From 81a13f6bc6bf0572fe106651988b4923bceea735 Mon Sep 17 00:00:00 2001
From: Oleh Prypin <oleh@pryp.in>
Date: Sun, 17 Jan 2021 10:38:03 +0100
Subject: [PATCH] Optimized nested navigation rendering: don't cross template
 boundary (#2213)

The number of calls to sub-templates when rendering the navigation is O(n^2) relative to the number of pages. This is the only such instance, which is why I think this is worth optimizing.

The optimization here doesn't improve the complexity, it just removes the overhead of instantiating a new Jinja template for each of these calls.

E.g. for 710 pages on the site, the number of calls to Jinja's `get_template` (implying `new_context` and others) crosses a million ==(710**2)*2. They're not expensive but also not super cheap, and add up to a big percentage of overall site build times.
---
 material/partials/nav-item.html |  7 ++++---
 src/partials/nav-item.html      | 11 ++++++++---
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/material/partials/nav-item.html b/material/partials/nav-item.html
index 8a90ad49c..b8325bc46 100644
--- a/material/partials/nav-item.html
+++ b/material/partials/nav-item.html
@@ -2,6 +2,7 @@
   This file was automatically generated - do not edit
 -#}
 {% set features = config.theme.features or [] %}
+{% macro do_nav_item(nav_item, path, level) %}
 {% set class = "md-nav__item" %}
 {% if nav_item.active %}
   {% set class = class ~ " md-nav__item--active" %}
@@ -31,9 +32,7 @@
       <ul class="md-nav__list" data-md-scrollfix>
         {% set base = path %}
         {% for nav_item in nav_item.children %}
-          {% set path = base ~ "-" ~ loop.index %}
-          {% set level = level + 1 %}
-          {% include "partials/nav-item.html"  %}
+          {{ do_nav_item(nav_item, path = base ~ "-" ~ loop.index, level = level + 1) }}
         {% endfor %}
       </ul>
     </nav>
@@ -65,3 +64,5 @@
     </a>
   </li>
 {% endif %}
+{% endmacro %}
+{{ do_nav_item(nav_item, path, level) }}
diff --git a/src/partials/nav-item.html b/src/partials/nav-item.html
index c9637f158..42187a696 100644
--- a/src/partials/nav-item.html
+++ b/src/partials/nav-item.html
@@ -23,6 +23,9 @@
 <!-- Retrieve features from configuration -->
 {% set features = config.theme.features or [] %}
 
+<!-- Wrap everything into a macro to reduce file roundtrips -->
+{% macro do_nav_item(nav_item, path, level) %}
+
 <!-- Determine class according to state -->
 {% set class = "md-nav__item" %}
 {% if nav_item.active %}
@@ -82,9 +85,7 @@
         <!-- Render nested item list -->
         {% set base = path %}
         {% for nav_item in nav_item.children %}
-          {% set path = base ~ "-" ~ loop.index %}
-          {% set level = level + 1 %}
-          {% include "partials/nav-item.html"  %}
+          {{ do_nav_item(nav_item, path = base ~ "-" ~ loop.index, level = level + 1) }}
         {% endfor %}
       </ul>
     </nav>
@@ -136,3 +137,7 @@
     </a>
   </li>
 {% endif %}
+
+{% endmacro %}
+
+{{ do_nav_item(nav_item, path, level) }}