Revert "Fix: check if param is assignable when parsing arrow return type annotation" (#12198)

This reverts commit 84987a00e632e65bdafdf7f70df46ded7fb083c8.

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

@@ -1453,7 +1453,7 @@ export default class ExpressionParser extends LValParser {
     if (
       canBeArrow &&
       this.shouldParseArrow() &&
-      (arrowNode = this.parseArrow(arrowNode, exprList))
+      (arrowNode = this.parseArrow(arrowNode))
     ) {
       if (!this.isAwaitAllowed() && !this.state.maybeInAsyncArrowHead) {
         this.state.awaitPos = oldAwaitPos;
@@ -1509,10 +1509,7 @@ export default class ExpressionParser extends LValParser {
     return !this.canInsertSemicolon();
   }
 
-  parseArrow(
+  parseArrow(node: N.ArrowFunctionExpression): ?N.ArrowFunctionExpression {
-    node: N.ArrowFunctionExpression,
-    exprList: N.Node[], // eslint-disable-line no-unused-vars
-  ): ?N.ArrowFunctionExpression {
     if (this.eat(tt.arrow)) {
       return node;
     }

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

@@ -51,60 +51,10 @@ export default class LValParser extends NodeUtils {
   +parseDecorator: () => Decorator;
   */
 
-  /**
-   * Check if a node can be converted to a binding identifier or binding pattern.
-   * https://tc39.es/ecma262/#prod-BindingIdentifier
-   * https://tc39.es/ecma262/#prod-BindingPattern
-   * Note that although a mebmer expression can serve as a LHS in the init of for loop,
-   * i.e. `for (a.b of []);`, it is not a binding pattern
-   *
-   * @param {Node} node
-   * @returns {boolean}
-   * @memberof LValParser
-   */
-  isAssignable(node: Node): boolean {
-    switch (node.type) {
-      case "Identifier":
-      case "ObjectPattern":
-      case "ArrayPattern":
-      case "AssignmentPattern":
-      case "RestElement":
-        return true;
-
-      case "ObjectExpression": {
-        const last = node.properties.length - 1;
-        return node.properties.every((prop, i) => {
-          return (
-            prop.type !== "ObjectMethod" &&
-            (i === last || prop.type === "SpreadElement") &&
-            this.isAssignable(prop)
-          );
-        });
-      }
-
-      case "ObjectProperty":
-        return this.isAssignable(node.value);
-
-      case "SpreadElement":
-        return this.isAssignable(node.argument);
-
-      case "ArrayExpression":
-        return node.elements.every(element => this.isAssignable(element));
-
-      case "AssignmentExpression":
-        return node.operator === "=";
-
-      case "ParenthesizedExpression":
-        return this.isAssignable(node.expression);
-
-      default:
-        return false;
-    }
-  }
-
   // Convert existing expression atom to assignable pattern
   // if possible.
-  // When this one is updated, please check if `isAssignable` also needs to be updated.
+  // NOTE: There is a corresponding "isAssignable" method in flow.js.
+  // When this one is updated, please check if also that one needs to be updated.
 
   toAssignable(node: Node): Node {
     let parenthesized = undefined;

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

@@ -1943,7 +1943,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
 
       return partition(arrows, node =>
-        node.params.every(param => this.isAssignable(param)),
+        node.params.every(param => this.isAssignable(param, true)),
       );
     }
 
@@ -2146,12 +2146,47 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
     }
 
-    isAssignable(node: N.Node): boolean {
+    isAssignable(node: N.Node, isBinding?: boolean): boolean {
       switch (node.type) {
+        case "Identifier":
+        case "ObjectPattern":
+        case "ArrayPattern":
+        case "AssignmentPattern":
+          return true;
+
+        case "ObjectExpression": {
+          const last = node.properties.length - 1;
+          return node.properties.every((prop, i) => {
+            return (
+              prop.type !== "ObjectMethod" &&
+              (i === last || prop.type === "SpreadElement") &&
+              this.isAssignable(prop)
+            );
+          });
+        }
+
+        case "ObjectProperty":
+          return this.isAssignable(node.value);
+
+        case "SpreadElement":
+          return this.isAssignable(node.argument);
+
+        case "ArrayExpression":
+          return node.elements.every(element => this.isAssignable(element));
+
+        case "AssignmentExpression":
+          return node.operator === "=";
+
+        case "ParenthesizedExpression":
         case "TypeCastExpression":
           return this.isAssignable(node.expression);
+
+        case "MemberExpression":
+        case "OptionalMemberExpression":
+          return !isBinding;
+
         default:
-          return super.isAssignable(node);
+          return false;
       }
     }
 
@@ -2737,10 +2772,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     }
 
     // handle return types for arrow functions
-    parseArrow(
+    parseArrow(node: N.ArrowFunctionExpression): ?N.ArrowFunctionExpression {
-      node: N.ArrowFunctionExpression,
-      exprList: N.Node[],
-    ): ?N.ArrowFunctionExpression {
       if (this.match(tt.colon)) {
         const result = this.tryParse(() => {
           const oldNoAnonFunctionType = this.state.noAnonFunctionType;
@@ -2774,7 +2806,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           : null;
       }
 
-      return super.parseArrow(node, exprList);
+      return super.parseArrow(node);
     }
 
     shouldParseArrow(): boolean {
@@ -2945,8 +2977,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     ): ?N.ArrowFunctionExpression {
       const node = this.startNodeAt(startPos, startLoc);
       this.parseFunctionParams(node);
-      // set exprList to `[]` as the parameters has been validated in `parseFunctionParams`
+      if (!this.parseArrow(node)) return;
-      if (!this.parseArrow(node, [])) return;
       return this.parseArrowExpression(
         node,
         /* params */ undefined,

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

@@ -2540,10 +2540,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
     }
 
-    parseArrow(
+    parseArrow(node: N.ArrowFunctionExpression): ?N.ArrowFunctionExpression {
-      node: N.ArrowFunctionExpression,
-      exprList,
-    ): ?N.ArrowFunctionExpression {
       if (this.match(tt.colon)) {
         // This is different from how the TS parser does it.
         // TS uses lookahead. The Babel Parser parses it as a parenthesized expression and converts.
@@ -2553,10 +2550,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
             tt.colon,
           );
           if (this.canInsertSemicolon() || !this.match(tt.arrow)) abort();
-          // check if the exprList is assignable because `: TSType` can be part of conditional expression
-          // i.e. we can only know `: v` is not a return type by checking that `sum(v)` can not be a pattern.
-          // 0 ? v => (sum(v)) : v => 0
-          if (exprList.some(param => !this.isAssignable(param))) abort();
           return returnType;
         });
 
@@ -2568,7 +2561,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         }
       }
 
-      return super.parseArrow(node, exprList);
+      return super.parseArrow(node);
     }
 
     // Allow type annotations inside of a parameter list.
@@ -2587,18 +2580,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return param;
     }
 
-    isAssignable(node: N.Node): boolean {
-      switch (node.type) {
-        case "TSAsExpression":
-        case "TSNonNullExpression":
-        case "TSTypeAssertion":
-        case "TSTypeCastExpression":
-          return this.isAssignable(node.expression);
-        default:
-          return super.isAssignable(node);
-      }
-    }
-
     toAssignable(node: N.Node): N.Node {
       switch (node.type) {
         case "TSTypeCastExpression":

packages/babel-parser/test/fixtures/typescript/arrow-function/ambiguous-ternary-arrow-return-type-typescript-issue-16241/input.ts

@@ -1 +0,0 @@
-0 ? v => (v) : v => 0;

packages/babel-parser/test/fixtures/typescript/arrow-function/ambiguous-ternary-arrow-return-type-typescript-issue-16241/options.json

@@ -1,7 +0,0 @@
-{
-  "sourceType": "module",
-  "plugins": [
-    "typescript"
-  ],
-  "throws": "Unexpected token, expected \":\" (1:21)"
-}

packages/babel-parser/test/fixtures/typescript/arrow-function/return-type-like-conditional/input.ts

@@ -1,4 +0,0 @@
-0 ? v => (sum += v) : v => 0;
-0 ? v => (sum(v)) : v => 0;
-0 ? v => (v.w) : v => 0;
-0 ? v => ([ v.w ]) : v => {};

packages/babel-parser/test/fixtures/typescript/arrow-function/return-type-like-conditional/options.json

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

packages/babel-parser/test/fixtures/typescript/arrow-function/return-type-like-conditional/output.json

@@ -1,309 +0,0 @@
-{
-  "type": "File",
-  "start":0,"end":112,"loc":{"start":{"line":1,"column":0},"end":{"line":4,"column":29}},
-  "program": {
-    "type": "Program",
-    "start":0,"end":112,"loc":{"start":{"line":1,"column":0},"end":{"line":4,"column":29}},
-    "sourceType": "module",
-    "interpreter": null,
-    "body": [
-      {
-        "type": "ExpressionStatement",
-        "start":0,"end":29,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":29}},
-        "expression": {
-          "type": "ConditionalExpression",
-          "start":0,"end":28,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":28}},
-          "test": {
-            "type": "NumericLiteral",
-            "start":0,"end":1,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":1}},
-            "extra": {
-              "rawValue": 0,
-              "raw": "0"
-            },
-            "value": 0
-          },
-          "consequent": {
-            "type": "ArrowFunctionExpression",
-            "start":4,"end":19,"loc":{"start":{"line":1,"column":4},"end":{"line":1,"column":19}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":4,"end":5,"loc":{"start":{"line":1,"column":4},"end":{"line":1,"column":5},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "AssignmentExpression",
-              "start":10,"end":18,"loc":{"start":{"line":1,"column":10},"end":{"line":1,"column":18}},
-              "operator": "+=",
-              "left": {
-                "type": "Identifier",
-                "start":10,"end":13,"loc":{"start":{"line":1,"column":10},"end":{"line":1,"column":13},"identifierName":"sum"},
-                "name": "sum"
-              },
-              "right": {
-                "type": "Identifier",
-                "start":17,"end":18,"loc":{"start":{"line":1,"column":17},"end":{"line":1,"column":18},"identifierName":"v"},
-                "name": "v"
-              },
-              "extra": {
-                "parenthesized": true,
-                "parenStart": 9
-              }
-            }
-          },
-          "alternate": {
-            "type": "ArrowFunctionExpression",
-            "start":22,"end":28,"loc":{"start":{"line":1,"column":22},"end":{"line":1,"column":28}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":22,"end":23,"loc":{"start":{"line":1,"column":22},"end":{"line":1,"column":23},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "NumericLiteral",
-              "start":27,"end":28,"loc":{"start":{"line":1,"column":27},"end":{"line":1,"column":28}},
-              "extra": {
-                "rawValue": 0,
-                "raw": "0"
-              },
-              "value": 0
-            }
-          }
-        }
-      },
-      {
-        "type": "ExpressionStatement",
-        "start":30,"end":57,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":27}},
-        "expression": {
-          "type": "ConditionalExpression",
-          "start":30,"end":56,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":26}},
-          "test": {
-            "type": "NumericLiteral",
-            "start":30,"end":31,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":1}},
-            "extra": {
-              "rawValue": 0,
-              "raw": "0"
-            },
-            "value": 0
-          },
-          "consequent": {
-            "type": "ArrowFunctionExpression",
-            "start":34,"end":47,"loc":{"start":{"line":2,"column":4},"end":{"line":2,"column":17}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":34,"end":35,"loc":{"start":{"line":2,"column":4},"end":{"line":2,"column":5},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "CallExpression",
-              "start":40,"end":46,"loc":{"start":{"line":2,"column":10},"end":{"line":2,"column":16}},
-              "callee": {
-                "type": "Identifier",
-                "start":40,"end":43,"loc":{"start":{"line":2,"column":10},"end":{"line":2,"column":13},"identifierName":"sum"},
-                "name": "sum"
-              },
-              "arguments": [
-                {
-                  "type": "Identifier",
-                  "start":44,"end":45,"loc":{"start":{"line":2,"column":14},"end":{"line":2,"column":15},"identifierName":"v"},
-                  "name": "v"
-                }
-              ],
-              "extra": {
-                "parenthesized": true,
-                "parenStart": 39
-              }
-            }
-          },
-          "alternate": {
-            "type": "ArrowFunctionExpression",
-            "start":50,"end":56,"loc":{"start":{"line":2,"column":20},"end":{"line":2,"column":26}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":50,"end":51,"loc":{"start":{"line":2,"column":20},"end":{"line":2,"column":21},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "NumericLiteral",
-              "start":55,"end":56,"loc":{"start":{"line":2,"column":25},"end":{"line":2,"column":26}},
-              "extra": {
-                "rawValue": 0,
-                "raw": "0"
-              },
-              "value": 0
-            }
-          }
-        }
-      },
-      {
-        "type": "ExpressionStatement",
-        "start":58,"end":82,"loc":{"start":{"line":3,"column":0},"end":{"line":3,"column":24}},
-        "expression": {
-          "type": "ConditionalExpression",
-          "start":58,"end":81,"loc":{"start":{"line":3,"column":0},"end":{"line":3,"column":23}},
-          "test": {
-            "type": "NumericLiteral",
-            "start":58,"end":59,"loc":{"start":{"line":3,"column":0},"end":{"line":3,"column":1}},
-            "extra": {
-              "rawValue": 0,
-              "raw": "0"
-            },
-            "value": 0
-          },
-          "consequent": {
-            "type": "ArrowFunctionExpression",
-            "start":62,"end":72,"loc":{"start":{"line":3,"column":4},"end":{"line":3,"column":14}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":62,"end":63,"loc":{"start":{"line":3,"column":4},"end":{"line":3,"column":5},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "MemberExpression",
-              "start":68,"end":71,"loc":{"start":{"line":3,"column":10},"end":{"line":3,"column":13}},
-              "object": {
-                "type": "Identifier",
-                "start":68,"end":69,"loc":{"start":{"line":3,"column":10},"end":{"line":3,"column":11},"identifierName":"v"},
-                "name": "v"
-              },
-              "computed": false,
-              "property": {
-                "type": "Identifier",
-                "start":70,"end":71,"loc":{"start":{"line":3,"column":12},"end":{"line":3,"column":13},"identifierName":"w"},
-                "name": "w"
-              },
-              "extra": {
-                "parenthesized": true,
-                "parenStart": 67
-              }
-            }
-          },
-          "alternate": {
-            "type": "ArrowFunctionExpression",
-            "start":75,"end":81,"loc":{"start":{"line":3,"column":17},"end":{"line":3,"column":23}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":75,"end":76,"loc":{"start":{"line":3,"column":17},"end":{"line":3,"column":18},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "NumericLiteral",
-              "start":80,"end":81,"loc":{"start":{"line":3,"column":22},"end":{"line":3,"column":23}},
-              "extra": {
-                "rawValue": 0,
-                "raw": "0"
-              },
-              "value": 0
-            }
-          }
-        }
-      },
-      {
-        "type": "ExpressionStatement",
-        "start":83,"end":112,"loc":{"start":{"line":4,"column":0},"end":{"line":4,"column":29}},
-        "expression": {
-          "type": "ConditionalExpression",
-          "start":83,"end":111,"loc":{"start":{"line":4,"column":0},"end":{"line":4,"column":28}},
-          "test": {
-            "type": "NumericLiteral",
-            "start":83,"end":84,"loc":{"start":{"line":4,"column":0},"end":{"line":4,"column":1}},
-            "extra": {
-              "rawValue": 0,
-              "raw": "0"
-            },
-            "value": 0
-          },
-          "consequent": {
-            "type": "ArrowFunctionExpression",
-            "start":87,"end":101,"loc":{"start":{"line":4,"column":4},"end":{"line":4,"column":18}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":87,"end":88,"loc":{"start":{"line":4,"column":4},"end":{"line":4,"column":5},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "ArrayExpression",
-              "start":93,"end":100,"loc":{"start":{"line":4,"column":10},"end":{"line":4,"column":17}},
-              "elements": [
-                {
-                  "type": "MemberExpression",
-                  "start":95,"end":98,"loc":{"start":{"line":4,"column":12},"end":{"line":4,"column":15}},
-                  "object": {
-                    "type": "Identifier",
-                    "start":95,"end":96,"loc":{"start":{"line":4,"column":12},"end":{"line":4,"column":13},"identifierName":"v"},
-                    "name": "v"
-                  },
-                  "computed": false,
-                  "property": {
-                    "type": "Identifier",
-                    "start":97,"end":98,"loc":{"start":{"line":4,"column":14},"end":{"line":4,"column":15},"identifierName":"w"},
-                    "name": "w"
-                  }
-                }
-              ],
-              "extra": {
-                "parenthesized": true,
-                "parenStart": 92
-              }
-            }
-          },
-          "alternate": {
-            "type": "ArrowFunctionExpression",
-            "start":104,"end":111,"loc":{"start":{"line":4,"column":21},"end":{"line":4,"column":28}},
-            "id": null,
-            "generator": false,
-            "async": false,
-            "params": [
-              {
-                "type": "Identifier",
-                "start":104,"end":105,"loc":{"start":{"line":4,"column":21},"end":{"line":4,"column":22},"identifierName":"v"},
-                "name": "v"
-              }
-            ],
-            "body": {
-              "type": "BlockStatement",
-              "start":109,"end":111,"loc":{"start":{"line":4,"column":26},"end":{"line":4,"column":28}},
-              "body": [],
-              "directives": []
-            }
-          }
-        }
-      }
-    ],
-    "directives": []
-  }
-}

packages/babel-parser/test/fixtures/typescript/regression/rest-in-arrow/input.ts

@@ -1 +0,0 @@
-const f = (...args): void => {};

packages/babel-parser/test/fixtures/typescript/regression/rest-in-arrow/output.json

@@ -1,61 +0,0 @@
-{
-  "type": "File",
-  "start":0,"end":32,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":32}},
-  "program": {
-    "type": "Program",
-    "start":0,"end":32,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":32}},
-    "sourceType": "module",
-    "interpreter": null,
-    "body": [
-      {
-        "type": "VariableDeclaration",
-        "start":0,"end":32,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":32}},
-        "declarations": [
-          {
-            "type": "VariableDeclarator",
-            "start":6,"end":31,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":31}},
-            "id": {
-              "type": "Identifier",
-              "start":6,"end":7,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":7},"identifierName":"f"},
-              "name": "f"
-            },
-            "init": {
-              "type": "ArrowFunctionExpression",
-              "start":10,"end":31,"loc":{"start":{"line":1,"column":10},"end":{"line":1,"column":31}},
-              "returnType": {
-                "type": "TSTypeAnnotation",
-                "start":19,"end":25,"loc":{"start":{"line":1,"column":19},"end":{"line":1,"column":25}},
-                "typeAnnotation": {
-                  "type": "TSVoidKeyword",
-                  "start":21,"end":25,"loc":{"start":{"line":1,"column":21},"end":{"line":1,"column":25}}
-                }
-              },
-              "id": null,
-              "generator": false,
-              "async": false,
-              "params": [
-                {
-                  "type": "RestElement",
-                  "start":11,"end":18,"loc":{"start":{"line":1,"column":11},"end":{"line":1,"column":18}},
-                  "argument": {
-                    "type": "Identifier",
-                    "start":14,"end":18,"loc":{"start":{"line":1,"column":14},"end":{"line":1,"column":18},"identifierName":"args"},
-                    "name": "args"
-                  }
-                }
-              ],
-              "body": {
-                "type": "BlockStatement",
-                "start":29,"end":31,"loc":{"start":{"line":1,"column":29},"end":{"line":1,"column":31}},
-                "body": [],
-                "directives": []
-              }
-            }
-          }
-        ],
-        "kind": "const"
-      }
-    ],
-    "directives": []
-  }
-}