fix(check): ignore TS2306 (#14940)

Fixes a regression where this type checking error was being surfaced in certain scenarios.

cli/tests/integration/check_tests.rs

@@ -37,3 +37,9 @@ itest!(module_detection_force {
   args: "check --quiet module_detection_force.ts",
   output_str: Some(""),
 });
+
+// Regression test for https://github.com/denoland/deno/issues/14937.
+itest!(declaration_header_file_with_no_exports {
+  args: "check --quiet declaration_header_file_with_no_exports.ts",
+  output_str: Some(""),
+});

cli/tests/testdata/declaration_header_file_with_no_exports.ts

@@ -0,0 +1,2 @@
+import * as foo from "./declaration_header_file_with_no_exports_js.js";
+console.log(foo);

cli/tests/testdata/declaration_header_file_with_no_exports_js.js

@@ -0,0 +1 @@
+/// <reference types="./declaration_header_file_with_no_exports_js.d.ts" />

cli/tsc/99_main_compiler.js

@@ -188,6 +188,10 @@ delete Object.prototype.__proto__;
   /** Diagnostics that are intentionally ignored when compiling TypeScript in
    * Deno, as they provide misleading or incorrect information. */
   const IGNORED_DIAGNOSTICS = [
+    // TS2306: File '.../index.d.ts' is not a module.
+    // We get this for `x-typescript-types` declaration files which don't export
+    // anything. We prefer to treat these as modules with no exports.
+    2306,
     // TS2688: Cannot find type definition file for '...'.
     // We ignore because type defintion files can end with '.ts'.
     2688,