new: support links referencing headings

Previously, links referencing a heading (`[[note#heading]]`) would just
link to the file name without including an anchor in the link target.
Now, such references will include an appropriate `#anchor` attribute.

Note that neither the original Markdown specification, nor the more
recent CommonMark standard, specify how anchors should be constructed
for a given heading.

There are also some differences between the various Markdown rendering
implementations.

Obsidian-export uses the [slug] crate to generate anchors which should
be compatible with most implementations, however your mileage may vary.

(For example, GitHub may leave a trailing `-` on anchors when headings
end with a smiley. The slug library, and thus obsidian-export, will
avoid such dangling dashes).

[slug]: https://crates.io/crates/slug

Cargo.lock

@@ -113,6 +113,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "deunicode"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "850878694b7933ca4c9569d30a34b55031b9b139ee1fc7b94a527c4ef960d690"
+
 [[package]]
 name = "difference"
 version = "2.0.0"
@@ -305,6 +311,7 @@ dependencies = [
  "pulldown-cmark-to-cmark",
  "rayon",
  "regex",
+ "slug",
  "snafu",
  "tempfile",
  "walkdir",
@@ -508,6 +515,15 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
+[[package]]
+name = "slug"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b3bc762e6a4b6c6fcaade73e77f9ebc6991b676f88bb2358bddb56560f073373"
+dependencies = [
+ "deunicode",
+]
+
 [[package]]
 name = "snafu"
 version = "0.6.10"

Cargo.toml

@@ -35,6 +35,7 @@ pulldown-cmark = "0.8.0"
 pulldown-cmark-to-cmark = "6.0.0"
 rayon = "1.5.0"
 regex = "1.4.2"
+slug = "0.1.4"
 snafu = "0.6.10"
 
 [dev-dependencies]

src/lib.rs

@@ -11,8 +11,10 @@ use pulldown_cmark::{CodeBlockKind, CowStr, Event, Options, Parser, Tag};
 use pulldown_cmark_to_cmark::cmark_with_options;
 use rayon::prelude::*;
 use regex::Regex;
+use slug::slugify;
 use snafu::{ResultExt, Snafu};
 use std::ffi::OsString;
+use std::fmt;
 use std::fs::{self, File};
 use std::io::prelude::*;
 use std::io::ErrorKind;
@@ -196,6 +198,24 @@ impl<'a> ObsidianNoteReference<'a> {
             section,
         }
     }
+
+    fn display(&self) -> String {
+        format!("{}", self)
+    }
+}
+
+impl<'a> fmt::Display for ObsidianNoteReference<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let label = self
+            .label
+            .map(|v| v.to_string())
+            .unwrap_or_else(|| match self.section {
+                Some(section) => format!("{} > {}", self.file, section),
+                None => self.file.to_string(),
+            })
+            .to_string();
+        write!(f, "{}", label)
+    }
 }
 
 impl<'a> Exporter<'a> {
@@ -384,9 +404,11 @@ impl<'a> Exporter<'a> {
                     if let Event::Text(CowStr::Borrowed(text)) = buffer[2] {
                         match buffer[0] {
                             Event::Text(CowStr::Borrowed("[")) => {
-                                let mut link_events =
+                                let mut elements = self.make_link_to_file(
-                                    self.obsidian_note_link_to_markdown(&text, context);
+                                    ObsidianNoteReference::from_str(&text),
-                                tree.append(&mut link_events);
+                                    context,
+                                );
+                                tree.append(&mut elements);
                                 buffer.clear();
                                 continue;
                             }
@@ -445,7 +467,7 @@ impl<'a> Exporter<'a> {
                 tree
             }
             Some("png") | Some("jpg") | Some("jpeg") | Some("gif") | Some("webp") => {
-                self.make_link_to_file(&note_ref.file, &note_ref.file, &context)
+                self.make_link_to_file(note_ref, &context)
                     .into_iter()
                     .map(|event| match event {
                         // make_link_to_file returns a link to a file. With this we turn the link
@@ -470,34 +492,28 @@ impl<'a> Exporter<'a> {
                     })
                     .collect()
             }
-            _ => self.make_link_to_file(&note_ref.file, &note_ref.file, &context),
+            _ => self.make_link_to_file(note_ref, &context),
         };
         Ok(tree)
     }
 
-    fn obsidian_note_link_to_markdown(&self, content: &'a str, context: &Context) -> MarkdownTree {
-        let note_ref = ObsidianNoteReference::from_str(content);
-        let label = note_ref.label.unwrap_or(note_ref.file);
-        self.make_link_to_file(note_ref.file, label, context)
-    }
-
     fn make_link_to_file<'b>(
         &self,
-        file: &'b str,
+        reference: ObsidianNoteReference<'b>,
-        label: &'b str,
         context: &Context,
     ) -> MarkdownTree<'b> {
-        let target_file = lookup_filename_in_vault(file, &self.vault_contents.as_ref().unwrap());
+        let target_file =
+            lookup_filename_in_vault(reference.file, &self.vault_contents.as_ref().unwrap());
         if target_file.is_none() {
             // TODO: Extract into configurable function.
             println!(
                 "Warning: Unable to find referenced note\n\tReference: '{}'\n\tSource: '{}'\n",
-                file,
+                reference.file,
                 context.current_file().display(),
             );
             return vec![
                 Event::Start(Tag::Emphasis),
-                Event::Text(CowStr::from(String::from(label))),
+                Event::Text(CowStr::from(reference.display())),
                 Event::End(Tag::Emphasis),
             ];
         }
@@ -513,19 +529,25 @@ impl<'a> Exporter<'a> {
                 .expect("obsidian content files should always have a parent"),
         )
         .expect("should be able to build relative path when target file is found in vault");
-        let rel_link = rel_link.to_string_lossy();
-        let encoded_link = utf8_percent_encode(&rel_link, PERCENTENCODE_CHARS);
 
-        let link = pulldown_cmark::Tag::Link(
+        let rel_link = rel_link.to_string_lossy();
+        let mut link = utf8_percent_encode(&rel_link, PERCENTENCODE_CHARS).to_string();
+
+        if let Some(section) = reference.section {
+            link.push('#');
+            link.push_str(&slugify(section));
+        }
+
+        let link_tag = pulldown_cmark::Tag::Link(
             pulldown_cmark::LinkType::Inline,
-            CowStr::from(encoded_link.to_string()),
+            CowStr::from(link.to_string()),
             CowStr::from(""),
         );
 
         vec![
-            Event::Start(link.clone()),
+            Event::Start(link_tag.clone()),
-            Event::Text(CowStr::from(label)),
+            Event::Text(CowStr::from(reference.display())),
-            Event::End(link.clone()),
+            Event::End(link_tag.clone()),
         ]
     }
 }

tests/testdata/expected/main-samples/obsidian-wikilinks.md

@@ -2,6 +2,10 @@ Link to [pure-markdown-examples](pure-markdown-examples.md) and the same [Pure-M
 
 Link to [pure markdown examples](pure-markdown-examples.md).
 
+Link to [pure-markdown-examples > Heading 1](pure-markdown-examples.md#heading-1).
+
+Link to [pure markdown examples](pure-markdown-examples.md#heading-1).
+
 Link within backticks: `[[pure-markdown-examples]]`
 
 ````

tests/testdata/input/main-samples/obsidian-wikilinks.md

@@ -2,6 +2,10 @@ Link to [[pure-markdown-examples]] and the same [[Pure-Markdown-Examples]].
 
 Link to [[pure-markdown-examples|pure markdown examples]].
 
+Link to [[pure-markdown-examples#Heading 1]].
+
+Link to [[pure-markdown-examples#Heading 1|pure markdown examples]].
+
 Link within backticks: `[[pure-markdown-examples]]`
 
 ```