Improve line breaks for code

kuchiki’s NodeRef::text_contents() implementation does not take into
account the value of the display attribute or line breaks caused by br
elements.  Therefore we have to implement our own converter that
produces readable output for the HTML code generated by rustdoc.

CHANGELOG.md

@@ -19,6 +19,7 @@ SPDX-License-Identifier: MIT
     configuration file can be used to set defaults for the command-line
     options.
   - Add the `--config-file [file]` option to set a custom configuration file.
+- Improve line break rendering when displaying code.
 
 ## v0.1.3 (2020-07-28)
 

src/parser.rs

@@ -27,7 +27,7 @@ impl From<kuchiki::NodeRef> for doc::Text {
 impl From<&kuchiki::NodeRef> for doc::Text {
     fn from(node: &kuchiki::NodeRef) -> doc::Text {
         doc::Text {
-            plain: node.text_contents(),
+            plain: node_to_text(node),
             html: node.to_string(),
         }
     }
@@ -39,6 +39,39 @@ impl<T> From<kuchiki::NodeDataRef<T>> for doc::Text {
     }
 }
 
+fn node_to_text(node: &kuchiki::NodeRef) -> String {
+    let mut s = String::new();
+    push_node_to_text(&mut s, node);
+    s.trim().to_string()
+}
+
+fn push_node_to_text(s: &mut String, node: &kuchiki::NodeRef) {
+    let is_docblock = has_class(node, "docblock");
+
+    let add_newline = if is_element(node, &local_name!("br")) {
+        true
+    } else if has_class(node, "fmt-newline") || is_docblock {
+        !s.is_empty() && !s.ends_with('\n')
+    } else {
+        false
+    };
+    if add_newline {
+        s.push_str("\n");
+    }
+
+    if let Some(text) = node.as_text() {
+        s.push_str(&text.borrow())
+    }
+
+    for child in node.children() {
+        push_node_to_text(s, &child);
+    }
+
+    if is_docblock && !s.is_empty() && !s.ends_with('\n') {
+        s.push_str("\n");
+    }
+}
+
 /// Parses the HTML document at the given path and returns the DOM.
 fn parse_file<P: AsRef<path::Path>>(path: P) -> anyhow::Result<kuchiki::NodeRef> {
     use kuchiki::traits::TendrilSink;