scrollbar: Let the vertical scrollbar sit on the left side

crates/base/src/input/base/element.rs

@@ -16,7 +16,7 @@ use smallvec::SmallVec;
 use std::{ops::Range, rc::Rc};
 
 use crate::{
-    Scrollbar,
+    Scrollbar, ScrollbarPlacement,
     input::{RopeExt as _, blink_cursor::CURSOR_WIDTH, display_map::LineLayout},
 };
 
@@ -138,6 +138,7 @@ pub(super) struct EditorScrollbarSnapshot {
     layout: EditorScrollbarLayout,
     cursor_scroll_offset: Point<Pixels>,
     soft_wrap: bool,
+    placement: ScrollbarPlacement,
 }
 
 impl EditorScrollbarSnapshot {
@@ -154,9 +155,11 @@ impl EditorScrollbarSnapshot {
                 last_layout.line_number_width,
                 scroll_size,
                 state.editor_paddings,
+                state.scrollbar_placement,
             ),
             cursor_scroll_offset,
             soft_wrap: state.soft_wrap,
+            placement: state.scrollbar_placement,
         }
     }
 }
@@ -167,8 +170,11 @@ impl EditorScrollbarLayout {
         line_number_width: Pixels,
         scroll_size: Size<Pixels>,
         paddings: Edges<Pixels>,
+        placement: ScrollbarPlacement,
     ) -> Self {
-        let left = if line_number_width == px(0.) {
+        let left = if placement.is_left() {
+            -paddings.left
+        } else if line_number_width == px(0.) {
             px(0.)
         } else {
             paddings.left + line_number_width - LINE_NUMBER_RIGHT_MARGIN
@@ -262,6 +268,7 @@ impl<M: InputModeKind> Element for EditorScrollbar<M> {
         } else {
             Scrollbar::vertical(&scroll_handle)
         }
+        .placement(snapshot.placement)
         .viewport_bounds(snapshot.layout.bounds)
         .scroll_size(snapshot.layout.scroll_size)
         .into_any_element();
@@ -4811,17 +4818,27 @@ mod tests {
             left: px(7.),
         };
 
-        let layout =
-            EditorScrollbarLayout::new(input_bounds, px(40.), size(px(1000.), px(200.)), paddings);
+        let layout = EditorScrollbarLayout::new(
+            input_bounds,
+            px(40.),
+            size(px(1000.), px(200.)),
+            paddings,
+            ScrollbarPlacement::BottomRight,
+        );
 
         assert_eq!(
             layout.bounds,
             Bounds::new(point(px(51.), px(18.)), size(px(262.), px(87.)))
         );
         assert_eq!(layout.scroll_size, size(px(972.), px(200.)));
 
-        let layout_without_gutter =
-            EditorScrollbarLayout::new(input_bounds, px(0.), size(px(500.), px(120.)), paddings);
+        let layout_without_gutter = EditorScrollbarLayout::new(
+            input_bounds,
+            px(0.),
+            size(px(500.), px(120.)),
+            paddings,
+            ScrollbarPlacement::BottomRight,
+        );
 
         assert_eq!(
             layout_without_gutter.bounds,
@@ -4830,6 +4847,41 @@ mod tests {
         assert_eq!(layout_without_gutter.scroll_size, size(px(513.), px(120.)));
     }
 
+    #[test]
+    fn test_editor_scrollbar_layout_on_the_left_covers_the_gutter() {
+        let input_bounds = Bounds::new(point(px(10.), px(20.)), size(px(300.), px(80.)));
+        let paddings = Edges {
+            top: px(2.),
+            right: px(3.),
+            bottom: px(5.),
+            left: px(7.),
+        };
+
+        let layout = EditorScrollbarLayout::new(
+            input_bounds,
+            px(40.),
+            size(px(1000.), px(200.)),
+            paddings,
+            ScrollbarPlacement::BottomLeft,
+        );
+
+        assert_eq!(
+            layout.bounds,
+            Bounds::new(point(px(3.), px(18.)), size(px(310.), px(87.)))
+        );
+        assert_eq!(layout.scroll_size, size(px(1020.), px(200.)));
+        assert_eq!(
+            EditorScrollbarLayout::new(
+                input_bounds,
+                px(40.),
+                size(px(1000.), px(200.)),
+                paddings,
+                ScrollbarPlacement::TopLeft,
+            ),
+            layout
+        );
+    }
+
     #[test]
     fn test_editor_gutter_covers_the_complete_fixed_column() {
         let input_bounds = Bounds::new(point(px(10.), px(20.)), size(px(300.), px(80.)));

crates/base/src/input/base/state.rs

@@ -34,6 +34,7 @@ use super::{
     mode::LayoutMode,
     undo_manager::{EditIntent, UndoManager},
 };
+use crate::ScrollbarPlacement;
 use crate::actions::{SelectDown, SelectLeft, SelectRight, SelectUp};
 use crate::input::blink_cursor::CURSOR_WIDTH;
 use crate::input::movement::MoveDirection;
@@ -430,6 +431,7 @@ pub struct InputBaseState<M: InputModeKind> {
     /// The size of the scrollable content.
     pub(crate) scroll_size: gpui::Size<Pixels>,
     pub(super) editor_scrollbar_snapshot: Cell<Option<EditorScrollbarSnapshot>>,
+    pub(super) scrollbar_placement: ScrollbarPlacement,
     /// The unwrapped width of the longest line and what it was measured for.
     pub(super) longest_line_width: Cell<Option<(LongestLineKey, Pixels)>>,
     pub(super) editor_paddings: Edges<Pixels>,
@@ -765,6 +767,7 @@ impl<M: InputModeKind> InputBaseState<M> {
             scroll_handle: ScrollHandle::new(),
             scroll_size: gpui::size(px(0.), px(0.)),
             editor_scrollbar_snapshot: Cell::new(None),
+            scrollbar_placement: ScrollbarPlacement::default(),
             longest_line_width: Cell::new(None),
             editor_paddings: Edges::default(),
             deferred_scroll_offset: None,
@@ -10667,6 +10670,26 @@ impl<M: crate::input::MultiLineMode> InputBaseState<M> {
         cx.notify();
     }
 
+    /// The placement of the scrollbars, default is [`ScrollbarPlacement::BottomRight`].
+    ///
+    /// On the left, the vertical scrollbar sits on the input's left edge, over
+    /// the line numbers. At the top, the horizontal scrollbar overlays the
+    /// first line, as at the bottom it overlays the last.
+    pub fn scrollbar_placement(mut self, placement: ScrollbarPlacement) -> Self {
+        self.scrollbar_placement = placement;
+        self
+    }
+
+    /// See [`InputBaseState::scrollbar_placement`].
+    pub fn set_scrollbar_placement(
+        &mut self,
+        placement: ScrollbarPlacement,
+        cx: &mut Context<Self>,
+    ) {
+        self.scrollbar_placement = placement;
+        cx.notify();
+    }
+
     /// Set the soft wrap mode, default is true.
     #[doc(hidden)]
     pub fn soft_wrap(mut self, wrap: bool) -> Self {

crates/base/src/lib.rs

@@ -161,7 +161,7 @@ pub use scroll_bounce::{ScrollBounce, ScrollBounceMotion};
 pub use scrollable_mask::ScrollableMask;
 pub use scrollbar::{
     Scrollbar, ScrollbarAxis, ScrollbarEntrance, ScrollbarHandle, ScrollbarMode, ScrollbarMotion,
-    ScrollbarStyles, ScrollbarThumbStyle, ScrollbarTrackStyle,
+    ScrollbarPlacement, ScrollbarStyles, ScrollbarThumbStyle, ScrollbarTrackStyle,
 };
 pub use select::Select;
 pub use selectable_text::SelectableText;