Show file preview in split pane in fuzzy finder (#534)

* Add preview pane for fuzzy finder

* Fix picker preview lag by caching

* Add picker preview for document symbols

* Cache picker preview per document instead of view

* Use line instead of range for preview doc

* Add picker preview for buffer picker

* Fix render bug and refactor picker

* Refactor picker preview rendering

* Split picker and preview and compose

The current selected item is cloned on every event, which is
undesirable

* Refactor out clones in previewed picker

* Retrieve doc from editor if possible in filepicker

* Disable syntax highlight for picker preview

Files already loaded in memory have syntax highlighting enabled

* Ignore directory symlinks in file picker

* Cleanup unnecessary pubs and derives

* Remove unnecessary highlight from file picker

* Reorganize buffer rendering

* Use normal picker for code actions

* Remove unnecessary generics and trait impls

* Remove prepare_for_render and make render mutable

* Skip picker preview if screen small, less padding

12 files changed, 464 insertions, 234 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 2b1b859b..0d118dbc 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -27,7 +27,7 @@ use movement::Movement;
 
 use crate::{
     compositor::{self, Component, Compositor},
-    ui::{self, Picker, Popup, Prompt, PromptEvent},
+    ui::{self, FilePicker, Picker, Popup, Prompt, PromptEvent},
 };
 
 use crate::job::{self, Job, Jobs};
@@ -2212,7 +2212,7 @@ fn file_picker(cx: &mut Context) {
 fn buffer_picker(cx: &mut Context) {
     let current = view!(cx.editor).doc;
 
-    let picker = Picker::new(
+    let picker = FilePicker::new(
         cx.editor
             .documents
             .iter()
@@ -2234,6 +2234,15 @@ fn buffer_picker(cx: &mut Context) {
         |editor: &mut Editor, (id, _path): &(DocumentId, Option<PathBuf>), _action| {
             editor.switch(*id, Action::Replace);
         },
+        |editor, (id, path)| {
+            let doc = &editor.documents.get(*id)?;
+            let &view_id = doc.selections().keys().next()?;
+            let line = doc
+                .selection(view_id)
+                .primary()
+                .cursor_line(doc.text().slice(..));
+            Some((path.clone()?, Some(line)))
+        },
     );
     cx.push_layer(Box::new(picker));
 }
@@ -2287,7 +2296,7 @@ fn symbol_picker(cx: &mut Context) {
                     }
                 };
 
-                let picker = Picker::new(
+                let picker = FilePicker::new(
                     symbols,
                     |symbol| (&symbol.name).into(),
                     move |editor: &mut Editor, symbol, _action| {
@@ -2297,10 +2306,15 @@ fn symbol_picker(cx: &mut Context) {
                         if let Some(range) =
                             lsp_range_to_range(doc.text(), symbol.location.range, offset_encoding)
                         {
-                            doc.set_selection(view.id, Selection::single(range.to(), range.from()));
+                            doc.set_selection(view.id, Selection::single(range.anchor, range.head));
                             align_view(doc, view, Align::Center);
                         }
                     },
+                    move |_editor, symbol| {
+                        let path = symbol.location.uri.to_file_path().unwrap();
+                        let line = Some(symbol.location.range.start.line as usize);
+                        Some((path, line))
+                    },
                 );
                 compositor.push(Box::new(picker))
             }
@@ -2332,6 +2346,7 @@ pub fn code_action(cx: &mut Context) {
               response: Option<lsp::CodeActionResponse>| {
             if let Some(actions) = response {
                 let picker = Picker::new(
+                    true,
                     actions,
                     |action| match action {
                         lsp::CodeActionOrCommand::CodeAction(action) => {
@@ -2703,7 +2718,7 @@ fn goto_impl(
             editor.set_error("No definition found.".to_string());
         }
         _locations => {
-            let picker = ui::Picker::new(
+            let picker = FilePicker::new(
                 locations,
                 move |location| {
                     let file: Cow<'_, str> = (location.uri.scheme() == "file")
@@ -2728,6 +2743,11 @@ fn goto_impl(
                 move |editor: &mut Editor, location, action| {
                     jump_to(editor, location, offset_encoding, action)
                 },
+                |_editor, location| {
+                    let path = location.uri.to_file_path().unwrap();
+                    let line = Some(location.range.start.line as usize);
+                    Some((path, line))
+                },
             );
             compositor.push(Box::new(picker));
         }
@@ -3729,8 +3749,7 @@ fn keep_primary_selection(cx: &mut Context) {
     let (view, doc) = current!(cx.editor);
 
     let range = doc.selection(view.id).primary();
-    let selection = Selection::single(range.anchor, range.head);
-    doc.set_selection(view.id, selection);
+    doc.set_selection(view.id, Selection::single(range.anchor, range.head));
 }
 
 fn completion(cx: &mut Context) {
diff --git a/helix-term/src/compositor.rs b/helix-term/src/compositor.rs
index 628c4e13..36e54ede 100644
--- a/helix-term/src/compositor.rs
+++ b/helix-term/src/compositor.rs
@@ -46,7 +46,7 @@ pub trait Component: Any + AnyComponent {
     }
 
     /// Render the component onto the provided surface.
-    fn render(&self, area: Rect, frame: &mut Surface, ctx: &mut Context);
+    fn render(&mut self, area: Rect, frame: &mut Surface, ctx: &mut Context);
 
     /// Get cursor position and cursor kind.
     fn cursor(&self, _area: Rect, _ctx: &Editor) -> (Option<Position>, CursorKind) {
@@ -152,8 +152,8 @@ impl Compositor {
 
         let area = *surface.area();
 
-        for layer in &self.layers {
-            layer.render(area, surface, cx)
+        for layer in &mut self.layers {
+            layer.render(area, surface, cx);
         }
 
         let (pos, kind) = self.cursor(area, cx.editor);
diff --git a/helix-term/src/ui/completion.rs b/helix-term/src/ui/completion.rs
index 6d737652..4e01ce1c 100644
--- a/helix-term/src/ui/completion.rs
+++ b/helix-term/src/ui/completion.rs
@@ -241,7 +241,7 @@ impl Component for Completion {
         self.popup.required_size(viewport)
     }
 
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         self.popup.render(area, surface, cx);
 
         // if we have a selection, render a markdown popup on top/below with info
@@ -263,7 +263,7 @@ impl Component for Completion {
             let cursor_pos = (helix_core::coords_at_pos(doc.text().slice(..), cursor_pos).row
                 - view.first_line) as u16;
 
-            let doc = match &option.documentation {
+            let mut doc = match &option.documentation {
                 Some(lsp::Documentation::String(contents))
                 | Some(lsp::Documentation::MarkupContent(lsp::MarkupContent {
                     kind: lsp::MarkupKind::PlainText,
diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 96a4afe8..8c46eef9 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -34,7 +34,7 @@ pub struct EditorView {
     last_insert: (commands::Command, Vec<KeyEvent>),
     completion: Option<Completion>,
     spinners: ProgressSpinners,
-    pub autoinfo: Option<Info>,
+    autoinfo: Option<Info>,
 }
 
 pub const GUTTER_OFFSET: u16 = 7; // 1 diagnostic + 5 linenr + 1 gutter
@@ -78,8 +78,26 @@ impl EditorView {
             view.area.width - GUTTER_OFFSET,
             view.area.height.saturating_sub(1),
         ); // - 1 for statusline
+        let offset = Position::new(view.first_line, view.first_col);
+        let height = view.area.height.saturating_sub(1); // - 1 for statusline
 
-        self.render_buffer(doc, view, area, surface, theme, is_focused, loader);
+        let highlights = Self::doc_syntax_highlights(doc, offset, height, theme, loader);
+        let highlights = syntax::merge(highlights, Self::doc_diagnostics_highlights(doc, theme));
+        let highlights: Box<dyn Iterator<Item = HighlightEvent>> = if is_focused {
+            Box::new(syntax::merge(
+                highlights,
+                Self::doc_selection_highlights(doc, view, theme),
+            ))
+        } else {
+            Box::new(highlights)
+        };
+
+        Self::render_text_highlights(doc, offset, area, surface, theme, highlights);
+        Self::render_gutter(doc, view, area, surface, theme);
+
+        if is_focused {
+            Self::render_focused_view_elements(view, doc, area, theme, surface);
+        }
 
         // if we're not at the edge of the screen, draw a right border
         if viewport.right() != view.area.right() {
@@ -94,7 +112,7 @@ impl EditorView {
             }
         }
 
-        self.render_diagnostics(doc, view, area, surface, theme, is_focused);
+        self.render_diagnostics(doc, view, area, surface, theme);
 
         let area = Rect::new(
             view.area.x,
@@ -105,31 +123,34 @@ impl EditorView {
         self.render_statusline(doc, view, area, surface, theme, is_focused);
     }
 
+    /// Get syntax highlights for a document in a view represented by the first line
+    /// and column (`offset`) and the last line. This is done instead of using a view
+    /// directly to enable rendering syntax highlighted docs anywhere (eg. picker preview)
     #[allow(clippy::too_many_arguments)]
-    pub fn render_buffer(
-        &self,
-        doc: &Document,
-        view: &View,
-        viewport: Rect,
-        surface: &mut Surface,
+    pub fn doc_syntax_highlights<'doc>(
+        doc: &'doc Document,
+        offset: Position,
+        height: u16,
         theme: &Theme,
-        is_focused: bool,
         loader: &syntax::Loader,
-    ) {
+    ) -> Box<dyn Iterator<Item = HighlightEvent> + 'doc> {
         let text = doc.text().slice(..);
-
-        let last_line = view.last_line(doc);
+        let last_line = std::cmp::min(
+            // Saturating subs to make it inclusive zero indexing.
+            (offset.row + height as usize).saturating_sub(1),
+            doc.text().len_lines().saturating_sub(1),
+        );
 
         let range = {
             // calculate viewport byte ranges
-            let start = text.line_to_byte(view.first_line);
+            let start = text.line_to_byte(offset.row);
             let end = text.line_to_byte(last_line + 1);
 
             start..end
         };
 
         // TODO: range doesn't actually restrict source, just highlight range
-        let highlights: Vec<_> = match doc.syntax() {
+        let highlights = match doc.syntax() {
             Some(syntax) => {
                 let scopes = theme.scopes();
                 syntax
@@ -151,20 +172,16 @@ impl EditorView {
                                     Some(config_ref)
                                 })
                     })
+                    .map(|event| event.unwrap())
                     .collect() // TODO: we collect here to avoid holding the lock, fix later
             }
-            None => vec![Ok(HighlightEvent::Source {
+            None => vec![HighlightEvent::Source {
                 start: range.start,
                 end: range.end,
-            })],
-        };
-        let mut spans = Vec::new();
-        let mut visual_x = 0u16;
-        let mut line = 0u16;
-        let tab_width = doc.tab_width();
-        let tab = " ".repeat(tab_width);
-
-        let highlights = highlights.into_iter().map(|event| match event.unwrap() {
+            }],
+        }
+        .into_iter()
+        .map(move |event| match event {
             // convert byte offsets to char offset
             HighlightEvent::Source { start, end } => {
                 let start = ensure_grapheme_boundary_next(text, text.byte_to_char(start));
@@ -174,13 +191,44 @@ impl EditorView {
             event => event,
         });
 
-        let selections = doc.selection(view.id);
-        let primary_idx = selections.primary_index();
+        Box::new(highlights)
+    }
+
+    /// Get highlight spans for document diagnostics
+    pub fn doc_diagnostics_highlights(
+        doc: &Document,
+        theme: &Theme,
+    ) -> Vec<(usize, std::ops::Range<usize>)> {
+        let diagnostic_scope = theme
+            .find_scope_index("diagnostic")
+            .or_else(|| theme.find_scope_index("ui.cursor"))
+            .or_else(|| theme.find_scope_index("ui.selection"))
+            .expect("no selection scope found!");
+
+        doc.diagnostics()
+            .iter()
+            .map(|diagnostic| {
+                (
+                    diagnostic_scope,
+                    diagnostic.range.start..diagnostic.range.end,
+                )
+            })
+            .collect()
+    }
+
+    /// Get highlight spans for selections in a document view.
+    pub fn doc_selection_highlights(
+        doc: &Document,
+        view: &View,
+        theme: &Theme,
+    ) -> Vec<(usize, std::ops::Range<usize>)> {
+        let text = doc.text().slice(..);
+        let selection = doc.selection(view.id);
+        let primary_idx = selection.primary_index();
 
         let selection_scope = theme
             .find_scope_index("ui.selection")
             .expect("no selection scope found!");
-
         let base_cursor_scope = theme
             .find_scope_index("ui.cursor")
             .unwrap_or(selection_scope);
@@ -192,64 +240,59 @@ impl EditorView {
         }
         .unwrap_or(base_cursor_scope);
 
-        let highlights: Box<dyn Iterator<Item = HighlightEvent>> = if is_focused {
-            // TODO: primary + insert mode patching:
-            // (ui.cursor.primary).patch(mode).unwrap_or(cursor)
-            let primary_cursor_scope = theme
-                .find_scope_index("ui.cursor.primary")
-                .unwrap_or(cursor_scope);
-            let primary_selection_scope = theme
-                .find_scope_index("ui.selection.primary")
-                .unwrap_or(selection_scope);
-
-            // inject selections as highlight scopes
-            let mut spans: Vec<(usize, std::ops::Range<usize>)> = Vec::new();
-            for (i, range) in selections.iter().enumerate() {
-                let (cursor_scope, selection_scope) = if i == primary_idx {
-                    (primary_cursor_scope, primary_selection_scope)
-                } else {
-                    (cursor_scope, selection_scope)
-                };
+        let primary_cursor_scope = theme
+            .find_scope_index("ui.cursor.primary")
+            .unwrap_or(cursor_scope);
+        let primary_selection_scope = theme
+            .find_scope_index("ui.selection.primary")
+            .unwrap_or(selection_scope);
 
-                // Special-case: cursor at end of the rope.
-                if range.head == range.anchor && range.head == text.len_chars() {
-                    spans.push((cursor_scope, range.head..range.head + 1));
-                    continue;
-                }
+        let mut spans: Vec<(usize, std::ops::Range<usize>)> = Vec::new();
+        for (i, range) in selection.iter().enumerate() {
+            let (cursor_scope, selection_scope) = if i == primary_idx {
+                (primary_cursor_scope, primary_selection_scope)
+            } else {
+                (cursor_scope, selection_scope)
+            };
 
-                let range = range.min_width_1(text);
-                if range.head > range.anchor {
-                    // Standard case.
-                    let cursor_start = prev_grapheme_boundary(text, range.head);
-                    spans.push((selection_scope, range.anchor..cursor_start));
-                    spans.push((cursor_scope, cursor_start..range.head));
-                } else {
-                    // Reverse case.
-                    let cursor_end = next_grapheme_boundary(text, range.head);
-                    spans.push((cursor_scope, range.head..cursor_end));
-                    spans.push((selection_scope, cursor_end..range.anchor));
-                }
+            // Special-case: cursor at end of the rope.
+            if range.head == range.anchor && range.head == text.len_chars() {
+                spans.push((cursor_scope, range.head..range.head + 1));
+                continue;
             }
 
-            Box::new(syntax::merge(highlights, spans))
-        } else {
-            Box::new(highlights)
-        };
+            let range = range.min_width_1(text);
+            if range.head > range.anchor {
+                // Standard case.
+                let cursor_start = prev_grapheme_boundary(text, range.head);
+                spans.push((selection_scope, range.anchor..cursor_start));
+                spans.push((cursor_scope, cursor_start..range.head));
+            } else {
+                // Reverse case.
+                let cursor_end = next_grapheme_boundary(text, range.head);
+                spans.push((cursor_scope, range.head..cursor_end));
+                spans.push((selection_scope, cursor_end..range.anchor));
+            }
+        }
+
+        spans
+    }
+
+    pub fn render_text_highlights<H: Iterator<Item = HighlightEvent>>(
+        doc: &Document,
+        offset: Position,
+        viewport: Rect,
+        surface: &mut Surface,
+        theme: &Theme,
+        highlights: H,
+    ) {
+        let text = doc.text().slice(..);
 
-        // diagnostic injection
-        let diagnostic_scope = theme.find_scope_index("diagnostic").unwrap_or(cursor_scope);
-        let highlights = Box::new(syntax::merge(
-            highlights,
-            doc.diagnostics()
-                .iter()
-                .map(|diagnostic| {
-                    (
-                        diagnostic_scope,
-                        diagnostic.range.start..diagnostic.range.end,
-                    )
-                })
-                .collect(),
-        ));
+        let mut spans = Vec::new();
+        let mut visual_x = 0u16;
+        let mut line = 0u16;
+        let tab_width = doc.tab_width();
+        let tab = " ".repeat(tab_width);
 
         'outer: for event in highlights {
             match event {
@@ -273,14 +316,14 @@ impl EditorView {
                     });
 
                     for grapheme in RopeGraphemes::new(text) {
-                        let out_of_bounds = visual_x < view.first_col as u16
-                            || visual_x >= viewport.width + view.first_col as u16;
+                        let out_of_bounds = visual_x < offset.col as u16
+                            || visual_x >= viewport.width + offset.col as u16;
 
                         if LineEnding::from_rope_slice(&grapheme).is_some() {
                             if !out_of_bounds {
                                 // we still want to render an empty cell with the style
                                 surface.set_string(
-                                    viewport.x + visual_x - view.first_col as u16,
+                                    viewport.x + visual_x - offset.col as u16,
                                     viewport.y + line,
                                     " ",
                                     style,
@@ -310,7 +353,7 @@ impl EditorView {
                             if !out_of_bounds {
                                 // if we're offscreen just keep going until we hit a new line
                                 surface.set_string(
-                                    viewport.x + visual_x - view.first_col as u16,
+                                    viewport.x + visual_x - offset.col as u16,
                                     viewport.y + line,
                                     grapheme,
                                     style,
@@ -323,14 +366,108 @@ impl EditorView {
                 }
             }
         }
+    }
+
+    /// Render brace match, selected line numbers, etc (meant for the focused view only)
+    pub fn render_focused_view_elements(
+        view: &View,
+        doc: &Document,
+        viewport: Rect,
+        theme: &Theme,
+        surface: &mut Surface,
+    ) {
+        let text = doc.text().slice(..);
+        let selection = doc.selection(view.id);
+        let last_line = view.last_line(doc);
+        let screen = {
+            let start = text.line_to_char(view.first_line);
+            let end = text.line_to_char(last_line + 1) + 1; // +1 for cursor at end of text.
+            Range::new(start, end)
+        };
+
+        // render selected linenr(s)
+        let linenr_select: Style = theme
+            .try_get("ui.linenr.selected")
+            .unwrap_or_else(|| theme.get("ui.linenr"));
+
+        // 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();
+
+        for selection in selection.iter().filter(|range| range.overlaps(&screen)) {
+            let head = view.screen_coords_at_pos(
+                doc,
+                text,
+                if selection.head > selection.anchor {
+                    selection.head - 1
+                } else {
+                    selection.head
+                },
+            );
+            if let Some(head) = head {
+                // Highlight line number for selected lines.
+                let line_number = view.first_line + head.row;
+                let line_number_text = if line_number == last_line && !draw_last {
+                    "    ~".into()
+                } else {
+                    format!("{:>5}", line_number + 1)
+                };
+                surface.set_stringn(
+                    viewport.x - GUTTER_OFFSET + 1,
+                    viewport.y + head.row as u16,
+                    line_number_text,
+                    5,
+                    linenr_select,
+                );
+
+                // Highlight matching braces
+                // TODO: set cursor position for IME
+                if let Some(syntax) = doc.syntax() {
+                    use helix_core::match_brackets;
+                    let pos = doc
+                        .selection(view.id)
+                        .primary()
+                        .cursor(doc.text().slice(..));
+                    let pos = match_brackets::find(syntax, doc.text(), pos)
+                        .and_then(|pos| view.screen_coords_at_pos(doc, text, pos));
+
+                    if let Some(pos) = pos {
+                        // ensure col is on screen
+                        if (pos.col as u16) < viewport.width + view.first_col as u16
+                            && pos.col >= view.first_col
+                        {
+                            let style = theme.try_get("ui.cursor.match").unwrap_or_else(|| {
+                                Style::default()
+                                    .add_modifier(Modifier::REVERSED)
+                                    .add_modifier(Modifier::DIM)
+                            });
+
+                            surface
+                                .get_mut(viewport.x + pos.col as u16, viewport.y + pos.row as u16)
+                                .set_style(style);
+                        }
+                    }
+                }
+            }
+        }
+    }
 
-        // render gutters
+    #[allow(clippy::too_many_arguments)]
+    pub fn render_gutter(
+        doc: &Document,
+        view: &View,
+        viewport: Rect,
+        surface: &mut Surface,
+        theme: &Theme,
+    ) {
+        let text = doc.text().slice(..);
+        let last_line = view.last_line(doc);
 
-        let linenr: Style = theme.get("ui.linenr");
-        let warning: Style = theme.get("warning");
-        let error: Style = theme.get("error");
-        let info: Style = theme.get("info");
-        let hint: Style = theme.get("hint");
+        let linenr = theme.get("ui.linenr");
+        let warning = theme.get("warning");
+        let error = theme.get("error");
+        let info = theme.get("info");
+        let hint = theme.get("hint");
 
         // 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.
@@ -368,80 +505,6 @@ impl EditorView {
                 linenr,
             );
         }
-
-        // render selections and selected linenr(s)
-        let linenr_select: Style = theme
-            .try_get("ui.linenr.selected")
-            .unwrap_or_else(|| theme.get("ui.linenr"));
-
-        if is_focused {
-            let screen = {
-                let start = text.line_to_char(view.first_line);
-                let end = text.line_to_char(last_line + 1) + 1; // +1 for cursor at end of text.
-                Range::new(start, end)
-            };
-
-            let selection = doc.selection(view.id);
-
-            for selection in selection.iter().filter(|range| range.overlaps(&screen)) {
-                let head = view.screen_coords_at_pos(
-                    doc,
-                    text,
-                    if selection.head > selection.anchor {
-                        selection.head - 1
-                    } else {
-                        selection.head
-                    },
-                );
-                if let Some(head) = head {
-                    // Draw line number for selected lines.
-                    let line_number = view.first_line + head.row;
-                    let line_number_text = if line_number == last_line && !draw_last {
-                        "    ~".into()
-                    } else {
-                        format!("{:>5}", line_number + 1)
-                    };
-                    surface.set_stringn(
-                        viewport.x + 1 - GUTTER_OFFSET,
-                        viewport.y + head.row as u16,
-                        line_number_text,
-                        5,
-                        linenr_select,
-                    );
-
-                    // TODO: set cursor position for IME
-                    if let Some(syntax) = doc.syntax() {
-                        use helix_core::match_brackets;
-                        let pos = doc
-                            .selection(view.id)
-                            .primary()
-                            .cursor(doc.text().slice(..));
-                        let pos = match_brackets::find(syntax, doc.text(), pos)
-                            .and_then(|pos| view.screen_coords_at_pos(doc, text, pos));
-
-                        if let Some(pos) = pos {
-                            // ensure col is on screen
-                            if (pos.col as u16) < viewport.width + view.first_col as u16
-                                && pos.col >= view.first_col
-                            {
-                                let style = theme.try_get("ui.cursor.match").unwrap_or_else(|| {
-                                    Style::default()
-                                        .add_modifier(Modifier::REVERSED)
-                                        .add_modifier(Modifier::DIM)
-                                });
-
-                                surface
-                                    .get_mut(
-                                        viewport.x + pos.col as u16,
-                                        viewport.y + pos.row as u16,
-                                    )
-                                    .set_style(style);
-                            }
-                        }
-                    }
-                }
-            }
-        }
     }
 
     pub fn render_diagnostics(
@@ -451,7 +514,6 @@ impl EditorView {
         viewport: Rect,
         surface: &mut Surface,
         theme: &Theme,
-        _is_focused: bool,
     ) {
         use helix_core::diagnostic::Severity;
         use tui::{
@@ -469,10 +531,10 @@ impl EditorView {
             diagnostic.range.start <= cursor && diagnostic.range.end >= cursor
         });
 
-        let warning: Style = theme.get("warning");
-        let error: Style = theme.get("error");
-        let info: Style = theme.get("info");
-        let hint: Style = theme.get("hint");
+        let warning = theme.get("warning");
+        let error = theme.get("error");
+        let info = theme.get("info");
+        let hint = theme.get("hint");
 
         // Vec::with_capacity(diagnostics.len()); // rough estimate
         let mut lines = Vec::new();
@@ -961,7 +1023,7 @@ impl Component for EditorView {
         }
     }
 
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+    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"));
 
@@ -983,7 +1045,7 @@ impl Component for EditorView {
             );
         }
 
-        if let Some(ref info) = self.autoinfo {
+        if let Some(ref mut info) = self.autoinfo {
             info.render(area, surface, cx);
         }
 
@@ -1030,7 +1092,7 @@ impl Component for EditorView {
             );
         }
 
-        if let Some(completion) = &self.completion {
+        if let Some(completion) = self.completion.as_mut() {
             completion.render(area, surface, cx);
         }
     }
diff --git a/helix-term/src/ui/info.rs b/helix-term/src/ui/info.rs
index 6e810b86..0f14260e 100644
--- a/helix-term/src/ui/info.rs
+++ b/helix-term/src/ui/info.rs
@@ -5,7 +5,7 @@ use tui::buffer::Buffer as Surface;
 use tui::widgets::{Block, Borders, Widget};
 
 impl Component for Info {
-    fn render(&self, viewport: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, viewport: Rect, surface: &mut Surface, cx: &mut Context) {
         let style = cx.editor.theme.get("ui.popup");
 
         // Calculate the area of the terminal to modify. Because we want to
diff --git a/helix-term/src/ui/markdown.rs b/helix-term/src/ui/markdown.rs
index 6c79ca67..b7e29f21 100644
--- a/helix-term/src/ui/markdown.rs
+++ b/helix-term/src/ui/markdown.rs
@@ -198,7 +198,7 @@ fn parse<'a>(
     Text::from(lines)
 }
 impl Component for Markdown {
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         use tui::widgets::{Paragraph, Widget, Wrap};
 
         let text = parse(&self.contents, Some(&cx.editor.theme), &self.config_loader);
diff --git a/helix-term/src/ui/menu.rs b/helix-term/src/ui/menu.rs
index 26eff1d8..3e63db35 100644
--- a/helix-term/src/ui/menu.rs
+++ b/helix-term/src/ui/menu.rs
@@ -258,7 +258,7 @@ impl<T: Item + 'static> Component for Menu<T> {
 
     // TODO: required size should re-trigger when we filter items so we can draw a smaller menu
 
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         let style = cx.editor.theme.get("ui.text");
         let selected = cx.editor.theme.get("ui.menu.selected");
 
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index f68ad0a7..d1af0e48 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -13,7 +13,7 @@ pub use completion::Completion;
 pub use editor::EditorView;
 pub use markdown::Markdown;
 pub use menu::Menu;
-pub use picker::Picker;
+pub use picker::{FilePicker, Picker};
 pub use popup::Popup;
 pub use prompt::{Prompt, PromptEvent};
 pub use spinner::{ProgressSpinners, Spinner};
@@ -73,29 +73,26 @@ pub fn regex_prompt(
     )
 }
 
-pub fn file_picker(root: PathBuf) -> Picker<PathBuf> {
+pub fn file_picker(root: PathBuf) -> FilePicker<PathBuf> {
     use ignore::Walk;
     use std::time;
-    let files = Walk::new(root.clone()).filter_map(|entry| match entry {
-        Ok(entry) => {
-            // filter dirs, but we might need special handling for symlinks!
-            if !entry.file_type().map_or(false, |entry| entry.is_dir()) {
-                let time = if let Ok(metadata) = entry.metadata() {
-                    metadata
-                        .accessed()
-                        .or_else(|_| metadata.modified())
-                        .or_else(|_| metadata.created())
-                        .unwrap_or(time::UNIX_EPOCH)
-                } else {
-                    time::UNIX_EPOCH
-                };
-
-                Some((entry.into_path(), time))
-            } else {
-                None
-            }
+    let files = Walk::new(root.clone()).filter_map(|entry| {
+        let entry = entry.ok()?;
+        // Path::is_dir() traverses symlinks, so we use it over DirEntry::is_dir
+        if entry.path().is_dir() {
+            // Will give a false positive if metadata cannot be read (eg. permission error)
+            return None;
         }
-        Err(_err) => None,
+
+        let time = entry.metadata().map_or(time::UNIX_EPOCH, |metadata| {
+            metadata
+                .accessed()
+                .or_else(|_| metadata.modified())
+                .or_else(|_| metadata.created())
+                .unwrap_or(time::UNIX_EPOCH)
+        });
+
+        Some((entry.into_path(), time))
     });
 
     let mut files: Vec<_> = if root.join(".git").is_dir() {
@@ -109,7 +106,7 @@ pub fn file_picker(root: PathBuf) -> Picker<PathBuf> {
 
     let files = files.into_iter().map(|(path, _)| path).collect();
 
-    Picker::new(
+    FilePicker::new(
         files,
         move |path: &PathBuf| {
             // format_fn
@@ -124,6 +121,7 @@ pub fn file_picker(root: PathBuf) -> Picker<PathBuf> {
                 .open(path.into(), action)
                 .expect("editor.open failed");
         },
+        |_editor, path| Some((path.clone(), None)),
     )
 }
 
diff --git a/helix-term/src/ui/picker.rs b/helix-term/src/ui/picker.rs
index 0b67cd9c..9c6b328f 100644
--- a/helix-term/src/ui/picker.rs
+++ b/helix-term/src/ui/picker.rs
@@ -1,4 +1,7 @@
-use crate::compositor::{Component, Compositor, Context, EventResult};
+use crate::{
+    compositor::{Component, Compositor, Context, EventResult},
+    ui::EditorView,
+};
 use crossterm::event::{Event, KeyCode, KeyEvent, KeyModifiers};
 use tui::{
     buffer::Buffer as Surface,
@@ -7,17 +10,153 @@ use tui::{
 
 use fuzzy_matcher::skim::SkimMatcherV2 as Matcher;
 use fuzzy_matcher::FuzzyMatcher;
+use tui::widgets::Widget;
 
-use std::borrow::Cow;
+use std::{borrow::Cow, collections::HashMap, path::PathBuf};
 
 use crate::ui::{Prompt, PromptEvent};
 use helix_core::Position;
 use helix_view::{
+    document::canonicalize_path,
     editor::Action,
     graphics::{Color, CursorKind, Rect, Style},
-    Editor,
+    Document, Editor,
 };
 
+pub const MIN_SCREEN_WIDTH_FOR_PREVIEW: u16 = 80;
+
+/// File path and line number (used to align and highlight a line)
+type FileLocation = (PathBuf, Option<usize>);
+
+pub struct FilePicker<T> {
+    picker: Picker<T>,
+    /// Caches paths to documents
+    preview_cache: HashMap<PathBuf, Document>,
+    /// Given an item in the picker, return the file path and line number to display.
+    file_fn: Box<dyn Fn(&Editor, &T) -> Option<FileLocation>>,
+}
+
+impl<T> FilePicker<T> {
+    pub fn new(
+        options: Vec<T>,
+        format_fn: impl Fn(&T) -> Cow<str> + 'static,
+        callback_fn: impl Fn(&mut Editor, &T, Action) + 'static,
+        preview_fn: impl Fn(&Editor, &T) -> Option<FileLocation> + 'static,
+    ) -> Self {
+        Self {
+            picker: Picker::new(false, options, format_fn, callback_fn),
+            preview_cache: HashMap::new(),
+            file_fn: Box::new(preview_fn),
+        }
+    }
+
+    fn current_file(&self, editor: &Editor) -> Option<FileLocation> {
+        self.picker
+            .selection()
+            .and_then(|current| (self.file_fn)(editor, current))
+            .and_then(|(path, line)| canonicalize_path(&path).ok().zip(Some(line)))
+    }
+
+    fn calculate_preview(&mut self, editor: &Editor) {
+        if let Some((path, _line)) = self.current_file(editor) {
+            if !self.preview_cache.contains_key(&path) && editor.document_by_path(&path).is_none() {
+                // TODO: enable syntax highlighting; blocked by async rendering
+                let doc = Document::open(&path, None, Some(&editor.theme), None).unwrap();
+                self.preview_cache.insert(path, doc);
+            }
+        }
+    }
+}
+
+impl<T: 'static> Component for FilePicker<T> {
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+        // +---------+ +---------+
+        // |prompt   | |preview  |
+        // +---------+ |         |
+        // |picker   | |         |
+        // |         | |         |
+        // +---------+ +---------+
+        self.calculate_preview(cx.editor);
+        let render_preview = area.width > MIN_SCREEN_WIDTH_FOR_PREVIEW;
+        let area = inner_rect(area);
+        // -- Render the frame:
+        // clear area
+        let background = cx.editor.theme.get("ui.background");
+        surface.clear_with(area, background);
+
+        let picker_width = if render_preview {
+            area.width / 2
+        } else {
+            area.width
+        };
+
+        let picker_area = Rect::new(area.x, area.y, picker_width, area.height);
+        self.picker.render(picker_area, surface, cx);
+
+        if !render_preview {
+            return;
+        }
+
+        let preview_area = Rect::new(area.x + picker_width, area.y, area.width / 2, area.height);
+
+        // don't like this but the lifetime sucks
+        let block = Block::default().borders(Borders::ALL);
+
+        // calculate the inner area inside the box
+        let mut inner = block.inner(preview_area);
+        // 1 column gap on either side
+        inner.x += 1;
+        inner.width = inner.width.saturating_sub(2);
+
+        block.render(preview_area, surface);
+
+        if let Some((doc, line)) = self.current_file(cx.editor).and_then(|(path, line)| {
+            cx.editor
+                .document_by_path(&path)
+                .or_else(|| self.preview_cache.get(&path))
+                .zip(Some(line))
+        }) {
+            // align to middle
+            let first_line = line.unwrap_or(0).saturating_sub(inner.height as usize / 2);
+            let offset = Position::new(first_line, 0);
+
+            let highlights = EditorView::doc_syntax_highlights(
+                doc,
+                offset,
+                area.height,
+                &cx.editor.theme,
+                &cx.editor.syn_loader,
+            );
+            EditorView::render_text_highlights(
+                doc,
+                offset,
+                inner,
+                surface,
+                &cx.editor.theme,
+                highlights,
+            );
+
+            // highlight the line
+            if let Some(line) = line {
+                for x in inner.left()..inner.right() {
+                    surface
+                        .get_mut(x, inner.y + line.saturating_sub(first_line) as u16)
+                        .set_style(cx.editor.theme.get("ui.selection.primary"));
+                }
+            }
+        }
+    }
+
+    fn handle_event(&mut self, event: Event, ctx: &mut Context) -> EventResult {
+        // TODO: keybinds for scrolling preview
+        self.picker.handle_event(event, ctx)
+    }
+
+    fn cursor(&self, area: Rect, ctx: &Editor) -> (Option<Position>, CursorKind) {
+        self.picker.cursor(area, ctx)
+    }
+}
+
 pub struct Picker<T> {
     options: Vec<T>,
     // filter: String,
@@ -30,6 +169,8 @@ pub struct Picker<T> {
     cursor: usize,
     // pattern: String,
     prompt: Prompt,
+    /// Whether to render in the middle of the area
+    render_centered: bool,
 
     format_fn: Box<dyn Fn(&T) -> Cow<str>>,
     callback_fn: Box<dyn Fn(&mut Editor, &T, Action)>,
@@ -37,6 +178,7 @@ pub struct Picker<T> {
 
 impl<T> Picker<T> {
     pub fn new(
+        render_centered: bool,
         options: Vec<T>,
         format_fn: impl Fn(&T) -> Cow<str> + 'static,
         callback_fn: impl Fn(&mut Editor, &T, Action) + 'static,
@@ -57,6 +199,7 @@ impl<T> Picker<T> {
             filters: Vec::new(),
             cursor: 0,
             prompt,
+            render_centered,
             format_fn: Box::new(format_fn),
             callback_fn: Box::new(callback_fn),
         };
@@ -139,8 +282,8 @@ impl<T> Picker<T> {
 //  - score all the names in relation to input
 
 fn inner_rect(area: Rect) -> Rect {
-    let padding_vertical = area.height * 20 / 100;
-    let padding_horizontal = area.width * 20 / 100;
+    let padding_vertical = area.height * 10 / 100;
+    let padding_horizontal = area.width * 10 / 100;
 
     Rect::new(
         area.x + padding_horizontal,
@@ -174,7 +317,9 @@ impl<T: 'static> Component for Picker<T> {
             | KeyEvent {
                 code: KeyCode::Char('p'),
                 modifiers: KeyModifiers::CONTROL,
-            } => self.move_up(),
+            } => {
+                self.move_up();
+            }
             KeyEvent {
                 code: KeyCode::Down,
                 ..
@@ -185,7 +330,9 @@ impl<T: 'static> Component for Picker<T> {
             | KeyEvent {
                 code: KeyCode::Char('n'),
                 modifiers: KeyModifiers::CONTROL,
-            } => self.move_down(),
+            } => {
+                self.move_down();
+            }
             KeyEvent {
                 code: KeyCode::Esc, ..
             }
@@ -239,16 +386,18 @@ impl<T: 'static> Component for Picker<T> {
         EventResult::Consumed(None)
     }
 
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
-        let area = inner_rect(area);
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+        let area = if self.render_centered {
+            inner_rect(area)
+        } else {
+            area
+        };
 
         // -- Render the frame:
-
         // clear area
         let background = cx.editor.theme.get("ui.background");
         surface.clear_with(area, background);
 
-        use tui::widgets::Widget;
         // don't like this but the lifetime sucks
         let block = Block::default().borders(Borders::ALL);
 
@@ -263,21 +412,23 @@ impl<T: 'static> Component for Picker<T> {
         self.prompt.render(area, surface, cx);
 
         // -- Separator
-        let style = Style::default().fg(Color::Rgb(90, 89, 119));
-        let symbols = BorderType::line_symbols(BorderType::Plain);
+        let sep_style = Style::default().fg(Color::Rgb(90, 89, 119));
+        let borders = BorderType::line_symbols(BorderType::Plain);
         for x in inner.left()..inner.right() {
             surface
                 .get_mut(x, inner.y + 1)
-                .set_symbol(symbols.horizontal)
-                .set_style(style);
+                .set_symbol(borders.horizontal)
+                .set_style(sep_style);
         }
 
         // -- Render the contents:
+        // subtract the area of the prompt (-2) and current item marker " > " (-3)
+        let inner = Rect::new(inner.x + 3, inner.y + 2, inner.width - 3, inner.height - 2);
 
         let style = cx.editor.theme.get("ui.text");
         let selected = Style::default().fg(Color::Rgb(255, 255, 255));
 
-        let rows = inner.height - 2; // -1 for search bar
+        let rows = inner.height;
         let offset = self.cursor / (rows as usize) * (rows as usize);
 
         let files = self.matches.iter().skip(offset).map(|(index, _score)| {
@@ -286,14 +437,14 @@ impl<T: 'static> Component for Picker<T> {
 
         for (i, (_index, option)) in files.take(rows as usize).enumerate() {
             if i == (self.cursor - offset) {
-                surface.set_string(inner.x + 1, inner.y + 2 + i as u16, ">", selected);
+                surface.set_string(inner.x - 2, inner.y + i as u16, ">", selected);
             }
 
             surface.set_string_truncated(
-                inner.x + 3,
-                inner.y + 2 + i as u16,
+                inner.x,
+                inner.y + i as u16,
                 (self.format_fn)(option),
-                (inner.width as usize).saturating_sub(3), // account for the " > "
+                inner.width as usize,
                 if i == (self.cursor - offset) {
                     selected
                 } else {
diff --git a/helix-term/src/ui/popup.rs b/helix-term/src/ui/popup.rs
index 29ffb4ad..e31d4d7b 100644
--- a/helix-term/src/ui/popup.rs
+++ b/helix-term/src/ui/popup.rs
@@ -105,7 +105,7 @@ impl<T: Component> Component for Popup<T> {
         Some(self.size)
     }
 
-    fn render(&self, viewport: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, viewport: Rect, surface: &mut Surface, cx: &mut Context) {
         cx.scroll = Some(self.scroll);
 
         let position = self
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index 57daef3a..8ec3674e 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -352,7 +352,7 @@ impl Prompt {
         }
 
         if let Some(doc) = (self.doc_fn)(&self.line) {
-            let text = ui::Text::new(doc.to_string());
+            let mut text = ui::Text::new(doc.to_string());
 
             let viewport = area;
             let area = viewport.intersection(Rect::new(
@@ -546,7 +546,7 @@ impl Component for Prompt {
         EventResult::Consumed(None)
     }
 
-    fn render(&self, area: Rect, surface: &mut Surface, cx: &mut Context) {
+    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         self.render_prompt(area, surface, cx)
     }
 
diff --git a/helix-term/src/ui/text.rs b/helix-term/src/ui/text.rs
index 249cf89e..65a75a4a 100644
--- a/helix-term/src/ui/text.rs
+++ b/helix-term/src/ui/text.rs
@@ -13,7 +13,7 @@ impl Text {
     }
 }
 impl Component for Text {
-    fn render(&self, area: Rect, surface: &mut Surface, _cx: &mut Context) {
+    fn render(&mut self, area: Rect, surface: &mut Surface, _cx: &mut Context) {
         use tui::widgets::{Paragraph, Widget, Wrap};
         let contents = tui::text::Text::from(self.contents.clone());