fix(es/typescript): Treat export default declarations as declarations (#7017)

**Related issue:**

 - Closes #6953.

Author: kdy1

crates/swc_ecma_transforms_typescript/src/strip.rs

@@ -1581,6 +1581,23 @@ where
         self.non_top_level = old;
     }
 
+    fn visit_default_decl(&mut self, decl: &DefaultDecl) {
+        decl.visit_children_with(self);
+        match decl {
+            DefaultDecl::Class(d) => {
+                if let Some(id) = &d.ident {
+                    self.store(id.sym.clone(), id.span.ctxt, true);
+                }
+            }
+            DefaultDecl::Fn(d) => {
+                if let Some(id) = &d.ident {
+                    self.store(id.sym.clone(), id.span.ctxt, true);
+                }
+            }
+            _ => {}
+        }
+    }
+
     fn visit_expr(&mut self, n: &Expr) {
         let old = self.in_var_pat;
         self.in_var_pat = false;

crates/swc_ecma_transforms_typescript/tests/fixture/issue-6953/1/input.ts

@@ -0,0 +1,15 @@
+import { Scope } from "../../scopes";
+import {
+    AnyNode,
+    TSUnknownKeywordTypeAnnotation,
+    tsUnknownKeywordTypeAnnotation,
+} from "@internal/ast";
+
+export default function TSUnknownKeywordTypeAnnotation(
+    node: AnyNode,
+    scope: Scope,
+) {
+    node = tsUnknownKeywordTypeAnnotation.assert(node);
+    scope;
+    throw new Error("unimplemented");
+}

crates/swc_ecma_transforms_typescript/tests/fixture/issue-6953/1/output.js

@@ -0,0 +1,6 @@
+import { tsUnknownKeywordTypeAnnotation } from "@internal/ast";
+export default function TSUnknownKeywordTypeAnnotation(node, scope) {
+    node = tsUnknownKeywordTypeAnnotation.assert(node);
+    scope;
+    throw new Error("unimplemented");
+}