From 248c47f60a12d12371bc74fac56ea83061f084a5 Mon Sep 17 00:00:00 2001
From: Dan <DanOfTheRoses@gmail.com>
Date: Wed, 2 Mar 2022 06:16:32 -0600
Subject: [PATCH] fix "editor.formatOnSaveMode": "modifications"

---
 CHANGELOG.md               |  4 ++++
 src/PrettierEditService.ts | 35 +++++++++++++++++++++++++++++------
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f62704eb5..311a7a85d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to the "prettier-vscode" extension will be documented in thi
 
 <!-- Check [Keep a Changelog](http://keepachangelog.com/) for recommendations on how to structure this file. -->
 
+## [9.4.0]
+
+- Fix `"editor.formatOnSaveMode": "modifications"`/`"modificationsIfAvailable"`
+
 ## [9.3.0]
 
 - Remove `.gts` and `.gjs` from Handlebars extensions
diff --git a/src/PrettierEditService.ts b/src/PrettierEditService.ts
index 0b4d4934c..6c6845f53 100644
--- a/src/PrettierEditService.ts
+++ b/src/PrettierEditService.ts
@@ -323,9 +323,37 @@ export default class PrettierEditService implements Disposable {
     this.loggingService.logInfo(
       `Formatting completed in ${duration / 1000}ms.`
     );
-    return [TextEdit.replace(this.fullDocumentRange(document), result)];
+    const edit = this.minimalEdit(document, result);
+    return [edit];
   };
 
+  private minimalEdit(document: TextDocument, string1: string) {
+    const string0 = document.getText();
+    // length of common prefix
+    let i = 0;
+    while (
+      i < string0.length &&
+      i < string1.length &&
+      string0[i] === string1[i]
+    ) {
+      ++i;
+    }
+    // length of common suffix
+    let j = 0;
+    while (
+      i + j < string0.length &&
+      i + j < string1.length &&
+      string0[string0.length - j - 1] === string1[string1.length - j - 1]
+    ) {
+      ++j;
+    }
+    const newText = string1.substring(i, string1.length - j);
+    const pos0 = document.positionAt(i);
+    const pos1 = document.positionAt(string0.length - j);
+
+    return TextEdit.replace(new Range(pos0, pos1), newText);
+  }
+
   /**
    * Format the given text with user's configuration.
    * @param text Text to format
@@ -507,9 +535,4 @@ export default class PrettierEditService implements Disposable {
 
     return options;
   }
-
-  private fullDocumentRange(document: TextDocument): Range {
-    const lastLineId = document.lineCount - 1;
-    return new Range(0, 0, lastLineId, document.lineAt(lastLineId).text.length);
-  }
 }