3 files changed, 116 insertions, 4 deletions

diff --git a/helix-view/src/gutter.rs b/helix-view/src/gutter.rs
new file mode 100644
index 00000000..86773c1d
--- /dev/null
+++ b/helix-view/src/gutter.rs
@@ -0,0 +1,95 @@
+use std::fmt::Write;
+
+use crate::{editor::Config, graphics::Style, Document, Theme, View};
+
+pub type GutterFn<'doc> = Box<dyn Fn(usize, bool, &mut String) -> Option<Style> + 'doc>;
+pub type Gutter =
+    for<'doc> fn(&'doc Document, &View, &Theme, &Config, bool, usize) -> GutterFn<'doc>;
+
+pub fn diagnostic<'doc>(
+    doc: &'doc Document,
+    _view: &View,
+    theme: &Theme,
+    _config: &Config,
+    _is_focused: bool,
+    _width: usize,
+) -> GutterFn<'doc> {
+    let warning = theme.get("warning");
+    let error = theme.get("error");
+    let info = theme.get("info");
+    let hint = theme.get("hint");
+    let diagnostics = doc.diagnostics();
+
+    Box::new(move |line: usize, _selected: bool, out: &mut String| {
+        use helix_core::diagnostic::Severity;
+        if let Some(diagnostic) = diagnostics.iter().find(|d| d.line == line) {
+            write!(out, "●").unwrap();
+            return Some(match diagnostic.severity {
+                Some(Severity::Error) => error,
+                Some(Severity::Warning) | None => warning,
+                Some(Severity::Info) => info,
+                Some(Severity::Hint) => hint,
+            });
+        }
+        None
+    })
+}
+
+pub fn line_number<'doc>(
+    doc: &'doc Document,
+    view: &View,
+    theme: &Theme,
+    config: &Config,
+    is_focused: bool,
+    width: usize,
+) -> GutterFn<'doc> {
+    let text = doc.text().slice(..);
+    let last_line = view.last_line(doc);
+    // Whether to draw the line number for the last line of the
+    // document or not.  We only draw it if it's not an empty line.
+    let draw_last = text.line_to_byte(last_line) < text.len_bytes();
+
+    let linenr = theme.get("ui.linenr");
+    let linenr_select: Style = theme.try_get("ui.linenr.selected").unwrap_or(linenr);
+
+    let current_line = doc
+        .text()
+        .char_to_line(doc.selection(view.id).primary().cursor(text));
+
+    let config = config.line_number;
+
+    Box::new(move |line: usize, selected: bool, out: &mut String| {
+        if line == last_line && !draw_last {
+            write!(out, "{:>1$}", '~', width).unwrap();
+            Some(linenr)
+        } else {
+            use crate::editor::LineNumber;
+            let line = match config {
+                LineNumber::Absolute => line + 1,
+                LineNumber::Relative => {
+                    if current_line == line {
+                        line + 1
+                    } else {
+                        abs_diff(current_line, line)
+                    }
+                }
+            };
+            let style = if selected && is_focused {
+                linenr_select
+            } else {
+                linenr
+            };
+            write!(out, "{:>1$}", line, width).unwrap();
+            Some(style)
+        }
+    })
+}
+
+#[inline(always)]
+const fn abs_diff(a: usize, b: usize) -> usize {
+    if a > b {
+        a - b
+    } else {
+        b - a
+    }
+}
diff --git a/helix-view/src/lib.rs b/helix-view/src/lib.rs
index 4d19ee2e..a56c914d 100644
--- a/helix-view/src/lib.rs
+++ b/helix-view/src/lib.rs
@@ -5,6 +5,7 @@ pub mod clipboard;
 pub mod document;
 pub mod editor;
 pub mod graphics;
+pub mod gutter;
 pub mod info;
 pub mod input;
 pub mod keyboard;
diff --git a/helix-view/src/view.rs b/helix-view/src/view.rs
index a77f1562..217a4940 100644
--- a/helix-view/src/view.rs
+++ b/helix-view/src/view.rs
@@ -1,6 +1,10 @@
 use std::borrow::Cow;
 
-use crate::{graphics::Rect, Document, DocumentId, ViewId};
+use crate::{
+    graphics::Rect,
+    gutter::{self, Gutter},
+    Document, DocumentId, ViewId,
+};
 use helix_core::{
     graphemes::{grapheme_width, RopeGraphemes},
     line_ending::line_end_char_index,
@@ -60,6 +64,8 @@ impl JumpList {
     }
 }
 
+const GUTTERS: &[(Gutter, usize)] = &[(gutter::diagnostic, 1), (gutter::line_number, 5)];
+
 #[derive(Debug)]
 pub struct View {
     pub id: ViewId,
@@ -83,10 +89,19 @@ impl View {
         }
     }
 
+    pub fn gutters(&self) -> &[(Gutter, usize)] {
+        GUTTERS
+    }
+
     pub fn inner_area(&self) -> Rect {
-        // TODO: not ideal
-        const OFFSET: u16 = 7; // 1 diagnostic + 5 linenr + 1 gutter
-        self.area.clip_left(OFFSET).clip_bottom(1) // -1 for statusline
+        // TODO: cache this
+        let offset = self
+            .gutters()
+            .iter()
+            .map(|(_, width)| *width as u16)
+            .sum::<u16>()
+            + 1; // +1 for some space between gutters and line
+        self.area.clip_left(offset).clip_bottom(1) // -1 for statusline
     }
 
     //
@@ -276,6 +291,7 @@ mod tests {
     use super::*;
     use helix_core::Rope;
     const OFFSET: u16 = 7; // 1 diagnostic + 5 linenr + 1 gutter
+                           // const OFFSET: u16 = GUTTERS.iter().map(|(_, width)| *width as u16).sum();
 
     #[test]
     fn test_text_pos_at_screen_coords() {