From 50a55a0d5258654212376808d4b1965c12a67d18 Mon Sep 17 00:00:00 2001
From: Cristian Maglie <c.maglie@arduino.cc>
Date: Fri, 21 May 2021 12:16:24 +0200
Subject: [PATCH] Autoformat keeps cursor position after Undo

---
 .../formatter/clangformat/ClangFormat.java     | 18 ++++++++++++++----
 .../AutoformatProducesOneUndoActionTest.java   |  3 ++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/app/src/cc/arduino/packages/formatter/clangformat/ClangFormat.java b/app/src/cc/arduino/packages/formatter/clangformat/ClangFormat.java
index 85cd940566e..d4a69b6480b 100644
--- a/app/src/cc/arduino/packages/formatter/clangformat/ClangFormat.java
+++ b/app/src/cc/arduino/packages/formatter/clangformat/ClangFormat.java
@@ -46,7 +46,7 @@
 import processing.app.Base;
 import processing.app.BaseNoGui;
 import processing.app.Editor;
-import processing.app.EditorTab;
+import processing.app.syntax.SketchTextArea;
 
 public class ClangFormat implements Runnable {
 
@@ -60,17 +60,27 @@ public ClangFormat(Editor editor) {
 
   @Override
   public void run() {
-    EditorTab tab = editor.getCurrentTab();
+    SketchTextArea tab = editor.getCurrentTab().getTextArea();
     String originalText = tab.getText();
-    int cursorOffset = tab.getTextArea().getCaretPosition();
+    int cursorOffset = tab.getCaretPosition();
     try {
       FormatResult result = runClangFormatOn(originalText, cursorOffset);
       if (result.FormattedText.equals(originalText)) {
         editor.statusNotice(tr("No changes necessary for Auto Format."));
         return;
       }
+
+      // To keep cursor position after UNDO we produce a bogus edit (insertion
+      // and removal of a " " at cursor position) and we compound this change
+      // with the full auto-format update.
+      tab.beginAtomicEdit();
+      tab.insert(" ", cursorOffset);
+      tab.replaceRange("", cursorOffset, cursorOffset + 1);
       tab.setText(result.FormattedText);
-      tab.getTextArea().setCaretPosition(result.Cursor);
+      tab.endAtomicEdit();
+
+      tab.setCaretPosition(result.Cursor);
+
       editor.statusNotice(tr("Auto Format finished."));
     } catch (IOException | InterruptedException e) {
       editor.statusError("Auto format error: " + e.getMessage());
diff --git a/app/test/processing/app/AutoformatProducesOneUndoActionTest.java b/app/test/processing/app/AutoformatProducesOneUndoActionTest.java
index 3d23e068de1..f24ec92eaff 100644
--- a/app/test/processing/app/AutoformatProducesOneUndoActionTest.java
+++ b/app/test/processing/app/AutoformatProducesOneUndoActionTest.java
@@ -72,7 +72,8 @@ public void shouldSaveCaretPositionAfterAutoformat() {
     String formattedText = editor.getText();
     assertEquals(SOURCE_AFTER, formattedText);
 
-    assertEquals(29, editor.getCaretPosition());
+    // Autoformat with clang-format keeps cursor relative to source code
+    assertEquals(17, editor.getCaretPosition());
 
     menuEditUndo.requireEnabled();
     menuEditUndo.click();