "decoratorsBeforeExport")
+      ) {
+        this.unexpected();
+      }
       this.parseDecorators(false);
       return this.parseClass(expr, true, true);
     } else if (
@@ -1518,14 +1527,24 @@ export default class StatementParser extends ExpressionParser {
   }
 
   shouldParseExportDeclaration(): boolean {
+    if (this.match(tt.at)) {
+      this.expectOnePlugin(["decorators", "decorators-legacy"]);
+      if (this.hasPlugin("decorators")) {
+        if (this.getPluginOption("decorators", "decoratorsBeforeExport")) {
+          this.unexpected();
+        } else {
+          return true;
+        }
+      }
+    }
+
     return (
       this.state.type.keyword === "var" ||
       this.state.type.keyword === "const" ||
       this.state.type.keyword === "let" ||
       this.state.type.keyword === "function" ||
       this.state.type.keyword === "class" ||
-      this.isContextual("async") ||
-      (this.match(tt.at) && this.expectPlugin("decorators"))
+      this.isContextual("async")
     );
   }
 

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default-decorated-expression-with-parens/input.mjs

@@ -0,0 +1 @@
+export default (@decorator class Foo {})

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default-decorated-expression-with-parens/options.json

@@ -0,0 +1,6 @@
+{
+  "sourceType": "module",
+  "plugins": [
+    ["decorators", { "decoratorsBeforeExport": true }]
+  ]
+}

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default-decorated-expression-with-parens/output.json

@@ -0,0 +1,136 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 40,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 40
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 40,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 40
+      }
+    },
+    "sourceType": "module",
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start": 0,
+        "end": 40,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 40
+          }
+        },
+        "declaration": {
+          "type": "ClassExpression",
+          "start": 16,
+          "end": 39,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 16
+            },
+            "end": {
+              "line": 1,
+              "column": 39
+            }
+          },
+          "decorators": [
+            {
+              "type": "Decorator",
+              "start": 16,
+              "end": 26,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 16
+                },
+                "end": {
+                  "line": 1,
+                  "column": 26
+                }
+              },
+              "callee": {
+                "type": "Identifier",
+                "start": 17,
+                "end": 26,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 17
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 26
+                  },
+                  "identifierName": "decorator"
+                },
+                "name": "decorator"
+              }
+            }
+          ],
+          "id": {
+            "type": "Identifier",
+            "start": 33,
+            "end": 36,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 33
+              },
+              "end": {
+                "line": 1,
+                "column": 36
+              },
+              "identifierName": "Foo"
+            },
+            "name": "Foo"
+          },
+          "superClass": null,
+          "body": {
+            "type": "ClassBody",
+            "start": 37,
+            "end": 39,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 37
+              },
+              "end": {
+                "line": 1,
+                "column": 39
+              }
+            },
+            "body": []
+          },
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 15
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default-decorated-expression-without-parens/input.mjs

@@ -0,0 +1 @@
+export default @decorator class Foo {}

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default-decorated-expression-without-parens/options.json

@@ -0,0 +1,7 @@
+{
+  "sourceType": "module",
+  "plugins": [
+    ["decorators", { "decoratorsBeforeExport": true }]
+  ],
+  "throws": "Unexpected token (1:15)"
+}

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default/input.mjs

@@ -0,0 +1,2 @@
+@decorator
+export default class Foo {}

packages/babylon/test/fixtures/experimental/decorators-2/decoratorsBeforeExport-export-default/options.json

@@ -0,0 +1,6 @@
+{
+  "sourceType": "module",
+  "plugins": [
+    ["decorators", { "decoratorsBeforeExport": true }]
+  ]
+}