Sphinx 6: Use logo_url instead of logo (readthedocs#1405)

* Sphinx 6: Use logo_url instead of logo

* Handle removal of favicon template context + refactor display of logo and link so it's easier to see what belongs to <4.0 and what is >=4.0

* Adds a favicon to the demo

* Import condensed version logic @agjohnson

* Update sphinx_rtd_theme/layout.html

Co-authored-by: Anthony <aj@ohess.org>

Co-authored-by: Anthony <aj@ohess.org>

docs/conf.py

@@ -70,6 +70,7 @@
 
 html_logo = "demo/static/logo-wordmark-light.svg"
 html_show_sourcelink = True
+html_favicon = "demo/static/favicon.ico"
 
 htmlhelp_basename = slug
 

sphinx_rtd_theme/layout.html

@@ -40,14 +40,14 @@
     <link rel="stylesheet" href="{{ pathto(cssfile, 1) }}" type="text/css" />
   {%- endfor -%}
 
-  {#- FAVICON #}
-  {%- if favicon %}
-    {%- if sphinx_version_info < (4, 0) -%}
-    <link rel="shortcut icon" href="{{ pathto('_static/' + favicon, 1) }}"/>
-    {%- else %}
-    <link rel="shortcut icon" href="{{ favicon_url }}"/>
-    {%- endif %}
-  {%- endif -%}
+  {#- FAVICON
+      favicon_url is the only context var necessary since Sphinx 4.
+      In Sphinx<4, we use favicon but need to prepend path info.
+  #}
+  {%- set _favicon_url = favicon_url | default(pathto('_static/' + (favicon or ""), 1)) %}
+  {%- if favicon_url or favicon %}
+    <link rel="shortcut icon" href="{{ _favicon_url }}"/>
+  {%- endif %}
 
   {#- CANONICAL URL (deprecated) #}
   {%- if theme_canonical_url and not pageurl %}
@@ -133,22 +133,15 @@
         <div class="wy-side-nav-search" {% if theme_style_nav_header_background %} style="background: {{theme_style_nav_header_background}}" {% endif %}>
           {%- block sidebartitle %}
 
-          {%- if logo and theme_logo_only %}
-            <a href="{{ pathto(master_doc) }}">
-          {%- else %}
-            <a href="{{ pathto(master_doc) }}" class="icon icon-home"> {{ project }}
-          {%- endif %}
-
-          {%- if logo %}
-            {#- Not strictly valid HTML, but it's the only way to display/scale
-                it properly, without weird scripting or heaps of work
-            #}
-            {%- if sphinx_version_info < (4, 0) -%}
-            <img src="{{ pathto('_static/' + logo, 1) }}" class="logo" alt="{{ _('Logo') }}"/>
-            {%- else %}
-            <img src="{{ logo_url }}" class="logo" alt="{{ _('Logo') }}"/>
+          {# the logo helper function was removed in Sphinx 6 and deprecated since Sphinx 4 #}
+          {# the master_doc variable was renamed to root_doc in Sphinx 4 (master_doc still exists in later Sphinx versions) #}
+          {%- set _logo_url = logo_url|default(pathto('_static/' + (logo or ""), 1)) %}
+          {%- set _root_doc = root_doc|default(master_doc) %}
+          <a href="{{ pathto(_root_doc) }}"{% if not theme_logo_only %} class="icon icon-home"{% endif %}>
+            {% if not theme_logo_only %}{{ project }}{% endif %}
+            {%- if logo or logo_url %}
+              <img src="{{ _logo_url }}" class="logo" alt="{{ _('Logo') }}"/>
             {%- endif %}
-          {%- endif %}
           </a>
 
           {%- if theme_display_version %}