[babel 8] Recover from error when parsing <T>() => {}</T>

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

@@ -3233,10 +3233,12 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       // Either way, we're looking at a '<': tt.jsxTagStart or relational.
 
-      let typeParameters: ?N.TsTypeParameterDeclaration;
-      let invalidSingleType: ?N.TsTypeParameter;
-      state = state || this.state.clone();
+      // If the state was cloned in the JSX parsing branch above but there
+      // have been any error in the tryParse call, this.state is set to state
+      // so we still need to clone it.
+      if (!state || state === this.state) state = this.state.clone();
 
+      let typeParameters: ?N.TsTypeParameterDeclaration;
       const arrow = this.tryParse(abort => {
         // This is similar to TypeScript's `tryParseParenthesizedArrowFunctionExpression`.
         typeParameters = this.tsParseTypeParameters();
@@ -3255,32 +3257,28 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         }
         expr.typeParameters = typeParameters;
 
-        // report error if single type parameter used without trailing comma.
-        if (
-          this.hasPlugin("jsx") &&
-          expr.typeParameters.params.length === 1 &&
-          !expr.typeParameters.extra?.trailingComma
-        ) {
-          const parameter = expr.typeParameters.params[0];
-          if (!parameter.constraint) {
-            // A single type parameter must either have constraints
-            // or a trailing comma, otherwise it's ambiguous with JSX.
-            invalidSingleType = parameter;
+        if (process.env.BABEL_8_BREAKING) {
+          if (
+            this.hasPlugin("jsx") &&
+            expr.typeParameters.params.length === 1 &&
+            !expr.typeParameters.extra?.trailingComma
+          ) {
+            // report error if single type parameter used without trailing comma.
+            const parameter = expr.typeParameters.params[0];
+            if (!parameter.constraint) {
+              // A single type parameter must either have constraints
+              // or a trailing comma, otherwise it's ambiguous with JSX.
+              this.raise(TSErrors.SingleTypeParameterWithoutTrailingComma, {
+                at: createPositionWithColumnOffset(parameter.loc.end, 1),
+                typeParameterName: parameter.name.name,
+              });
+            }
           }
         }
 
         return expr;
       }, state);
 
-      if (process.env.BABEL_8_BREAKING) {
-        if (invalidSingleType) {
-          this.raise(TSErrors.SingleTypeParameterWithoutTrailingComma, {
-            at: createPositionWithColumnOffset(invalidSingleType.loc.end, 1),
-            typeParameterName: invalidSingleType.name.name,
-          });
-        }
-      }
-
       /*:: invariant(arrow.node != null) */
       if (!arrow.error && !arrow.aborted) {
         // This error is reported outside of the this.tryParse call so that

packages/babel-parser/test/fixtures/typescript/tsx/invalid-gt-arrow-like/input.ts

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

packages/babel-parser/test/fixtures/typescript/tsx/invalid-gt-arrow-like/options.json

@@ -0,0 +1,3 @@
+{
+  "BABEL_8_BREAKING": true
+}

packages/babel-parser/test/fixtures/typescript/tsx/invalid-gt-arrow-like/output.json

@@ -0,0 +1,63 @@
+{
+  "type": "File",
+  "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+  "errors": [
+    "SyntaxError: Unexpected token `>`. Did you mean `>` or `{'>'}`? (1:7)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+        "expression": {
+          "type": "JSXElement",
+          "start":0,"end":15,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":15,"index":15}},
+          "openingElement": {
+            "type": "JSXOpeningElement",
+            "start":0,"end":3,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":3,"index":3}},
+            "name": {
+              "type": "JSXIdentifier",
+              "start":1,"end":2,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":2,"index":2}},
+              "name": "T"
+            },
+            "attributes": [],
+            "selfClosing": false
+          },
+          "closingElement": {
+            "type": "JSXClosingElement",
+            "start":11,"end":15,"loc":{"start":{"line":1,"column":11,"index":11},"end":{"line":1,"column":15,"index":15}},
+            "name": {
+              "type": "JSXIdentifier",
+              "start":13,"end":14,"loc":{"start":{"line":1,"column":13,"index":13},"end":{"line":1,"column":14,"index":14}},
+              "name": "T"
+            }
+          },
+          "children": [
+            {
+              "type": "JSXText",
+              "start":3,"end":9,"loc":{"start":{"line":1,"column":3,"index":3},"end":{"line":1,"column":9,"index":9}},
+              "extra": {
+                "rawValue": "() => ",
+                "raw": "() => "
+              },
+              "value": "() => "
+            },
+            {
+              "type": "JSXExpressionContainer",
+              "start":9,"end":11,"loc":{"start":{"line":1,"column":9,"index":9},"end":{"line":1,"column":11,"index":11}},
+              "expression": {
+                "type": "JSXEmptyExpression",
+                "start":10,"end":10,"loc":{"start":{"line":1,"column":10,"index":10},"end":{"line":1,"column":10,"index":10}}
+              }
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}