initial implementation of bufferline (#2759)

* initial implementation of bufferline

* fixed lint

* changed to 'bufferline', added enum for config modes, some cleanup

* fixed lint

* added file modification indicator

* removed redundant code, added proper themeing with fallback, changed 'file modified' indicator

* remove commented code

* Update helix-term/src/ui/editor.rs

simplify text and offset computation

Co-authored-by: Gokul Soumya <gokulps15@gmail.com>

* add ui.bufferline.background key for themes

Co-authored-by: lazytanuki <43273245+lazytanuki@users.noreply.github.com>

* address PR comments

* Update helix-term/src/ui/editor.rs

* simplify computation of editor area:

* change to set_stringn to avoid overflow

* Update configuration.md

Updates documentation to reflect decision re: defaulting to never showing bufferline.

* addressed pr comments

* fix build error

* address pr comments

* revert accidental change

Co-authored-by: Gokul Soumya <gokulps15@gmail.com>
Co-authored-by: lazytanuki <43273245+lazytanuki@users.noreply.github.com>
Co-authored-by: Seth Bromberger <sbromberger@users.noreply.github.com>

book/src/configuration.md

@@ -49,6 +49,7 @@ ### `[editor]` Section
 | `auto-info` | Whether to display infoboxes | `true` |
 | `true-color` | Set to `true` to override automatic detection of terminal truecolor support in the event of a false negative. | `false` |
 | `rulers` | List of column positions at which to display the rulers. Can be overridden by language specific `rulers` in `languages.toml` file. | `[]` |
+| `bufferline` | Renders a line at the top of the editor displaying open buffers. Can be `always`, `never` or `multiple` (only shown if more than one buffer is in use) | `never` |
 | `color-modes` | Whether to color the mode indicator with different colors depending on the mode itself | `false` |
 
 ### `[editor.statusline]` Section

helix-term/src/ui/editor.rs

@@ -16,14 +16,14 @@
     LineEnding, Position, Range, Selection, Transaction,
 };
 use helix_view::{
-    document::Mode,
+    document::{Mode, SCRATCH_BUFFER_NAME},
     editor::{CompleteAction, CursorShapeConfig},
     graphics::{Color, CursorKind, Modifier, Rect, Style},
     input::{KeyEvent, MouseButton, MouseEvent, MouseEventKind},
     keyboard::{KeyCode, KeyModifiers},
     Document, Editor, Theme, View,
 };
-use std::borrow::Cow;
+use std::{borrow::Cow, path::PathBuf};
 
 use tui::buffer::Buffer as Surface;
 
@@ -619,6 +619,59 @@ pub fn render_focused_view_elements(
         }
     }
 
+    /// Render bufferline at the top
+    pub fn render_bufferline(editor: &Editor, viewport: Rect, surface: &mut Surface) {
+        let scratch = PathBuf::from(SCRATCH_BUFFER_NAME); // default filename to use for scratch buffer
+        surface.clear_with(
+            viewport,
+            editor
+                .theme
+                .try_get("ui.bufferline.background")
+                .unwrap_or_else(|| editor.theme.get("ui.statusline")),
+        );
+
+        let bufferline_active = editor
+            .theme
+            .try_get("ui.bufferline.active")
+            .unwrap_or_else(|| editor.theme.get("ui.statusline.active"));
+
+        let bufferline_inactive = editor
+            .theme
+            .try_get("ui.bufferline")
+            .unwrap_or_else(|| editor.theme.get("ui.statusline.inactive"));
+
+        let mut x = viewport.x;
+        let current_doc = view!(editor).doc;
+
+        for doc in editor.documents() {
+            let fname = doc
+                .path()
+                .unwrap_or(&scratch)
+                .file_name()
+                .unwrap_or_default()
+                .to_str()
+                .unwrap_or_default();
+
+            let style = if current_doc == doc.id() {
+                bufferline_active
+            } else {
+                bufferline_inactive
+            };
+
+            let text = format!(" {}{} ", fname, if doc.is_modified() { "[+]" } else { "" });
+            let used_width = viewport.x.saturating_sub(x);
+            let rem_width = surface.area.width.saturating_sub(used_width);
+
+            x = surface
+                .set_stringn(x, viewport.y, text, rem_width as usize, style)
+                .0;
+
+            if x >= surface.area.right() {
+                break;
+            }
+        }
+    }
+
     pub fn render_gutter(
         editor: &Editor,
         doc: &Document,
@@ -1291,8 +1344,27 @@ fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         // clear with background color
         surface.set_style(area, cx.editor.theme.get("ui.background"));
         let config = cx.editor.config();
+
+        // check if bufferline should be rendered
+        use helix_view::editor::BufferLine;
+        let use_bufferline = match config.bufferline {
+            BufferLine::Always => true,
+            BufferLine::Multiple if cx.editor.documents.len() > 1 => true,
+            _ => false,
+        };
+
+        // -1 for commandline and -1 for bufferline
+        let mut editor_area = area.clip_bottom(1);
+        if use_bufferline {
+            editor_area = editor_area.clip_top(1);
+        }
+
         // if the terminal size suddenly changed, we need to trigger a resize
-        cx.editor.resize(area.clip_bottom(1)); // -1 from bottom for commandline
+        cx.editor.resize(editor_area);
+
+        if use_bufferline {
+            Self::render_bufferline(cx.editor, area.with_height(1), surface);
+        }
 
         for (view, is_focused) in cx.editor.tree.views() {
             let doc = cx.editor.document(view.doc).unwrap();

helix-view/src/editor.rs

@@ -162,6 +162,8 @@ pub struct Config {
     pub rulers: Vec<u16>,
     #[serde(default)]
     pub whitespace: WhitespaceConfig,
+    /// Persistently display open buffers along the top
+    pub bufferline: BufferLine,
     /// Vertical indent width guides.
     pub indent_guides: IndentGuidesConfig,
     /// Whether to color modes with different colors. Defaults to `false`.
@@ -367,6 +369,24 @@ fn default() -> Self {
     }
 }
 
+/// bufferline render modes
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum BufferLine {
+    /// Don't render bufferline
+    Never,
+    /// Always render
+    Always,
+    /// Only if multiple buffers are open
+    Multiple,
+}
+
+impl Default for BufferLine {
+    fn default() -> Self {
+        BufferLine::Never
+    }
+}
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub enum LineNumber {
@@ -554,6 +574,7 @@ fn default() -> Self {
             terminal: get_terminal_provider(),
             rulers: Vec::new(),
             whitespace: WhitespaceConfig::default(),
+            bufferline: BufferLine::default(),
             indent_guides: IndentGuidesConfig::default(),
             color_modes: false,
         }