Better Error message if no backend installed #1042 (#1045)

* Better Error message if no backend installed #1042 * change the error message as requested * Update src/py/reactpy/reactpy/backend/default.py Co-authored-by: Ryan Morshead <ryan.morshead@gmail.com> * fix linting issues * Update src/py/reactpy/reactpy/backend/default.py Co-authored-by: Ryan Morshead <ryan.morshead@gmail.com> * Improve readability * Update src/py/reactpy/reactpy/backend/default.py * make text bold --------- Co-authored-by: Ryan Morshead <ryan.morshead@gmail.com>

Author: geckguy

src/py/reactpy/reactpy/backend/default.py

@@ -6,7 +6,7 @@
 from typing import Any, NoReturn
 
 from reactpy.backend.types import BackendImplementation
-from reactpy.backend.utils import all_implementations
+from reactpy.backend.utils import SUPPORTED_PACKAGES, all_implementations
 from reactpy.types import RootComponentConstructor
 
 logger = getLogger(__name__)
@@ -59,7 +59,13 @@ def _default_implementation() -> BackendImplementation[Any]:
  implementation = next(all_implementations())
  except StopIteration: # nocov
  logger.debug("Backend implementation import failed", exc_info=exc_info())
- msg = "No built-in server implementation installed."
+ supported_backends = ", ".join(SUPPORTED_PACKAGES)
+ msg = (
+ "It seems you haven't installed a backend. To resolve this issue, "
+ "you can install a backend by running:\n\n"
+ '\033[1mpip install "reactpy[starlette]"\033[0m\n\n'
+ f"Other supported backends include: {supported_backends}."
+ )
  raise RuntimeError(msg) from None
  else:
  _DEFAULT_IMPLEMENTATION = implementation