Better error if plugin file in baseline not found

Fixes: #718

detect_secrets/core/plugins/initialize.py

@@ -31,7 +31,17 @@ def from_plugin_classname(classname: str) -> Plugin:
     """
     :raises: TypeError
     """
-    for plugin_type in get_mapping_from_secret_type_to_class().values():
+    try:
+        plugin_types = get_mapping_from_secret_type_to_class().values()
+    except FileNotFoundError as e:
+        log.error(f'Error: Failed to load `{classname}` plugin: {e}')
+        log.error(
+            'This error can occur when using a baseline that references a '
+            'custom plugin with a path that does not exist.',
+        )
+        raise
+
+    for plugin_type in plugin_types:
         if plugin_type.__name__ == classname:
             break
     else:

detect_secrets/core/scan.py

@@ -138,8 +138,12 @@ def scan_line(line: str) -> Generator[PotentialSecret, None, None]:
 
 
 def scan_file(filename: str) -> Generator[PotentialSecret, None, None]:
-    if not get_plugins():   # pragma: no cover
-        log.error('No plugins to scan with!')
+    try:
+        if not get_plugins():   # pragma: no cover
+            log.error('No plugins to scan with!')
+            return
+    except FileNotFoundError:
+        log.error('Unable to load plugins!')
         return
 
     if _is_filtered_out(required_filter_parameters=['filename'], filename=filename):

detect_secrets/util/importlib.py

@@ -1,3 +1,4 @@
+import errno
 import importlib.util
 import os
 import pkgutil
@@ -85,7 +86,8 @@ def import_file_as_module(filename: str, name: Optional[str] = None) -> ModuleTy
     for you.
     """
     if not os.path.exists(filename):
-        raise FileNotFoundError
+        # Source: https://stackoverflow.com/a/36077407
+        raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT), filename)
 
     if not name:
         # NOTE: After several trial and error attempts, I could not discern the importance

tests/core/baseline_test.py

@@ -102,6 +102,25 @@ def test_load_and_output():
             break
 
 
+def test_plugin_not_found_in_baseline():
+    # Test fix for the issue in #718
+    data = {
+        'version': '1.4.0',
+        'plugins_used': [{
+            'name': 'FakeCustomPlugin',
+            'path': 'file://./path/to/plugin/that/does/not/exist/plugin.py',
+        }],
+        'results': {},
+    }
+    secrets = baseline.load(data)
+    with pytest.raises(FileNotFoundError) as exc_info:
+        baseline.format_for_output(secrets)
+
+    # Check that filename of file that was not found is in the error message
+    # (#718)
+    exc_info.match(r'\./path/to/plugin/that/does/not/exist/plugin\.py')
+
+
 def test_upgrade_does_nothing_if_newer_version():
     current_baseline = {'version': '3.0.0'}
     assert baseline.upgrade(current_baseline) == current_baseline