Better formatting for config errors from modules (#8874)

The idea is that the parse_config method of extension modules can raise either a ConfigError or a JsonValidationError,
and it will be magically turned into a legible error message. There's a few components to it:

* Separating the "path" and the "message" parts of a ConfigError, so that we can fiddle with the path bit to turn it
   into an absolute path.
* Generally improving the way ConfigErrors get printed.
* Passing in the config path to load_module so that it can wrap any exceptions that get caught appropriately.

1 files changed, 4 insertions, 2 deletions

diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index ba1e9d2361..17ce9145ef 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -142,7 +142,7 @@ class ContentRepositoryConfig(Config):
         # them to be started.
         self.media_storage_providers = []  # type: List[tuple]
 
-        for provider_config in storage_providers:
+        for i, provider_config in enumerate(storage_providers):
             # We special case the module "file_system" so as not to need to
             # expose FileStorageProviderBackend
             if provider_config["module"] == "file_system":
@@ -151,7 +151,9 @@ class ContentRepositoryConfig(Config):
                     ".FileStorageProviderBackend"
                 )
 
-            provider_class, parsed_config = load_module(provider_config)
+            provider_class, parsed_config = load_module(
+                provider_config, ("media_storage_providers", "<item %i>" % i)
+            )
 
             wrapper_config = MediaStorageProviderConfig(
                 provider_config.get("store_local", False),