From 93bc6616c697bee1ecf178e41597f0b294b0826b Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukas@zed.dev>
Date: Thu, 4 Dec 2025 16:41:48 +0100
Subject: [PATCH] editor: Improve performance of
 `update_visible_edit_prediction` (#44161)

One half of https://github.com/zed-industries/zed/issues/42861

This basically reduces the main thread work for large enough json (and
other) files from multiple milliseconds (15ms was observed in that test
case) down to microseconds (100ms here).

Release Notes:

- Improved cursor movement performance when edit predictions are enabled
---
 crates/editor/src/editor.rs             | 15 ++++++++----
 crates/multi_buffer/src/multi_buffer.rs | 32 +++++++++++++++++++------
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/crates/editor/src/editor.rs b/crates/editor/src/editor.rs
index 0528784719..4b352e2d82 100644
--- a/crates/editor/src/editor.rs
+++ b/crates/editor/src/editor.rs
@@ -182,7 +182,7 @@ use std::{
     iter::{self, Peekable},
     mem,
     num::NonZeroU32,
-    ops::{Deref, DerefMut, Not, Range, RangeInclusive},
+    ops::{ControlFlow, Deref, DerefMut, Not, Range, RangeInclusive},
     path::{Path, PathBuf},
     rc::Rc,
     sync::Arc,
@@ -8073,10 +8073,17 @@ impl Editor {
 
         if self.edit_prediction_indent_conflict {
             let cursor_point = cursor.to_point(&multibuffer);
+            let mut suggested_indent = None;
+            multibuffer.suggested_indents_callback(
+                cursor_point.row..cursor_point.row + 1,
+                |_, indent| {
+                    suggested_indent = Some(indent);
+                    ControlFlow::Break(())
+                },
+                cx,
+            );
 
-            let indents = multibuffer.suggested_indents(cursor_point.row..cursor_point.row + 1, cx);
-
-            if let Some((_, indent)) = indents.iter().next()
+            if let Some(indent) = suggested_indent
                 && indent.len == cursor_point.column
             {
                 self.edit_prediction_indent_conflict = false;
diff --git a/crates/multi_buffer/src/multi_buffer.rs b/crates/multi_buffer/src/multi_buffer.rs
index 02adb79e70..af36aaadf0 100644
--- a/crates/multi_buffer/src/multi_buffer.rs
+++ b/crates/multi_buffer/src/multi_buffer.rs
@@ -43,7 +43,7 @@ use std::{
     io,
     iter::{self, FromIterator},
     mem,
-    ops::{self, AddAssign, Range, RangeBounds, Sub, SubAssign},
+    ops::{self, AddAssign, ControlFlow, Range, RangeBounds, Sub, SubAssign},
     rc::Rc,
     str,
     sync::Arc,
@@ -4618,7 +4618,24 @@ impl MultiBufferSnapshot {
         cx: &App,
     ) -> BTreeMap<MultiBufferRow, IndentSize> {
         let mut result = BTreeMap::new();
+        self.suggested_indents_callback(
+            rows,
+            |row, indent| {
+                result.insert(row, indent);
+                ControlFlow::Continue(())
+            },
+            cx,
+        );
+        result
+    }
 
+    // move this to be a generator once those are a thing
+    pub fn suggested_indents_callback(
+        &self,
+        rows: impl IntoIterator<Item = u32>,
+        mut cb: impl FnMut(MultiBufferRow, IndentSize) -> ControlFlow<()>,
+        cx: &App,
+    ) {
         let mut rows_for_excerpt = Vec::new();
         let mut cursor = self.cursor::<Point, Point>();
         let mut rows = rows.into_iter().peekable();
@@ -4662,16 +4679,17 @@ impl MultiBufferSnapshot {
             let buffer_indents = region
                 .buffer
                 .suggested_indents(buffer_rows, single_indent_size);
-            let multibuffer_indents = buffer_indents.into_iter().map(|(row, indent)| {
-                (
+            for (row, indent) in buffer_indents {
+                if cb(
                     MultiBufferRow(start_multibuffer_row + row - start_buffer_row),
                     indent,
                 )
-            });
-            result.extend(multibuffer_indents);
+                .is_break()
+                {
+                    return;
+                }
+            }
         }
-
-        result
     }
 
     pub fn indent_size_for_line(&self, row: MultiBufferRow) -> IndentSize {