Add a nagging message when "properdocs" is imported but the executable is "mkdocs"

Plugin authors can join in on this message by simply importing our special module.

Author: oprypin

properdocs/__init__.py

@@ -3,3 +3,8 @@
 
 # For acceptable version formats, see https://www.python.org/dev/peps/pep-0440/
 __version__ = '1.6.1'
+
+
+from . import replacement_warning
+
+replacement_warning.setup()

properdocs/replacement_warning.py

@@ -0,0 +1,48 @@
+import os
+import os.path
+import sys
+
+
+def _is_running_from_mkdocs():
+    if 'mkdocs' not in sys.modules:
+        return False
+
+    dir, name = os.path.split(sys.argv[0])
+    if name == 'mkdocs':
+        return True
+    elif name == '__main__.py':
+        dir, name = os.path.split(dir)
+        if name == 'mkdocs':
+            return True
+    return False
+
+
+_WARNING_MESSAGE = '''
+WARNING: TODO (Some concerning message)
+
+We have published a forked project that is an instant drop-in replacement of "mkdocs", supports all its plugins and currently works exactly the same other than bug fixes that we're actively working on.
+Please visit https://github.com/properdocs for more details.
+
+Please replace the "mkdocs" dependency with "properdocs" (within `pip install`). Note that the plugins should stay under their previous name, they will simply keep working).
+And most importantly, replace all command line invocations of `mkdocs` with `properdocs`.
+
+Doing this will also get rid of this warning.
+(This warning was initiated by one of the plugins that you depend on.)
+'''
+
+
+def setup():
+    if _is_running_from_mkdocs():
+        # Silence this warning with NO_MKDOCS_2_WARNING=true
+        if os.environ.get("NO_MKDOCS_2_WARNING", "").lower() != "true":
+            message = _WARNING_MESSAGE
+            try:
+                import click
+
+                message = click.style(message, fg='red')
+            except ImportError:
+                pass
+            print(message, file=sys.stderr)  # noqa: T201
+
+    # Prevent warnings from the theme that already uses this environment variable.
+    os.environ["NO_MKDOCS_2_WARNING"] = "true"