Sphinx extension for adding Remix links to code snippets

docs/_static/css/custom.css

@@ -45,4 +45,40 @@ pre {
 /* menu section headers */
 .wy-menu .caption {
     color: #65afff !important;
+
+/* Link to Remix IDE shown next to code snippets */
+p.remix-link-container {
+    position: relative;
+    right: -100%;        /* Positioned next to the the top-right corner of the code block following it. */
 }
+
+a.remix-link {
+    position: absolute;  /* Remove it from normal flow not to affect the original position of the snippet. */
+    top: 0.5em;
+    width: 3.236em;      /* Size of the margin (= right-side padding in .wy-nav-content in the current theme). */
+}
+
+a.remix-link .link-icon {
+    background: url("../img/share-solid.svg") no-repeat;
+    display: block;
+    width: 1.5em;
+    height: 1.5em;
+    margin: auto;
+}
+
+a.remix-link .link-text {
+    display: none;       /* Visible only on hover. */
+    width: 3.3em;        /* Narrow enough to get two lines of text. */
+    margin: auto;
+    text-align: center;
+    font-size: 0.8em;
+    line-height: normal;
+    color: black;
+}
+
+a.remix-link:hover {
+    opacity: 0.5;
+}
+
+a.remix-link:hover .link-text {
+    display: block;

docs/_static/css/dark.css

@@ -627,3 +627,9 @@ code.docutils.literal.notranslate {
 
 
 /* Literal.Number.Integer.Long */
+
+
+/* Link to Remix IDE shown over code snippets */
+a.remix-link {
+    filter: invert(1); /* The icon is black. In dark mode we want it white. */
+}

docs/conf.py

@@ -44,6 +44,7 @@ def setup(sphinx):
 extensions = [
     'sphinx_a4doc',
     'html_extra_template_renderer',
+    'remix_code_links',
 ]
 
 a4_base_path = os.path.dirname(__file__) + '/grammar'

docs/ext/remix_code_links.py

@@ -0,0 +1,80 @@
+import base64
+import docutils  # pragma pylint: disable=import-error
+
+from sphinx.util import logging  # pragma pylint: disable=import-error
+
+# NOTE: 2000 should generally be safe for all browsers, while 8000 for most of them.
+MAX_SAFE_URL_LENGTH = 10000
+
+logger = logging.getLogger(__name__)
+
+
+def insert_node_before(child, new_sibling):
+    assert child in child.parent.children
+
+    for position, node in enumerate(child.parent.children):
+        if node == child:
+            child.parent.insert(position, new_sibling)
+            break
+
+
+def remix_code_url(source_code):
+    # NOTE: base64 encoded data may contain +, = and / characters. Remix seems to handle them just
+    # fine without any escaping.
+    base64_encoded_source = base64.b64encode(source_code.encode('utf-8')).decode('ascii')
+    return f"https://remix.ethereum.org/?code={base64_encoded_source}"
+
+
+def build_remix_link_node(url):
+    link_icon_node = docutils.nodes.inline()
+    link_icon_node.set_class('link-icon')
+
+    link_text_node = docutils.nodes.inline(text="open in Remix")
+    link_text_node.set_class('link-text')
+
+    reference_node = docutils.nodes.reference('', '', internal=False, refuri=url)
+    reference_node.set_class('remix-link')
+    reference_node += [link_icon_node, link_text_node]
+
+    paragraph_node = docutils.nodes.paragraph()
+    paragraph_node.set_class('remix-link-container')
+    paragraph_node += reference_node
+    return paragraph_node
+
+
+def insert_remix_link(app, doctree):
+    if app.builder.format != 'html' or app.builder.name == 'epub':
+        return
+
+    for literal_block_node in doctree.traverse(docutils.nodes.literal_block):
+        assert 'language' in literal_block_node.attributes
+        if literal_block_node.attributes['language'].lower() == 'solidity':
+            text_nodes = list(literal_block_node.traverse(docutils.nodes.Text))
+            assert len(text_nodes) == 1
+
+            remix_url = remix_code_url(text_nodes[0])
+            url_length = len(remix_url.encode('utf-8'))
+            if url_length > MAX_SAFE_URL_LENGTH:
+                logger.warning(
+                    "Remix URL generated from the code snippet exceeds the maximum safe URL length "
+                    " (%d > %d bytes).",
+                    url_length,
+                    MAX_SAFE_URL_LENGTH,
+                    location=(literal_block_node.source, literal_block_node.line),
+                )
+
+            insert_node_before(literal_block_node, build_remix_link_node(remix_url))
+
+
+def setup(app):
+    app.connect(
+        'doctree-resolved',
+        lambda app, doctree, docname: insert_remix_link(app, doctree)
+    )
+
+    return {
+        # NOTE: Need to access _raw_config here because setup() runs before app.config is ready.
+        'version': app.config._raw_config['version'],  # pylint: disable=protected-access
+        'parallel_read_safe': True,
+        'parallel_write_safe': True,
+    }