Allow force run app on cloud if loading locally errors (#15019)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: manskx

src/lightning_app/CHANGELOG.md

@@ -26,7 +26,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Add a `JustPyFrontend` to ease UI creation with `https://github.com/justpy-org/justpy` ([#15002](https://github.com/Lightning-AI/lightning/pull/15002))
 - Added a layout endpoint to the Rest API and enable to disable pulling or pushing to the state ([#15367](https://github.com/Lightning-AI/lightning/pull/15367)
 - Added support for functions for `configure_api` and `configure_commands` to be executed in the Rest API process ([#15098](https://github.com/Lightning-AI/lightning/pull/15098)
-
+- Added support to start lightning app on cloud without needing to install dependencies locally ([#15019](https://github.com/Lightning-AI/lightning/pull/15019)
 
 ### Changed
 

src/lightning_app/runners/cloud.py

@@ -4,6 +4,7 @@
 import string
 import sys
 import time
+import traceback
 from dataclasses import dataclass
 from pathlib import Path
 from typing import Any, Callable, List, Optional, Union
@@ -60,6 +61,7 @@
 from lightning_app.utilities.app_helpers import Logger
 from lightning_app.utilities.cloud import _get_project
 from lightning_app.utilities.dependency_caching import get_hash
+from lightning_app.utilities.load_app import _prettifiy_exception, load_app_from_file
 from lightning_app.utilities.packaging.app_config import AppConfig, find_config_file
 from lightning_app.utilities.packaging.lightning_utils import _prepare_lightning_wheels_and_requirements
 from lightning_app.utilities.secrets import _names_to_ids
@@ -463,6 +465,30 @@ def _project_has_sufficient_credits(self, project: V1Membership, app: Optional[L
 
         return balance >= 1
 
+    @classmethod
+    def load_app_from_file(cls, filepath: str) -> "LightningApp":
+        """This is meant to use only locally for cloud runtime."""
+        try:
+            app = load_app_from_file(filepath, raise_exception=True)
+        except ModuleNotFoundError:
+            # this is very generic exception.
+            logger.info("Could not load the app locally. Starting the app directly on the cloud.")
+            # we want to format the exception as if no frame was on top.
+            exp, val, tb = sys.exc_info()
+            listing = traceback.format_exception(exp, val, tb)
+            # remove the entry for the first frame
+            del listing[1]
+            from lightning_app.testing.helpers import EmptyFlow
+
+            # Create a mocking app.
+            app = LightningApp(EmptyFlow())
+
+        except FileNotFoundError as e:
+            raise e
+        except Exception:
+            _prettifiy_exception(filepath)
+        return app
+
 
 def _create_mount_drive_spec(work_name: str, mount: Mount) -> V1LightningworkDrives:
     if mount.protocol == "s3://":

src/lightning_app/runners/runtime.py

@@ -56,7 +56,7 @@ def dispatch(
 
     runtime_type = RuntimeType(runtime_type)
     runtime_cls: Type[Runtime] = runtime_type.get_runtime()
-    app = load_app_from_file(str(entrypoint_file))
+    app = runtime_cls.load_app_from_file(str(entrypoint_file))
 
     env_vars = {} if env_vars is None else env_vars
     secrets = {} if secrets is None else secrets
@@ -151,3 +151,8 @@ def _add_stopped_status_to_work(self, work: "lightning_app.LightningWork") -> No
         latest_call_hash = work._calls[CacheCallsKeys.LATEST_CALL_HASH]
         if latest_call_hash in work._calls:
             work._calls[latest_call_hash]["statuses"].append(make_status(WorkStageStatus.STOPPED))
+
+    @classmethod
+    def load_app_from_file(cls, filepath: str) -> "LightningApp":
+
+        return load_app_from_file(filepath)

src/lightning_app/utilities/load_app.py

@@ -16,7 +16,28 @@
 logger = Logger(__name__)
 
 
-def load_app_from_file(filepath: str) -> "LightningApp":
+def _prettifiy_exception(filepath: str):
+    """Pretty print the exception that occurred when loading the app."""
+    # we want to format the exception as if no frame was on top.
+    exp, val, tb = sys.exc_info()
+    listing = traceback.format_exception(exp, val, tb)
+    # remove the entry for the first frame
+    del listing[1]
+    listing = [
+        f"Found an exception when loading your application from {filepath}. Please, resolve it to run your app.\n\n"
+    ] + listing
+    logger.error("".join(listing))
+    sys.exit(1)
+
+
+def load_app_from_file(filepath: str, raise_exception: bool = False) -> "LightningApp":
+    """Load a LightningApp from a file.
+
+    Arguments:
+        filepath:  The path to the file containing the LightningApp.
+        raise_exception: If True, raise an exception if the app cannot be loaded.
+    """
+
     # Taken from StreamLit: https://github.com/streamlit/streamlit/blob/develop/lib/streamlit/script_runner.py#L313
 
     from lightning_app.core.app import LightningApp
@@ -30,17 +51,10 @@ def load_app_from_file(filepath: str) -> "LightningApp":
     try:
         with _patch_sys_argv():
             exec(code, module.__dict__)
-    except Exception:
-        # we want to format the exception as if no frame was on top.
-        exp, val, tb = sys.exc_info()
-        listing = traceback.format_exception(exp, val, tb)
-        # remove the entry for the first frame
-        del listing[1]
-        listing = [
-            f"Found an exception when loading your application from {filepath}. Please, resolve it to run your app.\n\n"
-        ] + listing
-        logger.error("".join(listing))
-        sys.exit(1)
+    except Exception as e:
+        if raise_exception:
+            raise e
+        _prettifiy_exception(filepath)
 
     apps = [v for v in module.__dict__.values() if isinstance(v, LightningApp)]
     if len(apps) > 1:

tests/tests_app/runners/test_cloud.py

@@ -1,4 +1,5 @@
 import logging
+import os
 from copy import copy
 from pathlib import Path
 from unittest import mock
@@ -36,9 +37,10 @@
     V1Work,
 )
 
-from lightning_app import LightningApp, LightningWork
-from lightning_app.runners import backends, cloud
+from lightning_app import _PROJECT_ROOT, LightningApp, LightningWork
+from lightning_app.runners import backends, cloud, CloudRuntime
 from lightning_app.storage import Drive, Mount
+from lightning_app.testing.helpers import EmptyFlow
 from lightning_app.utilities.cloud import _get_project
 from lightning_app.utilities.dependency_caching import get_hash
 from lightning_app.utilities.packaging.cloud_compute import CloudCompute
@@ -1082,3 +1084,13 @@ def test_project_has_sufficient_credits():
     for balance, result in credits_and_test_value:
         project = V1Membership(name="test-project1", project_id="test-project-id1", balance=balance)
         assert cloud_runtime._project_has_sufficient_credits(project) is result
+
+
+@mock.patch(
+    "lightning_app.runners.cloud.load_app_from_file",
+    MagicMock(side_effect=ModuleNotFoundError("Module X not found")),
+)
+def test_load_app_from_file_module_error():
+    empty_app = CloudRuntime.load_app_from_file(os.path.join(_PROJECT_ROOT, "examples", "app_v0", "app.py"))
+    assert isinstance(empty_app, LightningApp)
+    assert isinstance(empty_app.root, EmptyFlow)