sphinx: adopt kernel readthedoc theme

The default "alabaster" sphinx theme has a couple shortcomings:
- the navbar moves along the page
- the search bar is not always at the same place
- it lacks some contrast and colours

The "rtd" theme from readthedocs.org is a popular third party theme used
notably by the kernel, with a custom style sheet. I like it better,
perhaps others do too. It also simplifies the "Edit on Gitlab" links.

Tweak a bit the custom theme to match qemu.org style, use the
QEMU logo, and favicon etc.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Message-Id: <20210323115328.4146052-1-marcandre.lureau@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>

10 files changed, 194 insertions, 59 deletions

diff --git a/docs/_templates/editpage.html b/docs/_templates/editpage.html
deleted file mode 100644
index 4319b0f5ac..0000000000
--- a/docs/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/conf.py b/docs/conf.py
index 2ee6111872..00cf66ab54 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -29,6 +29,7 @@
 import os
 import sys
 import sphinx
+from distutils.version import LooseVersion
 from sphinx.errors import ConfigError
 
 # Make Sphinx fail cleanly if using an old Python, rather than obscurely
@@ -150,38 +151,47 @@ with open(os.path.join(qemu_docdir, 'defs.rst.inc')) as f:
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'alabaster'
+try:
+    import sphinx_rtd_theme
+except ImportError:
+    raise ConfigError(
+        'The Sphinx \'sphinx_rtd_theme\' HTML theme was not found.\n'
+    )
+
+html_theme = 'sphinx_rtd_theme'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-# We initialize this to empty here, so the per-manual conf.py can just
-# add individual key/value entries.
-html_theme_options = {
-}
+if LooseVersion(sphinx_rtd_theme.__version__) >= LooseVersion("0.4.3"):
+    html_theme_options = {
+        "style_nav_header_background": "#802400",
+    }
+
+html_logo = os.path.join(qemu_docdir, "../ui/icons/qemu_128x128.png")
+
+html_favicon = os.path.join(qemu_docdir, "../ui/icons/qemu_32x32.png")
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-# QEMU doesn't yet have any static files, so comment this out so we don't
-# get a warning about a missing directory.
-# If we do ever add this then it would probably be better to call the
-# subdirectory sphinx_static, as the Linux kernel does.
-# html_static_path = ['_static']
+html_static_path = [os.path.join(qemu_docdir, "sphinx-static")]
+
+html_css_files = [
+    'theme_overrides.css',
+]
+
+html_context = {
+    "display_gitlab": True,
+    "gitlab_user": "qemu-project",
+    "gitlab_repo": "qemu",
+    "gitlab_version": "master",
+    "conf_py_path": "/docs/", # Path in the checkout to the docs root
+}
 
 # Custom sidebar templates, must be a dictionary that maps document names
 # to template names.
-#
-# This is required for the alabaster theme
-# refs: http://alabaster.readthedocs.io/en/latest/installation.html#sidebars
-html_sidebars = {
-    '**': [
-        'about.html',
-        'editpage.html',
-        'navigation.html',
-        'searchbox.html',
-    ]
-}
+#html_sidebars = {}
 
 # Don't copy the rST source files to the HTML output directory,
 # and don't put links to the sources into the output HTML.
diff --git a/docs/devel/_templates/editpage.html b/docs/devel/_templates/editpage.html
deleted file mode 100644
index a86d22bca8..0000000000
--- a/docs/devel/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/devel/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/interop/_templates/editpage.html b/docs/interop/_templates/editpage.html
deleted file mode 100644
index 215e562681..0000000000
--- a/docs/interop/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/interop/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/meson.build b/docs/meson.build
index f84306ba7e..855e3916e9 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -27,10 +27,9 @@ if sphinx_build.found()
   build_docs = (sphinx_build_test_out.returncode() == 0)
 
   if not build_docs
-    warning('@0@ is either too old or uses too old a Python version'
-            .format(sphinx_build.full_path()))
+    warning('@0@: @1@'.format(sphinx_build.full_path(), sphinx_build_test_out.stderr()))
     if get_option('docs').enabled()
-      error('Install a Python 3 version of python-sphinx')
+      error('Install a Python 3 version of python-sphinx and the readthedoc theme')
     endif
   endif
 endif
diff --git a/docs/specs/_templates/editpage.html b/docs/specs/_templates/editpage.html
deleted file mode 100644
index aaa468aa98..0000000000
--- a/docs/specs/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/specs/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/sphinx-static/theme_overrides.css b/docs/sphinx-static/theme_overrides.css
new file mode 100644
index 0000000000..c70ef95128
--- /dev/null
+++ b/docs/sphinx-static/theme_overrides.css
@@ -0,0 +1,161 @@
+/* -*- coding: utf-8; mode: css -*-
+ *
+ * Sphinx HTML theme customization: read the doc
+ * Based on Linux Documentation/sphinx-static/theme_overrides.css
+ */
+
+/* Improve contrast and increase size for easier reading. */
+
+body {
+    font-family: serif;
+    color: black;
+    font-size: 100%;
+}
+
+h1, h2, .rst-content .toctree-wrapper p.caption, h3, h4, h5, h6, legend {
+    font-family: sans-serif;
+}
+
+.rst-content dl:not(.docutils) dt {
+    border-top: none;
+    border-left: solid 3px #ccc;
+    background-color: #f0f0f0;
+    color: black;
+}
+
+.wy-nav-top {
+    background: #802400;
+}
+
+.wy-side-nav-search input[type="text"] {
+    border-color: #f60;
+}
+
+.wy-menu-vertical p.caption {
+    color: white;
+}
+
+.wy-menu-vertical li.current a {
+    color: #505050;
+}
+
+.wy-menu-vertical li.on a, .wy-menu-vertical li.current > a {
+    color: #303030;
+}
+
+.fa-gitlab {
+      box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2), 0 3px 10px 0 rgba(0,0,0,0.19);
+      border-radius: 5px;
+}
+
+div[class^="highlight"] pre {
+    font-family: monospace;
+    color: black;
+    font-size: 100%;
+}
+
+.wy-menu-vertical {
+    font-family: sans-serif;
+}
+
+.c {
+    font-style: normal;
+}
+
+p {
+    font-size: 100%;
+}
+
+/* Interim: Code-blocks with line nos - lines and line numbers don't line up.
+ * see: https://github.com/rtfd/sphinx_rtd_theme/issues/419
+ */
+
+div[class^="highlight"] pre {
+    line-height: normal;
+}
+.rst-content .highlight > pre {
+    line-height: normal;
+}
+
+/* Keep fields from being strangely far apart due to inheirited table CSS. */
+.rst-content table.field-list th.field-name {
+    padding-top: 1px;
+    padding-bottom: 1px;
+}
+.rst-content table.field-list td.field-body {
+    padding-top: 1px;
+    padding-bottom: 1px;
+}
+
+@media screen {
+
+    /* content column
+     *
+     * RTD theme's default is 800px as max width for the content, but we have
+     * tables with tons of columns, which need the full width of the view-port.
+     */
+
+    .wy-nav-content{max-width: none; }
+
+    /* table:
+     *
+     *   - Sequences of whitespace should collapse into a single whitespace.
+     *   - make the overflow auto (scrollbar if needed)
+     *   - align caption "left" ("center" is unsuitable on vast tables)
+     */
+
+    .wy-table-responsive table td { white-space: normal; }
+    .wy-table-responsive { overflow: auto; }
+    .rst-content table.docutils caption { text-align: left; font-size: 100%; }
+
+    /* captions:
+     *
+     *   - captions should have 100% (not 85%) font size
+     *   - hide the permalink symbol as long as link is not hovered
+     */
+
+    .toc-title {
+        font-size: 150%;
+        font-weight: bold;
+    }
+
+    caption, .wy-table caption, .rst-content table.field-list caption {
+        font-size: 100%;
+    }
+    caption a.headerlink { opacity: 0; }
+    caption a.headerlink:hover { opacity: 1; }
+
+    /* Menu selection and keystrokes */
+
+    span.menuselection {
+        color: blue;
+        font-family: "Courier New", Courier, monospace
+    }
+
+    code.kbd, code.kbd span {
+        color: white;
+        background-color: darkblue;
+        font-weight: bold;
+        font-family: "Courier New", Courier, monospace
+    }
+
+    /* fix bottom margin of lists items */
+
+    .rst-content .section ul li:last-child, .rst-content .section ul li p:last-child {
+          margin-bottom: 12px;
+    }
+
+    /* inline literal: drop the borderbox, padding and red color */
+
+    code, .rst-content tt, .rst-content code {
+        color: inherit;
+        border: none;
+        padding: unset;
+        background: inherit;
+        font-size: 85%;
+    }
+
+    .rst-content tt.literal,.rst-content tt.literal,.rst-content code.literal {
+        color: inherit;
+    }
+}
diff --git a/docs/system/_templates/editpage.html b/docs/system/_templates/editpage.html
deleted file mode 100644
index 6586b2e257..0000000000
--- a/docs/system/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/system/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/tools/_templates/editpage.html b/docs/tools/_templates/editpage.html
deleted file mode 100644
index 2a9c8fc92b..0000000000
--- a/docs/tools/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/tools/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>
diff --git a/docs/user/_templates/editpage.html b/docs/user/_templates/editpage.html
deleted file mode 100644
index 1f5ee01e60..0000000000
--- a/docs/user/_templates/editpage.html
+++ /dev/null
@@ -1,5 +0,0 @@
-<div id="editpage">
-  <ul>
-    <li><a href="https://gitlab.com/qemu-project/qemu/-/blob/master/docs/user/{{pagename}}.rst">Page source</a></li>
-  </ul>
-</div>