vimhelp: Add redirect page which allows us to serve a permanent link

This way, even if a tag changes location later, the redirect will always
be able to find it and redirect to the correct location. Only issue is
that it does require JavaScript to work.

The way it works is by embedding the tags.json directly in the page, and
then the JS can just simply do a check to see if the tag match.

Author: ychin

vimhelp/scripts/h2h.py

@@ -70,7 +70,7 @@ def main():
         "--output-tags-json",
         "-J",
         action="store_true",
-        help="Output a tags.json file, used for client-side search (when not using online version)",
+        help="Output tags.json file and client-side tags redirect/search, useful for static page",
     )
     parser.add_argument(
         "--profile", "-P", action="store_true", help="Profile performance"
@@ -153,6 +153,13 @@ def run(args):
         if args.out_dir is not None:
             with (args.out_dir / out_filename).open("w") as f:
                 f.write(json)
+        print("Generating redirect.html...")
+        redirect_html = h2h.to_redirect_html()
+        out_filename = "redirect.html"
+        if args.out_dir is not None:
+            with (args.out_dir / out_filename).open("w") as f:
+                f.write(prelude)
+                f.write(redirect_html)
 
     if args.out_dir is not None:
         print("Symlinking static files...")

vimhelp/static/vimhelp-redirect.js

@@ -0,0 +1,9 @@
+"use strict";
+
+var tagname = new URL(document.URL).searchParams.get('tag')
+if (tagname && window.vimtags) {
+    var redirectUrl = window.vimtags[tagname];
+    if (redirectUrl) {
+        window.location = redirectUrl;
+    }
+}

vimhelp/templates/page.html

@@ -28,6 +28,10 @@
 
 <link rel="stylesheet" href="{{static_dir}}vimhelp-v5.css" type="text/css">
 <noscript><link rel="stylesheet" href="{{static_dir}}noscript.css" type="text/css"></noscript>
+{% if redirect %}
+<script>window.vimtags = {{tags_json|safe}}</script>
+<script src="{{static_dir}}vimhelp-redirect.js"></script>
+{% endif %}
 <script defer src="{{static_dir}}vimhelp-v5.js"></script>
 {# MacVim extension: Offline light/dark mode selection using JavaScript #}
 {% if project.name == 'MacVim' %}
@@ -119,6 +123,10 @@ <h1>{{project.name}} help files</h1>
 <pre>
 {{content}}
 </pre>
+{% if redirect %}
+<noscript>Redirect requires JavaScript to work.</noscript>
+Could not find tag.
+{% endif %}
 </div>
 </main>
 <p>{{sitenavi}}</p>

vimhelp/vimhelp/vimh2h.py

@@ -240,6 +240,34 @@ def gen_tags_json(self):
         return json.dumps(obj, sort_keys=True)
         return out
 
+    def to_redirect_html(self):
+        tags_json = self.gen_tags_json()
+
+        content = ""
+
+        filename = "redirect"
+        static_dir = "/" if self._mode == "online" else ""
+        helptxt = "./" if self._mode == "online" else "index.html"
+        sidebar_headings = None
+
+        current_time = datetime.utcnow().strftime("%Y-%m-%d %H:%M:%SZ")
+
+        return flask.render_template(
+            "page.html",
+            redirect=True,
+            tags_json=tags_json,
+            mode=self._mode,
+            project=self._project,
+            version=self._version,
+            filename=filename,
+            static_dir=static_dir,
+            helptxt=helptxt,
+            content=content,
+            sidebar_headings=sidebar_headings,
+            current_time=current_time,
+            commit=self._commit,
+        )
+
     def to_html(self, filename, contents):
         is_help_txt = filename == "help.txt"
         lines = [line.rstrip("\r\n") for line in RE_NEWLINE.split(contents)]