commonmark: experimental minimize

examples/iterator_replace.rs

@@ -27,7 +27,7 @@ fn main() {
     let doc = "This is my input.\n\n1. Also [my](#) input.\n2. Certainly *my* input.\n";
     let orig = "my";
     let repl = "your";
-    let html = replace_text(&doc, &orig, &repl);
+    let html = replace_text(doc, orig, repl);
 
     println!("{}", html);
 }

examples/sample.rs

@@ -38,7 +38,7 @@ fn large() {
         let doc = "This is my input.\n\n1. Also [my](#) input.\n2. Certainly *my* input.\n";
         let orig = "my";
         let repl = "your";
-        let html = replace_text(&doc, &orig, &repl);
+        let html = replace_text(doc, orig, repl);
 
         println!("{}", html);
         // Output:

examples/update-readme.rs

@@ -49,7 +49,7 @@ fn main() -> Result<(), Box<dyn Error>> {
 
                 if next_block_is_help_body {
                     next_block_is_help_body = false;
-                    assert!(ncb.info == "" && ncb.literal.starts_with(HELP_START));
+                    assert!(ncb.info.is_empty() && ncb.literal.starts_with(HELP_START));
                     let mut content = String::new();
                     let mut cmd = std::process::Command::new("cargo");
                     content.push_str(

flake.nix

@@ -121,6 +121,7 @@
             "cargo"
             "rustc"
             "rust-analyzer"
+            "clippy"
           ])
           pkgs.cargo-fuzz
           pkgs.python3

src/cm.rs

@@ -10,9 +10,12 @@ use crate::parser::{Options, WikiLinksMode};
 use crate::scanners;
 use crate::strings::trim_start_match;
 use crate::{nodes, Plugins};
+pub use typed_arena::Arena;
 
 use std::cmp::max;
+use std::io::BufWriter;
 use std::io::{self, Write};
+use std::str;
 
 /// Formats an AST as CommonMark, modified by the given options.
 pub fn format_document<'a>(
@@ -40,10 +43,14 @@ pub fn format_document_with_plugins<'a>(
 ) -> io::Result<()> {
     let mut f = CommonMarkFormatter::new(root, options);
     f.format(root);
-    if !f.v.is_empty() && f.v[f.v.len() - 1] != b'\n' {
-        f.v.push(b'\n');
+    let mut result = f.v;
+    if !result.is_empty() && result[result.len() - 1] != b'\n' {
+        result.push(b'\n');
     }
-    output.write_all(&f.v)?;
+    if options.render.experimental_minimize_commonmark {
+        minimize_commonmark(&mut result, options);
+    }
+    output.write_all(&result)?;
     Ok(())
 }
 
@@ -1001,3 +1008,33 @@ fn table_escape<'a>(node: &'a AstNode<'a>, c: u8) -> bool {
         _ => c == b'|',
     }
 }
+
+fn minimize_commonmark(text: &mut Vec<u8>, original_options: &Options) {
+    let mut options_without = original_options.clone();
+    options_without.render.experimental_minimize_commonmark = false;
+
+    let ixs: Vec<usize> = text
+        .iter()
+        .enumerate()
+        .filter_map(|(ix, &c)| if c == b'\\' { Some(ix) } else { None })
+        .collect();
+    let original = text.clone();
+
+    let mut adjust = 0;
+    for ix in ixs {
+        text.remove(ix - adjust);
+
+        let arena = Arena::new();
+        let root = crate::parse_document(&arena, str::from_utf8(text).unwrap(), &options_without);
+
+        let mut bw = BufWriter::new(Vec::new());
+        format_document(root, &options_without, &mut bw).unwrap();
+        let result = bw.into_inner().unwrap();
+
+        if original == result {
+            adjust += 1;
+        } else {
+            text.insert(ix - adjust, b'\\');
+        }
+    }
+}

src/main.rs

@@ -156,6 +156,10 @@ struct Cli {
     /// Ignore empty links
     #[arg(long)]
     ignore_empty_links: bool,
+
+    // Minimize escapes in CommonMark output using a trial-and-error algorithm.
+    #[arg(long)]
+    experimental_minimize_commonmark: bool,
 }
 
 #[derive(Clone, Copy, Debug, ValueEnum)]
@@ -297,6 +301,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         .list_style(cli.list_style.into())
         .sourcepos(cli.sourcepos)
         .experimental_inline_sourcepos(cli.experimental_inline_sourcepos)
+        .experimental_minimize_commonmark(cli.experimental_minimize_commonmark)
         .escaped_char_spans(cli.escaped_char_spans)
         .ignore_setext(cli.ignore_setext)
         .ignore_empty_links(cli.ignore_empty_links)
@@ -364,7 +369,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         formatter(root, &options, &mut bw, &plugins)?;
         bw.flush()?;
     } else if cli.inplace {
-        let output_filename = cli.files.unwrap().get(0).unwrap().clone();
+        let output_filename = cli.files.unwrap().first().unwrap().clone();
         let mut bw = BufWriter::new(fs::File::create(output_filename)?);
         formatter(root, &options, &mut bw, &plugins)?;
         bw.flush()?;

src/parser/mod.rs

@@ -1083,6 +1083,26 @@ pub struct RenderOptions {
     /// ```
     #[cfg_attr(feature = "bon", builder(default))]
     pub ol_width: usize,
+
+    /// Minimise escapes used in CommonMark output (`-t commonmark`) by removing
+    /// each individually and seeing if the resulting document roundtrips.
+    /// Brute-force and expensive, but produces nicer output.  Note that the
+    /// result may not in fact be minimal.
+    ///
+    /// ```rust
+    /// # use comrak::{markdown_to_commonmark, Options};
+    /// let mut options = Options::default();
+    /// let input = "__hi";
+    ///
+    /// assert_eq!(markdown_to_commonmark(input, &options),
+    ///            "\\_\\_hi\n");
+    ///
+    /// options.render.experimental_minimize_commonmark = true;
+    /// assert_eq!(markdown_to_commonmark(input, &options),
+    ///            "__hi\n");
+    /// ```
+    #[cfg_attr(feature = "bon", builder(default))]
+    pub experimental_minimize_commonmark: bool,
 }
 
 #[derive(Default, Debug, Clone)]

src/tests/front_matter.rs

@@ -10,7 +10,7 @@ fn round_trip_one_field() {
     let input = "---\nlayout: post\n---\nText\n";
     let root = parse_document(&arena, input, &options);
     let mut buf = Vec::new();
-    format_commonmark(&root, &options, &mut buf).unwrap();
+    format_commonmark(root, &options, &mut buf).unwrap();
     assert_eq!(&String::from_utf8(buf).unwrap(), input);
 }
 
@@ -22,7 +22,7 @@ fn round_trip_wide_delimiter() {
     let input = "\u{04fc}\nlayout: post\n\u{04fc}\nText\n";
     let root = parse_document(&arena, input, &options);
     let mut buf = Vec::new();
-    format_commonmark(&root, &options, &mut buf).unwrap();
+    format_commonmark(root, &options, &mut buf).unwrap();
     assert_eq!(&String::from_utf8(buf).unwrap(), input);
 }
 
@@ -106,8 +106,7 @@ fn trailing_space_open() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_none(), "no FrontMatter expected");
 }
@@ -123,8 +122,7 @@ fn leading_space_open() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_none(), "no FrontMatter expected");
 }
@@ -140,8 +138,7 @@ fn leading_space_close() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_none(), "no FrontMatter expected");
 }
@@ -157,8 +154,7 @@ fn trailing_space_close() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_none(), "no FrontMatter expected");
 }
@@ -174,8 +170,7 @@ fn second_line() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_none(), "no FrontMatter expected");
 }
@@ -191,8 +186,7 @@ fn fm_only_with_trailing_newline() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_some(), "front matter expected");
 }
@@ -208,8 +202,7 @@ fn fm_only_without_trailing_newline() {
 
     let found = root
         .descendants()
-        .filter(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)))
-        .next();
+        .find(|n| matches!(n.data.borrow().value, NodeValue::FrontMatter(..)));
 
     assert!(found.is_some(), "front matter expected");
 }