Adds the accessor modifier to public and private class properties.

This is the first part of the implementation of the latest version of
the decorators proposal: https://github.com/tc39/proposal-decorators

The keyword is outlined here in the README: https://github.com/tc39/proposal-decorators#class-auto-accessors

packages/babel-parser/ast/spec.md

@@ -1235,6 +1235,7 @@ interface ClassProperty <: Node {
   value: Expression;
   static: boolean;
   computed: boolean;
+  accessor: boolean;
 }
 ```
 

packages/babel-parser/src/parser/statement.js

@@ -1373,6 +1373,14 @@ export default class StatementParser extends ExpressionParser {
       prop.computed = false;
       prop.key = key;
       prop.static = false;
+
+      if (
+        this.hasPlugin("decorators") &&
+        this.getPluginOption("decorators", "version") === "modern"
+      ) {
+        prop.accessor = false;
+      }
+
       classBody.body.push(this.parseClassProperty(prop));
       return true;
     }
@@ -1409,10 +1417,11 @@ export default class StatementParser extends ExpressionParser {
   ) {
     const publicMethod: $FlowSubtype<N.ClassMethod> = member;
     const privateMethod: $FlowSubtype<N.ClassPrivateMethod> = member;
-    const publicProp: $FlowSubtype<N.ClassMethod> = member;
-    const privateProp: $FlowSubtype<N.ClassPrivateMethod> = member;
+    const publicProp: $FlowSubtype<N.ClassProperty> = member;
+    const privateProp: $FlowSubtype<N.ClassPrivateProperty> = member;
 
     const method: typeof publicMethod | typeof privateMethod = publicMethod;
+    const prop: typeof publicProp | typeof privateProp = publicProp;
     const publicMember: typeof publicMethod | typeof publicProp = publicMethod;
 
     member.static = isStatic;
@@ -1486,6 +1495,13 @@ export default class StatementParser extends ExpressionParser {
         allowsDirectSuper,
       );
     } else if (this.isClassProperty()) {
+      if (
+        this.hasPlugin("decorators") &&
+        this.getPluginOption("decorators", "version") === "modern"
+      ) {
+        prop.accessor = false;
+      }
+
       if (isPrivate) {
         this.pushClassPrivateProperty(classBody, privateProp);
       } else {
@@ -1563,6 +1579,26 @@ export default class StatementParser extends ExpressionParser {
       }
 
       this.checkGetterSetterParams(publicMethod);
+    } else if (
+      isContextual &&
+      key.name === "accessor" &&
+      this.hasPlugin("decorators") &&
+      this.getPluginOption("decorators", "version") === "modern" &&
+      !this.isLineTerminator()
+    ) {
+      this.resetPreviousNodeTrailingComments(key);
+
+      // The so-called parsed name would have been "get/set": get the real name.
+      const isPrivate = this.match(tt.privateName);
+      this.parseClassElementName(publicProp);
+
+      prop.accessor = true;
+
+      if (isPrivate) {
+        this.pushClassPrivateProperty(classBody, privateProp);
+      } else {
+        this.pushClassProperty(classBody, publicProp);
+      }
     } else if (this.isLineTerminator()) {
       // an uninitialized class property (due to ASI, since we don't otherwise recognize the next token)
       if (isPrivate) {

packages/babel-parser/src/types.js

@@ -813,6 +813,7 @@ export type ClassProperty = ClassMemberBase &
     type: "ClassProperty",
     key: Expression,
     value: ?Expression, // TODO: Not in spec that this is nullable.
+    accessor?: boolean, // Decorators proposal
 
     typeAnnotation?: ?TypeAnnotationBase, // TODO: Not in spec
     variance?: ?FlowVariance, // TODO: Not in spec
@@ -828,6 +829,7 @@ export type ClassPrivateProperty = NodeBase & {
   value: ?Expression, // TODO: Not in spec that this is nullable.
   static: boolean,
   computed: false,
+  accessor?: boolean, // Decorators proposal
 
   // Flow and Typescript
   typeAnnotation?: ?TypeAnnotationBase,

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/basic-accessor/input.js

@@ -0,0 +1,3 @@
+class Foo {
+  accessor bar;
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/basic-accessor/output.json

@@ -0,0 +1,42 @@
+{
+  "type": "File",
+  "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":6,"end":9,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":9},"identifierName":"Foo"},
+          "name": "Foo"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start":10,"end":29,"loc":{"start":{"line":1,"column":10},"end":{"line":3,"column":1}},
+          "body": [
+            {
+              "type": "ClassProperty",
+              "start":14,"end":27,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":15}},
+              "static": false,
+              "key": {
+                "type": "Identifier",
+                "start":23,"end":26,"loc":{"start":{"line":2,"column":11},"end":{"line":2,"column":14},"identifierName":"bar"},
+                "name": "bar"
+              },
+              "computed": false,
+              "accessor": true,
+              "value": null
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/field-named-accessor/input.js

@@ -0,0 +1,3 @@
+class Foo {
+  accessor = 123;
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/field-named-accessor/output.json

@@ -0,0 +1,50 @@
+{
+  "type": "File",
+  "start":0,"end":31,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":31,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start":0,"end":31,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":6,"end":9,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":9},"identifierName":"Foo"},
+          "name": "Foo"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start":10,"end":31,"loc":{"start":{"line":1,"column":10},"end":{"line":3,"column":1}},
+          "body": [
+            {
+              "type": "ClassProperty",
+              "start":14,"end":29,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":17}},
+              "static": false,
+              "key": {
+                "type": "Identifier",
+                "start":14,"end":22,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":10},"identifierName":"accessor"},
+                "name": "accessor"
+              },
+              "computed": false,
+              "accessor": false,
+              "value": {
+                "type": "NumericLiteral",
+                "start":25,"end":28,"loc":{"start":{"line":2,"column":13},"end":{"line":2,"column":16}},
+                "extra": {
+                  "rawValue": 123,
+                  "raw": "123"
+                },
+                "value": 123
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/method-named-accessor/input.js

@@ -0,0 +1,3 @@
+class Foo {
+  accessor() {}
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/method-named-accessor/output.json

@@ -0,0 +1,51 @@
+{
+  "type": "File",
+  "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":6,"end":9,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":9},"identifierName":"Foo"},
+          "name": "Foo"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start":10,"end":29,"loc":{"start":{"line":1,"column":10},"end":{"line":3,"column":1}},
+          "body": [
+            {
+              "type": "ClassMethod",
+              "start":14,"end":27,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":15}},
+              "static": false,
+              "key": {
+                "type": "Identifier",
+                "start":14,"end":22,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":10},"identifierName":"accessor"},
+                "name": "accessor"
+              },
+              "computed": false,
+              "kind": "method",
+              "id": null,
+              "generator": false,
+              "async": false,
+              "params": [],
+              "body": {
+                "type": "BlockStatement",
+                "start":25,"end":27,"loc":{"start":{"line":2,"column":13},"end":{"line":2,"column":15}},
+                "body": [],
+                "directives": []
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/not-allowed-on-methods/input.js

@@ -0,0 +1,5 @@
+class Foo {
+  accessor bar() {
+
+  }
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/not-allowed-on-methods/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected token (2:14)"
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/private-accessor/input.js

@@ -0,0 +1,3 @@
+class Foo {
+  accessor #bar;
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/accessor/private-accessor/output.json

@@ -0,0 +1,46 @@
+{
+  "type": "File",
+  "start":0,"end":30,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":30,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start":0,"end":30,"loc":{"start":{"line":1,"column":0},"end":{"line":3,"column":1}},
+        "id": {
+          "type": "Identifier",
+          "start":6,"end":9,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":9},"identifierName":"Foo"},
+          "name": "Foo"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start":10,"end":30,"loc":{"start":{"line":1,"column":10},"end":{"line":3,"column":1}},
+          "body": [
+            {
+              "type": "ClassPrivateProperty",
+              "start":14,"end":28,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":16}},
+              "static": false,
+              "key": {
+                "type": "PrivateName",
+                "start":23,"end":27,"loc":{"start":{"line":2,"column":11},"end":{"line":2,"column":15}},
+                "id": {
+                  "type": "Identifier",
+                  "start":24,"end":27,"loc":{"start":{"line":2,"column":12},"end":{"line":2,"column":15},"identifierName":"bar"},
+                  "name": "bar"
+                }
+              },
+              "computed": false,
+              "accessor": true,
+              "value": null
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/decorators-modern/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["decorators", { "decoratorsBeforeExport": false, "version": "modern" }]]
+}