Merge remote-tracking branch 'origin/main' into anchor-enum

# Conflicts:
#	crates/multi_buffer/src/multi_buffer.rs

crates/assistant/src/assistant_panel.rs

@@ -2794,7 +2794,7 @@ impl ContextEditor {
                 let multibuffer = editor.buffer().read(cx).snapshot(cx);
                 let (&excerpt_id, _, buffer) = multibuffer.as_singleton().unwrap();
                 let anchor = if group.context_range.start.to_offset(buffer) == 0 {
-                    Anchor::min()
+                    Anchor::Start
                 } else {
                     multibuffer
                         .anchor_in_excerpt(excerpt_id, group.context_range.start)

crates/assistant/src/inline_assistant.rs

@@ -1208,7 +1208,7 @@ impl InlineAssistant {
                     editor.set_read_only(true);
                     editor.set_show_inline_completions(Some(false), cx);
                     editor.highlight_rows::<DeletedLines>(
-                        Anchor::min()..=Anchor::max(),
+                        Anchor::Start..=Anchor::End,
                         Some(cx.theme().status().deleted_background),
                         false,
                         cx,

crates/assistant/src/workflow.rs

@@ -138,7 +138,7 @@ impl WorkflowSuggestion {
             }
             Self::CreateFile { description } => {
                 initial_prompt = description.clone();
-                suggestion_range = editor::Anchor::min()..editor::Anchor::min();
+                suggestion_range = Anchor::Start..Anchor::Start;
             }
             Self::InsertBefore {
                 position,

crates/collab/src/tests/channel_buffer_tests.rs

@@ -297,7 +297,7 @@ fn assert_remote_selections(
     cx: &mut ViewContext<Editor>,
 ) {
     let snapshot = editor.snapshot(cx);
-    let range = Anchor::min()..Anchor::max();
+    let range = Anchor::Start..Anchor::End;
     let remote_selections = snapshot
         .remote_selections_in_range(&range, editor.collaboration_hub().unwrap(), cx)
         .map(|s| {

crates/editor/src/display_map/crease_map.rs

@@ -271,7 +271,7 @@ pub struct ItemSummary {
 impl Default for ItemSummary {
     fn default() -> Self {
         Self {
-            range: Anchor::min()..Anchor::min(),
+            range: Anchor::Start..Anchor::Start,
         }
     }
 }

crates/editor/src/display_map/fold_map.rs

@@ -376,7 +376,7 @@ impl FoldMap {
                     .folds
                     .cursor::<FoldRange>(&inlay_snapshot.buffer);
                 folds_cursor.seek(
-                    &FoldRange(anchor..Anchor::max()),
+                    &FoldRange(anchor..Anchor::End),
                     Bias::Left,
                     &inlay_snapshot.buffer,
                 );
@@ -997,7 +997,7 @@ impl DerefMut for FoldRange {
 
 impl Default for FoldRange {
     fn default() -> Self {
-        Self(Anchor::min()..Anchor::max())
+        Self(Anchor::Start..Anchor::End)
     }
 }
 
@@ -1027,10 +1027,10 @@ pub struct FoldSummary {
 impl Default for FoldSummary {
     fn default() -> Self {
         Self {
-            start: Anchor::min(),
-            end: Anchor::max(),
-            min_start: Anchor::max(),
-            max_end: Anchor::min(),
+            start: Anchor::Start,
+            end: Anchor::End,
+            min_start: Anchor::End,
+            max_end: Anchor::Start,
             count: 0,
         }
     }

crates/editor/src/editor.rs

@@ -3101,9 +3101,19 @@ impl Editor {
         if self.linked_edit_ranges.is_empty() {
             return None;
         }
-        let ((base_range, linked_ranges), buffer_snapshot, buffer) =
-            selection.end.buffer_id.and_then(|end_buffer_id| {
-                if selection.start.buffer_id != Some(end_buffer_id) {
+
+        let selection_start_buffer_id = match selection.start {
+            text::Anchor::Start | text::Anchor::End => None,
+            text::Anchor::Character { buffer_id, .. } => Some(buffer_id),
+        };
+        let selection_end_buffer_id = match selection.end {
+            text::Anchor::Start | text::Anchor::End => None,
+            text::Anchor::Character { buffer_id, .. } => Some(buffer_id),
+        };
+
+        let ((base_range, linked_ranges), buffer_snapshot, buffer) = selection_end_buffer_id
+            .and_then(|end_buffer_id| {
+                if selection_start_buffer_id != Some(end_buffer_id) {
                     return None;
                 }
                 let buffer = self.buffer.read(cx).buffer(end_buffer_id)?;
@@ -3130,8 +3140,8 @@ impl Editor {
                 continue;
             }
             if self.selections.disjoint_anchor_ranges().iter().any(|s| {
-                if s.start.buffer_id != selection.start.buffer_id
-                    || s.end.buffer_id != selection.end.buffer_id
+                if s.start.buffer_id != selection_start_buffer_id
+                    || s.end.buffer_id != selection_end_buffer_id
                 {
                     return false;
                 }
@@ -5014,12 +5024,10 @@ impl Editor {
                                 continue;
                             }
 
-                            let range = Anchor {
-                                buffer_id,
+                            let range = Anchor::Text {
                                 excerpt_id,
                                 text_anchor: start,
-                            }..Anchor {
-                                buffer_id,
+                            }..Anchor::Text {
                                 excerpt_id,
                                 text_anchor: end,
                             };
@@ -5611,7 +5619,15 @@ impl Editor {
                 for selection in selections.iter() {
                     let selection_start = snapshot.anchor_before(selection.start).text_anchor;
                     let selection_end = snapshot.anchor_after(selection.end).text_anchor;
-                    if selection_start.buffer_id != selection_end.buffer_id {
+                    let selection_start_buffer_id = match selection_start {
+                        text::Anchor::Start | text::Anchor::End => None,
+                        text::Anchor::Character { buffer_id, .. } => Some(buffer_id),
+                    };
+                    let selection_end_buffer_id = match selection_end {
+                        text::Anchor::Start | text::Anchor::End => None,
+                        text::Anchor::Character { buffer_id, .. } => Some(buffer_id),
+                    };
+                    if selection_start_buffer_id != selection_end_buffer_id {
                         continue;
                     }
                     if let Some(ranges) =
@@ -8974,7 +8990,7 @@ impl Editor {
                     .spawn({
                         let snapshot = display_snapshot.clone();
                         async move {
-                            Self::fetch_runnable_ranges(&snapshot, Anchor::min()..Anchor::max())
+                            Self::fetch_runnable_ranges(&snapshot, Anchor::Start..Anchor::End)
                         }
                     })
                     .await;
@@ -12686,7 +12702,7 @@ fn snippet_completions(
         return vec![];
     }
     let snapshot = buffer.read(cx).text_snapshot();
-    let chunks = snapshot.reversed_chunks_in_range(text::Anchor::MIN..buffer_position);
+    let chunks = snapshot.reversed_chunks_in_range(text::Anchor::Start..buffer_position);
 
     let mut lines = chunks.lines();
     let Some(line_at) = lines.next().filter(|line| !line.is_empty()) else {

crates/editor/src/editor_tests.rs

@@ -739,7 +739,9 @@ async fn test_navigation_history(cx: &mut TestAppContext) {
 
             // Ensure we don't panic when navigation data contains invalid anchors *and* points.
             let mut invalid_anchor = editor.scroll_manager.anchor().anchor;
-            invalid_anchor.text_anchor.buffer_id = BufferId::new(999).ok();
+            invalid_anchor.text_anchor = text::Anchor::Start {
+                buffer_id: BufferId::new(999).unwrap(),
+            };
             let invalid_point = Point::new(9999, 0);
             editor.navigate(
                 Box::new(NavigationData {

crates/editor/src/element.rs

@@ -950,7 +950,7 @@ impl EditorElement {
         // Remote cursors
         if let Some(collaboration_hub) = &editor.collaboration_hub {
             for remote_selection in snapshot.remote_selections_in_range(
-                &(Anchor::min()..Anchor::max()),
+                &(Anchor::Start..Anchor::End),
                 collaboration_hub.deref(),
                 cx,
             ) {
@@ -5087,14 +5087,14 @@ impl Element for EditorElement {
                         .collect::<Vec<_>>();
 
                     let start_anchor = if start_row == Default::default() {
-                        Anchor::min()
+                        Anchor::Start
                     } else {
                         snapshot.buffer_snapshot.anchor_before(
                             DisplayPoint::new(start_row, 0).to_offset(&snapshot, Bias::Left),
                         )
                     };
                     let end_anchor = if end_row > max_row {
-                        Anchor::max()
+                        Anchor::End
                     } else {
                         snapshot.buffer_snapshot.anchor_before(
                             DisplayPoint::new(end_row, 0).to_offset(&snapshot, Bias::Right),

crates/editor/src/hunk_diff.rs

@@ -784,7 +784,7 @@ fn editor_with_deleted_text(
         editor.set_read_only(true);
         editor.set_show_inline_completions(Some(false), cx);
         editor.highlight_rows::<DiffRowHighlight>(
-            Anchor::min()..=Anchor::max(),
+            Anchor::Start..=Anchor::End,
             Some(deleted_color),
             false,
             cx,

crates/editor/src/scroll.rs

@@ -40,13 +40,13 @@ impl ScrollAnchor {
     fn new() -> Self {
         Self {
             offset: gpui::Point::default(),
-            anchor: Anchor::min(),
+            anchor: Anchor::Start,
         }
     }
 
     pub fn scroll_position(&self, snapshot: &DisplaySnapshot) -> gpui::Point<f32> {
         let mut scroll_position = self.offset;
-        if self.anchor == Anchor::min() {
+        if self.anchor == Anchor::Start {
             scroll_position.y = 0.;
         } else {
             let scroll_top = self.anchor.to_display_point(snapshot).row().as_f32();
@@ -194,7 +194,7 @@ impl ScrollManager {
         let (new_anchor, top_row) = if scroll_position.y <= 0. {
             (
                 ScrollAnchor {
-                    anchor: Anchor::min(),
+                    anchor: Anchor::Start,
                     offset: scroll_position.max(&gpui::Point::default()),
                 },
                 0,

crates/editor/src/selections_collection.rs

@@ -48,8 +48,8 @@ impl SelectionsCollection {
             pending: Some(PendingSelection {
                 selection: Selection {
                     id: 0,
-                    start: Anchor::min(),
-                    end: Anchor::min(),
+                    start: Anchor::Start,
+                    end: Anchor::Start,
                     reversed: false,
                     goal: SelectionGoal::None,
                 },

crates/git/src/diff.rs

@@ -41,7 +41,7 @@ impl sum_tree::Item for InternalDiffHunk {
     }
 }
 
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Clone)]
 pub struct DiffHunkSummary {
     buffer_range: Range<Anchor>,
 }
@@ -49,8 +49,10 @@ pub struct DiffHunkSummary {
 impl sum_tree::Summary for DiffHunkSummary {
     type Context = text::BufferSnapshot;
 
-    fn zero(_cx: &Self::Context) -> Self {
-        Default::default()
+    fn zero(buffer: &Self::Context) -> Self {
+        Self {
+            buffer_range: buffer.min_anchor()..buffer.min_anchor(),
+        }
     }
 
     fn add_summary(&mut self, other: &Self, buffer: &Self::Context) {

crates/language/src/buffer_tests.rs

@@ -2768,7 +2768,7 @@ fn test_random_collaboration(cx: &mut AppContext, mut rng: StdRng) {
     for buffer in &buffers {
         let buffer = buffer.read(cx).snapshot();
         let actual_remote_selections = buffer
-            .selections_in_range(Anchor::MIN..Anchor::MAX, false)
+            .selections_in_range(buffer.min_anchor()..buffer.max_anchor(), false)
             .map(|(replica_id, _, _, selections)| (replica_id, selections.collect::<Vec<_>>()))
             .collect::<Vec<_>>();
         let expected_remote_selections = active_selections

crates/language/src/diagnostic_set.rs

@@ -246,23 +246,17 @@ impl DiagnosticEntry<Anchor> {
     }
 }
 
-impl Default for Summary {
-    fn default() -> Self {
-        Self {
-            start: Anchor::MIN,
-            end: Anchor::MAX,
-            min_start: Anchor::MAX,
-            max_end: Anchor::MIN,
-            count: 0,
-        }
-    }
-}
-
 impl sum_tree::Summary for Summary {
     type Context = text::BufferSnapshot;
 
-    fn zero(_cx: &Self::Context) -> Self {
-        Default::default()
+    fn zero(buffer: &Self::Context) -> Self {
+        Self {
+            start: buffer.min_anchor(),
+            end: buffer.max_anchor(),
+            min_start: buffer.max_anchor(),
+            max_end: buffer.min_anchor(),
+            count: 0,
+        }
     }
 
     fn add_summary(&mut self, other: &Self, buffer: &Self::Context) {

crates/language/src/proto.rs

@@ -6,7 +6,7 @@ use clock::ReplicaId;
 use lsp::{DiagnosticSeverity, LanguageServerId};
 use rpc::proto;
 use serde_json::Value;
-use std::{ops::Range, str::FromStr, sync::Arc};
+use std::{ops::Range, str::FromStr, sync::Arc, u32};
 use text::*;
 
 pub use proto::{BufferState, Operation};
@@ -221,15 +221,36 @@ pub fn serialize_diagnostics<'a>(
 
 /// Serializes an [`Anchor`] to be sent over RPC.
 pub fn serialize_anchor(anchor: &Anchor) -> proto::Anchor {
-    proto::Anchor {
-        replica_id: anchor.timestamp.replica_id as u32,
-        timestamp: anchor.timestamp.value,
-        offset: anchor.offset as u64,
-        bias: match anchor.bias {
-            Bias::Left => proto::Bias::Left as i32,
-            Bias::Right => proto::Bias::Right as i32,
+    match *anchor {
+        Anchor::Start { buffer_id } => proto::Anchor {
+            replica_id: 0,
+            timestamp: 0,
+            offset: 0,
+            bias: proto::Bias::Left as i32,
+            buffer_id: Some(buffer_id.into()),
+        },
+        Anchor::End { buffer_id } => proto::Anchor {
+            replica_id: u32::MAX,
+            timestamp: u32::MAX,
+            offset: u64::MAX,
+            bias: proto::Bias::Right as i32,
+            buffer_id: Some(buffer_id.into()),
+        },
+        Anchor::Character {
+            buffer_id,
+            insertion_id,
+            offset,
+            bias,
+        } => proto::Anchor {
+            replica_id: insertion_id.replica_id as u32,
+            timestamp: insertion_id.value,
+            offset: offset as u64,
+            bias: match bias {
+                Bias::Left => proto::Bias::Left as i32,
+                Bias::Right => proto::Bias::Right as i32,
+            },
+            buffer_id: Some(buffer_id.into()),
         },
-        buffer_id: anchor.buffer_id.map(Into::into),
     }
 }
 
@@ -429,23 +450,33 @@ pub fn deserialize_diagnostics(
 
 /// Deserializes an [`Anchor`] from the RPC representation.
 pub fn deserialize_anchor(anchor: proto::Anchor) -> Option<Anchor> {
-    let buffer_id = if let Some(id) = anchor.buffer_id {
-        Some(BufferId::new(id).ok()?)
+    let buffer_id = BufferId::new(anchor.buffer_id?).ok()?;
+    if anchor.replica_id == 0
+        && anchor.timestamp == 0
+        && anchor.offset == 0
+        && anchor.bias == proto::Bias::Left as i32
+    {
+        Some(Anchor::Start { buffer_id })
+    } else if anchor.replica_id == u32::MAX
+        && anchor.timestamp == u32::MAX
+        && anchor.offset == u64::MAX
+        && anchor.bias == proto::Bias::Right as i32
+    {
+        Some(Anchor::End { buffer_id })
     } else {
-        None
-    };
-    Some(Anchor {
-        timestamp: clock::Lamport {
-            replica_id: anchor.replica_id as ReplicaId,
-            value: anchor.timestamp,
-        },
-        offset: anchor.offset as usize,
-        bias: match proto::Bias::from_i32(anchor.bias)? {
-            proto::Bias::Left => Bias::Left,
-            proto::Bias::Right => Bias::Right,
-        },
-        buffer_id,
-    })
+        Some(Anchor::Character {
+            insertion_id: clock::Lamport {
+                replica_id: anchor.replica_id as ReplicaId,
+                value: anchor.timestamp,
+            },
+            offset: anchor.offset as usize,
+            bias: match proto::Bias::from_i32(anchor.bias)? {
+                proto::Bias::Left => Bias::Left,
+                proto::Bias::Right => Bias::Right,
+            },
+            buffer_id,
+        })
+    }
 }
 
 /// Returns a `[clock::Lamport`] timestamp for the given [`proto::Operation`].

crates/language/src/syntax_map.rs

@@ -303,7 +303,7 @@ impl SyntaxSnapshot {
                 let slice = cursor.slice(
                     &SyntaxLayerPosition {
                         depth: depth + 1,
-                        range: Anchor::MIN..Anchor::MAX,
+                        range: text.min_anchor()..text.max_anchor(),
                         language: None,
                     },
                     Bias::Left,
@@ -459,7 +459,7 @@ impl SyntaxSnapshot {
                 start_point: Point::zero().to_ts_point(),
                 end_point: text.max_point().to_ts_point(),
             }],
-            range: Anchor::MIN..Anchor::MAX,
+            range: text.min_anchor()..text.max_anchor(),
             mode: ParseMode::Single,
         });
 
@@ -474,7 +474,7 @@ impl SyntaxSnapshot {
             } else {
                 SyntaxLayerPosition {
                     depth: max_depth + 1,
-                    range: Anchor::MAX..Anchor::MAX,
+                    range: text.max_anchor()..text.max_anchor(),
                     language: None,
                 }
             };
@@ -485,7 +485,7 @@ impl SyntaxSnapshot {
 
                 let bounded_position = SyntaxLayerPositionBeforeChange {
                     position: position.clone(),
-                    change: changed_regions.start_position(),
+                    change: changed_regions.start_position(text),
                 };
                 if bounded_position.cmp(cursor.start(), text).is_gt() {
                     let slice = cursor.slice(&bounded_position, Bias::Left, text);
@@ -1608,11 +1608,11 @@ impl ChangedRegion {
 }
 
 impl ChangeRegionSet {
-    fn start_position(&self) -> ChangeStartPosition {
+    fn start_position(&self, text: &BufferSnapshot) -> ChangeStartPosition {
         self.0.first().map_or(
             ChangeStartPosition {
                 depth: usize::MAX,
-                position: Anchor::MAX,
+                position: text.max_anchor(),
             },
             |region| ChangeStartPosition {
                 depth: region.depth,
@@ -1661,24 +1661,18 @@ impl ChangeRegionSet {
     }
 }
 
-impl Default for SyntaxLayerSummary {
-    fn default() -> Self {
-        Self {
-            max_depth: 0,
-            min_depth: 0,
-            range: Anchor::MAX..Anchor::MIN,
-            last_layer_range: Anchor::MIN..Anchor::MAX,
-            last_layer_language: None,
-            contains_unknown_injections: false,
-        }
-    }
-}
-
 impl sum_tree::Summary for SyntaxLayerSummary {
     type Context = BufferSnapshot;
 
-    fn zero(_cx: &BufferSnapshot) -> Self {
-        Default::default()
+    fn zero(buffer: &BufferSnapshot) -> Self {
+        Self {
+            max_depth: 0,
+            min_depth: 0,
+            range: buffer.max_anchor()..buffer.min_anchor(),
+            last_layer_range: buffer.min_anchor()..buffer.max_anchor(),
+            last_layer_language: None,
+            contains_unknown_injections: false,
+        }
     }
 
     fn add_summary(&mut self, other: &Self, buffer: &Self::Context) {
@@ -1686,7 +1680,7 @@ impl sum_tree::Summary for SyntaxLayerSummary {
             self.max_depth = other.max_depth;
             self.range = other.range.clone();
         } else {
-            if self.range == (Anchor::MAX..Anchor::MAX) {
+            if self.range == (buffer.max_anchor()..buffer.max_anchor()) {
                 self.range.start = other.range.start;
             }
             if other.range.end.cmp(&self.range.end, buffer).is_gt() {

crates/multi_buffer/src/anchor.rs

@@ -5,75 +5,105 @@ use std::{
     ops::{Range, Sub},
 };
 use sum_tree::Bias;
-use text::BufferId;
 
 #[derive(Clone, Copy, Eq, PartialEq, Debug, Hash)]
-pub struct Anchor {
-    pub buffer_id: Option<BufferId>,
-    pub excerpt_id: ExcerptId,
-    pub text_anchor: text::Anchor,
+pub enum Anchor {
+    Start,
+    End,
+    Text {
+        excerpt_id: ExcerptId,
+        text_anchor: text::Anchor,
+    },
 }
 
 impl Anchor {
-    pub fn min() -> Self {
-        Self {
-            buffer_id: None,
-            excerpt_id: ExcerptId::min(),
-            text_anchor: text::Anchor::MIN,
-        }
-    }
-
-    pub fn max() -> Self {
-        Self {
-            buffer_id: None,
-            excerpt_id: ExcerptId::max(),
-            text_anchor: text::Anchor::MAX,
+    pub fn excerpt_id(&self) -> ExcerptId {
+        match self {
+            Anchor::Start => ExcerptId::min(),
+            Anchor::End => ExcerptId::max(),
+            Anchor::Text { excerpt_id, .. } => *excerpt_id,
         }
     }
 
     pub fn cmp(&self, other: &Anchor, snapshot: &MultiBufferSnapshot) -> Ordering {
-        let excerpt_id_cmp = self.excerpt_id.cmp(&other.excerpt_id, snapshot);
-        if excerpt_id_cmp.is_eq() {
-            if self.excerpt_id == ExcerptId::min() || self.excerpt_id == ExcerptId::max() {
-                Ordering::Equal
-            } else if let Some(excerpt) = snapshot.excerpt(self.excerpt_id) {
-                self.text_anchor.cmp(&other.text_anchor, &excerpt.buffer)
-            } else {
-                Ordering::Equal
+        match (self, other) {
+            (Anchor::Start, Anchor::Start) | (Anchor::End, Anchor::End) => Ordering::Equal,
+            (_, Anchor::Start) | (Anchor::End, _) => Ordering::Greater,
+            (Anchor::Start, _) | (_, Anchor::End) => Ordering::Less,
+            (
+                Anchor::Text {
+                    excerpt_id: id1,
+                    text_anchor: anchor1,
+                },
+                Anchor::Text {
+                    excerpt_id: id2,
+                    text_anchor: anchor2,
+                },
+            ) => {
+                let excerpt_id_cmp = id1.cmp(id2, snapshot);
+                if excerpt_id_cmp.is_eq() {
+                    if let Some(excerpt) = snapshot.excerpt(*id1) {
+                        anchor1.cmp(anchor2, &excerpt.buffer)
+                    } else {
+                        Ordering::Equal
+                    }
+                } else {
+                    excerpt_id_cmp
+                }
             }
-        } else {
-            excerpt_id_cmp
         }
     }
 
     pub fn bias(&self) -> Bias {
-        self.text_anchor.bias
+        match self {
+            Anchor::Start => Bias::Left,
+            Anchor::End => Bias::Right,
+            Anchor::Text { text_anchor, .. } => match text_anchor {
+                text::Anchor::Start { .. } => Bias::Left,
+                text::Anchor::End { .. } => Bias::Right,
+                text::Anchor::Character { bias, .. } => *bias,
+            },
+        }
     }
 
     pub fn bias_left(&self, snapshot: &MultiBufferSnapshot) -> Anchor {
-        if self.text_anchor.bias != Bias::Left {
-            if let Some(excerpt) = snapshot.excerpt(self.excerpt_id) {
-                return Self {
-                    buffer_id: self.buffer_id,
-                    excerpt_id: self.excerpt_id,
-                    text_anchor: self.text_anchor.bias_left(&excerpt.buffer),
-                };
+        match self {
+            Anchor::Start => *self,
+            Anchor::End => snapshot.anchor_before(snapshot.len()),
+            Anchor::Text {
+                excerpt_id,
+                text_anchor,
+            } => {
+                if let Some(excerpt) = snapshot.excerpt(*excerpt_id) {
+                    Anchor::Text {
+                        excerpt_id: *excerpt_id,
+                        text_anchor: text_anchor.bias_left(&excerpt.buffer),
+                    }
+                } else {
+                    *self
+                }
             }
         }
-        *self
     }
 
     pub fn bias_right(&self, snapshot: &MultiBufferSnapshot) -> Anchor {
-        if self.text_anchor.bias != Bias::Right {
-            if let Some(excerpt) = snapshot.excerpt(self.excerpt_id) {
-                return Self {
-                    buffer_id: self.buffer_id,
-                    excerpt_id: self.excerpt_id,
-                    text_anchor: self.text_anchor.bias_right(&excerpt.buffer),
-                };
+        match self {
+            Anchor::Start => snapshot.anchor_after(0),
+            Anchor::End => *self,
+            Anchor::Text {
+                excerpt_id,
+                text_anchor,
+            } => {
+                if let Some(excerpt) = snapshot.excerpt(*excerpt_id) {
+                    Anchor::Text {
+                        excerpt_id: *excerpt_id,
+                        text_anchor: text_anchor.bias_right(&excerpt.buffer),
+                    }
+                } else {
+                    *self
+                }
             }
         }
-        *self
     }
 
     pub fn summary<D>(&self, snapshot: &MultiBufferSnapshot) -> D
@@ -84,15 +114,18 @@ impl Anchor {
     }
 
     pub fn is_valid(&self, snapshot: &MultiBufferSnapshot) -> bool {
-        if *self == Anchor::min() || *self == Anchor::max() {
-            true
-        } else if let Some(excerpt) = snapshot.excerpt(self.excerpt_id) {
-            excerpt.contains(self)
-                && (self.text_anchor == excerpt.range.context.start
-                    || self.text_anchor == excerpt.range.context.end
-                    || self.text_anchor.is_valid(&excerpt.buffer))
-        } else {
-            false
+        match self {
+            Self::Start | Anchor::End => true,
+            Anchor::Text {
+                excerpt_id,
+                text_anchor,
+            } => {
+                if let Some(excerpt) = snapshot.excerpt(*excerpt_id) {
+                    excerpt.contains(self) && text_anchor.is_valid(&excerpt.buffer)
+                } else {
+                    false
+                }
+            }
         }
     }
 }

crates/multi_buffer/src/multi_buffer.rs

@@ -437,13 +437,14 @@ impl MultiBuffer {
         self.capability == Capability::ReadOnly
     }
 
-    pub fn singleton(buffer: Model<Buffer>, cx: &mut ModelContext<Self>) -> Self {
-        let mut this = Self::new(buffer.read(cx).capability());
+    pub fn singleton(buffer_model: Model<Buffer>, cx: &mut ModelContext<Self>) -> Self {
+        let buffer = buffer_model.read(cx);
+        let mut this = Self::new(buffer.capability());
         this.singleton = true;
         this.push_excerpts(
-            buffer,
+            buffer_model,
             [ExcerptRange {
-                context: text::Anchor::MIN..text::Anchor::MAX,
+                context: buffer.min_anchor()..buffer.max_anchor(),
                 primary: None,
             }],
             cx,
@@ -962,9 +963,27 @@ impl MultiBuffer {
             Default::default();
         let snapshot = self.read(cx);
         let mut cursor = snapshot.excerpts.cursor::<Option<&Locator>>(&());
-        for selection in selections {
-            let start_locator = snapshot.excerpt_locator_for_id(selection.start.excerpt_id);
-            let end_locator = snapshot.excerpt_locator_for_id(selection.end.excerpt_id);
+        for mut selection in selections {
+            if selection.start == Anchor::Start {
+                if let Some(first_excerpt) = snapshot.excerpts.first() {
+                    selection.start = Anchor::Text {
+                        excerpt_id: first_excerpt.id,
+                        text_anchor: first_excerpt.range.context.start,
+                    };
+                }
+            }
+
+            if selection.end == Anchor::End {
+                if let Some(last_excerpt) = snapshot.excerpts.last() {
+                    selection.end = Anchor::Text {
+                        excerpt_id: last_excerpt.id,
+                        text_anchor: last_excerpt.range.context.end,
+                    };
+                }
+            }
+
+            let start_locator = snapshot.excerpt_locator_for_id(selection.start.excerpt_id());
+            let end_locator = snapshot.excerpt_locator_for_id(selection.end.excerpt_id());
 
             cursor.seek(&Some(start_locator), Bias::Left, &());
             while let Some(excerpt) = cursor.item() {
@@ -974,11 +993,15 @@ impl MultiBuffer {
 
                 let mut start = excerpt.range.context.start;
                 let mut end = excerpt.range.context.end;
-                if excerpt.id == selection.start.excerpt_id {
-                    start = selection.start.text_anchor;
+                if excerpt.id == selection.start.excerpt_id() {
+                    if let Anchor::Text { text_anchor, .. } = selection.start {
+                        start = text_anchor;
+                    }
                 }
-                if excerpt.id == selection.end.excerpt_id {
-                    end = selection.end.text_anchor;
+                if excerpt.id == selection.end.excerpt_id() {
+                    if let Anchor::Text { text_anchor, .. } = selection.end {
+                        end = text_anchor;
+                    }
                 }
                 selections_by_buffer
                     .entry(excerpt.buffer_id)
@@ -1168,13 +1191,11 @@ impl MultiBuffer {
                 for (excerpt_id, range_count) in excerpt_ids.into_iter().zip(range_counts.by_ref())
                 {
                     for range in ranges.by_ref().take(range_count) {
-                        let start = Anchor {
-                            buffer_id: Some(buffer_id),
+                        let start = Anchor::Text {
                             excerpt_id,
                             text_anchor: range.start,
                         };
-                        let end = Anchor {
-                            buffer_id: Some(buffer_id),
+                        let end = Anchor::Text {
                             excerpt_id,
                             text_anchor: range.end,
                         };
@@ -1223,13 +1244,11 @@ impl MultiBuffer {
         let mut ranges = ranges.into_iter();
         for (excerpt_id, range_count) in excerpt_ids.into_iter().zip(range_counts.into_iter()) {
             anchor_ranges.extend(ranges.by_ref().take(range_count).map(|range| {
-                let start = Anchor {
-                    buffer_id: Some(buffer_id),
+                let start = Anchor::Text {
                     excerpt_id,
                     text_anchor: buffer_snapshot.anchor_after(range.start),
                 };
-                let end = Anchor {
-                    buffer_id: Some(buffer_id),
+                let end = Anchor::Text {
                     excerpt_id,
                     text_anchor: buffer_snapshot.anchor_after(range.end),
                 };
@@ -1654,14 +1673,15 @@ impl MultiBuffer {
         let mut error = None;
         let mut futures = Vec::new();
         for anchor in anchors {
-            if let Some(buffer_id) = anchor.buffer_id {
-                if let Some(buffer) = borrow.get(&buffer_id) {
+            if let Anchor::Text { text_anchor, .. } = anchor {
+                if let Some(buffer) = borrow.get(&text_anchor.buffer_id()) {
                     buffer.buffer.update(cx, |buffer, _| {
-                        futures.push(buffer.wait_for_anchors([anchor.text_anchor]))
+                        futures.push(buffer.wait_for_anchors([text_anchor]))
                     });
                 } else {
                     error = Some(anyhow!(
-                        "buffer {buffer_id} is not part of this multi-buffer"
+                        "buffer {:?} is not part of this multi-buffer",
+                        text_anchor.buffer_id()
                     ));
                     break;
                 }
@@ -1684,14 +1704,43 @@ impl MultiBuffer {
         cx: &AppContext,
     ) -> Option<(Model<Buffer>, language::Anchor)> {
         let snapshot = self.read(cx);
-        let anchor = snapshot.anchor_before(position);
-        let buffer = self
-            .buffers
-            .borrow()
-            .get(&anchor.buffer_id?)?
-            .buffer
-            .clone();
-        Some((buffer, anchor.text_anchor))
+        match snapshot.anchor_before(position) {
+            Anchor::Start => {
+                if let Some(first_excerpt) = snapshot.excerpts.first() {
+                    let buffer = self
+                        .buffers
+                        .borrow()
+                        .get(&first_excerpt.buffer_id)?
+                        .buffer
+                        .clone();
+                    Some((buffer, first_excerpt.range.context.start))
+                } else {
+                    None
+                }
+            }
+            Anchor::End => {
+                if let Some(last_excerpt) = snapshot.excerpts.last() {
+                    let buffer = self
+                        .buffers
+                        .borrow()
+                        .get(&last_excerpt.buffer_id)?
+                        .buffer
+                        .clone();
+                    Some((buffer, last_excerpt.range.context.end))
+                } else {
+                    None
+                }
+            }
+            Anchor::Text { text_anchor, .. } => {
+                let buffer = self
+                    .buffers
+                    .borrow()
+                    .get(&text_anchor.buffer_id())?
+                    .buffer
+                    .clone();
+                Some((buffer, text_anchor))
+            }
+        }
     }
 
     fn on_buffer_event(
@@ -2944,7 +2993,7 @@ impl MultiBufferSnapshot {
         D: TextDimension + Ord + Sub<D, Output = D>,
     {
         let mut cursor = self.excerpts.cursor::<ExcerptSummary>(&());
-        let locator = self.excerpt_locator_for_id(anchor.excerpt_id);
+        let locator = self.excerpt_locator_for_id(anchor.excerpt_id());
 
         cursor.seek(locator, Bias::Left, &());
         if cursor.item().is_none() {
@@ -2953,7 +3002,7 @@ impl MultiBufferSnapshot {
 
         let mut position = D::from_text_summary(&cursor.start().text);
         if let Some(excerpt) = cursor.item() {
-            if excerpt.id == anchor.excerpt_id {
+            if excerpt.id == anchor.excerpt_id() {
                 let excerpt_buffer_start =
                     excerpt.range.context.start.summary::<D>(&excerpt.buffer);
                 let excerpt_buffer_end = excerpt.range.context.end.summary::<D>(&excerpt.buffer);
@@ -3085,12 +3134,11 @@ impl MultiBufferSnapshot {
                 // If there's no adjacent excerpt that contains the anchor's position,
                 // then report that the anchor has lost its position.
                 if !kept_position {
+                    let bias = anchor.bias();
                     anchor = if let Some(excerpt) = next_excerpt {
-                        let mut text_anchor = excerpt
-                            .range
-                            .context
-                            .start
-                            .bias(anchor.text_anchor.bias, &excerpt.buffer);
+                        let mut text_anchor =
+                            excerpt.range.context.start.bias(bias, &excerpt.buffer);
+
                         if text_anchor
                             .cmp(&excerpt.range.context.end, &excerpt.buffer)
                             .is_gt()
@@ -3103,11 +3151,7 @@ impl MultiBufferSnapshot {
                             text_anchor,
                         }
                     } else if let Some(excerpt) = prev_excerpt {
-                        let mut text_anchor = excerpt
-                            .range
-                            .context
-                            .end
-                            .bias(anchor.text_anchor.bias, &excerpt.buffer);
+                        let mut text_anchor = excerpt.range.context.end.bias(bias, &excerpt.buffer);
                         if text_anchor
                             .cmp(&excerpt.range.context.start, &excerpt.buffer)
                             .is_lt()
@@ -3119,10 +3163,10 @@ impl MultiBufferSnapshot {
                             excerpt_id: excerpt.id,
                             text_anchor,
                         }
-                    } else if anchor.text_anchor.bias == Bias::Left {
-                        Anchor::min()
+                    } else if bias == Bias::Left {
+                        Anchor::Start
                     } else {
-                        Anchor::max()
+                        Anchor::End
                     };
                 }
 
@@ -3172,9 +3216,9 @@ impl MultiBufferSnapshot {
                 text_anchor,
             }
         } else if offset == 0 && bias == Bias::Left {
-            Anchor::min()
+            Anchor::Start
         } else {
-            Anchor::max()
+            Anchor::End
         }
     }
 

crates/project/src/lsp_store.rs

@@ -999,7 +999,7 @@ impl LspStore {
             let actions = this
                 .update(cx, move |this, cx| {
                     let request = GetCodeActions {
-                        range: text::Anchor::MIN..text::Anchor::MAX,
+                        range: buffer.read(cx).min_anchor()..buffer.read(cx).max_anchor(),
                         kinds: Some(code_actions),
                     };
                     let server = LanguageServerToQuery::Other(language_server.server_id());
@@ -1323,9 +1323,7 @@ impl LspStore {
                 });
 
                 buffer
-                    .update(&mut cx, |buffer, _| {
-                        buffer.wait_for_edits(Some(position.timestamp))
-                    })?
+                    .update(&mut cx, |buffer, _| buffer.wait_for_anchors(Some(position)))?
                     .await?;
                 this.update(&mut cx, |this, cx| {
                     let position = position.to_point_utf16(buffer.read(cx));
@@ -1969,7 +1967,7 @@ impl LspStore {
             cx.spawn(move |_, mut cx| async move {
                 buffer_handle
                     .update(&mut cx, |buffer, _| {
-                        buffer.wait_for_edits(vec![range_start.timestamp, range_end.timestamp])
+                        buffer.wait_for_anchors([range_start, range_end])
                     })?
                     .await
                     .context("waiting for inlay hint request range edits")?;

crates/project/src/project_tests.rs

@@ -537,7 +537,7 @@ async fn test_managing_language_servers(cx: &mut gpui::TestAppContext) {
             DiagnosticSet::from_sorted_entries(
                 vec![DiagnosticEntry {
                     diagnostic: Default::default(),
-                    range: Anchor::MIN..Anchor::MAX,
+                    range: buffer.min_anchor()..buffer.max_anchor(),
                 }],
                 &buffer.snapshot(),
             ),

crates/text/src/anchor.rs

@@ -6,43 +6,68 @@ use std::{cmp::Ordering, fmt::Debug, ops::Range};
 use sum_tree::Bias;
 
 /// A timestamped position in a buffer
-#[derive(Copy, Clone, Eq, PartialEq, Debug, Hash, Default)]
-pub struct Anchor {
-    pub timestamp: clock::Lamport,
-    /// The byte offset in the buffer
-    pub offset: usize,
-    /// Describes which character the anchor is biased towards
-    pub bias: Bias,
-    pub buffer_id: Option<BufferId>,
+#[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
+pub enum Anchor {
+    Start {
+        buffer_id: BufferId,
+    },
+    End {
+        buffer_id: BufferId,
+    },
+    Character {
+        buffer_id: BufferId,
+        insertion_id: clock::Lamport,
+        offset: usize,
+        bias: Bias,
+    },
 }
 
 impl Anchor {
-    pub const MIN: Self = Self {
-        timestamp: clock::Lamport::MIN,
-        offset: usize::MIN,
-        bias: Bias::Left,
-        buffer_id: None,
-    };
-
-    pub const MAX: Self = Self {
-        timestamp: clock::Lamport::MAX,
-        offset: usize::MAX,
-        bias: Bias::Right,
-        buffer_id: None,
-    };
+    pub fn buffer_id(&self) -> BufferId {
+        match self {
+            Anchor::Start { buffer_id } => *buffer_id,
+            Anchor::End { buffer_id } => *buffer_id,
+            Anchor::Character { buffer_id, .. } => *buffer_id,
+        }
+    }
 
     pub fn cmp(&self, other: &Anchor, buffer: &BufferSnapshot) -> Ordering {
-        let fragment_id_comparison = if self.timestamp == other.timestamp {
-            Ordering::Equal
-        } else {
-            buffer
-                .fragment_id_for_anchor(self)
-                .cmp(buffer.fragment_id_for_anchor(other))
-        };
+        debug_assert_eq!(
+            self.buffer_id(),
+            other.buffer_id(),
+            "anchors belong to different buffers"
+        );
 
-        fragment_id_comparison
-            .then_with(|| self.offset.cmp(&other.offset))
-            .then_with(|| self.bias.cmp(&other.bias))
+        match (self, other) {
+            (Anchor::Start { .. }, Anchor::Start { .. }) => Ordering::Equal,
+            (Anchor::End { .. }, Anchor::End { .. }) => Ordering::Equal,
+            (Anchor::Start { .. }, _) | (_, Anchor::End { .. }) => Ordering::Less,
+            (_, Anchor::Start { .. }) | (Anchor::End { .. }, _) => Ordering::Greater,
+            (
+                Anchor::Character {
+                    insertion_id,
+                    offset,
+                    bias,
+                    ..
+                },
+                Anchor::Character {
+                    insertion_id: other_insertion_id,
+                    offset: other_offset,
+                    bias: other_bias,
+                    ..
+                },
+            ) => {
+                if insertion_id == other_insertion_id {
+                    offset
+                        .cmp(&other_offset)
+                        .then_with(|| bias.cmp(&other_bias))
+                } else {
+                    buffer
+                        .fragment_id_for_anchor(self)
+                        .cmp(buffer.fragment_id_for_anchor(other))
+                }
+            }
+        }
     }
 
     pub fn min(&self, other: &Self, buffer: &BufferSnapshot) -> Self {
@@ -70,18 +95,42 @@ impl Anchor {
     }
 
     pub fn bias_left(&self, buffer: &BufferSnapshot) -> Anchor {
-        if self.bias == Bias::Left {
-            *self
-        } else {
-            buffer.anchor_before(self)
+        match self {
+            Anchor::Start { buffer_id } => Anchor::Start {
+                buffer_id: *buffer_id,
+            },
+            Anchor::End { .. } => buffer.anchor_before(buffer.len()),
+            Anchor::Character {
+                buffer_id,
+                insertion_id,
+                offset,
+                ..
+            } => Anchor::Character {
+                buffer_id: *buffer_id,
+                insertion_id: *insertion_id,
+                offset: *offset,
+                bias: Bias::Left,
+            },
         }
     }
 
     pub fn bias_right(&self, buffer: &BufferSnapshot) -> Anchor {
-        if self.bias == Bias::Right {
-            *self
-        } else {
-            buffer.anchor_after(self)
+        match self {
+            Anchor::Start { .. } => buffer.anchor_after(0),
+            Anchor::End { buffer_id } => Anchor::End {
+                buffer_id: *buffer_id,
+            },
+            Anchor::Character {
+                buffer_id,
+                insertion_id,
+                offset,
+                ..
+            } => Anchor::Character {
+                buffer_id: *buffer_id,
+                insertion_id: *insertion_id,
+                offset: *offset,
+                bias: Bias::Right,
+            },
         }
     }
 
@@ -94,17 +143,23 @@ impl Anchor {
 
     /// Returns true when the [`Anchor`] is located inside a visible fragment.
     pub fn is_valid(&self, buffer: &BufferSnapshot) -> bool {
-        if *self == Anchor::MIN || *self == Anchor::MAX {
-            true
-        } else if self.buffer_id != Some(buffer.remote_id) {
-            false
-        } else {
-            let fragment_id = buffer.fragment_id_for_anchor(self);
-            let mut fragment_cursor = buffer.fragments.cursor::<(Option<&Locator>, usize)>(&None);
-            fragment_cursor.seek(&Some(fragment_id), Bias::Left, &None);
-            fragment_cursor
-                .item()
-                .map_or(false, |fragment| fragment.visible)
+        match self {
+            Anchor::Start { buffer_id } | Anchor::End { buffer_id } => {
+                *buffer_id == buffer.remote_id
+            }
+            Anchor::Character { buffer_id, .. } => {
+                if *buffer_id == buffer.remote_id {
+                    let fragment_id = buffer.fragment_id_for_anchor(self);
+                    let mut fragment_cursor =
+                        buffer.fragments.cursor::<(Option<&Locator>, usize)>(&None);
+                    fragment_cursor.seek(&Some(fragment_id), Bias::Left, &None);
+                    fragment_cursor
+                        .item()
+                        .map_or(false, |fragment| fragment.visible)
+                } else {
+                    false
+                }
+            }
         }
     }
 }

crates/text/src/text.rs

@@ -1542,16 +1542,15 @@ impl Buffer {
     ) -> impl 'static + Future<Output = Result<()>> {
         let mut futures = Vec::new();
         for anchor in anchors {
-            if !self.version.observed(anchor.timestamp)
-                && anchor != Anchor::MAX
-                && anchor != Anchor::MIN
-            {
-                let (tx, rx) = oneshot::channel();
-                self.edit_id_resolvers
-                    .entry(anchor.timestamp)
-                    .or_default()
-                    .push(tx);
-                futures.push(rx);
+            if let Anchor::Character { insertion_id, .. } = anchor {
+                if !self.version.observed(insertion_id) {
+                    let (tx, rx) = oneshot::channel();
+                    self.edit_id_resolvers
+                        .entry(insertion_id)
+                        .or_default()
+                        .push(tx);
+                    futures.push(rx);
+                }
             }
         }
 
@@ -1928,6 +1927,18 @@ impl BufferSnapshot {
         self.visible_text.summary()
     }
 
+    pub fn min_anchor(&self) -> Anchor {
+        Anchor::Start {
+            buffer_id: self.remote_id,
+        }
+    }
+
+    pub fn max_anchor(&self) -> Anchor {
+        Anchor::End {
+            buffer_id: self.remote_id,
+        }
+    }
+
     pub fn max_point(&self) -> Point {
         self.visible_text.max_point()
     }
@@ -2129,41 +2140,50 @@ impl BufferSnapshot {
         let mut position = D::zero(&());
 
         anchors.map(move |(anchor, payload)| {
-            if *anchor == Anchor::MIN {
-                return (D::zero(&()), payload);
-            } else if *anchor == Anchor::MAX {
-                return (D::from_text_summary(&self.visible_text.summary()), payload);
-            }
+            debug_assert_eq!(
+                anchor.buffer_id(),
+                self.remote_id,
+                "anchor belongs to a different buffer"
+            );
 
-            let anchor_key = InsertionFragmentKey {
-                timestamp: anchor.timestamp,
-                split_offset: anchor.offset,
-            };
-            insertion_cursor.seek(&anchor_key, anchor.bias, &());
-            if let Some(insertion) = insertion_cursor.item() {
-                let comparison = sum_tree::KeyedItem::key(insertion).cmp(&anchor_key);
-                if comparison == Ordering::Greater
-                    || (anchor.bias == Bias::Left
-                        && comparison == Ordering::Equal
-                        && anchor.offset > 0)
-                {
-                    insertion_cursor.prev(&());
+            match *anchor {
+                Anchor::Start { .. } => (D::zero(&()), payload),
+                Anchor::End { .. } => (D::from_text_summary(&self.visible_text.summary()), payload),
+                Anchor::Character {
+                    insertion_id,
+                    offset,
+                    bias,
+                    ..
+                } => {
+                    let anchor_key = InsertionFragmentKey {
+                        timestamp: insertion_id,
+                        split_offset: offset,
+                    };
+                    insertion_cursor.seek(&anchor_key, bias, &());
+                    if let Some(insertion) = insertion_cursor.item() {
+                        let comparison = sum_tree::KeyedItem::key(insertion).cmp(&anchor_key);
+                        if comparison == Ordering::Greater
+                            || (bias == Bias::Left && comparison == Ordering::Equal && offset > 0)
+                        {
+                            insertion_cursor.prev(&());
+                        }
+                    } else {
+                        insertion_cursor.prev(&());
+                    }
+                    let insertion = insertion_cursor.item().expect("invalid insertion");
+                    assert_eq!(insertion.timestamp, insertion_id, "invalid insertion");
+
+                    fragment_cursor.seek_forward(&Some(&insertion.fragment_id), Bias::Left, &None);
+                    let fragment = fragment_cursor.item().unwrap();
+                    let mut fragment_offset = fragment_cursor.start().1;
+                    if fragment.visible {
+                        fragment_offset += offset - insertion.split_offset;
+                    }
+
+                    position.add_assign(&text_cursor.summary(fragment_offset));
+                    (position.clone(), payload)
                 }
-            } else {
-                insertion_cursor.prev(&());
             }
-            let insertion = insertion_cursor.item().expect("invalid insertion");
-            assert_eq!(insertion.timestamp, anchor.timestamp, "invalid insertion");
-
-            fragment_cursor.seek_forward(&Some(&insertion.fragment_id), Bias::Left, &None);
-            let fragment = fragment_cursor.item().unwrap();
-            let mut fragment_offset = fragment_cursor.start().1;
-            if fragment.visible {
-                fragment_offset += anchor.offset - insertion.split_offset;
-            }
-
-            position.add_assign(&text_cursor.summary(fragment_offset));
-            (position.clone(), payload)
         })
     }
 
@@ -2171,90 +2191,57 @@ impl BufferSnapshot {
     where
         D: TextDimension,
     {
-        if *anchor == Anchor::MIN {
-            D::zero(&())
-        } else if *anchor == Anchor::MAX {
-            D::from_text_summary(&self.visible_text.summary())
-        } else {
-            let anchor_key = InsertionFragmentKey {
-                timestamp: anchor.timestamp,
-                split_offset: anchor.offset,
-            };
-            let mut insertion_cursor = self.insertions.cursor::<InsertionFragmentKey>(&());
-            insertion_cursor.seek(&anchor_key, anchor.bias, &());
-            if let Some(insertion) = insertion_cursor.item() {
-                let comparison = sum_tree::KeyedItem::key(insertion).cmp(&anchor_key);
-                if comparison == Ordering::Greater
-                    || (anchor.bias == Bias::Left
-                        && comparison == Ordering::Equal
-                        && anchor.offset > 0)
-                {
-                    insertion_cursor.prev(&());
-                }
-            } else {
-                insertion_cursor.prev(&());
-            }
-
-            let Some(insertion) = insertion_cursor
-                .item()
-                .filter(|insertion| insertion.timestamp == anchor.timestamp)
-            else {
-                panic!(
-                    "invalid anchor {:?}. buffer id: {}, version: {:?}",
-                    anchor, self.remote_id, self.version
-                );
-            };
-
-            let mut fragment_cursor = self.fragments.cursor::<(Option<&Locator>, usize)>(&None);
-            fragment_cursor.seek(&Some(&insertion.fragment_id), Bias::Left, &None);
-            let fragment = fragment_cursor.item().unwrap();
-            let mut fragment_offset = fragment_cursor.start().1;
-            if fragment.visible {
-                fragment_offset += anchor.offset - insertion.split_offset;
-            }
-            self.text_summary_for_range(0..fragment_offset)
-        }
+        self.summaries_for_anchors([anchor]).next().unwrap()
     }
 
     fn fragment_id_for_anchor(&self, anchor: &Anchor) -> &Locator {
-        if *anchor == Anchor::MIN {
-            Locator::min_ref()
-        } else if *anchor == Anchor::MAX {
-            Locator::max_ref()
-        } else {
-            let anchor_key = InsertionFragmentKey {
-                timestamp: anchor.timestamp,
-                split_offset: anchor.offset,
-            };
-            let mut insertion_cursor = self.insertions.cursor::<InsertionFragmentKey>(&());
-            insertion_cursor.seek(&anchor_key, anchor.bias, &());
-            if let Some(insertion) = insertion_cursor.item() {
-                let comparison = sum_tree::KeyedItem::key(insertion).cmp(&anchor_key);
-                if comparison == Ordering::Greater
-                    || (anchor.bias == Bias::Left
-                        && comparison == Ordering::Equal
-                        && anchor.offset > 0)
-                {
+        debug_assert_eq!(
+            anchor.buffer_id(),
+            self.remote_id,
+            "anchor belongs to a different buffer"
+        );
+
+        match *anchor {
+            Anchor::Start { .. } => Locator::min_ref(),
+            Anchor::End { .. } => Locator::max_ref(),
+            Anchor::Character {
+                insertion_id,
+                offset,
+                bias,
+                ..
+            } => {
+                let anchor_key = InsertionFragmentKey {
+                    timestamp: insertion_id,
+                    split_offset: offset,
+                };
+                let mut insertion_cursor = self.insertions.cursor::<InsertionFragmentKey>(&());
+                insertion_cursor.seek(&anchor_key, bias, &());
+                if let Some(insertion) = insertion_cursor.item() {
+                    let comparison = sum_tree::KeyedItem::key(insertion).cmp(&anchor_key);
+                    if comparison == Ordering::Greater
+                        || (bias == Bias::Left && comparison == Ordering::Equal && offset > 0)
+                    {
+                        insertion_cursor.prev(&());
+                    }
+                } else {
                     insertion_cursor.prev(&());
                 }
-            } else {
-                insertion_cursor.prev(&());
+
+                let Some(insertion) = insertion_cursor.item().filter(|insertion| {
+                    if cfg!(debug_assertions) {
+                        insertion.timestamp == insertion_id
+                    } else {
+                        true
+                    }
+                }) else {
+                    panic!(
+                        "invalid anchor {:?}. buffer id: {}, version: {:?}",
+                        anchor, self.remote_id, self.version
+                    );
+                };
+
+                &insertion.fragment_id
             }
-
-            let Some(insertion) = insertion_cursor.item().filter(|insertion| {
-                if cfg!(debug_assertions) {
-                    insertion.timestamp == anchor.timestamp
-                } else {
-                    true
-                }
-            }) else {
-                panic!(
-                    "invalid anchor {:?}. buffer id: {}, version: {:?}",
-                    anchor, self.remote_id, self.version
-                );
-            };
-
-            &insertion.fragment_id
         }
     }
 
@@ -2272,27 +2259,33 @@ impl BufferSnapshot {
 
     fn anchor_at_offset(&self, offset: usize, bias: Bias) -> Anchor {
         if bias == Bias::Left && offset == 0 {
-            Anchor::MIN
+            self.min_anchor()
         } else if bias == Bias::Right && offset == self.len() {
-            Anchor::MAX
+            self.max_anchor()
         } else {
             let mut fragment_cursor = self.fragments.cursor::<usize>(&None);
             fragment_cursor.seek(&offset, bias, &None);
             let fragment = fragment_cursor.item().unwrap();
             let overshoot = offset - *fragment_cursor.start();
-            Anchor {
-                timestamp: fragment.timestamp,
+            Anchor::Character {
+                insertion_id: fragment.timestamp,
                 offset: fragment.insertion_offset + overshoot,
                 bias,
-                buffer_id: Some(self.remote_id),
+                buffer_id: self.remote_id,
             }
         }
     }
 
     pub fn can_resolve(&self, anchor: &Anchor) -> bool {
-        *anchor == Anchor::MIN
-            || *anchor == Anchor::MAX
-            || (Some(self.remote_id) == anchor.buffer_id && self.version.observed(anchor.timestamp))
+        match *anchor {
+            Anchor::Start { buffer_id } => self.remote_id == buffer_id,
+            Anchor::End { buffer_id } => self.remote_id == buffer_id,
+            Anchor::Character {
+                buffer_id,
+                insertion_id,
+                ..
+            } => self.remote_id == buffer_id && self.version.observed(insertion_id),
+        }
     }
 
     pub fn clip_offset(&self, offset: usize, bias: Bias) -> usize {
@@ -2318,7 +2311,7 @@ impl BufferSnapshot {
     where
         D: TextDimension + Ord,
     {
-        self.edits_since_in_range(since, Anchor::MIN..Anchor::MAX)
+        self.edits_since_in_range(since, self.min_anchor()..self.max_anchor())
     }
 
     pub fn anchored_edits_since<'a, D>(
@@ -2328,7 +2321,7 @@ impl BufferSnapshot {
     where
         D: TextDimension + Ord,
     {
-        self.anchored_edits_since_in_range(since, Anchor::MIN..Anchor::MAX)
+        self.anchored_edits_since_in_range(since, self.min_anchor()..self.max_anchor())
     }
 
     pub fn edits_since_in_range<'a, D>(
@@ -2366,10 +2359,20 @@ impl BufferSnapshot {
 
         let start_fragment_id = self.fragment_id_for_anchor(&range.start);
         cursor.seek(&Some(start_fragment_id), Bias::Left, &None);
+        let start_fragment_offset = if let Anchor::Character { offset, .. } = range.start {
+            offset
+        } else {
+            0
+        };
+
         let mut visible_start = cursor.start().1.visible;
         let mut deleted_start = cursor.start().1.deleted;
         if let Some(fragment) = cursor.item() {
-            let overshoot = range.start.offset - fragment.insertion_offset;
+            let overshoot = if let Anchor::Character { offset, .. } = range.start {
+                offset - fragment.insertion_offset
+            } else {
+                0
+            };
             if fragment.visible {
                 visible_start += overshoot;
             } else {
@@ -2377,6 +2380,11 @@ impl BufferSnapshot {
             }
         }
         let end_fragment_id = self.fragment_id_for_anchor(&range.end);
+        let end_fragment_offset = if let Anchor::Character { offset, .. } = range.end {
+            offset
+        } else {
+            0
+        };
 
         Edits {
             visible_cursor: self.visible_text.cursor(visible_start),
@@ -2386,7 +2394,8 @@ impl BufferSnapshot {
             since,
             old_end: D::zero(&()),
             new_end: D::zero(&()),
-            range: (start_fragment_id, range.start.offset)..(end_fragment_id, range.end.offset),
+            range: (start_fragment_id, start_fragment_offset)
+                ..(end_fragment_id, end_fragment_offset),
             buffer_id: self.remote_id,
         }
     }
@@ -2516,17 +2525,17 @@ impl<'a, D: TextDimension + Ord, F: FnMut(&FragmentSummary) -> bool> Iterator fo
                 break;
             }
 
-            let start_anchor = Anchor {
-                timestamp: fragment.timestamp,
+            let start_anchor = Anchor::Character {
+                insertion_id: fragment.timestamp,
                 offset: fragment.insertion_offset,
                 bias: Bias::Right,
-                buffer_id: Some(self.buffer_id),
+                buffer_id: self.buffer_id,
             };
-            let end_anchor = Anchor {
-                timestamp: fragment.timestamp,
+            let end_anchor = Anchor::Character {
+                insertion_id: fragment.timestamp,
                 offset: fragment.insertion_offset + fragment.len,
                 bias: Bias::Left,
-                buffer_id: Some(self.buffer_id),
+                buffer_id: self.buffer_id,
             };
 
             if !fragment.was_visible(self.since, self.undos) && fragment.visible {