Allow TSInterfaceDeclaration to be default export (#8408)

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| Q                        | A <!--(Can use an emoji 👍) -->
| ------------------------ | ---
| Fixed Issues?            | Fixes #7118
| Patch: Bug Fix?          | Y
| Major: Breaking Change?  | N
| Minor: New Feature?      | N
| Tests Added + Pass?      | Yes
| Documentation PR Link    | 
| Any Dependency Changes?  |
| License                  | MIT

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

@@ -1535,6 +1535,17 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         cls.abstract = true;
         return cls;
       }
+
+      // export default interface allowed in:
+      // https://github.com/Microsoft/TypeScript/pull/16040
+      if (this.state.value === "interface") {
+        return this.tsParseDeclaration(
+          this.startNode(),
+          this.state.value,
+          true,
+        );
+      }
+
       return super.parseExportDefaultExpression();
     }
 

packages/babel-parser/test/fixtures/typescript/interface/export/input.js

@@ -1,2 +1,2 @@
 export interface I {}
-// `export default` does not work with interfaces
+export default interface A {}

packages/babel-parser/test/fixtures/typescript/interface/export/output.json

@@ -1,7 +1,7 @@
 {
   "type": "File",
   "start": 0,
-  "end": 71,
+  "end": 51,
   "loc": {
     "start": {
       "line": 1,
@@ -9,13 +9,13 @@
     },
     "end": {
       "line": 2,
-      "column": 49
+      "column": 29
     }
   },
   "program": {
     "type": "Program",
     "start": 0,
-    "end": 71,
+    "end": 51,
     "loc": {
       "start": {
         "line": 1,
@@ -23,7 +23,7 @@
       },
       "end": {
         "line": 2,
-        "column": 49
+        "column": 29
       }
     },
     "sourceType": "module",
@@ -92,13 +92,12 @@
             },
             "body": []
           }
+        }
       },
-        "trailingComments": [
       {
-            "type": "CommentLine",
+        "type": "ExportDefaultDeclaration",
-            "value": " `export default` does not work with interfaces",
         "start": 22,
-            "end": 71,
+        "end": 51,
         "loc": {
           "start": {
             "line": 2,
@@ -106,31 +105,59 @@
           },
           "end": {
             "line": 2,
-                "column": 49
+            "column": 29
+          }
+        },
+        "declaration": {
+          "type": "TSInterfaceDeclaration",
+          "start": 37,
+          "end": 51,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 15
+            },
+            "end": {
+              "line": 2,
+              "column": 29
+            }
+          },
+          "id": {
+            "type": "Identifier",
+            "start": 47,
+            "end": 48,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 25
+              },
+              "end": {
+                "line": 2,
+                "column": 26
+              },
+              "identifierName": "A"
+            },
+            "name": "A"
+          },
+          "body": {
+            "type": "TSInterfaceBody",
+            "start": 49,
+            "end": 51,
+            "loc": {
+              "start": {
+                "line": 2,
+                "column": 27
+              },
+              "end": {
+                "line": 2,
+                "column": 29
+              }
+            },
+            "body": []
           }
         }
       }
-        ]
-      }
     ],
     "directives": []
-  },
-  "comments": [
-    {
-      "type": "CommentLine",
-      "value": " `export default` does not work with interfaces",
-      "start": 22,
-      "end": 71,
-      "loc": {
-        "start": {
-          "line": 2,
-          "column": 0
-        },
-        "end": {
-          "line": 2,
-          "column": 49
   }
 }
-    }
-  ]
-}

packages/babel-plugin-transform-typescript/test/fixtures/exports/interface/input.mjs

@@ -0,0 +1,2 @@
+export interface I {}
+export default interface A {}