Adjust to RTD's upcoming addon changes

conf.py

@@ -10,11 +10,10 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
-# import os
 # import sys
 # sys.path.insert(0, os.path.abspath('.'))
-
 import datetime
+import os
 
 # -- Project information -----------------------------------------------------
 
@@ -38,7 +37,7 @@
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This pattern also affects html_static_path and html_extra_path.
-exclude_patterns = []
+exclude_patterns: list[str] = []
 
 # -- Intersphinx -------------------------------------------------------------
 
@@ -69,10 +68,19 @@
     "iiasa.css",
 ]
 
+# Define the canonical URL if you are using a custom domain on Read the Docs
+html_baseurl = os.environ.get("READTHEDOCS_CANONICAL_URL", "")
+
+# Tell Jinja2 templates the build is running on Read the Docs
+if os.environ.get("READTHEDOCS", "") == "True":
+    if "html_context" not in globals():
+        html_context = {}
+    html_context["READTHEDOCS"] = True
+
 # prolog for all rst files
 rst_prolog = """
 .. |br| raw:: html
 
    <br>
 
-"""
+"""