Check dependencies on setup in the nicer way.

changelog.d/5989.misc

@@ -0,0 +1 @@
+Clean up dependency checking at setup.

synapse/config/metrics.py

@@ -16,11 +16,9 @@
 
 import attr
 
-from ._base import Config, ConfigError
+from synapse.python_dependencies import DependencyException, check_requirements
 
-MISSING_SENTRY = """Missing sentry-sdk library. This is required to enable sentry
-    integration.
-    """
+from ._base import Config, ConfigError
 
 
 @attr.s
@@ -51,9 +49,9 @@ def read_config(self, config, **kwargs):
         self.sentry_enabled = "sentry" in config
         if self.sentry_enabled:
             try:
-                import sentry_sdk  # noqa F401
-            except ImportError:
-                raise ConfigError(MISSING_SENTRY)
+                check_requirements("sentry")
+            except DependencyException as e:
+                raise ConfigError(e.message)
 
             self.sentry_dsn = config["sentry"].get("dsn")
             if not self.sentry_dsn:

synapse/config/repository.py

@@ -16,6 +16,7 @@
 import os
 from collections import namedtuple
 
+from synapse.python_dependencies import DependencyException, check_requirements
 from synapse.util.module_loader import load_module
 
 from ._base import Config, ConfigError
@@ -34,17 +35,6 @@
         #    method: %(method)s
 """
 
-MISSING_NETADDR = "Missing netaddr library. This is required for URL preview API."
-
-MISSING_LXML = """Missing lxml library. This is required for URL preview API.
-
-    Install by running:
-        pip install lxml
-
-    Requires libxslt1-dev system package.
-    """
-
-
 ThumbnailRequirement = namedtuple(
     "ThumbnailRequirement", ["width", "height", "method", "media_type"]
 )
@@ -171,16 +161,10 @@ def read_config(self, config, **kwargs):
         self.url_preview_enabled = config.get("url_preview_enabled", False)
         if self.url_preview_enabled:
             try:
-                import lxml
-
-                lxml  # To stop unused lint.
-            except ImportError:
-                raise ConfigError(MISSING_LXML)
+                check_requirements("url_preview")
 
-            try:
-                from netaddr import IPSet
-            except ImportError:
-                raise ConfigError(MISSING_NETADDR)
+            except DependencyException as e:
+                raise ConfigError(e.message)
 
             if "url_preview_ip_range_blacklist" not in config:
                 raise ConfigError(
@@ -189,6 +173,9 @@ def read_config(self, config, **kwargs):
                     "to work"
                 )
 
+            # netaddr is a dependency for url_preview
+            from netaddr import IPSet
+
             self.url_preview_ip_range_blacklist = IPSet(
                 config["url_preview_ip_range_blacklist"]
             )

synapse/python_dependencies.py

@@ -147,7 +147,13 @@ def check_requirements(for_feature=None):
             )
         except DistributionNotFound:
             deps_needed.append(dependency)
-            errors.append("Needed %s but it was not installed" % (dependency,))
+            if for_feature:
+                errors.append(
+                    "Needed %s for the '%s' feature but it was not installed"
+                    % (dependency, for_feature)
+                )
+            else:
+                errors.append("Needed %s but it was not installed" % (dependency,))
 
     if not for_feature:
         # Check the optional dependencies are up to date. We allow them to not be