Rewrite "Edit on ..." template logic for readability

If `display_...` is not set, do not show anything.
If some `..._url` is defined on document level, use that.

Author: abitrolly

sphinx_rtd_theme/breadcrumbs.html

@@ -1,19 +1,32 @@
-{%- if meta is defined and meta is not none %}
-   {%- set check_meta = True %}
-{%- else %}
-   {%- set check_meta = False %}
-{%- endif %}
-
-{%- if check_meta and 'github_url' in meta %}
-   {%- set display_github = True %}
+{%- if display_github %}
+   {% set github_sourcelink %}
+      {%- if meta and 'github_url' in meta %}
+      {#- "meta" or "front matter" is data defined inside a page -#}
+<a href="{{ meta['github_url'] }}" class="fa fa-github"> {{ _('Edit on GitHub') }}</a>
+      {%- else %}
+<a href="https://{{ github_host|default("github.com") }}/{{ github_user }}/{{ github_repo }}/{{ theme_vcs_pageview_mode or "blob" }}/{{ github_version }}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}" class="fa fa-github"> {{ _('Edit on GitHub') }}</a>
+      {%- endif %}
+   {% endset %}
 {%- endif %}
 
-{%- if check_meta and 'bitbucket_url' in meta %}
-   {%- set display_bitbucket = True %}
+{%- if display_bitbucket %}
+   {% set bitbucket_sourcelink %}
+     {%- if meta and 'bitbucket_url' in meta %}
+<a href="{{ meta['bitbucket_url'] }}" class="fa fa-bitbucket"> {{ _('Edit on Bitbucket') }}</a>
+     {%- else %}
+<a href="https://bitbucket.org/{{ bitbucket_user }}/{{ bitbucket_repo }}/src/{{ bitbucket_version}}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}?mode={{ theme_vcs_pageview_mode or "view" }}" class="fa fa-bitbucket"> {{ _('Edit on Bitbucket') }}</a>
+     {%- endif %}
+   {% endset %}
 {%- endif %}
 
-{%- if check_meta and 'gitlab_url' in meta %}
-   {%- set display_gitlab = True %}
+{%- if display_gitlab %}
+   {% set gitlab_sourcelink %}
+      {%- if meta and 'gitlab_url' in meta %}
+<a href="{{ meta['gitlab_url'] }}" class="fa fa-gitlab"> {{ _('Edit on GitLab') }}</a>
+      {%- else %}
+<a href="https://{{ gitlab_host|default("gitlab.com") }}/{{ gitlab_user }}/{{ gitlab_repo }}/{{ theme_vcs_pageview_mode or "blob" }}/{{ gitlab_version }}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}" class="fa fa-gitlab"> {{ _('Edit on GitLab') }}</a>
+      {%- endif %}
+   {% endset %}
 {%- endif %}
 
 {%- set display_vcs_links = display_vcs_links if display_vcs_links is defined else True %}
@@ -31,27 +44,12 @@
     {%- block breadcrumbs_aside %}
       <li class="wy-breadcrumbs-aside">
         {%- if hasdoc(pagename) and display_vcs_links %}
-          {%- if display_github %}
-            {%- if check_meta and 'github_url' in meta %}
-              <!-- User defined GitHub URL -->
-              <a href="{{ meta['github_url'] }}" class="fa fa-github"> {{ _('Edit on GitHub') }}</a>
-            {%- else %}
-              <a href="https://{{ github_host|default("github.com") }}/{{ github_user }}/{{ github_repo }}/{{ theme_vcs_pageview_mode or "blob" }}/{{ github_version }}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}" class="fa fa-github"> {{ _('Edit on GitHub') }}</a>
-            {%- endif %}
-          {%- elif display_bitbucket %}
-            {%- if check_meta and 'bitbucket_url' in meta %}
-              <!-- User defined Bitbucket URL -->
-              <a href="{{ meta['bitbucket_url'] }}" class="fa fa-bitbucket"> {{ _('Edit on Bitbucket') }}</a>
-            {%- else %}
-              <a href="https://bitbucket.org/{{ bitbucket_user }}/{{ bitbucket_repo }}/src/{{ bitbucket_version}}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}?mode={{ theme_vcs_pageview_mode or "view" }}" class="fa fa-bitbucket"> {{ _('Edit on Bitbucket') }}</a>
-            {%- endif %}
-          {%- elif display_gitlab %}
-            {%- if check_meta and 'gitlab_url' in meta %}
-              <!-- User defined GitLab URL -->
-              <a href="{{ meta['gitlab_url'] }}" class="fa fa-gitlab"> {{ _('Edit on GitLab') }}</a>
-            {%- else %}
-              <a href="https://{{ gitlab_host|default("gitlab.com") }}/{{ gitlab_user }}/{{ gitlab_repo }}/{{ theme_vcs_pageview_mode or "blob" }}/{{ gitlab_version }}{{ conf_py_path }}{{ pagename }}{{ page_source_suffix }}" class="fa fa-gitlab"> {{ _('Edit on GitLab') }}</a>
-            {%- endif %}
+          {%- if github_sourcelink %}
+            {{ github_sourcelink }}
+          {%- elif bitbucket_sourcelink %}
+            {{ bitbucket_sourcelink }}
+          {%- elif gitlab_sourcelink %}
+            {{ gitlab_sourcelink }}
           {%- elif show_source and source_url_prefix %}
             <a href="{{ source_url_prefix }}{{ pagename }}{{ page_source_suffix }}">{{ _('View page source') }}</a>
           {%- elif show_source and has_source and sourcename %}