Fix parsing type casted generic flow arrow exprs (#11955)

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

@@ -2674,28 +2674,57 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
         let typeParameters;
 
-        const arrow = this.tryParse(() => {
+        const arrow = this.tryParse(abort => {
           typeParameters = this.flowParseTypeParameterDeclaration();
 
           const arrowExpression = this.forwardNoArrowParamsConversionAt(
             typeParameters,
-            () =>
+            () => {
-              super.parseMaybeAssign(
+              const result = super.parseMaybeAssign(
                 refExpressionErrors,
                 afterLeftParse,
                 refNeedsArrowPos,
-              ),
               );
-          arrowExpression.typeParameters = typeParameters;
+
-          this.resetStartLocationFromNode(arrowExpression, typeParameters);
+              this.resetStartLocationFromNode(result, typeParameters);
+
+              return result;
+            },
+          );
+
+          // <T>(() => {}: any);
+          if (
+            arrowExpression.type !== "ArrowFunctionExpression" &&
+            arrowExpression.extra?.parenthesized
+          ) {
+            abort();
+          }
+
+          // The above can return a TypeCastExpression when the arrow
+          // expression is not wrapped in parens. See also `this.parseParenItem`.
+          const expr = this.maybeUnwrapTypeCastExpression(arrowExpression);
+          expr.typeParameters = typeParameters;
+          this.resetStartLocationFromNode(expr, typeParameters);
 
           return arrowExpression;
         }, state);
 
-        const arrowExpression: ?N.ArrowFunctionExpression =
+        let arrowExpression: ?(
-          arrow.node?.type === "ArrowFunctionExpression" ? arrow.node : null;
+          | N.ArrowFunctionExpression
+          | N.TypeCastExpression
+        ) = null;
 
-        if (!arrow.error && arrowExpression) return arrowExpression;
+        if (
+          arrow.node &&
+          this.maybeUnwrapTypeCastExpression(arrow.node).type ===
+            "ArrowFunctionExpression"
+        ) {
+          if (!arrow.error && !arrow.aborted) {
+            return arrow.node;
+          }
+
+          arrowExpression = arrow.node;
+        }
 
         // If we are here, both JSX and Flow parsing attempts failed.
         // Give the precedence to the JSX error, except if JSX had an
@@ -3482,4 +3511,8 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
       return false;
     }
+
+    maybeUnwrapTypeCastExpression(node: N.Node) {
+      return node.type === "TypeCastExpression" ? node.expression : node;
+    }
   };

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-invalid-parenthesized/input.js

@@ -0,0 +1 @@
+<T>(() => {}: any);

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-invalid-parenthesized/options.json

@@ -0,0 +1,6 @@
+{
+  "sourceType": "module",
+  "plugins": ["flow"],
+  "createParenthesizedExpressions": true,
+  "throws": "Expected an arrow function after this type parameter declaration (1:0)"
+}

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-invalid/input.js

@@ -0,0 +1 @@
+<T>(() => {}: any);

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-invalid/options.json

@@ -0,0 +1,5 @@
+{
+  "sourceType": "module",
+  "plugins": ["flow"],
+  "throws": "Expected an arrow function after this type parameter declaration (1:0)"
+}

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-parenthesized/input.js

@@ -0,0 +1,2 @@
+(<T>() => {}: any);
+((<T>() => {}): any);

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-parenthesized/options.json

@@ -0,0 +1,5 @@
+{
+  "sourceType": "module",
+  "plugins": ["flow"],
+  "createParenthesizedExpressions": true
+}

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func-parenthesized/output.json

@@ -0,0 +1,109 @@
+{
+  "type": "File",
+  "start":0,"end":41,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":21}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":41,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":21}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":19,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":19}},
+        "expression": {
+          "type": "ParenthesizedExpression",
+          "start":0,"end":18,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":18}},
+          "expression": {
+            "type": "TypeCastExpression",
+            "start":1,"end":17,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":17}},
+            "expression": {
+              "type": "ArrowFunctionExpression",
+              "start":1,"end":12,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":12}},
+              "id": null,
+              "generator": false,
+              "async": false,
+              "params": [],
+              "body": {
+                "type": "BlockStatement",
+                "start":10,"end":12,"loc":{"start":{"line":1,"column":10},"end":{"line":1,"column":12}},
+                "body": [],
+                "directives": []
+              },
+              "typeParameters": {
+                "type": "TypeParameterDeclaration",
+                "start":1,"end":4,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":4}},
+                "params": [
+                  {
+                    "type": "TypeParameter",
+                    "start":2,"end":3,"loc":{"start":{"line":1,"column":2},"end":{"line":1,"column":3}},
+                    "name": "T",
+                    "variance": null
+                  }
+                ]
+              }
+            },
+            "typeAnnotation": {
+              "type": "TypeAnnotation",
+              "start":12,"end":17,"loc":{"start":{"line":1,"column":12},"end":{"line":1,"column":17}},
+              "typeAnnotation": {
+                "type": "AnyTypeAnnotation",
+                "start":14,"end":17,"loc":{"start":{"line":1,"column":14},"end":{"line":1,"column":17}}
+              }
+            }
+          }
+        }
+      },
+      {
+        "type": "ExpressionStatement",
+        "start":20,"end":41,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":21}},
+        "expression": {
+          "type": "ParenthesizedExpression",
+          "start":20,"end":40,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":20}},
+          "expression": {
+            "type": "TypeCastExpression",
+            "start":21,"end":39,"loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":19}},
+            "expression": {
+              "type": "ParenthesizedExpression",
+              "start":21,"end":34,"loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":14}},
+              "expression": {
+                "type": "ArrowFunctionExpression",
+                "start":22,"end":33,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":13}},
+                "id": null,
+                "generator": false,
+                "async": false,
+                "params": [],
+                "body": {
+                  "type": "BlockStatement",
+                  "start":31,"end":33,"loc":{"start":{"line":2,"column":11},"end":{"line":2,"column":13}},
+                  "body": [],
+                  "directives": []
+                },
+                "typeParameters": {
+                  "type": "TypeParameterDeclaration",
+                  "start":22,"end":25,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":5}},
+                  "params": [
+                    {
+                      "type": "TypeParameter",
+                      "start":23,"end":24,"loc":{"start":{"line":2,"column":3},"end":{"line":2,"column":4}},
+                      "name": "T",
+                      "variance": null
+                    }
+                  ]
+                }
+              }
+            },
+            "typeAnnotation": {
+              "type": "TypeAnnotation",
+              "start":34,"end":39,"loc":{"start":{"line":2,"column":14},"end":{"line":2,"column":19}},
+              "typeAnnotation": {
+                "type": "AnyTypeAnnotation",
+                "start":36,"end":39,"loc":{"start":{"line":2,"column":16},"end":{"line":2,"column":19}}
+              }
+            }
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func/input.js

@@ -0,0 +1,2 @@
+(<T>() => {}: any);
+((<T>() => {}): any);

packages/babel-parser/test/fixtures/flow/typecasts/generic-arrow-func/output.json

@@ -0,0 +1,109 @@
+{
+  "type": "File",
+  "start":0,"end":41,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":21}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":41,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":21}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":19,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":19}},
+        "expression": {
+          "type": "TypeCastExpression",
+          "start":1,"end":17,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":17}},
+          "expression": {
+            "type": "ArrowFunctionExpression",
+            "start":1,"end":12,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":12}},
+            "id": null,
+            "generator": false,
+            "async": false,
+            "params": [],
+            "body": {
+              "type": "BlockStatement",
+              "start":10,"end":12,"loc":{"start":{"line":1,"column":10},"end":{"line":1,"column":12}},
+              "body": [],
+              "directives": []
+            },
+            "typeParameters": {
+              "type": "TypeParameterDeclaration",
+              "start":1,"end":4,"loc":{"start":{"line":1,"column":1},"end":{"line":1,"column":4}},
+              "params": [
+                {
+                  "type": "TypeParameter",
+                  "start":2,"end":3,"loc":{"start":{"line":1,"column":2},"end":{"line":1,"column":3}},
+                  "name": "T",
+                  "variance": null
+                }
+              ]
+            }
+          },
+          "typeAnnotation": {
+            "type": "TypeAnnotation",
+            "start":12,"end":17,"loc":{"start":{"line":1,"column":12},"end":{"line":1,"column":17}},
+            "typeAnnotation": {
+              "type": "AnyTypeAnnotation",
+              "start":14,"end":17,"loc":{"start":{"line":1,"column":14},"end":{"line":1,"column":17}}
+            }
+          },
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 0
+          }
+        }
+      },
+      {
+        "type": "ExpressionStatement",
+        "start":20,"end":41,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":21}},
+        "expression": {
+          "type": "TypeCastExpression",
+          "start":21,"end":39,"loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":19}},
+          "expression": {
+            "type": "ArrowFunctionExpression",
+            "start":22,"end":33,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":13}},
+            "id": null,
+            "generator": false,
+            "async": false,
+            "params": [],
+            "body": {
+              "type": "BlockStatement",
+              "start":31,"end":33,"loc":{"start":{"line":2,"column":11},"end":{"line":2,"column":13}},
+              "body": [],
+              "directives": []
+            },
+            "typeParameters": {
+              "type": "TypeParameterDeclaration",
+              "start":22,"end":25,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":5}},
+              "params": [
+                {
+                  "type": "TypeParameter",
+                  "start":23,"end":24,"loc":{"start":{"line":2,"column":3},"end":{"line":2,"column":4}},
+                  "name": "T",
+                  "variance": null
+                }
+              ]
+            },
+            "extra": {
+              "parenthesized": true,
+              "parenStart": 21
+            }
+          },
+          "typeAnnotation": {
+            "type": "TypeAnnotation",
+            "start":34,"end":39,"loc":{"start":{"line":2,"column":14},"end":{"line":2,"column":19}},
+            "typeAnnotation": {
+              "type": "AnyTypeAnnotation",
+              "start":36,"end":39,"loc":{"start":{"line":2,"column":16},"end":{"line":2,"column":19}}
+            }
+          },
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 20
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}