Improve markdown list rendering (#2687)

* Cleanup old commented code

* Implement line breaks in markdown rendering

* Implement markdown nested, numbered and multiparagraph lists

1 files changed, 61 insertions, 16 deletions

diff --git a/helix-term/src/ui/markdown.rs b/helix-term/src/ui/markdown.rs
index 45273002..037e2f13 100644
--- a/helix-term/src/ui/markdown.rs
+++ b/helix-term/src/ui/markdown.rs
@@ -135,6 +135,7 @@ impl Markdown {
         "markup.heading.5",
         "markup.heading.6",
     ];
+    const INDENT: &'static str = "  ";
 
     pub fn new(contents: String, config_loader: Arc<syntax::Loader>) -> Self {
         Self {
@@ -144,8 +145,12 @@ impl Markdown {
     }
 
     fn parse(&self, theme: Option<&Theme>) -> tui::text::Text<'_> {
-        // // also 2021-03-04T16:33:58.553 helix_lsp::transport [INFO] <- {"contents":{"kind":"markdown","value":"\n```rust\ncore::num\n```\n\n```rust\npub const fn saturating_sub(self, rhs:Self) ->Self\n```\n\n---\n\n```rust\n```"},"range":{"end":{"character":61,"line":101},"start":{"character":47,"line":101}}}
-        // let text = "\n```rust\ncore::iter::traits::iterator::Iterator\n```\n\n```rust\nfn collect<B: FromIterator<Self::Item>>(self) -> B\nwhere\n        Self: Sized,\n```\n\n---\n\nTransforms an iterator into a collection.\n\n`collect()` can take anything iterable, and turn it into a relevant\ncollection. This is one of the more powerful methods in the standard\nlibrary, used in a variety of contexts.\n\nThe most basic pattern in which `collect()` is used is to turn one\ncollection into another. You take a collection, call [`iter`](https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html) on it,\ndo a bunch of transformations, and then `collect()` at the end.\n\n`collect()` can also create instances of types that are not typical\ncollections. For example, a [`String`](https://doc.rust-lang.org/nightly/core/iter/std/string/struct.String.html) can be built from [`char`](type@char)s,\nand an iterator of [`Result<T, E>`](https://doc.rust-lang.org/nightly/core/result/enum.Result.html) items can be collected\ninto `Result<Collection<T>, E>`. See the examples below for more.\n\nBecause `collect()` is so general, it can cause problems with type\ninference. As such, `collect()` is one of the few times you'll see\nthe syntax affectionately known as the 'turbofish': `::<>`. This\nhelps the inference algorithm understand specifically which collection\nyou're trying to collect into.\n\n# Examples\n\nBasic usage:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled: Vec<i32> = a.iter()\n                         .map(|&x| x * 2)\n                         .collect();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nNote that we needed the `: Vec<i32>` on the left-hand side. This is because\nwe could collect into, for example, a [`VecDeque<T>`](https://doc.rust-lang.org/nightly/core/iter/std/collections/struct.VecDeque.html) instead:\n\n```rust\nuse std::collections::VecDeque;\n\nlet a = [1, 2, 3];\n\nlet doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect();\n\nassert_eq!(2, doubled[0]);\nassert_eq!(4, doubled[1]);\nassert_eq!(6, doubled[2]);\n```\n\nUsing the 'turbofish' instead of annotating `doubled`:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nBecause `collect()` only cares about what you're collecting into, you can\nstill use a partial type hint, `_`, with the turbofish:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nUsing `collect()` to make a [`String`](https://doc.rust-lang.org/nightly/core/iter/std/string/struct.String.html):\n\n```rust\nlet chars = ['g', 'd', 'k', 'k', 'n'];\n\nlet hello: String = chars.iter()\n    .map(|&x| x as u8)\n    .map(|x| (x + 1) as char)\n    .collect();\n\nassert_eq!(\"hello\", hello);\n```\n\nIf you have a list of [`Result<T, E>`](https://doc.rust-lang.org/nightly/core/result/enum.Result.html)s, you can use `collect()` to\nsee if any of them failed:\n\n```rust\nlet results = [Ok(1), Err(\"nope\"), Ok(3), Err(\"bad\")];\n\nlet result: Result<Vec<_>, &str> = results.iter().cloned().collect();\n\n// gives us the first error\nassert_eq!(Err(\"nope\"), result);\n\nlet results = [Ok(1), Ok(3)];\n\nlet result: Result<Vec<_>, &str> = results.iter().cloned().collect();\n\n// gives us the list of answers\nassert_eq!(Ok(vec![1, 3]), result);\n```";
+        fn push_line<'a>(spans: &mut Vec<Span<'a>>, lines: &mut Vec<Spans<'a>>) {
+            let spans = std::mem::take(spans);
+            if !spans.is_empty() {
+                lines.push(Spans::from(spans));
+            }
+        }
 
         let mut options = Options::empty();
         options.insert(Options::ENABLE_STRIKETHROUGH);
@@ -155,6 +160,15 @@ impl Markdown {
         let mut tags = Vec::new();
         let mut spans = Vec::new();
         let mut lines = Vec::new();
+        let mut list_stack = Vec::new();
+
+        let get_indent = |level: usize| {
+            if level < 1 {
+                String::new()
+            } else {
+                Self::INDENT.repeat(level - 1)
+            }
+        };
 
         let get_theme = |key: &str| -> Style { theme.map(|t| t.get(key)).unwrap_or_default() };
         let text_style = get_theme(Self::TEXT_STYLE);
@@ -164,22 +178,53 @@ impl Markdown {
             .map(|key| get_theme(key))
             .collect();
 
-        let mut list_stack = Vec::new();
-
         for event in parser {
             match event {
-                Event::Start(Tag::List(list)) => list_stack.push(list),
+                Event::Start(Tag::List(list)) => {
+                    // if the list stack is not empty this is a sub list, in that
+                    // case we need to push the current line before proceeding
+                    if !list_stack.is_empty() {
+                        push_line(&mut spans, &mut lines);
+                    }
+
+                    list_stack.push(list);
+                }
                 Event::End(Tag::List(_)) => {
                     list_stack.pop();
-                    // whenever list closes, new line
-                    lines.push(Spans::default());
+
+                    // whenever top-level list closes, empty line
+                    if list_stack.is_empty() {
+                        lines.push(Spans::default());
+                    }
                 }
                 Event::Start(Tag::Item) => {
+                    if list_stack.is_empty() {
+                        log::warn!("markdown parsing error, list item without list");
+                    }
+
                     tags.push(Tag::Item);
-                    spans.push(Span::from("- "));
+
+                    // get the approriate bullet for the current list
+                    let bullet = list_stack
+                        .last()
+                        .unwrap_or(&None) // use the '- ' bullet in case the list stack would be empty
+                        .map_or(String::from("- "), |number| format!("{}. ", number));
+
+                    // increment the current list number if there is one
+                    if let Some(v) = list_stack.last_mut().unwrap_or(&mut None).as_mut() {
+                        *v += 1;
+                    }
+
+                    let prefix = get_indent(list_stack.len()) + bullet.as_str();
+                    spans.push(Span::from(prefix));
                 }
                 Event::Start(tag) => {
                     tags.push(tag);
+                    if spans.is_empty() && !list_stack.is_empty() {
+                        // TODO: could push indent + 2 or 3 spaces to align with
+                        // the rest of the list.
+                        spans.push(Span::from(get_indent(list_stack.len())));
+                    }
                 }
                 Event::End(tag) => {
                     tags.pop();
@@ -188,15 +233,12 @@ impl Markdown {
                         | Tag::Paragraph
                         | Tag::CodeBlock(CodeBlockKind::Fenced(_))
                         | Tag::Item => {
-                            let spans = std::mem::take(&mut spans);
-                            if !spans.is_empty() {
-                                lines.push(Spans::from(spans));
-                            }
+                            push_line(&mut spans, &mut lines);
                         }
                         _ => (),
                     }
 
-                    // whenever heading, code block or paragraph closes, new line
+                    // whenever heading, code block or paragraph closes, empty line
                     match tag {
                         Tag::Heading(_, _, _)
                         | Tag::Paragraph
@@ -237,9 +279,12 @@ impl Markdown {
                     spans.push(Span::styled(text, code_style));
                 }
                 Event::SoftBreak | Event::HardBreak => {
-                    // let spans = std::mem::replace(&mut spans, Vec::new());
-                    // lines.push(Spans::from(spans));
-                    spans.push(Span::raw(" "));
+                    push_line(&mut spans, &mut lines);
+                    if !list_stack.is_empty() {
+                        // TODO: could push indent + 2 or 3 spaces to align with
+                        // the rest of the list.
+                        spans.push(Span::from(get_indent(list_stack.len())));
+                    }
                 }
                 Event::Rule => {
                     lines.push(Spans::from(Span::styled("---", code_style)));