New: support Obsidian's "Strict line breaks" setting

This change introduces a new `--hard-linebreaks` CLI argument. When
used, this converts soft line breaks to hard line breaks, mimicking
Obsidian's "Strict line breaks" setting.

Implementation detail: I considered naming this flag
`--strict-line-breaks` to be consistent with Obsidian itself, however I
feel the name is somewhat misleading and ill-chosen.

src/lib.rs

@@ -6,6 +6,7 @@ extern crate lazy_static;
 
 mod context;
 mod frontmatter;
+pub mod postprocessors;
 mod references;
 mod walker;
 

src/main.rs

@@ -1,5 +1,6 @@
 use eyre::{eyre, Result};
 use gumdrop::Options;
+use obsidian_export::postprocessors::softbreaks_to_hardbreaks;
 use obsidian_export::{ExportError, Exporter, FrontmatterStrategy, WalkOptions};
 use std::{env, path::PathBuf};
 
@@ -46,6 +47,13 @@ struct Opts {
 
     #[options(no_short, help = "Don't process embeds recursively", default = "false")]
     no_recursive_embeds: bool,
+
+    #[options(
+        no_short,
+        help = "Convert soft line breaks to hard line breaks. This mimics Obsidian's 'Strict line breaks' setting",
+        default = "false"
+    )]
+    hard_linebreaks: bool,
 }
 
 fn frontmatter_strategy_from_str(input: &str) -> Result<FrontmatterStrategy> {
@@ -82,6 +90,10 @@ fn main() {
     exporter.process_embeds_recursively(!args.no_recursive_embeds);
     exporter.walk_options(walk_options);
 
+    if args.hard_linebreaks {
+        exporter.add_postprocessor(&softbreaks_to_hardbreaks);
+    }
+
     if let Some(path) = args.start_at {
         exporter.start_at(path);
     }

src/postprocessors.rs

@@ -0,0 +1,20 @@
+//! A collection of officially maintained [postprocessors][crate::Postprocessor].
+
+use super::{Context, MarkdownEvents, PostprocessorResult};
+use pulldown_cmark::Event;
+
+/// This postprocessor converts all soft line breaks to hard line breaks. Enabling this mimics
+/// Obsidian's _'Strict line breaks'_ setting.
+pub fn softbreaks_to_hardbreaks(
+    context: Context,
+    events: MarkdownEvents,
+) -> (Context, MarkdownEvents, PostprocessorResult) {
+    let events = events
+        .into_iter()
+        .map(|event| match event {
+            Event::SoftBreak => Event::HardBreak,
+            _ => event,
+        })
+        .collect();
+    (context, events, PostprocessorResult::Continue)
+}

tests/postprocessors_test.rs

@@ -1,3 +1,4 @@
+use obsidian_export::postprocessors::softbreaks_to_hardbreaks;
 use obsidian_export::{Context, Exporter, MarkdownEvents, PostprocessorResult};
 use pretty_assertions::assert_eq;
 use pulldown_cmark::{CowStr, Event};
@@ -208,3 +209,25 @@ fn test_embed_postprocessors_context() {
 
     exporter.run().unwrap();
 }
+
+#[test]
+fn test_softbreaks_to_hardbreaks() {
+    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(),
+    );
+    exporter.add_postprocessor(&softbreaks_to_hardbreaks);
+    exporter.run().unwrap();
+
+    let expected =
+        read_to_string("tests/testdata/expected/postprocessors/hard_linebreaks.md").unwrap();
+    let actual = read_to_string(
+        tmp_dir
+            .path()
+            .clone()
+            .join(PathBuf::from("hard_linebreaks.md")),
+    )
+    .unwrap();
+    assert_eq!(expected, actual);
+}

tests/testdata/expected/postprocessors/hard_linebreaks.md

@@ -0,0 +1,18 @@
+# Heading 1
+
+Here's a random quote from fortune(6):
+
+"I don't have to take this abuse from you -- I've got hundreds of  
+people waiting to abuse me."  
+-- Bill Murray, "Ghostbusters"
+
+## Heading 2
+
+Here's another random quote from fortune(6):
+
+````
+Cinemuck, n.:
+	The combination of popcorn, soda, and melted chocolate which
+	covers the floors of movie theaters.
+		-- Rich Hall, "Sniglets"
+````

tests/testdata/input/postprocessors/hard_linebreaks.md

@@ -0,0 +1,18 @@
+# Heading 1
+
+Here's a random quote from fortune(6):
+
+"I don't have to take this abuse from you -- I've got hundreds of
+people waiting to abuse me."
+    -- Bill Murray, "Ghostbusters"
+
+## Heading 2
+
+Here's another random quote from fortune(6):
+
+```
+Cinemuck, n.:
+	The combination of popcorn, soda, and melted chocolate which
+	covers the floors of movie theaters.
+		-- Rich Hall, "Sniglets"
+```