fix: catch errors in remote.AUTO provider list (#1834)

* remote: catch errors in AUTO provider list

The AUTO remote imports and initialises all remote providers, however
some remote providers assume they will only be imported or instantiated
if their dependencies and/or configuration is set within the environment.
This leads to a situation where *all* remote dependencies and *all*
remote configuration must be installed/configured before using the AUTO
provider.

This patch avoids this issue by skipping remote providers that raise
exceptions when either imported or instantiated.

* tests: add tests of snakemake.remote.AUTO

snakemake/remote/__init__.py

@@ -471,10 +471,14 @@ def protocol_mapping(self):
         # assemble scheme mapping
         protocol_dict = {}
         for Provider in provider_list:
-            for protocol in Provider().available_protocols:
-                protocol_short = protocol[:-3]  # remove "://" suffix
-                protocol_dict[protocol_short] = Provider
-
+            try:
+                for protocol in Provider().available_protocols:
+                    protocol_short = protocol[:-3]  # remove "://" suffix
+                    protocol_dict[protocol_short] = Provider
+            except Exception as e:
+                # If for any reason Provider() fails (e.g. missing python
+                # packages or config env vars), skip this provider.
+                logger.debug(f"Instantiating {Provider.__class__.__name__} failed: {e}")
         return protocol_dict
 
     def remote(self, value, *args, provider_kws=None, **kwargs):

tests/test_remote_auto/Snakefile

@@ -0,0 +1,10 @@
+#import re, os, sys
+shell.executable("bash")
+
+from snakemake.remote import AUTO
+
+rule all:
+    input:
+        AUTO.remote("https://github.com/snakemake/snakemake/raw/main/images/logo.png")
+    run:
+        shell("cp {input} ./")