Refactor await/yield production parameter tracking (#10956)

* test: add test fixtures

* refactor: track AWAIT and YIELD in separate handler

* fix flow errors

* add flow type annotation to production-parameter

* address review comments

* refactor: track [Return] parameter

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

@@ -5,6 +5,7 @@ import type State from "../tokenizer/state";
 import type { PluginsMap } from "./index";
 import type ScopeHandler from "../util/scope";
 import type ClassScopeHandler from "../util/class-scope";
+import type ProductionParameterHandler from "../util/production-parameter";
 
 export default class BaseParser {
   // Properties set by constructor in index.js
@@ -12,6 +13,7 @@ export default class BaseParser {
   inModule: boolean;
   scope: ScopeHandler<*>;
   classScope: ClassScopeHandler;
+  prodParam: ProductionParameterHandler;
   plugins: PluginsMap;
   filename: ?string;
   sawUnambiguousESM: boolean = false;

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

@@ -33,15 +33,20 @@ import * as charCodes from "charcodes";
 import {
   BIND_OUTSIDE,
   BIND_VAR,
-  functionFlags,
   SCOPE_ARROW,
   SCOPE_CLASS,
   SCOPE_DIRECT_SUPER,
+  SCOPE_FUNCTION,
   SCOPE_SUPER,
   SCOPE_PROGRAM,
-  SCOPE_ASYNC,
 } from "../util/scopeflags";
 import { ExpressionErrors } from "./util";
+import {
+  PARAM_AWAIT,
+  PARAM_RETURN,
+  PARAM,
+  functionFlags,
+} from "../util/production-parameter";
 
 export default class ExpressionParser extends LValParser {
   // Forward-declaration: defined in statement.js
@@ -108,11 +113,12 @@ export default class ExpressionParser extends LValParser {
 
   // Convenience method to parse an Expression only
   getExpression(): N.Expression {
-    let scopeFlags = SCOPE_PROGRAM;
+    let paramFlags = PARAM;
     if (this.hasPlugin("topLevelAwait") && this.inModule) {
-      scopeFlags |= SCOPE_ASYNC;
+      paramFlags |= PARAM_AWAIT;
     }
-    this.scope.enter(scopeFlags);
+    this.scope.enter(SCOPE_PROGRAM);
+    this.prodParam.enter(paramFlags);
     this.nextToken();
     const expr = this.parseExpression();
     if (!this.match(tt.eof)) {
@@ -131,9 +137,15 @@ export default class ExpressionParser extends LValParser {
   // and, *if* the syntactic construct they handle is present, wrap
   // the AST node that the inner parser gave them in another node.
 
-  // Parse a full expression. The optional arguments are used to
+  // Parse a full expression.
-  // forbid the `in` operator (in for loops initialization expressions)
+  // - `noIn`
-  // and provide reference for storing '=' operator inside shorthand
+  //   is used to forbid the `in` operator (in for loops initialization expressions)
+  //   When `noIn` is true, the production parameter [In] is not present.
+  //   Whenever [?In] appears in the right-hand sides of a production, we pass
+  //   `noIn` to the subroutine calls.
+
+  // - `refExpressionErrors `
+  //   provides reference for storing '=' operator inside shorthand
   //   property assignment in contexts where both object expression
   //   and object pattern might appear (so it's possible to raise
   //   delayed syntax error at correct position).
@@ -169,7 +181,7 @@ export default class ExpressionParser extends LValParser {
     const startPos = this.state.start;
     const startLoc = this.state.startLoc;
     if (this.isContextual("yield")) {
-      if (this.scope.inGenerator) {
+      if (this.prodParam.hasYield) {
         let left = this.parseYield(noIn);
         if (afterLeftParse) {
           left = afterLeftParse.call(this, left, startPos, startLoc);
@@ -367,7 +379,7 @@ export default class ExpressionParser extends LValParser {
           if (
             this.match(tt.name) &&
             this.state.value === "await" &&
-            this.scope.inAsync
+            this.prodParam.hasAwait
           ) {
             throw this.raise(
               this.state.start,
@@ -1161,7 +1173,7 @@ export default class ExpressionParser extends LValParser {
     this.next();
     meta = this.createIdentifier(meta, "function");
 
-    if (this.scope.inGenerator && this.eat(tt.dot)) {
+    if (this.prodParam.hasYield && this.eat(tt.dot)) {
       return this.parseMetaProperty(node, meta, "sent");
     }
     return this.parseFunction(node);
@@ -1833,13 +1845,15 @@ export default class ExpressionParser extends LValParser {
     node.generator = !!isGenerator;
     const allowModifiers = isConstructor; // For TypeScript parameter properties
     this.scope.enter(
-      functionFlags(isAsync, node.generator) |
+      SCOPE_FUNCTION |
         SCOPE_SUPER |
         (inClassScope ? SCOPE_CLASS : 0) |
         (allowDirectSuper ? SCOPE_DIRECT_SUPER : 0),
     );
+    this.prodParam.enter(functionFlags(isAsync, node.generator));
     this.parseFunctionParams((node: any), allowModifiers);
     this.parseFunctionBodyAndFinish(node, type, true);
+    this.prodParam.exit();
     this.scope.exit();
 
     this.state.yieldPos = oldYieldPos;
@@ -1857,7 +1871,8 @@ export default class ExpressionParser extends LValParser {
     isAsync: boolean,
     trailingCommaPos: ?number,
   ): N.ArrowFunctionExpression {
-    this.scope.enter(functionFlags(isAsync, false) | SCOPE_ARROW);
+    this.scope.enter(SCOPE_FUNCTION | SCOPE_ARROW);
+    this.prodParam.enter(functionFlags(isAsync, false));
     this.initFunction(node, isAsync);
     const oldMaybeInArrowParameters = this.state.maybeInArrowParameters;
     const oldYieldPos = this.state.yieldPos;
@@ -1872,6 +1887,7 @@ export default class ExpressionParser extends LValParser {
     this.state.awaitPos = -1;
     this.parseFunctionBody(node, true);
 
+    this.prodParam.exit();
     this.scope.exit();
     this.state.maybeInArrowParameters = oldMaybeInArrowParameters;
     this.state.yieldPos = oldYieldPos;
@@ -1949,7 +1965,11 @@ export default class ExpressionParser extends LValParser {
         allowExpression,
         !oldStrict && useStrict,
       );
+      // FunctionBody[Yield, Await]:
+      //   StatementList[?Yield, ?Await, +Return] opt
+      this.prodParam.enter(this.prodParam.currentFlags() | PARAM_RETURN);
       node.body = this.parseBlock(true, false);
+      this.prodParam.exit();
       this.state.labels = oldLabels;
     }
 
@@ -2140,7 +2160,7 @@ export default class ExpressionParser extends LValParser {
     checkKeywords: boolean,
     isBinding: boolean,
   ): void {
-    if (this.scope.inGenerator && word === "yield") {
+    if (this.prodParam.hasYield && word === "yield") {
       this.raise(
         startLoc,
         "Can not use 'yield' as identifier inside a generator",
@@ -2149,7 +2169,7 @@ export default class ExpressionParser extends LValParser {
     }
 
     if (word === "await") {
-      if (this.scope.inAsync) {
+      if (this.prodParam.hasAwait) {
         this.raise(
           startLoc,
           "Can not use 'await' as identifier inside an async function",
@@ -2187,7 +2207,7 @@ export default class ExpressionParser extends LValParser {
       : isStrictReservedWord;
 
     if (reservedTest(word, this.inModule)) {
-      if (!this.scope.inAsync && word === "await") {
+      if (!this.prodParam.hasAwait && word === "await") {
         this.raise(
           startLoc,
           "Can not use keyword 'await' outside an async function",
@@ -2199,10 +2219,10 @@ export default class ExpressionParser extends LValParser {
   }
 
   isAwaitAllowed(): boolean {
-    if (this.scope.inFunction) return this.scope.inAsync;
+    if (this.scope.inFunction) return this.prodParam.hasAwait;
     if (this.options.allowAwaitOutsideFunction) return true;
     if (this.hasPlugin("topLevelAwait")) {
-      return this.inModule && this.scope.inAsync;
+      return this.inModule && this.prodParam.hasAwait;
     }
     return false;
   }

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

@@ -5,9 +5,13 @@ import type { File /*::, JSXOpeningElement */ } from "../types";
 import type { PluginList } from "../plugin-utils";
 import { getOptions } from "../options";
 import StatementParser from "./statement";
-import { SCOPE_ASYNC, SCOPE_PROGRAM } from "../util/scopeflags";
+import { SCOPE_PROGRAM } from "../util/scopeflags";
 import ScopeHandler from "../util/scope";
 import ClassScopeHandler from "../util/class-scope";
+import ProductionParameterHandler, {
+  PARAM_AWAIT,
+  PARAM,
+} from "../util/production-parameter";
 
 export type PluginsMap = Map<string, { [string]: any }>;
 
@@ -28,6 +32,7 @@ export default class Parser extends StatementParser {
     this.options = options;
     this.inModule = this.options.sourceType === "module";
     this.scope = new ScopeHandler(this.raise.bind(this), this.inModule);
+    this.prodParam = new ProductionParameterHandler();
     this.classScope = new ClassScopeHandler(this.raise.bind(this));
     this.plugins = pluginsMap(this.options.plugins);
     this.filename = options.sourceFilename;
@@ -39,11 +44,12 @@ export default class Parser extends StatementParser {
   }
 
   parse(): File {
-    let scopeFlags = SCOPE_PROGRAM;
+    let paramFlags = PARAM;
     if (this.hasPlugin("topLevelAwait") && this.inModule) {
-      scopeFlags |= SCOPE_ASYNC;
+      paramFlags |= PARAM_AWAIT;
     }
-    this.scope.enter(scopeFlags);
+    this.scope.enter(SCOPE_PROGRAM);
+    this.prodParam.enter(paramFlags);
     const file = this.startNode();
     const program = this.startNode();
     this.nextToken();

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

@@ -15,8 +15,8 @@ import {
   BIND_LEXICAL,
   BIND_VAR,
   BIND_FUNCTION,
-  functionFlags,
   SCOPE_CLASS,
+  SCOPE_FUNCTION,
   SCOPE_OTHER,
   SCOPE_SIMPLE_CATCH,
   SCOPE_SUPER,
@@ -28,6 +28,7 @@ import {
   type BindingTypes,
 } from "../util/scopeflags";
 import { ExpressionErrors } from "./util";
+import { PARAM, functionFlags } from "../util/production-parameter";
 
 const loopLabel = { kind: "loop" },
   switchLabel = { kind: "switch" };
@@ -574,7 +575,7 @@ export default class StatementParser extends ExpressionParser {
   }
 
   parseReturnStatement(node: N.ReturnStatement): N.ReturnStatement {
-    if (!this.scope.inFunction && !this.options.allowReturnOutsideFunction) {
+    if (!this.prodParam.hasReturn && !this.options.allowReturnOutsideFunction) {
       this.raise(this.state.start, "'return' outside of function");
     }
 
@@ -1059,7 +1060,8 @@ export default class StatementParser extends ExpressionParser {
     this.state.maybeInArrowParameters = false;
     this.state.yieldPos = -1;
     this.state.awaitPos = -1;
-    this.scope.enter(functionFlags(node.async, node.generator));
+    this.scope.enter(SCOPE_FUNCTION);
+    this.prodParam.enter(functionFlags(isAsync, node.generator));
 
     if (!isStatement) {
       node.id = this.parseFunctionId();
@@ -1078,6 +1080,7 @@ export default class StatementParser extends ExpressionParser {
       );
     });
 
+    this.prodParam.exit();
     this.scope.exit();
 
     if (isStatement && !isHangingStatement) {
@@ -1599,9 +1602,12 @@ export default class StatementParser extends ExpressionParser {
     node: N.ClassPrivateProperty,
   ): N.ClassPrivateProperty {
     this.scope.enter(SCOPE_CLASS | SCOPE_SUPER);
+    // [In] production parameter is tracked in parseMaybeAssign
+    this.prodParam.enter(PARAM);
 
     node.value = this.eat(tt.eq) ? this.parseMaybeAssign() : null;
     this.semicolon();
+    this.prodParam.exit();
 
     this.scope.exit();
 
@@ -1614,6 +1620,8 @@ export default class StatementParser extends ExpressionParser {
     }
 
     this.scope.enter(SCOPE_CLASS | SCOPE_SUPER);
+    // [In] production parameter is tracked in parseMaybeAssign
+    this.prodParam.enter(PARAM);
 
     if (this.match(tt.eq)) {
       this.expectPlugin("classProperties");
@@ -1624,6 +1632,7 @@ export default class StatementParser extends ExpressionParser {
     }
     this.semicolon();
 
+    this.prodParam.exit();
     this.scope.exit();
 
     return this.finishNode(node, "ClassProperty");

packages/babel-parser/src/plugins/flow.js

@@ -12,13 +12,13 @@ import { types as tc } from "../tokenizer/context";
 import * as charCodes from "charcodes";
 import { isIteratorStart } from "../util/identifier";
 import {
-  functionFlags,
   type BindingTypes,
   BIND_NONE,
   BIND_LEXICAL,
   BIND_VAR,
   BIND_FUNCTION,
   SCOPE_ARROW,
+  SCOPE_FUNCTION,
   SCOPE_OTHER,
 } from "../util/scopeflags";
 import type { ExpressionErrors } from "../parser/util";
@@ -1889,7 +1889,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         node.extra?.trailingComma,
       );
       // Enter scope, as checkParams defines bindings
-      this.scope.enter(functionFlags(false, false) | SCOPE_ARROW);
+      this.scope.enter(SCOPE_FUNCTION | SCOPE_ARROW);
       // Use super's method to force the parameters to be checked
       super.checkParams(node, false, true);
       this.scope.exit();

packages/babel-parser/src/plugins/typescript/index.js

@@ -26,6 +26,7 @@ import {
 import TypeScriptScopeHandler from "./scope";
 import * as charCodes from "charcodes";
 import type { ExpressionErrors } from "../../parser/util";
+import { PARAM } from "../../util/production-parameter";
 
 type TsModifier =
   | "readonly"
@@ -1265,7 +1266,9 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         node.body = inner;
       } else {
         this.scope.enter(SCOPE_TS_MODULE);
+        this.prodParam.enter(PARAM);
         node.body = this.tsParseModuleBlock();
+        this.prodParam.exit();
         this.scope.exit();
       }
       return this.finishNode(node, "TSModuleDeclaration");
@@ -1284,7 +1287,9 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
       if (this.match(tt.braceL)) {
         this.scope.enter(SCOPE_TS_MODULE);
+        this.prodParam.enter(PARAM);
         node.body = this.tsParseModuleBlock();
+        this.prodParam.exit();
         this.scope.exit();
       } else {
         this.semicolon();
@@ -1439,11 +1444,13 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           // Would like to use tsParseAmbientExternalModuleDeclaration here, but already ran past "global".
           if (this.match(tt.braceL)) {
             this.scope.enter(SCOPE_TS_MODULE);
+            this.prodParam.enter(PARAM);
             const mod: N.TsModuleDeclaration = node;
             mod.global = true;
             mod.id = expr;
             mod.body = this.tsParseModuleBlock();
             this.scope.exit();
+            this.prodParam.exit();
             return this.finishNode(mod, "TSModuleDeclaration");
           }
           break;

packages/babel-parser/src/tokenizer/context.js

@@ -60,7 +60,7 @@ tt.name.updateContext = function(prevType) {
   if (prevType !== tt.dot) {
     if (
       (this.state.value === "of" && !this.state.exprAllowed) ||
-      (this.state.value === "yield" && this.scope.inGenerator)
+      (this.state.value === "yield" && this.prodParam.hasYield)
     ) {
       allowed = true;
     }

packages/babel-parser/src/util/production-parameter.js

@@ -0,0 +1,63 @@
+// @flow
+export const PARAM = 0b000, // Initial Parameter flags
+  PARAM_YIELD = 0b001, // track [Yield] production parameter
+  PARAM_AWAIT = 0b010, // track [Await] production parameter
+  PARAM_RETURN = 0b100; // track [Return] production parameter
+
+// ProductionParameterHandler is a stack fashioned production parameter tracker
+// https://tc39.es/ecma262/#sec-grammar-notation
+// The tracked parameters are defined above. Note that the [In] parameter is
+// tracked in `noIn` argument of `parseExpression`.
+//
+// Whenever [+Await]/[+Yield] appears in the right-hand sides of a production,
+// we must enter a new tracking stack. For example when parsing
+//
+// AsyncFunctionDeclaration [Yield, Await]:
+//   async [no LineTerminator here] function BindingIdentifier[?Yield, ?Await]
+//     ( FormalParameters[~Yield, +Await] ) { AsyncFunctionBody }
+//
+// we must follow such process:
+//
+// 1. parse async keyword
+// 2. parse function keyword
+// 3. parse bindingIdentifier <= inherit current parameters: [?Await]
+// 4. enter new stack with (PARAM_AWAIT)
+// 5. parse formal parameters <= must have [Await] parameter [+Await]
+// 6. parse function body
+// 7. exit current stack
+
+export type ParamKind = typeof PARAM | typeof PARAM_AWAIT | typeof PARAM_YIELD;
+
+export default class ProductionParameterHandler {
+  stacks: Array<ParamKind> = [];
+  enter(flags: ParamKind) {
+    this.stacks.push(flags);
+  }
+
+  exit() {
+    this.stacks.pop();
+  }
+
+  currentFlags(): ParamKind {
+    return this.stacks[this.stacks.length - 1];
+  }
+
+  get hasAwait(): boolean {
+    return (this.currentFlags() & PARAM_AWAIT) > 0;
+  }
+
+  get hasYield(): boolean {
+    return (this.currentFlags() & PARAM_YIELD) > 0;
+  }
+
+  get hasReturn(): boolean {
+    return (this.currentFlags() & PARAM_RETURN) > 0;
+  }
+}
+
+export function functionFlags(
+  isAsync: boolean,
+  isGenerator: boolean,
+): ParamKind {
+  return (isAsync ? PARAM_AWAIT : 0) | (isGenerator ? PARAM_YIELD : 0);
+}

packages/babel-parser/src/util/scope.js

@@ -1,10 +1,8 @@
 // @flow
 import {
   SCOPE_ARROW,
-  SCOPE_ASYNC,
   SCOPE_DIRECT_SUPER,
   SCOPE_FUNCTION,
-  SCOPE_GENERATOR,
   SCOPE_SIMPLE_CATCH,
   SCOPE_SUPER,
   SCOPE_PROGRAM,
@@ -53,25 +51,6 @@ export default class ScopeHandler<IScope: Scope = Scope> {
   get inFunction() {
     return (this.currentVarScope().flags & SCOPE_FUNCTION) > 0;
   }
-  get inGenerator() {
-    return (this.currentVarScope().flags & SCOPE_GENERATOR) > 0;
-  }
-  // the following loop always exit because SCOPE_PROGRAM is SCOPE_VAR
-  // $FlowIgnore
-  get inAsync() {
-    for (let i = this.scopeStack.length - 1; ; i--) {
-      const scope = this.scopeStack[i];
-      const isVarScope = scope.flags & SCOPE_VAR;
-      const isClassScope = scope.flags & SCOPE_CLASS;
-      if (isClassScope && !isVarScope) {
-        // If it meets a class scope before a var scope, it means it is a class property initializer
-        // which does not have an [Await] parameter in its grammar
-        return false;
-      } else if (isVarScope) {
-        return (scope.flags & SCOPE_ASYNC) > 0;
-      }
-    }
-  }
   get allowSuper() {
     return (this.currentThisScope().flags & SCOPE_SUPER) > 0;
   }

packages/babel-parser/src/util/scopeflags.js

@@ -2,17 +2,15 @@
 
 // Each scope gets a bitset that may contain these flags
 // prettier-ignore
-export const SCOPE_OTHER        = 0b0000000000,
+export const SCOPE_OTHER        = 0b00000000,
-             SCOPE_PROGRAM      = 0b0000000001,
+             SCOPE_PROGRAM      = 0b00000001,
-             SCOPE_FUNCTION     = 0b0000000010,
+             SCOPE_FUNCTION     = 0b00000010,
-             SCOPE_ASYNC        = 0b0000000100,
+             SCOPE_ARROW        = 0b00000100,
-             SCOPE_GENERATOR    = 0b0000001000,
+             SCOPE_SIMPLE_CATCH = 0b00001000,
-             SCOPE_ARROW        = 0b0000010000,
+             SCOPE_SUPER        = 0b00010000,
-             SCOPE_SIMPLE_CATCH = 0b0000100000,
+             SCOPE_DIRECT_SUPER = 0b00100000,
-             SCOPE_SUPER        = 0b0001000000,
+             SCOPE_CLASS        = 0b01000000,
-             SCOPE_DIRECT_SUPER = 0b0010000000,
+             SCOPE_TS_MODULE    = 0b10000000,
-             SCOPE_CLASS        = 0b0100000000,
-             SCOPE_TS_MODULE    = 0b1000000000,
              SCOPE_VAR = SCOPE_PROGRAM | SCOPE_FUNCTION | SCOPE_TS_MODULE;
 
 export type ScopeFlags =
@@ -20,22 +18,12 @@ export type ScopeFlags =
   | typeof SCOPE_PROGRAM
   | typeof SCOPE_FUNCTION
   | typeof SCOPE_VAR
-  | typeof SCOPE_ASYNC
-  | typeof SCOPE_GENERATOR
   | typeof SCOPE_ARROW
   | typeof SCOPE_SIMPLE_CATCH
   | typeof SCOPE_SUPER
   | typeof SCOPE_DIRECT_SUPER
   | typeof SCOPE_CLASS;
 
-export function functionFlags(isAsync: boolean, isGenerator: boolean) {
-  return (
-    SCOPE_FUNCTION |
-    (isAsync ? SCOPE_ASYNC : 0) |
-    (isGenerator ? SCOPE_GENERATOR : 0)
-  );
-}
-
 // These flags are meant to be _only_ used inside the Scope class (or subclasses).
 // prettier-ignore
 export const BIND_KIND_VALUE           = 0b00000_0000_01,

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-class-property-in-generator/input.js

@@ -0,0 +1,6 @@
+function* foo() {
+  class C {
+    // here yield is an identifier reference
+    p = yield + 42;
+  }
+}

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-class-property-in-generator/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["classProperties"]
+}

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-class-property-in-generator/output.json

@@ -0,0 +1,264 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 100,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 6,
+      "column": 1
+    }
+  },
+  "errors": [
+    "SyntaxError: Unexpected reserved word 'yield' (4:8)"
+  ],
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 100,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 6,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "FunctionDeclaration",
+        "start": 0,
+        "end": 100,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 6,
+            "column": 1
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 10,
+          "end": 13,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 10
+            },
+            "end": {
+              "line": 1,
+              "column": 13
+            },
+            "identifierName": "foo"
+          },
+          "name": "foo"
+        },
+        "generator": true,
+        "async": false,
+        "params": [],
+        "body": {
+          "type": "BlockStatement",
+          "start": 16,
+          "end": 100,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 16
+            },
+            "end": {
+              "line": 6,
+              "column": 1
+            }
+          },
+          "body": [
+            {
+              "type": "ClassDeclaration",
+              "start": 20,
+              "end": 98,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 2
+                },
+                "end": {
+                  "line": 5,
+                  "column": 3
+                }
+              },
+              "id": {
+                "type": "Identifier",
+                "start": 26,
+                "end": 27,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 8
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 9
+                  },
+                  "identifierName": "C"
+                },
+                "name": "C"
+              },
+              "superClass": null,
+              "body": {
+                "type": "ClassBody",
+                "start": 28,
+                "end": 98,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 10
+                  },
+                  "end": {
+                    "line": 5,
+                    "column": 3
+                  }
+                },
+                "body": [
+                  {
+                    "type": "ClassProperty",
+                    "start": 79,
+                    "end": 94,
+                    "loc": {
+                      "start": {
+                        "line": 4,
+                        "column": 4
+                      },
+                      "end": {
+                        "line": 4,
+                        "column": 19
+                      }
+                    },
+                    "static": false,
+                    "key": {
+                      "type": "Identifier",
+                      "start": 79,
+                      "end": 80,
+                      "loc": {
+                        "start": {
+                          "line": 4,
+                          "column": 4
+                        },
+                        "end": {
+                          "line": 4,
+                          "column": 5
+                        },
+                        "identifierName": "p"
+                      },
+                      "name": "p"
+                    },
+                    "computed": false,
+                    "value": {
+                      "type": "BinaryExpression",
+                      "start": 83,
+                      "end": 93,
+                      "loc": {
+                        "start": {
+                          "line": 4,
+                          "column": 8
+                        },
+                        "end": {
+                          "line": 4,
+                          "column": 18
+                        }
+                      },
+                      "left": {
+                        "type": "Identifier",
+                        "start": 83,
+                        "end": 88,
+                        "loc": {
+                          "start": {
+                            "line": 4,
+                            "column": 8
+                          },
+                          "end": {
+                            "line": 4,
+                            "column": 13
+                          },
+                          "identifierName": "yield"
+                        },
+                        "name": "yield"
+                      },
+                      "operator": "+",
+                      "right": {
+                        "type": "NumericLiteral",
+                        "start": 91,
+                        "end": 93,
+                        "loc": {
+                          "start": {
+                            "line": 4,
+                            "column": 16
+                          },
+                          "end": {
+                            "line": 4,
+                            "column": 18
+                          }
+                        },
+                        "extra": {
+                          "rawValue": 42,
+                          "raw": "42"
+                        },
+                        "value": 42
+                      }
+                    },
+                    "leadingComments": [
+                      {
+                        "type": "CommentLine",
+                        "value": " here yield is an identifier reference",
+                        "start": 34,
+                        "end": 74,
+                        "loc": {
+                          "start": {
+                            "line": 3,
+                            "column": 4
+                          },
+                          "end": {
+                            "line": 3,
+                            "column": 44
+                          }
+                        }
+                      }
+                    ]
+                  }
+                ]
+              }
+            }
+          ],
+          "directives": []
+        }
+      }
+    ],
+    "directives": []
+  },
+  "comments": [
+    {
+      "type": "CommentLine",
+      "value": " here yield is an identifier reference",
+      "start": 34,
+      "end": 74,
+      "loc": {
+        "start": {
+          "line": 3,
+          "column": 4
+        },
+        "end": {
+          "line": 3,
+          "column": 44
+        }
+      }
+    }
+  ]
+}

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-generator-in-class-property/input.js

@@ -0,0 +1,3 @@
+class C {
+  p = function* () { yield + 42 };
+}

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-generator-in-class-property/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["classProperties"]
+}

packages/babel-parser/test/fixtures/experimental/class-properties/yield-in-generator-in-class-property/output.json

@@ -0,0 +1,224 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 46,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 3,
+      "column": 1
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 46,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 3,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start": 0,
+        "end": 46,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 3,
+            "column": 1
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 6,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 6
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            },
+            "identifierName": "C"
+          },
+          "name": "C"
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start": 8,
+          "end": 46,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 8
+            },
+            "end": {
+              "line": 3,
+              "column": 1
+            }
+          },
+          "body": [
+            {
+              "type": "ClassProperty",
+              "start": 12,
+              "end": 44,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 2
+                },
+                "end": {
+                  "line": 2,
+                  "column": 34
+                }
+              },
+              "static": false,
+              "key": {
+                "type": "Identifier",
+                "start": 12,
+                "end": 13,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 3
+                  },
+                  "identifierName": "p"
+                },
+                "name": "p"
+              },
+              "computed": false,
+              "value": {
+                "type": "FunctionExpression",
+                "start": 16,
+                "end": 43,
+                "loc": {
+                  "start": {
+                    "line": 2,
+                    "column": 6
+                  },
+                  "end": {
+                    "line": 2,
+                    "column": 33
+                  }
+                },
+                "id": null,
+                "generator": true,
+                "async": false,
+                "params": [],
+                "body": {
+                  "type": "BlockStatement",
+                  "start": 29,
+                  "end": 43,
+                  "loc": {
+                    "start": {
+                      "line": 2,
+                      "column": 19
+                    },
+                    "end": {
+                      "line": 2,
+                      "column": 33
+                    }
+                  },
+                  "body": [
+                    {
+                      "type": "ExpressionStatement",
+                      "start": 31,
+                      "end": 41,
+                      "loc": {
+                        "start": {
+                          "line": 2,
+                          "column": 21
+                        },
+                        "end": {
+                          "line": 2,
+                          "column": 31
+                        }
+                      },
+                      "expression": {
+                        "type": "YieldExpression",
+                        "start": 31,
+                        "end": 41,
+                        "loc": {
+                          "start": {
+                            "line": 2,
+                            "column": 21
+                          },
+                          "end": {
+                            "line": 2,
+                            "column": 31
+                          }
+                        },
+                        "delegate": false,
+                        "argument": {
+                          "type": "UnaryExpression",
+                          "start": 37,
+                          "end": 41,
+                          "loc": {
+                            "start": {
+                              "line": 2,
+                              "column": 27
+                            },
+                            "end": {
+                              "line": 2,
+                              "column": 31
+                            }
+                          },
+                          "operator": "+",
+                          "prefix": true,
+                          "argument": {
+                            "type": "NumericLiteral",
+                            "start": 39,
+                            "end": 41,
+                            "loc": {
+                              "start": {
+                                "line": 2,
+                                "column": 29
+                              },
+                              "end": {
+                                "line": 2,
+                                "column": 31
+                              }
+                            },
+                            "extra": {
+                              "rawValue": 42,
+                              "raw": "42"
+                            },
+                            "value": 42
+                          }
+                        }
+                      }
+                    }
+                  ],
+                  "directives": []
+                }
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}