From d0ca06d624cea8dc3584d64bc62bee2c1f445b2b Mon Sep 17 00:00:00 2001
From: Alexey Zimarev <alex@zimarev.com>
Date: Wed, 7 Oct 2026 17:56:08 +0200
Subject: [PATCH] Send ESC DEL for Alt+Backspace and BS for Ctrl+Backspace

The legacy generator mapped Backspace to DEL whatever the modifiers, so a shell deleted one character for Alt+Backspace. Mirrors xterm.js Keyboard.ts, case 8.
---
 src/XTerm.NET.Tests/KeyboardInputTests.cs     | 21 +++++++++++++++++++
 src/XTerm.NET/Input/KeyboardInputGenerator.cs | 10 ++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/XTerm.NET.Tests/KeyboardInputTests.cs b/src/XTerm.NET.Tests/KeyboardInputTests.cs
index 70abc2b0..9f1a83a8 100644
--- a/src/XTerm.NET.Tests/KeyboardInputTests.cs
+++ b/src/XTerm.NET.Tests/KeyboardInputTests.cs
@@ -200,6 +200,27 @@ public void ControlKeys_GenerateCorrectSequences()
         Assert.Equal(" ", terminal.GenerateKeyInput(Key.Space));
     }
 
+    [Fact]
+    public void Backspace_WithAlt_PrefixesEscape()
+    {
+        // Arrange
+        var terminal = CreateTerminal();
+
+        // Act & Assert
+        Assert.Equal("\x1B\x7F", terminal.GenerateKeyInput(Key.Backspace, KeyModifiers.Alt));
+    }
+
+    [Fact]
+    public void Backspace_WithControl_GeneratesBS()
+    {
+        // Arrange
+        var terminal = CreateTerminal();
+
+        // Act & Assert
+        Assert.Equal("\b", terminal.GenerateKeyInput(Key.Backspace, KeyModifiers.Control));
+        Assert.Equal("\x1B\b", terminal.GenerateKeyInput(Key.Backspace, KeyModifiers.Control | KeyModifiers.Alt));
+    }
+
     [Fact]
     public void Tab_WithShift_GeneratesBackTab()
     {
diff --git a/src/XTerm.NET/Input/KeyboardInputGenerator.cs b/src/XTerm.NET/Input/KeyboardInputGenerator.cs
index 1751f46e..1fce2a89 100644
--- a/src/XTerm.NET/Input/KeyboardInputGenerator.cs
+++ b/src/XTerm.NET/Input/KeyboardInputGenerator.cs
@@ -33,7 +33,7 @@ public string GenerateKeySequence(Key key, KeyModifiers modifiers = KeyModifiers
             // Control keys
             Key.Enter => "\r",
             Key.Tab => (modifiers & KeyModifiers.Shift) != 0 ? "\u001b[Z" : "\t",
-            Key.Backspace => "\u007f", // DEL (127)
+            Key.Backspace => GetBackspace(modifiers),
             // Escape sends ESC whatever the modifiers. CSI 27 ; mod ~ is not a sequence xterm
             // emits -- it belongs to the modifyOtherKeys and Kitty protocols, which an application
             // opts into. Sending it unasked meant a program that reads a bare ESC (vim leaving
@@ -161,6 +161,14 @@ public string GenerateCharSequence(char c, KeyModifiers modifiers = KeyModifiers
         };
     }
 
+    // xterm.js sends BS for Ctrl+Backspace and DEL otherwise, with an ESC prefix when Alt is
+    // held, which is how Alt+Backspace reaches a shell as backward-kill-word.
+    private static string GetBackspace(KeyModifiers modifiers)
+    {
+        var key = (modifiers & KeyModifiers.Control) != 0 ? "\b" : "\u007f";
+        return (modifiers & KeyModifiers.Alt) != 0 ? "\u001b" + key : key;
+    }
+
     private string GetArrowKey(char direction, KeyModifiers modifiers)
     {
         // Arrow keys respect ApplicationCursorKeys mode