Print an example "pip install" line for a missing requirement

2 files changed, 26 insertions, 8 deletions

diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index ffc6299146..2a85932b86 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -16,10 +16,23 @@
 
 import sys
 sys.dont_write_bytecode = True
-from synapse.python_dependencies import check_requirements, DEPENDENCY_LINKS
+from synapse.python_dependencies import (
+    check_requirements, DEPENDENCY_LINKS, MissingRequirementError
+)
 
 if __name__ == '__main__':
-    check_requirements()
+    try:
+        check_requirements()
+    except MissingRequirementError as e:
+        message = "\n".join([
+            "Missing Requirement: %s" % (e.message,),
+            "To install run:",
+            "    pip install --upgrade --force \"%s\"" % (e.dependency,),
+            "",
+        ])
+        sys.stderr.writelines(message)
+        sys.exit(1)
+
 
 from synapse.storage.engines import create_engine, IncorrectDatabaseSetup
 from synapse.storage import (
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 795ef27182..387183b50b 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -60,7 +60,10 @@ DEPENDENCY_LINKS = {
 
 
 class MissingRequirementError(Exception):
-    pass
+    def __init__(self, message, module_name, dependency):
+        super(MissingRequirementError, self).__init__(message)
+        self.module_name = module_name
+        self.dependency = dependency
 
 
 def check_requirements(config=None):
@@ -88,7 +91,7 @@ def check_requirements(config=None):
                 )
                 raise MissingRequirementError(
                     "Can't import %r which is part of %r"
-                    % (module_name, dependency)
+                    % (module_name, dependency), module_name, dependency
                 )
             version = getattr(module, "__version__", None)
             file_path = getattr(module, "__file__", None)
@@ -101,23 +104,25 @@ def check_requirements(config=None):
                 if version is None:
                     raise MissingRequirementError(
                         "Version of %r isn't set as __version__ of module %r"
-                        % (dependency, module_name)
+                        % (dependency, module_name), module_name, dependency
                     )
                 if LooseVersion(version) < LooseVersion(required_version):
                     raise MissingRequirementError(
                         "Version of %r in %r is too old. %r < %r"
-                        % (dependency, file_path, version, required_version)
+                        % (dependency, file_path, version, required_version),
+                        module_name, dependency
                     )
             elif version_test == "==":
                 if version is None:
                     raise MissingRequirementError(
                         "Version of %r isn't set as __version__ of module %r"
-                        % (dependency, module_name)
+                        % (dependency, module_name), module_name, dependency
                     )
                 if LooseVersion(version) != LooseVersion(required_version):
                     raise MissingRequirementError(
                         "Unexpected version of %r in %r. %r != %r"
-                        % (dependency, file_path, version, required_version)
+                        % (dependency, file_path, version, required_version),
+                        module_name, dependency
                     )