Add scrolling functionality to markdown preview mode (#44585)

Closes #21324

Adds four new commands:
- `markdown::MoveUp`, `markdown::MoveDown` - these scroll up and down in
markdown preview mode, by no more than the height of a large headline.

- `markdown::MoveUpByItem`, and `markdown::MoveDownByItem` - these
scroll up and down by the height of the item at the top of the markdown
preview window. So headlines and large codeblocks, for instance, scroll
further than individual paragraph lines.

Also attempts to create sensible defaults:
`down` -> `markdown::ScrollDown`
`up` -> `markdown::ScrollUp`
`alt-down` -> `markdown::ScrollDownByItem`
`alt-up` -> `markdown::ScrollUpByItem`

And in Vim:

`ctrl-u` -> `markdown::ScrollPageUp`
`ctrl-d` -> `markdown::ScrollPageDown`
`ctrl-e` -> `markdown::ScrollDown`
`ctrl-y` -> `markdown::ScrollUp`


Release Notes:

- Added commands `markdown::ScrollUp`, `markdown::ScrollDown`,
`markdown::ScrollUpByItem`, and `markdown::ScrollDownByItem`
- Changed commands `markdown::MovePageUp` to `markdown::ScrollPageUp`
and `markdown::MovePageDown` to `markdown::ScrollPageDown`

Cargo.lock

@@ -18097,6 +18097,7 @@ dependencies = [
  "language",
  "log",
  "lsp",
+ "markdown_preview",
  "menu",
  "multi_buffer",
  "nvim-rs",

assets/keymaps/default-linux.json

@@ -1192,8 +1192,12 @@
   {
     "context": "MarkdownPreview",
     "bindings": {
-      "pageup": "markdown::MovePageUp",
-      "pagedown": "markdown::MovePageDown"
+      "pageup": "markdown::ScrollPageUp",
+      "pagedown": "markdown::ScrollPageDown",
+      "up": "markdown::ScrollUp",
+      "down": "markdown::ScrollDown",
+      "alt-up": "markdown::ScrollUpByItem",
+      "alt-down": "markdown::ScrollDownByItem"
     }
   },
   {

assets/keymaps/default-macos.json

@@ -1296,8 +1296,12 @@
   {
     "context": "MarkdownPreview",
     "bindings": {
-      "pageup": "markdown::MovePageUp",
-      "pagedown": "markdown::MovePageDown"
+      "pageup": "markdown::ScrollPageUp",
+      "pagedown": "markdown::ScrollPageDown",
+      "up": "markdown::ScrollUp",
+      "down": "markdown::ScrollDown",
+      "alt-up": "markdown::ScrollUpByItem",
+      "alt-down": "markdown::ScrollDownByItem"
     }
   },
   {

assets/keymaps/default-windows.json

@@ -1220,8 +1220,12 @@
     "context": "MarkdownPreview",
     "use_key_equivalents": true,
     "bindings": {
-      "pageup": "markdown::MovePageUp",
-      "pagedown": "markdown::MovePageDown"
+      "pageup": "markdown::ScrollPageUp",
+      "pagedown": "markdown::ScrollPageDown",
+      "up": "markdown::ScrollUp",
+      "down": "markdown::ScrollDown",
+      "alt-up": "markdown::ScrollUpByItem",
+      "alt-down": "markdown::ScrollDownByItem"
     }
   },
   {

assets/keymaps/vim.json

@@ -1046,5 +1046,14 @@
       "g g": "settings_editor::FocusFirstNavEntry",
       "shift-g": "settings_editor::FocusLastNavEntry"
     }
+  },
+  {
+    "context": "MarkdownPreview",
+    "bindings": {
+      "ctrl-u": "markdown::ScrollPageUp",
+      "ctrl-d": "markdown::ScrollPageDown",
+      "ctrl-y": "markdown::ScrollUp",
+      "ctrl-e": "markdown::ScrollDown"
+    }
   }
 ]

crates/markdown_preview/src/markdown_preview.rs

@@ -11,9 +11,19 @@ actions!(
     markdown,
     [
         /// Scrolls up by one page in the markdown preview.
-        MovePageUp,
+        #[action(deprecated_aliases = ["markdown::MovePageUp"])]
+        ScrollPageUp,
         /// Scrolls down by one page in the markdown preview.
-        MovePageDown,
+        #[action(deprecated_aliases = ["markdown::MovePageDown"])]
+        ScrollPageDown,
+        /// Scrolls up by approximately one visual line.
+        ScrollUp,
+        /// Scrolls down by approximately one visual line.
+        ScrollDown,
+        /// Scrolls up by one markdown element in the markdown preview
+        ScrollUpByItem,
+        /// Scrolls down by one markdown element in the markdown preview
+        ScrollDownByItem,
         /// Opens a markdown preview for the current file.
         OpenPreview,
         /// Opens a markdown preview in a split pane.

crates/markdown_preview/src/markdown_preview_view.rs

@@ -1,3 +1,4 @@
+use std::cmp::min;
 use std::sync::Arc;
 use std::time::Duration;
 use std::{ops::Range, path::PathBuf};
@@ -20,11 +21,12 @@ use workspace::{Pane, Workspace};
 use crate::markdown_elements::ParsedMarkdownElement;
 use crate::markdown_renderer::CheckboxClickedEvent;
 use crate::{
-    MovePageDown, MovePageUp, OpenFollowingPreview, OpenPreview, OpenPreviewToTheSide,
+    OpenFollowingPreview, OpenPreview, OpenPreviewToTheSide, ScrollPageDown, ScrollPageUp,
     markdown_elements::ParsedMarkdown,
     markdown_parser::parse_markdown,
     markdown_renderer::{RenderContext, render_markdown_block},
 };
+use crate::{ScrollDown, ScrollDownByItem, ScrollUp, ScrollUpByItem};
 
 const REPARSE_DEBOUNCE: Duration = Duration::from_millis(200);
 
@@ -425,7 +427,7 @@ impl MarkdownPreviewView {
         !(current_block.is_list_item() && next_block.map(|b| b.is_list_item()).unwrap_or(false))
     }
 
-    fn scroll_page_up(&mut self, _: &MovePageUp, _window: &mut Window, cx: &mut Context<Self>) {
+    fn scroll_page_up(&mut self, _: &ScrollPageUp, _window: &mut Window, cx: &mut Context<Self>) {
         let viewport_height = self.list_state.viewport_bounds().size.height;
         if viewport_height.is_zero() {
             return;
@@ -435,7 +437,12 @@ impl MarkdownPreviewView {
         cx.notify();
     }
 
-    fn scroll_page_down(&mut self, _: &MovePageDown, _window: &mut Window, cx: &mut Context<Self>) {
+    fn scroll_page_down(
+        &mut self,
+        _: &ScrollPageDown,
+        _window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
         let viewport_height = self.list_state.viewport_bounds().size.height;
         if viewport_height.is_zero() {
             return;
@@ -444,6 +451,56 @@ impl MarkdownPreviewView {
         self.list_state.scroll_by(viewport_height);
         cx.notify();
     }
+
+    fn scroll_up(&mut self, _: &ScrollUp, window: &mut Window, cx: &mut Context<Self>) {
+        let scroll_top = self.list_state.logical_scroll_top();
+        if let Some(bounds) = self.list_state.bounds_for_item(scroll_top.item_ix) {
+            let item_height = bounds.size.height;
+            // Scroll no more than the rough equivalent of a large headline
+            let max_height = window.rem_size() * 2;
+            let scroll_height = min(item_height, max_height);
+            self.list_state.scroll_by(-scroll_height);
+        }
+        cx.notify();
+    }
+
+    fn scroll_down(&mut self, _: &ScrollDown, window: &mut Window, cx: &mut Context<Self>) {
+        let scroll_top = self.list_state.logical_scroll_top();
+        if let Some(bounds) = self.list_state.bounds_for_item(scroll_top.item_ix) {
+            let item_height = bounds.size.height;
+            // Scroll no more than the rough equivalent of a large headline
+            let max_height = window.rem_size() * 2;
+            let scroll_height = min(item_height, max_height);
+            self.list_state.scroll_by(scroll_height);
+        }
+        cx.notify();
+    }
+
+    fn scroll_up_by_item(
+        &mut self,
+        _: &ScrollUpByItem,
+        _window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        let scroll_top = self.list_state.logical_scroll_top();
+        if let Some(bounds) = self.list_state.bounds_for_item(scroll_top.item_ix) {
+            self.list_state.scroll_by(-bounds.size.height);
+        }
+        cx.notify();
+    }
+
+    fn scroll_down_by_item(
+        &mut self,
+        _: &ScrollDownByItem,
+        _window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        let scroll_top = self.list_state.logical_scroll_top();
+        if let Some(bounds) = self.list_state.bounds_for_item(scroll_top.item_ix) {
+            self.list_state.scroll_by(bounds.size.height);
+        }
+        cx.notify();
+    }
 }
 
 impl Focusable for MarkdownPreviewView {
@@ -496,6 +553,10 @@ impl Render for MarkdownPreviewView {
             .track_focus(&self.focus_handle(cx))
             .on_action(cx.listener(MarkdownPreviewView::scroll_page_up))
             .on_action(cx.listener(MarkdownPreviewView::scroll_page_down))
+            .on_action(cx.listener(MarkdownPreviewView::scroll_up))
+            .on_action(cx.listener(MarkdownPreviewView::scroll_down))
+            .on_action(cx.listener(MarkdownPreviewView::scroll_up_by_item))
+            .on_action(cx.listener(MarkdownPreviewView::scroll_down_by_item))
             .size_full()
             .bg(cx.theme().colors().editor_background)
             .p_4()

crates/vim/Cargo.toml

@@ -63,6 +63,7 @@ indoc.workspace = true
 language = { workspace = true, features = ["test-support"] }
 project = { workspace = true, features = ["test-support"] }
 lsp = { workspace = true, features = ["test-support"] }
+markdown_preview.workspace = true
 parking_lot.workspace = true
 project_panel.workspace = true
 release_channel.workspace = true

crates/vim/src/test/vim_test_context.rs

@@ -28,6 +28,7 @@ impl VimTestContext {
             search::init(cx);
             theme::init(theme::LoadThemes::JustBase, cx);
             settings_ui::init(cx);
+            markdown_preview::init(cx);
         });
     }