Add caching of parsed completion documentation markdown to reduce flicker when selecting (#31546)

Related to #31460 and #28635.

Release Notes:

- Fixed redraw delay of documentation from language server completions
and added caching to reduce flicker when using arrow keys to change
selection.

Cargo.lock

@@ -9567,6 +9567,7 @@ dependencies = [
  "assets",
  "base64 0.22.1",
  "env_logger 0.11.8",
+ "futures 0.3.31",
  "gpui",
  "language",
  "languages",

crates/editor/src/code_context_menus.rs

@@ -4,8 +4,9 @@ use gpui::{
     Size, StrikethroughStyle, StyledText, UniformListScrollHandle, div, px, uniform_list,
 };
 use gpui::{AsyncWindowContext, WeakEntity};
-use language::Buffer;
+use itertools::Itertools;
 use language::CodeLabel;
+use language::{Buffer, LanguageName, LanguageRegistry};
 use markdown::{Markdown, MarkdownElement};
 use multi_buffer::{Anchor, ExcerptId};
 use ordered_float::OrderedFloat;
@@ -15,6 +16,8 @@ use project::{CodeAction, Completion, TaskSourceKind};
 use task::DebugScenario;
 use task::TaskContext;
 
+use std::collections::VecDeque;
+use std::sync::Arc;
 use std::{
     cell::RefCell,
     cmp::{Reverse, min},
@@ -41,6 +44,25 @@ pub const MENU_ASIDE_X_PADDING: Pixels = px(16.);
 pub const MENU_ASIDE_MIN_WIDTH: Pixels = px(260.);
 pub const MENU_ASIDE_MAX_WIDTH: Pixels = px(500.);
 
+// Constants for the markdown cache. The purpose of this cache is to reduce flickering due to
+// documentation not yet being parsed.
+//
+// The size of the cache is set to the number of items fetched around the current selection plus one
+// for the current selection and another to avoid cases where and adjacent selection exits the
+// cache. The only current benefit of a larger cache would be doing less markdown parsing when the
+// selection revisits items.
+//
+// One future benefit of a larger cache would be reducing flicker on backspace. This would require
+// not recreating the menu on every change, by not re-querying the language server when
+// `is_incomplete = false`.
+const MARKDOWN_CACHE_MAX_SIZE: usize = MARKDOWN_CACHE_BEFORE_ITEMS + MARKDOWN_CACHE_AFTER_ITEMS + 2;
+const MARKDOWN_CACHE_BEFORE_ITEMS: usize = 2;
+const MARKDOWN_CACHE_AFTER_ITEMS: usize = 2;
+
+// Number of items beyond the visible items to resolve documentation.
+const RESOLVE_BEFORE_ITEMS: usize = 4;
+const RESOLVE_AFTER_ITEMS: usize = 4;
+
 pub enum CodeContextMenu {
     Completions(CompletionsMenu),
     CodeActions(CodeActionsMenu),
@@ -148,13 +170,12 @@ impl CodeContextMenu {
 
     pub fn render_aside(
         &mut self,
-        editor: &Editor,
         max_size: Size<Pixels>,
         window: &mut Window,
         cx: &mut Context<Editor>,
     ) -> Option<AnyElement> {
         match self {
-            CodeContextMenu::Completions(menu) => menu.render_aside(editor, max_size, window, cx),
+            CodeContextMenu::Completions(menu) => menu.render_aside(max_size, window, cx),
             CodeContextMenu::CodeActions(_) => None,
         }
     }
@@ -162,7 +183,7 @@ impl CodeContextMenu {
     pub fn focused(&self, window: &mut Window, cx: &mut Context<Editor>) -> bool {
         match self {
             CodeContextMenu::Completions(completions_menu) => completions_menu
-                .markdown_element
+                .get_or_create_entry_markdown(completions_menu.selected_item, cx)
                 .as_ref()
                 .is_some_and(|markdown| markdown.focus_handle(cx).contains_focused(window, cx)),
             CodeContextMenu::CodeActions(_) => false,
@@ -176,7 +197,7 @@ pub enum ContextMenuOrigin {
     QuickActionBar,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone)]
 pub struct CompletionsMenu {
     pub id: CompletionId,
     sort_completions: bool,
@@ -191,7 +212,9 @@ pub struct CompletionsMenu {
     show_completion_documentation: bool,
     pub(super) ignore_completion_provider: bool,
     last_rendered_range: Rc<RefCell<Option<Range<usize>>>>,
-    markdown_element: Option<Entity<Markdown>>,
+    markdown_cache: Rc<RefCell<VecDeque<(usize, Entity<Markdown>)>>>,
+    language_registry: Option<Arc<LanguageRegistry>>,
+    language: Option<LanguageName>,
     snippet_sort_order: SnippetSortOrder,
 }
 
@@ -205,6 +228,9 @@ impl CompletionsMenu {
         buffer: Entity<Buffer>,
         completions: Box<[Completion]>,
         snippet_sort_order: SnippetSortOrder,
+        language_registry: Option<Arc<LanguageRegistry>>,
+        language: Option<LanguageName>,
+        cx: &mut Context<Editor>,
     ) -> Self {
         let match_candidates = completions
             .iter()
@@ -212,7 +238,7 @@ impl CompletionsMenu {
             .map(|(id, completion)| StringMatchCandidate::new(id, &completion.label.filter_text()))
             .collect();
 
-        Self {
+        let completions_menu = Self {
             id,
             sort_completions,
             initial_position,
@@ -226,9 +252,15 @@ impl CompletionsMenu {
             scroll_handle: UniformListScrollHandle::new(),
             resolve_completions: true,
             last_rendered_range: RefCell::new(None).into(),
-            markdown_element: None,
+            markdown_cache: RefCell::new(VecDeque::with_capacity(MARKDOWN_CACHE_MAX_SIZE)).into(),
+            language_registry,
+            language,
             snippet_sort_order,
-        }
+        };
+
+        completions_menu.start_markdown_parse_for_nearby_entries(cx);
+
+        completions_menu
     }
 
     pub fn new_snippet_choices(
@@ -286,7 +318,9 @@ impl CompletionsMenu {
             show_completion_documentation: false,
             ignore_completion_provider: false,
             last_rendered_range: RefCell::new(None).into(),
-            markdown_element: None,
+            markdown_cache: RefCell::new(VecDeque::new()).into(),
+            language_registry: None,
+            language: None,
             snippet_sort_order,
         }
     }
@@ -359,6 +393,7 @@ impl CompletionsMenu {
             self.scroll_handle
                 .scroll_to_item(self.selected_item, ScrollStrategy::Top);
             self.resolve_visible_completions(provider, cx);
+            self.start_markdown_parse_for_nearby_entries(cx);
             if let Some(provider) = provider {
                 self.handle_selection_changed(provider, window, cx);
             }
@@ -433,11 +468,10 @@ impl CompletionsMenu {
 
         // Expand the range to resolve more completions than are predicted to be visible, to reduce
         // jank on navigation.
-        const EXTRA_TO_RESOLVE: usize = 4;
-        let entry_indices = util::iterate_expanded_and_wrapped_usize_range(
+        let entry_indices = util::expanded_and_wrapped_usize_range(
             entry_range.clone(),
-            EXTRA_TO_RESOLVE,
-            EXTRA_TO_RESOLVE,
+            RESOLVE_BEFORE_ITEMS,
+            RESOLVE_AFTER_ITEMS,
             entries.len(),
         );
 
@@ -467,14 +501,120 @@ impl CompletionsMenu {
             cx,
         );
 
+        let completion_id = self.id;
         cx.spawn(async move |editor, cx| {
             if let Some(true) = resolve_task.await.log_err() {
-                editor.update(cx, |_, cx| cx.notify()).ok();
+                editor
+                    .update(cx, |editor, cx| {
+                        // `resolve_completions` modified state affecting display.
+                        cx.notify();
+                        editor.with_completions_menu_matching_id(
+                            completion_id,
+                            || (),
+                            |this| this.start_markdown_parse_for_nearby_entries(cx),
+                        );
+                    })
+                    .ok();
             }
         })
         .detach();
     }
 
+    fn start_markdown_parse_for_nearby_entries(&self, cx: &mut Context<Editor>) {
+        // Enqueue parse tasks of nearer items first.
+        //
+        // TODO: This means that the nearer items will actually be further back in the cache, which
+        // is not ideal. In practice this is fine because `get_or_create_markdown` moves the current
+        // selection to the front (when `is_render = true`).
+        let entry_indices = util::wrapped_usize_outward_from(
+            self.selected_item,
+            MARKDOWN_CACHE_BEFORE_ITEMS,
+            MARKDOWN_CACHE_AFTER_ITEMS,
+            self.entries.borrow().len(),
+        );
+
+        for index in entry_indices {
+            self.get_or_create_entry_markdown(index, cx);
+        }
+    }
+
+    fn get_or_create_entry_markdown(
+        &self,
+        index: usize,
+        cx: &mut Context<Editor>,
+    ) -> Option<Entity<Markdown>> {
+        let entries = self.entries.borrow();
+        if index >= entries.len() {
+            return None;
+        }
+        let candidate_id = entries[index].candidate_id;
+        match &self.completions.borrow()[candidate_id].documentation {
+            Some(CompletionDocumentation::MultiLineMarkdown(source)) if !source.is_empty() => Some(
+                self.get_or_create_markdown(candidate_id, source.clone(), false, cx)
+                    .1,
+            ),
+            Some(_) => None,
+            _ => None,
+        }
+    }
+
+    fn get_or_create_markdown(
+        &self,
+        candidate_id: usize,
+        source: SharedString,
+        is_render: bool,
+        cx: &mut Context<Editor>,
+    ) -> (bool, Entity<Markdown>) {
+        let mut markdown_cache = self.markdown_cache.borrow_mut();
+        if let Some((cache_index, (_, markdown))) = markdown_cache
+            .iter()
+            .find_position(|(id, _)| *id == candidate_id)
+        {
+            let markdown = if is_render && cache_index != 0 {
+                // Move the current selection's cache entry to the front.
+                markdown_cache.rotate_right(1);
+                let cache_len = markdown_cache.len();
+                markdown_cache.swap(0, (cache_index + 1) % cache_len);
+                &markdown_cache[0].1
+            } else {
+                markdown
+            };
+
+            let is_parsing = markdown.update(cx, |markdown, cx| {
+                // `reset` is called as it's possible for documentation to change due to resolve
+                // requests. It does nothing if `source` is unchanged.
+                markdown.reset(source, cx);
+                markdown.is_parsing()
+            });
+            return (is_parsing, markdown.clone());
+        }
+
+        if markdown_cache.len() < MARKDOWN_CACHE_MAX_SIZE {
+            let markdown = cx.new(|cx| {
+                Markdown::new(
+                    source,
+                    self.language_registry.clone(),
+                    self.language.clone(),
+                    cx,
+                )
+            });
+            // Handles redraw when the markdown is done parsing. The current render is for a
+            // deferred draw, and so without this did not redraw when `markdown` notified.
+            cx.observe(&markdown, |_, _, cx| cx.notify()).detach();
+            markdown_cache.push_front((candidate_id, markdown.clone()));
+            (true, markdown)
+        } else {
+            debug_assert_eq!(markdown_cache.capacity(), MARKDOWN_CACHE_MAX_SIZE);
+            // Moves the last cache entry to the start. The ring buffer is full, so this does no
+            // copying and just shifts indexes.
+            markdown_cache.rotate_right(1);
+            markdown_cache[0].0 = candidate_id;
+            let markdown = &markdown_cache[0].1;
+            markdown.update(cx, |markdown, cx| markdown.reset(source, cx));
+            (true, markdown.clone())
+        }
+    }
+
     pub fn visible(&self) -> bool {
         !self.entries.borrow().is_empty()
     }
@@ -625,7 +765,6 @@ impl CompletionsMenu {
 
     fn render_aside(
         &mut self,
-        editor: &Editor,
         max_size: Size<Pixels>,
         window: &mut Window,
         cx: &mut Context<Editor>,
@@ -644,33 +783,14 @@ impl CompletionsMenu {
                 plain_text: Some(text),
                 ..
             } => div().child(text.clone()),
-            CompletionDocumentation::MultiLineMarkdown(parsed) if !parsed.is_empty() => {
-                let markdown = self.markdown_element.get_or_insert_with(|| {
-                    let markdown = cx.new(|cx| {
-                        let languages = editor
-                            .workspace
-                            .as_ref()
-                            .and_then(|(workspace, _)| workspace.upgrade())
-                            .map(|workspace| workspace.read(cx).app_state().languages.clone());
-                        let language = editor
-                            .language_at(self.initial_position, cx)
-                            .map(|l| l.name().to_proto());
-                        Markdown::new(SharedString::default(), languages, language, cx)
-                    });
-                    // Handles redraw when the markdown is done parsing. The current render is for a
-                    // deferred draw and so was not getting redrawn when `markdown` notified.
-                    cx.observe(&markdown, |_, _, cx| cx.notify()).detach();
-                    markdown
-                });
-                let is_parsing = markdown.update(cx, |markdown, cx| {
-                    markdown.reset(parsed.clone(), cx);
-                    markdown.is_parsing()
-                });
+            CompletionDocumentation::MultiLineMarkdown(source) if !source.is_empty() => {
+                let (is_parsing, markdown) =
+                    self.get_or_create_markdown(mat.candidate_id, source.clone(), true, cx);
                 if is_parsing {
                     return None;
                 }
                 div().child(
-                    MarkdownElement::new(markdown.clone(), hover_markdown_style(window, cx))
+                    MarkdownElement::new(markdown, hover_markdown_style(window, cx))
                         .code_block_renderer(markdown::CodeBlockRenderer::Default {
                             copy_button: false,
                             copy_button_on_hover: false,
@@ -882,13 +1002,7 @@ impl CompletionsMenu {
                 // another opened. `provider.selection_changed` should not be called in this case.
                 let this_menu_still_active = editor
                     .read_with(cx, |editor, _cx| {
-                        if let Some(CodeContextMenu::Completions(completions_menu)) =
-                            editor.context_menu.borrow().as_ref()
-                        {
-                            completions_menu.id == self.id
-                        } else {
-                            false
-                        }
+                        editor.with_completions_menu_matching_id(self.id, || false, |_| true)
                     })
                     .unwrap_or(false);
                 if this_menu_still_active {

crates/editor/src/editor.rs

@@ -4987,14 +4987,12 @@ impl Editor {
             (buffer_position..buffer_position, None)
         };
 
-        let completion_settings = language_settings(
-            buffer_snapshot
-                .language_at(buffer_position)
-                .map(|language| language.name()),
-            buffer_snapshot.file(),
-            cx,
-        )
-        .completions;
+        let language = buffer_snapshot
+            .language_at(buffer_position)
+            .map(|language| language.name());
+
+        let completion_settings =
+            language_settings(language.clone(), buffer_snapshot.file(), cx).completions;
 
         // The document can be large, so stay in reasonable bounds when searching for words,
         // otherwise completion pop-up might be slow to appear.
@@ -5106,16 +5104,26 @@ impl Editor {
                 let menu = if completions.is_empty() {
                     None
                 } else {
-                    let mut menu = CompletionsMenu::new(
-                        id,
-                        sort_completions,
-                        show_completion_documentation,
-                        ignore_completion_provider,
-                        position,
-                        buffer.clone(),
-                        completions.into(),
-                        snippet_sort_order,
-                    );
+                    let mut menu = editor.update(cx, |editor, cx| {
+                        let languages = editor
+                            .workspace
+                            .as_ref()
+                            .and_then(|(workspace, _)| workspace.upgrade())
+                            .map(|workspace| workspace.read(cx).app_state().languages.clone());
+                        CompletionsMenu::new(
+                            id,
+                            sort_completions,
+                            show_completion_documentation,
+                            ignore_completion_provider,
+                            position,
+                            buffer.clone(),
+                            completions.into(),
+                            snippet_sort_order,
+                            languages,
+                            language,
+                            cx,
+                        )
+                    })?;
 
                     menu.filter(
                         if filter_completions {
@@ -5190,6 +5198,22 @@ impl Editor {
         }
     }
 
+    pub fn with_completions_menu_matching_id<R>(
+        &self,
+        id: CompletionId,
+        on_absent: impl FnOnce() -> R,
+        on_match: impl FnOnce(&mut CompletionsMenu) -> R,
+    ) -> R {
+        let mut context_menu = self.context_menu.borrow_mut();
+        let Some(CodeContextMenu::Completions(completions_menu)) = &mut *context_menu else {
+            return on_absent();
+        };
+        if completions_menu.id != id {
+            return on_absent();
+        }
+        on_match(completions_menu)
+    }
+
     pub fn confirm_completion(
         &mut self,
         action: &ConfirmCompletion,
@@ -8686,7 +8710,7 @@ impl Editor {
     ) -> Option<AnyElement> {
         self.context_menu.borrow_mut().as_mut().and_then(|menu| {
             if menu.visible() {
-                menu.render_aside(self, max_size, window, cx)
+                menu.render_aside(max_size, window, cx)
             } else {
                 None
             }

crates/editor/src/hover_popover.rs

@@ -583,13 +583,6 @@ async fn parse_blocks(
     language: Option<Arc<Language>>,
     cx: &mut AsyncWindowContext,
 ) -> Option<Entity<Markdown>> {
-    let fallback_language_name = if let Some(ref l) = language {
-        let l = Arc::clone(l);
-        Some(l.lsp_id().clone())
-    } else {
-        None
-    };
-
     let combined_text = blocks
         .iter()
         .map(|block| match &block.kind {
@@ -607,7 +600,7 @@ async fn parse_blocks(
             Markdown::new(
                 combined_text.into(),
                 Some(language_registry.clone()),
-                fallback_language_name,
+                language.map(|language| language.name()),
                 cx,
             )
         })

crates/markdown/Cargo.toml

@@ -20,6 +20,7 @@ test-support = [
 
 [dependencies]
 base64.workspace = true
+futures.workspace = true
 gpui.workspace = true
 language.workspace = true
 linkify.workspace = true

crates/markdown/examples/markdown.rs

@@ -67,14 +67,8 @@ struct MarkdownExample {
 
 impl MarkdownExample {
     pub fn new(text: SharedString, language_registry: Arc<LanguageRegistry>, cx: &mut App) -> Self {
-        let markdown = cx.new(|cx| {
-            Markdown::new(
-                text,
-                Some(language_registry),
-                Some("TypeScript".to_string()),
-                cx,
-            )
-        });
+        let markdown = cx
+            .new(|cx| Markdown::new(text, Some(language_registry), Some("TypeScript".into()), cx));
         Self { markdown }
     }
 }

crates/markdown/src/markdown.rs

@@ -2,6 +2,8 @@ pub mod parser;
 mod path_range;
 
 use base64::Engine as _;
+use futures::FutureExt as _;
+use language::LanguageName;
 use log::Level;
 pub use path_range::{LineCol, PathWithRange};
 
@@ -101,7 +103,7 @@ pub struct Markdown {
     pending_parse: Option<Task<()>>,
     focus_handle: FocusHandle,
     language_registry: Option<Arc<LanguageRegistry>>,
-    fallback_code_block_language: Option<String>,
+    fallback_code_block_language: Option<LanguageName>,
     options: Options,
     copied_code_blocks: HashSet<ElementId>,
 }
@@ -144,7 +146,7 @@ impl Markdown {
     pub fn new(
         source: SharedString,
         language_registry: Option<Arc<LanguageRegistry>>,
-        fallback_code_block_language: Option<String>,
+        fallback_code_block_language: Option<LanguageName>,
         cx: &mut Context<Self>,
     ) -> Self {
         let focus_handle = cx.focus_handle();
@@ -310,9 +312,9 @@ impl Markdown {
             if let Some(registry) = language_registry.as_ref() {
                 for name in language_names {
                     let language = if !name.is_empty() {
-                        registry.language_for_name_or_extension(&name)
+                        registry.language_for_name_or_extension(&name).left_future()
                     } else if let Some(fallback) = &fallback {
-                        registry.language_for_name_or_extension(fallback)
+                        registry.language_for_name(fallback.as_ref()).right_future()
                     } else {
                         continue;
                     };

crates/util/src/util.rs

@@ -670,7 +670,7 @@ pub fn measure<R>(label: &str, f: impl FnOnce() -> R) -> R {
     }
 }
 
-pub fn iterate_expanded_and_wrapped_usize_range(
+pub fn expanded_and_wrapped_usize_range(
     range: Range<usize>,
     additional_before: usize,
     additional_after: usize,
@@ -699,6 +699,43 @@ pub fn iterate_expanded_and_wrapped_usize_range(
     }
 }
 
+/// Yields `[i, i + 1, i - 1, i + 2, ..]`, each modulo `wrap_length` and bounded by
+/// `additional_before` and `additional_after`. If the wrapping causes overlap, duplicates are not
+/// emitted. If wrap_length is 0, nothing is yielded.
+pub fn wrapped_usize_outward_from(
+    start: usize,
+    additional_before: usize,
+    additional_after: usize,
+    wrap_length: usize,
+) -> impl Iterator<Item = usize> {
+    let mut count = 0;
+    let mut after_offset = 1;
+    let mut before_offset = 1;
+
+    std::iter::from_fn(move || {
+        count += 1;
+        if count > wrap_length {
+            None
+        } else if count == 1 {
+            Some(start % wrap_length)
+        } else if after_offset <= additional_after && after_offset <= before_offset {
+            let value = (start + after_offset) % wrap_length;
+            after_offset += 1;
+            Some(value)
+        } else if before_offset <= additional_before {
+            let value = (start + wrap_length - before_offset) % wrap_length;
+            before_offset += 1;
+            Some(value)
+        } else if after_offset <= additional_after {
+            let value = (start + after_offset) % wrap_length;
+            after_offset += 1;
+            Some(value)
+        } else {
+            None
+        }
+    })
+}
+
 #[cfg(target_os = "windows")]
 pub fn get_windows_system_shell() -> String {
     use std::path::PathBuf;
@@ -1462,49 +1499,88 @@ Line 3"#
     }
 
     #[test]
-    fn test_iterate_expanded_and_wrapped_usize_range() {
+    fn test_expanded_and_wrapped_usize_range() {
         // Neither wrap
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(2..4, 1, 1, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(2..4, 1, 1, 8).collect::<Vec<usize>>(),
             (1..5).collect::<Vec<usize>>()
         );
         // Start wraps
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(2..4, 3, 1, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(2..4, 3, 1, 8).collect::<Vec<usize>>(),
             ((0..5).chain(7..8)).collect::<Vec<usize>>()
         );
         // Start wraps all the way around
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(2..4, 5, 1, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(2..4, 5, 1, 8).collect::<Vec<usize>>(),
             (0..8).collect::<Vec<usize>>()
         );
         // Start wraps all the way around and past 0
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(2..4, 10, 1, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(2..4, 10, 1, 8).collect::<Vec<usize>>(),
             (0..8).collect::<Vec<usize>>()
         );
         // End wraps
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(3..5, 1, 4, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(3..5, 1, 4, 8).collect::<Vec<usize>>(),
             (0..1).chain(2..8).collect::<Vec<usize>>()
         );
         // End wraps all the way around
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(3..5, 1, 5, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(3..5, 1, 5, 8).collect::<Vec<usize>>(),
             (0..8).collect::<Vec<usize>>()
         );
         // End wraps all the way around and past the end
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(3..5, 1, 10, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(3..5, 1, 10, 8).collect::<Vec<usize>>(),
             (0..8).collect::<Vec<usize>>()
         );
         // Both start and end wrap
         assert_eq!(
-            iterate_expanded_and_wrapped_usize_range(3..5, 4, 4, 8).collect::<Vec<usize>>(),
+            expanded_and_wrapped_usize_range(3..5, 4, 4, 8).collect::<Vec<usize>>(),
             (0..8).collect::<Vec<usize>>()
         );
     }
 
+    #[test]
+    fn test_wrapped_usize_outward_from() {
+        // No wrapping
+        assert_eq!(
+            wrapped_usize_outward_from(4, 2, 2, 10).collect::<Vec<usize>>(),
+            vec![4, 5, 3, 6, 2]
+        );
+        // Wrapping at end
+        assert_eq!(
+            wrapped_usize_outward_from(8, 2, 3, 10).collect::<Vec<usize>>(),
+            vec![8, 9, 7, 0, 6, 1]
+        );
+        // Wrapping at start
+        assert_eq!(
+            wrapped_usize_outward_from(1, 3, 2, 10).collect::<Vec<usize>>(),
+            vec![1, 2, 0, 3, 9, 8]
+        );
+        // All values wrap around
+        assert_eq!(
+            wrapped_usize_outward_from(5, 10, 10, 8).collect::<Vec<usize>>(),
+            vec![5, 6, 4, 7, 3, 0, 2, 1]
+        );
+        // None before / after
+        assert_eq!(
+            wrapped_usize_outward_from(3, 0, 0, 8).collect::<Vec<usize>>(),
+            vec![3]
+        );
+        // Starting point already wrapped
+        assert_eq!(
+            wrapped_usize_outward_from(15, 2, 2, 10).collect::<Vec<usize>>(),
+            vec![5, 6, 4, 7, 3]
+        );
+        // wrap_length of 0
+        assert_eq!(
+            wrapped_usize_outward_from(4, 2, 2, 0).collect::<Vec<usize>>(),
+            Vec::<usize>::new()
+        );
+    }
+
     #[test]
     fn test_truncate_lines_to_byte_limit() {
         let text = "Line 1\nLine 2\nLine 3\nLine 4";