Syntax highlighting (#691)

* Syntax highlighting mostly... Exists.

* Add dependency to dockerfile

* Handle non-existent languages better

* Make the default a bit nicer

* Improve highlighting. Clean up function

* Add dark theme, add the comment scope to the allowed classes

* update build env

* Address review comments

* Use find_syntax_by_token which produces the desired behavior

* Change flat_map into flatten
(commit cargo.lock)

plume-models/src/safe_string.rs

@@ -31,10 +31,41 @@ lazy_static! {
             .add_tag_attributes("label", ["for"].iter())
             .add_tag_attributes("input", ["type", "checked"].iter())
             .add_allowed_classes("input", ["cw-checkbox"].iter())
+            .add_allowed_classes(
+                "span",
+                [
+                    "cw-container",
+                    "cw-text",
+                    //Scope classes for the syntax highlighting.
+                    "attribute-name",
+                    "comment",
+                    "constant",
+                    "control",
+                    "declaration",
+                    "entity",
+                    "function",
+                    "invalid",
+                    "keyword",
+                    "language",
+                    "modifier",
+                    "name",
+                    "numeric",
+                    "operator",
+                    "parameter",
+                    "punctuation",
+                    "source",
+                    "storage",
+                    "string",
+                    "support",
+                    "tag",
+                    "type",
+                    "variable",
+                ]
+                .iter(),
+            )
             // Related to https://github.com/Plume-org/Plume/issues/637
             .add_allowed_classes("sup", ["footnote-reference", "footnote-definition-label"].iter())
             .add_allowed_classes("div", ["footnote-definition"].iter())
-            .add_allowed_classes("span", ["cw-container", "cw-text"].iter())
             .attribute_filter(|elem, att, val| match (elem, att) {
                 ("input", "type") => Some("checkbox".into()),
                 ("input", "checked") => Some("checked".into()),