Use importlib.metadata to read requirements (#12088)

* Pull runtime dep checks into their own module
* Reimplement `check_requirements` using `importlib`

I've tried to make this clearer. We start by working out which of
Synapse's requirements we need to be installed here and now. I was
surprised that there wasn't an easier way to see which packages were
installed by a given extra.

I've pulled out the error messages into functions that deal with "is
this for an extra or not". And I've rearranged the loop over two
different sets of requirements into one loop with a "must be instaled"
flag.

I hope you agree that this is clearer.

* Test cases

7 files changed, 7 insertions, 7 deletions

diff --git a/synapse/config/cache.py b/synapse/config/cache.py
index 387ac6d115..9a68da9c33 100644
--- a/synapse/config/cache.py
+++ b/synapse/config/cache.py
@@ -20,7 +20,7 @@ from typing import Callable, Dict, Optional
 
 import attr
 
-from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.util.check_dependencies import DependencyException, check_requirements
 
 from ._base import Config, ConfigError
 
diff --git a/synapse/config/metrics.py b/synapse/config/metrics.py
index 1cc26e7578..f62292ecf6 100644
--- a/synapse/config/metrics.py
+++ b/synapse/config/metrics.py
@@ -15,7 +15,7 @@
 
 import attr
 
-from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.util.check_dependencies import DependencyException, check_requirements
 
 from ._base import Config, ConfigError
 
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index e783b11315..f7e4f9ef22 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -20,11 +20,11 @@ import attr
 
 from synapse.config._util import validate_config
 from synapse.config.sso import SsoAttributeRequirement
-from synapse.python_dependencies import DependencyException, check_requirements
 from synapse.types import JsonDict
 from synapse.util.module_loader import load_module
 from synapse.util.stringutils import parse_and_validate_mxc_uri
 
+from ..util.check_dependencies import DependencyException, check_requirements
 from ._base import Config, ConfigError, read_file
 
 DEFAULT_USER_MAPPING_PROVIDER = "synapse.handlers.oidc.JinjaOidcMappingProvider"
diff --git a/synapse/config/redis.py b/synapse/config/redis.py
index 33104af734..bdb1aac3a2 100644
--- a/synapse/config/redis.py
+++ b/synapse/config/redis.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 from synapse.config._base import Config
-from synapse.python_dependencies import check_requirements
+from synapse.util.check_dependencies import check_requirements
 
 
 class RedisConfig(Config):
diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 1980351e77..0a0d901bfb 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -20,8 +20,8 @@ from urllib.request import getproxies_environment  # type: ignore
 import attr
 
 from synapse.config.server import DEFAULT_IP_RANGE_BLACKLIST, generate_ip_set
-from synapse.python_dependencies import DependencyException, check_requirements
 from synapse.types import JsonDict
+from synapse.util.check_dependencies import DependencyException, check_requirements
 from synapse.util.module_loader import load_module
 
 from ._base import Config, ConfigError
diff --git a/synapse/config/saml2.py b/synapse/config/saml2.py
index ec9d9f65e7..43c456d5c6 100644
--- a/synapse/config/saml2.py
+++ b/synapse/config/saml2.py
@@ -17,8 +17,8 @@ import logging
 from typing import Any, List, Set
 
 from synapse.config.sso import SsoAttributeRequirement
-from synapse.python_dependencies import DependencyException, check_requirements
 from synapse.types import JsonDict
+from synapse.util.check_dependencies import DependencyException, check_requirements
 from synapse.util.module_loader import load_module, load_python_module
 
 from ._base import Config, ConfigError
diff --git a/synapse/config/tracer.py b/synapse/config/tracer.py
index 21b9a88353..7aff618ea6 100644
--- a/synapse/config/tracer.py
+++ b/synapse/config/tracer.py
@@ -14,7 +14,7 @@
 
 from typing import Set
 
-from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.util.check_dependencies import DependencyException, check_requirements
 
 from ._base import Config, ConfigError