diff --git a/synapse/util/check_dependencies.py b/synapse/util/check_dependencies.py
new file mode 100644
index 0000000000..3a1f6b3c75
--- /dev/null
+++ b/synapse/util/check_dependencies.py
@@ -0,0 +1,127 @@
+import logging
+from typing import Iterable, NamedTuple, Optional
+
+from packaging.requirements import Requirement
+
+DISTRIBUTION_NAME = "matrix-synapse"
+
+try:
+ from importlib import metadata
+except ImportError:
+ import importlib_metadata as metadata # type: ignore[no-redef]
+
+
+class DependencyException(Exception):
+ @property
+ def message(self) -> str:
+ return "\n".join(
+ [
+ "Missing Requirements: %s" % (", ".join(self.dependencies),),
+ "To install run:",
+ " pip install --upgrade --force %s" % (" ".join(self.dependencies),),
+ "",
+ ]
+ )
+
+ @property
+ def dependencies(self) -> Iterable[str]:
+ for i in self.args[0]:
+ yield '"' + i + '"'
+
+
+EXTRAS = set(metadata.metadata(DISTRIBUTION_NAME).get_all("Provides-Extra"))
+
+
+class Dependency(NamedTuple):
+ requirement: Requirement
+ must_be_installed: bool
+
+
+def _generic_dependencies() -> Iterable[Dependency]:
+ """Yield pairs (requirement, must_be_installed)."""
+ requirements = metadata.requires(DISTRIBUTION_NAME)
+ assert requirements is not None
+ for raw_requirement in requirements:
+ req = Requirement(raw_requirement)
+ # https://packaging.pypa.io/en/latest/markers.html#usage notes that
+ # > Evaluating an extra marker with no environment is an error
+ # so we pass in a dummy empty extra value here.
+ must_be_installed = req.marker is None or req.marker.evaluate({"extra": ""})
+ yield Dependency(req, must_be_installed)
+
+
+def _dependencies_for_extra(extra: str) -> Iterable[Dependency]:
+ """Yield additional dependencies needed for a given `extra`."""
+ requirements = metadata.requires(DISTRIBUTION_NAME)
+ assert requirements is not None
+ for raw_requirement in requirements:
+ req = Requirement(raw_requirement)
+ # Exclude mandatory deps by only selecting deps needed with this extra.
+ if (
+ req.marker is not None
+ and req.marker.evaluate({"extra": extra})
+ and not req.marker.evaluate({"extra": ""})
+ ):
+ yield Dependency(req, True)
+
+
+def _not_installed(requirement: Requirement, extra: Optional[str] = None) -> str:
+ if extra:
+ return f"Need {requirement.name} for {extra}, but it is not installed"
+ else:
+ return f"Need {requirement.name}, but it is not installed"
+
+
+def _incorrect_version(
+ requirement: Requirement, got: str, extra: Optional[str] = None
+) -> str:
+ if extra:
+ return f"Need {requirement} for {extra}, but got {requirement.name}=={got}"
+ else:
+ return f"Need {requirement}, but got {requirement.name}=={got}"
+
+
+def check_requirements(extra: Optional[str] = None) -> None:
+ """Check Synapse's dependencies are present and correctly versioned.
+
+ If provided, `extra` must be the name of an pacakging extra (e.g. "saml2" in
+ `pip install matrix-synapse[saml2]`).
+
+ If `extra` is None, this function checks that
+ - all mandatory dependencies are installed and correctly versioned, and
+ - each optional dependency that's installed is correctly versioned.
+
+ If `extra` is not None, this function checks that
+ - the dependencies needed for that extra are installed and correctly versioned.
+
+ :raises DependencyException: if a dependency is missing or incorrectly versioned.
+ :raises ValueError: if this extra does not exist.
+ """
+ # First work out which dependencies are required, and which are optional.
+ if extra is None:
+ dependencies = _generic_dependencies()
+ elif extra in EXTRAS:
+ dependencies = _dependencies_for_extra(extra)
+ else:
+ raise ValueError(f"Synapse does not provide the feature '{extra}'")
+
+ deps_unfulfilled = []
+ errors = []
+
+ for (requirement, must_be_installed) in dependencies:
+ try:
+ dist: metadata.Distribution = metadata.distribution(requirement.name)
+ except metadata.PackageNotFoundError:
+ if must_be_installed:
+ deps_unfulfilled.append(requirement.name)
+ errors.append(_not_installed(requirement, extra))
+ else:
+ if not requirement.specifier.contains(dist.version):
+ deps_unfulfilled.append(requirement.name)
+ errors.append(_incorrect_version(requirement, dist.version, extra))
+
+ if deps_unfulfilled:
+ for err in errors:
+ logging.error(err)
+
+ raise DependencyException(deps_unfulfilled)
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