[clang-format] Fix a bug with C++ `export import <Foo/Bar>`

[owenpan]

Summary

Fixes https://github.com/llvm/llvm-project/issues/57798.

[MyDeveloperDay]

LGTM

clang/lib/Format/UnwrappedLineParser.cpp

if (Style.isVerilog()) {
       }
     }
     break;
   case tok::kw_export:
     if (Style.isJavaScript()) {
       parseJavaScriptEs6ImportExport();
       return;
     }
-    if (!Style.isCpp())
-      break;
-    // Handle C++ "(inline|export) namespace".
-    [[fallthrough]];
+    if (Style.isCpp()) {
+      nextToken();
+      if (FormatTok->is(Keywords.kw_import)) {
+        parseModuleImport();
+        return;
+      }
+      if (FormatTok->is(tok::kw_namespace)) {
+        parseNamespace();
+        return;
+      }
+    }
   case tok::kw_inline:
     nextToken();
     if (FormatTok->is(tok::kw_namespace)) {
       parseNamespace();
       return;
     }
     break;
   case tok::identifier:

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, Cpp20ModulesSupport) {
   verifyFormat("export import foo.bar;", Style);
   verifyFormat("export import foo.bar:baz;", Style);
   verifyFormat("export import :bar;", Style);
   verifyFormat("export module foo:bar;", Style);
   verifyFormat("export module foo;", Style);
   verifyFormat("export module foo.bar;", Style);
   verifyFormat("export module foo.bar:baz;", Style);
   verifyFormat("export import <string_view>;", Style);
+  verifyFormat("export import <Foo/Bar>;", Style);
 
   verifyFormat("export type_name var;", Style);
   verifyFormat("template <class T> export using A = B<T>;", Style);
   verifyFormat("export using A = B;", Style);
   verifyFormat("export int func() {\n"
                "  foo();\n"
                "}",
                Style);