let search plugin fail silently for non-html builders

Maybe there's a more elegant way to approach this, but I'm just hacking this into something passable for CI

sphinx_immaterial/plugins/search/plugin.py

@@ -143,6 +143,8 @@ def on_serve(self, server, *, config, builder):
     # Translate the given placeholder value
     def _translate(self, config, value):
         env = config.theme.get_env()
+        if env is None:  # not using a HTML builder
+            return value
 
         # Load language template and return translation for placeholder
         language = "partials/language.html"
@@ -406,7 +408,7 @@ def handle_starttag(self, tag, attrs):
 
         # Ignore self-closing tags
         el = Element(tag, attrs)
-        if not tag in void:
+        if tag not in void:
             self.context.append(el)
         else:
             return
@@ -509,7 +511,7 @@ def handle_data(self, data):
             return
 
         # Collapse whitespace in non-pre contexts
-        if not "pre" in self.context:
+        if "pre" not in self.context:
             if not data.isspace():
                 data = data.replace("\n", " ")
             else:

sphinx_immaterial/search.py

@@ -2,6 +2,7 @@
 
 import multiprocessing
 import pathlib
+from typing import Optional
 
 import docutils.nodes
 import jinja2.sandbox
@@ -46,9 +47,13 @@ class _Theme:
     def __init__(self, app: sphinx.application.Sphinx):
         self._app = app
         builder = self._app.builder
-        assert isinstance(builder, sphinx.builders.html.StandaloneHTMLBuilder)
-        self._jinja2_env = jinja2.sandbox.SandboxedEnvironment(loader=builder.templates)
-        self._jinja2_env.globals.update(builder.globalcontext)
+        self._jinja2_env: Optional[jinja2.sandbox.SandboxedEnvironment]
+        if isinstance(builder, sphinx.builders.html.StandaloneHTMLBuilder):
+            # only useful if using HTML output
+            self._jinja2_env = jinja2.sandbox.SandboxedEnvironment(loader=builder.templates)
+            self._jinja2_env.globals.update(builder.globalcontext)
+        else:
+            self._jinja2_env = None
 
     def get_env(self):
         return self._jinja2_env