Define new Postprocess and EmbedPostprocess traits

These are like the Postprocessor callback function type, but they can
be implemented on types for more ergonomic stateful postprocessing.

Fixes #175

Author: rsesek

src/lib.rs

@@ -39,8 +39,8 @@ pub type MarkdownEvents<'a> = Vec<Event<'a>>;
 /// converted to regular markdown syntax.
 ///
 /// Postprocessors are called in the order they've been added through [Exporter::add_postprocessor]
-/// just before notes are written out to their final destination.
-/// They may be used to achieve the following:
+/// or [Exporter::add_postprocessor_impl] just before notes are written out to their final
+/// destination. They may be used to achieve the following:
 ///
 /// 1. Modify a note's [Context], for example to change the destination filename or update its [Frontmatter] (see [Context::frontmatter]).
 /// 2. Change a note's contents by altering [MarkdownEvents].
@@ -54,7 +54,7 @@ pub type MarkdownEvents<'a> = Vec<Event<'a>>;
 ///
 /// In some cases it may be desirable to change the contents of these embedded notes *before* they
 /// are inserted into the final document. This is possible through the use of
-/// [Exporter::add_embed_postprocessor].
+/// [Exporter::add_embed_postprocessor] or [Exporter::add_embed_postprocessor_impl].
 /// These "embed postprocessors" run much the same way as regular postprocessors, but they're run on
 /// the note that is about to be embedded in another note. In addition:
 ///
@@ -137,6 +137,22 @@ pub type Postprocessor<'f> =
     dyn Fn(&mut Context, &mut MarkdownEvents) -> PostprocessorResult + Send + Sync + 'f;
 type Result<T, E = ExportError> = std::result::Result<T, E>;
 
+/// Postprocess is a trait form of the [Postprocessor] callback that can be passed to
+/// [Exporter::add_postprocessor_impl].
+pub trait Postprocess: Send + Sync {
+    fn postprocess(&self, ctx: &mut Context, events: &mut MarkdownEvents) -> PostprocessorResult;
+}
+
+/// EmbedPostprocess is a trait form of the [Postprocessor] callback that can be
+/// passed to [Exporter::add_embed_postprocessor_impl].
+pub trait EmbedPostprocess: Send + Sync {
+    fn embed_postprocess(
+        &self,
+        ctx: &mut Context,
+        events: &mut MarkdownEvents,
+    ) -> PostprocessorResult;
+}
+
 const PERCENTENCODE_CHARS: &AsciiSet = &CONTROLS.add(b' ').add(b'(').add(b')').add(b'%').add(b'?');
 const NOTE_RECURSION_LIMIT: usize = 10;
 
@@ -216,6 +232,23 @@ pub enum PostprocessorResult {
     StopAndSkipNote,
 }
 
+#[derive(Clone)]
+enum PostprocessorRef<'p> {
+    Function(&'p Postprocessor<'p>),
+    Trait(&'p dyn Postprocess),
+    EmbedTrait(&'p dyn EmbedPostprocess),
+}
+
+impl<'p> PostprocessorRef<'p> {
+    fn call(&'p self, ctx: &mut Context, events: &mut MarkdownEvents) -> PostprocessorResult {
+        match self {
+            PostprocessorRef::Function(f) => f(ctx, events),
+            PostprocessorRef::Trait(t) => t.postprocess(ctx, events),
+            PostprocessorRef::EmbedTrait(t) => t.embed_postprocess(ctx, events),
+        }
+    }
+}
+
 #[derive(Clone)]
 /// Exporter provides the main interface to this library.
 ///
@@ -231,8 +264,8 @@ pub struct Exporter<'a> {
     vault_contents: Option<Vec<PathBuf>>,
     walk_options: WalkOptions<'a>,
     process_embeds_recursively: bool,
-    postprocessors: Vec<&'a Postprocessor<'a>>,
-    embed_postprocessors: Vec<&'a Postprocessor<'a>>,
+    postprocessors: Vec<PostprocessorRef<'a>>,
+    embed_postprocessors: Vec<PostprocessorRef<'a>>,
 }
 
 impl<'a> fmt::Debug for Exporter<'a> {
@@ -315,13 +348,33 @@ impl<'a> Exporter<'a> {
 
     /// Append a function to the chain of [postprocessors][Postprocessor] to run on exported Obsidian Markdown notes.
     pub fn add_postprocessor(&mut self, processor: &'a Postprocessor) -> &mut Exporter<'a> {
-        self.postprocessors.push(processor);
+        self.postprocessors
+            .push(PostprocessorRef::Function(processor));
+        self
+    }
+
+    /// Append a trait implementation of [Postprocess] to the chain of [postprocessors] to run on
+    /// Obsidian Markdown notes.
+    pub fn add_postprocessor_impl(&mut self, processor: &'a dyn Postprocess) -> &mut Exporter<'a> {
+        self.postprocessors.push(PostprocessorRef::Trait(processor));
         self
     }
 
     /// Append a function to the chain of [postprocessors][Postprocessor] for embeds.
     pub fn add_embed_postprocessor(&mut self, processor: &'a Postprocessor) -> &mut Exporter<'a> {
-        self.embed_postprocessors.push(processor);
+        self.embed_postprocessors
+            .push(PostprocessorRef::Function(processor));
+        self
+    }
+
+    /// Append a trait implementation of [EmbedPostprocess] to the chain of [postprocessors] for
+    /// embeds.
+    pub fn add_embed_postprocessor_impl(
+        &mut self,
+        processor: &'a dyn EmbedPostprocess,
+    ) -> &mut Exporter<'a> {
+        self.embed_postprocessors
+            .push(PostprocessorRef::EmbedTrait(processor));
         self
     }
 
@@ -400,8 +453,8 @@ impl<'a> Exporter<'a> {
 
         let (frontmatter, mut markdown_events) = self.parse_obsidian_note(src, &context)?;
         context.frontmatter = frontmatter;
-        for func in &self.postprocessors {
-            match func(&mut context, &mut markdown_events) {
+        for processor in &self.postprocessors {
+            match processor.call(&mut context, &mut markdown_events) {
                 PostprocessorResult::StopHere => break,
                 PostprocessorResult::StopAndSkipNote => return Ok(()),
                 PostprocessorResult::Continue => (),
@@ -603,10 +656,10 @@ impl<'a> Exporter<'a> {
                 if let Some(section) = note_ref.section {
                     events = reduce_to_section(events, section);
                 }
-                for func in &self.embed_postprocessors {
+                for processor in &self.embed_postprocessors {
                     // Postprocessors running on embeds shouldn't be able to change frontmatter (or
                     // any other metadata), so we give them a clone of the context.
-                    match func(&mut child_context, &mut events) {
+                    match processor.call(&mut child_context, &mut events) {
                         PostprocessorResult::StopHere => break,
                         PostprocessorResult::StopAndSkipNote => {
                             events = vec![];

tests/postprocessors_test.rs

@@ -1,5 +1,7 @@
 use obsidian_export::postprocessors::softbreaks_to_hardbreaks;
-use obsidian_export::{Context, Exporter, MarkdownEvents, PostprocessorResult};
+use obsidian_export::{
+    Context, EmbedPostprocess, Exporter, MarkdownEvents, Postprocess, PostprocessorResult,
+};
 use pretty_assertions::assert_eq;
 use pulldown_cmark::{CowStr, Event};
 use serde_yaml::Value;
@@ -139,6 +141,62 @@ fn test_postprocessor_stateful_callback() {
     assert!(parents.contains(expected));
 }
 
+#[test]
+fn test_postprocessor_impl() {
+    #[derive(Default)]
+    struct Impl {
+        parents: Mutex<HashSet<PathBuf>>,
+        embeds: Mutex<u32>,
+    }
+    impl Postprocess for Impl {
+        fn postprocess(
+            &self,
+            ctx: &mut Context,
+            _events: &mut MarkdownEvents,
+        ) -> PostprocessorResult {
+            self.parents
+                .lock()
+                .unwrap()
+                .insert(ctx.destination.parent().unwrap().to_path_buf());
+            PostprocessorResult::Continue
+        }
+    }
+    impl EmbedPostprocess for Impl {
+        fn embed_postprocess(
+            &self,
+            _ctx: &mut Context,
+            _events: &mut MarkdownEvents,
+        ) -> PostprocessorResult {
+            let mut embeds = self.embeds.lock().unwrap();
+            *embeds += 1;
+            PostprocessorResult::Continue
+        }
+    }
+
+    let tmp_dir = TempDir::new().expect("failed to make tempdir");
+    let mut exporter = Exporter::new(
+        PathBuf::from("tests/testdata/input/postprocessors"),
+        tmp_dir.path().to_path_buf(),
+    );
+
+    let postprocessor = Impl {
+        ..Default::default()
+    };
+    exporter.add_postprocessor_impl(&postprocessor);
+    exporter.add_embed_postprocessor_impl(&postprocessor);
+
+    exporter.run().unwrap();
+
+    let expected = tmp_dir.path().clone();
+
+    let parents = postprocessor.parents.lock().unwrap();
+    println!("{:?}", parents);
+    assert_eq!(1, parents.len());
+    assert!(parents.contains(expected));
+
+    assert_eq!(1, *postprocessor.embeds.lock().unwrap());
+}
+
 // The purpose of this test to verify the `append_frontmatter` postprocessor is called to extend
 // the frontmatter, and the `foo_to_bar` postprocessor is called to replace instances of "foo" with
 // "bar" (only in the note body).