docs: Fix missing Edit Page button on stable branches

Author: daksh1403

docs/source/conf.py

@@ -1,14 +1,14 @@
 # -*- coding: utf-8 -*-
-#
+
 # Mypy documentation build configuration file, created by
 # sphinx-quickstart on Sun Sep 14 19:50:35 2014.
-#
+
 # This file is execfile()d with the current directory set to its
 # containing dir.
-#
+
 # Note that not all possible configuration values are present in this
 # autogenerated file.
-#
+
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
@@ -112,9 +112,27 @@
 # a list of builtin themes.
 html_theme = "furo"
 
+import os
+import subprocess
+
+def get_git_branch():
+    try:
+        # Check if running on ReadTheDocs
+        if os.environ.get("READTHEDOCS") == "True":
+            return os.environ.get("READTHEDOCS_GIT_IDENTIFIER", "master")
+        
+        # Otherwise, get the current branch from git locally
+        return subprocess.check_output(
+            ["git", "rev-parse", "--abbrev-ref", "HEAD"]
+        ).decode("utf-8").strip()
+    except Exception:
+        return "master"
+
+current_branch = get_git_branch()
+
 html_theme_options = {
     "source_repository": "https://github.com/python/mypy",
-    "source_branch": "master",
+    "source_branch": current_branch,
     "source_directory": "docs/source",
 }