Remove strict dependency on locust-plugins, but require a compatible …

…version of locust-plugins if (and only if) it is actuall installed.

setup.py

@@ -3,6 +3,7 @@
 import os
 import sys
 
+import importlib.util
 from setuptools import find_packages, setup
 from setuptools.command.install import install
 from setuptools.command.egg_info import egg_info
@@ -30,6 +31,16 @@ def run(self):
         egg_info.run(self)
 
 
+requirements_list = [
+    "keyring==21.4.0",
+    "psutil",
+    "ConfigArgParse>=1.0",
+]
+# if locust-plugins IS installed, then require a version known to work with this version of swarm.
+spec = importlib.util.find_spec("locust_plugins")
+if spec is not None:
+    requirements_list.append("locust-plugins>=2.7.0")
+
 setup(
     name="locust-swarm",
     description="Load test + test data distribution & launching tool for Locust",
@@ -57,12 +68,7 @@ def run(self):
     packages=find_packages(),
     include_package_data=True,
     zip_safe=False,
-    install_requires=[
-        "keyring==21.4.0",
-        "locust-plugins>=2.2.2",
-        "psutil",
-        "ConfigArgParse>=1.0",
-    ],
+    install_requires=requirements_list,
     entry_points={
         "console_scripts": ["swarm = locust_swarm.swarm:main"],
     },

tox.ini

@@ -5,6 +5,7 @@ envlist = py{37,38,39,310}
 deps =
     black
     pylint
+    locust-plugins # not strictly a requirement, but probably better to have it than not
 commands =
     pylint locust_swarm/
     black --check locust_swarm/