From 9fbb30a5c64e751cec0fc7fef8a94f7d581eab02 Mon Sep 17 00:00:00 2001
From: tlopex <820958424@qq.com>
Date: Wed, 5 Aug 2026 17:25:12 -0400
Subject: [PATCH] Preserve page when switching languages

---
 conf.py    | 14 +++++++++++++-
 zh/conf.py | 14 +++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/conf.py b/conf.py
index fd1a8295..5b61b998 100644
--- a/conf.py
+++ b/conf.py
@@ -2,6 +2,8 @@
 # Migrated off d2lbook to plain Sphinx + MyST-Parser + sphinx-book-theme.
 # Build:  sphinx-build -b html . _build/html
 
+from pathlib import Path
+
 project = "Modern GPU Programming For MLSys"
 author = "MLC Community"
 copyright = "2026, MLC Community"
@@ -76,7 +78,17 @@ def add_language_switch_button(app, pagename, templatename, context, doctree):
     if header_buttons is None:
         return
 
-    zh_url = context["pathto"]("zh/index.html", 1)
+    zh_source_root = Path(app.srcdir) / "zh"
+    has_translation = any(
+        (zh_source_root / f"{pagename}{suffix}").is_file()
+        for suffix in source_suffix
+    )
+    target_page = (
+        pagename
+        if has_translation or pagename in {"search", "genindex"}
+        else "index"
+    )
+    zh_url = context["pathto"](f"zh/{target_page}.html", 1)
     header_buttons.append(
         {
             "type": "javascript",
diff --git a/zh/conf.py b/zh/conf.py
index a9014f81..9162f7ba 100644
--- a/zh/conf.py
+++ b/zh/conf.py
@@ -1,6 +1,8 @@
 # Sphinx configuration for the Chinese edition.
 # Build: sphinx-build -b html zh _build/html/zh
 
+from pathlib import Path
+
 project = "面向 MLSys 的现代 GPU 编程"
 author = "MLC Community"
 copyright = "2026, MLC Community"
@@ -58,7 +60,17 @@ def add_language_switch_button(app, pagename, templatename, context, doctree):
     if header_buttons is None:
         return
 
-    en_url = context["pathto"]("../index.html", 1)
+    en_source_root = Path(app.srcdir).parent
+    has_translation = any(
+        (en_source_root / f"{pagename}{suffix}").is_file()
+        for suffix in source_suffix
+    )
+    target_page = (
+        pagename
+        if has_translation or pagename in {"search", "genindex"}
+        else "index"
+    )
+    en_url = context["pathto"](f"../{target_page}.html", 1)
     header_buttons.append(
         {
             "type": "javascript",