From 02b2e2ad8971ef25462e480a522e3d78a39eebc0 Mon Sep 17 00:00:00 2001
From: ilkin-overleaf <100852799+ilkin-overleaf@users.noreply.github.com>
Date: Fri, 7 Jul 2023 13:14:18 +0300
Subject: [PATCH] Merge pull request #13744 from overleaf/mj-big-projects

[cm6] Optimise getUpdatedProjection

GitOrigin-RevId: af321d3828185b245f557ab0e046851192c97296
---
 .../utils/tree-operations/commands.ts         |  8 ++++----
 .../utils/tree-operations/environments.ts     |  2 +-
 .../utils/tree-operations/outline.ts          |  4 ++--
 .../utils/tree-operations/projection.ts       | 19 ++++++++++++++-----
 4 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/services/web/frontend/js/features/source-editor/utils/tree-operations/commands.ts b/services/web/frontend/js/features/source-editor/utils/tree-operations/commands.ts
index 80c5e71a06..97123735d1 100644
--- a/services/web/frontend/js/features/source-editor/utils/tree-operations/commands.ts
+++ b/services/web/frontend/js/features/source-editor/utils/tree-operations/commands.ts
@@ -7,9 +7,9 @@ import { NodeIntersectsChangeFn, ProjectionItem } from './projection'
  * A projection of a command in the document
  */
 export class Command extends ProjectionItem {
-  title = ''
-  optionalArgCount = 0
-  requiredArgCount = 0
+  readonly title: string = ''
+  readonly optionalArgCount: number = 0
+  readonly requiredArgCount: number = 0
 }
 
 /**
@@ -62,7 +62,7 @@ export const enterNode = (
       argCountNumber--
     }
 
-    const thisCommand = {
+    const thisCommand: Readonly<Command> = {
       line: state.doc.lineAt(node.from).number,
       title: commandNameText,
       from: node.from,
diff --git a/services/web/frontend/js/features/source-editor/utils/tree-operations/environments.ts b/services/web/frontend/js/features/source-editor/utils/tree-operations/environments.ts
index fe754ff66c..d9287542a4 100644
--- a/services/web/frontend/js/features/source-editor/utils/tree-operations/environments.ts
+++ b/services/web/frontend/js/features/source-editor/utils/tree-operations/environments.ts
@@ -8,7 +8,7 @@ import { FigureData } from '../../extensions/figure-modal'
 const HUNDRED_MS = 100
 
 export class EnvironmentName extends ProjectionItem {
-  title = ''
+  readonly title: string = ''
 }
 
 export const enterNode = (
diff --git a/services/web/frontend/js/features/source-editor/utils/tree-operations/outline.ts b/services/web/frontend/js/features/source-editor/utils/tree-operations/outline.ts
index e353df50ce..d43f1d2bd6 100644
--- a/services/web/frontend/js/features/source-editor/utils/tree-operations/outline.ts
+++ b/services/web/frontend/js/features/source-editor/utils/tree-operations/outline.ts
@@ -15,8 +15,8 @@ export type Outline = {
  * A projection of a part of the file outline, typically a (sub)section heading
  */
 export class FlatOutlineItem extends ProjectionItem {
-  level = 0
-  title = ''
+  readonly level: number = 0
+  readonly title: string = ''
 }
 
 export type FlatOutline = FlatOutlineItem[]
diff --git a/services/web/frontend/js/features/source-editor/utils/tree-operations/projection.ts b/services/web/frontend/js/features/source-editor/utils/tree-operations/projection.ts
index 1614ee8df1..55c191784f 100644
--- a/services/web/frontend/js/features/source-editor/utils/tree-operations/projection.ts
+++ b/services/web/frontend/js/features/source-editor/utils/tree-operations/projection.ts
@@ -9,9 +9,9 @@ const FIVE_HUNDRED_MS = 500
  * A single item in the projection
  */
 export abstract class ProjectionItem {
-  from = 0
-  to = 0
-  line = 0
+  readonly from: number = 0
+  readonly to: number = 0
+  readonly line: number = 0
 }
 
 /* eslint-disable no-unused-vars */
@@ -47,11 +47,20 @@ export function updatePosition<T extends ProjectionItem>(
   }
   const { from, to } = item
   const newFrom = transaction.changes.mapPos(from)
+  const newTo = transaction.changes.mapPos(to)
+  const lineNumber = transaction.state.doc.lineAt(newFrom).number
+
+  if (newFrom === from && newTo === to && lineNumber === item.line) {
+    // Optimisation - if the item hasn't moved, don't create a new object
+    // If items are not immutable this can introduce problems
+    return item
+  }
+
   return {
     ...item,
     from: newFrom,
-    to: transaction.changes.mapPos(to),
-    line: transaction.state.doc.lineAt(newFrom).number,
+    to: newTo,
+    line: lineNumber,
   }
 }