From 80ec2dcc609c1630bea5e8ea2d22d85aa2822d6e Mon Sep 17 00:00:00 2001
From: Valentin Klein <vangel1976@googlemail.com>
Date: Tue, 13 Oct 2026 10:37:42 +0200
Subject: [PATCH] Ctrl+Z / U during LINE, PLINE... removes the last segment
 instead of the whole command (#750) (#831)

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 crates/engine/src/lib.rs   |  6 ++++++
 crates/engine/src/tests.rs | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 25a65974..40caf3b6 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -878,6 +878,12 @@ impl Session {
             }
         }
         let nested = transparent && spec.transparent && self.running.is_some() && spec.interactive.is_some();
+        // Ctrl+Z / U / UNDO while a command's prompt offers its own Undo keyword (LINE, PLINE…)
+        // takes back the last segment and keeps the command running, as the keyword does.
+        if !nested && matches!(spec.id, "u" | "undo") && self.current_prompt().is_some_and(|p| p.keywords.iter().any(|k| k == "Undo")) {
+            self.echo(format!("Command: {}", spec.id.to_ascii_uppercase()));
+            return self.input(Input::Keyword("Undo".into()));
+        }
         if !nested && self.running.is_some() {
             self.cancel();
         }
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 97ce8be9..3b972e32 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -76,6 +76,43 @@ fn programmatic_undo_during_a_command_ends_it_first() {
     assert_eq!(kinds(&s), vec!["Line", "Text"]);
 }
 
+#[test]
+fn undo_during_line_removes_the_last_segment_and_keeps_line_running() {
+    let mut s = Session::new();
+    s.cmdline("line 0,0 10,0 10,10 20,10").unwrap();
+    assert_eq!(kinds(&s), vec!["Line", "Line", "Line"]);
+    // Ctrl+Z / the U command / the menu (Session::start) act as the Undo keyword.
+    s.start("u").unwrap();
+    assert!(s.running.is_some());
+    assert_eq!(kinds(&s), vec!["Line", "Line"]);
+    s.start("u").unwrap();
+    assert!(s.running.is_some());
+    assert_eq!(kinds(&s), vec!["Line"]);
+    // The command goes on from the last remaining point.
+    s.cmdline("10,5").unwrap();
+    assert_eq!(kinds(&s), vec!["Line", "Line"]);
+    s.cmdline("").unwrap();
+    assert!(s.running.is_none());
+}
+
+#[test]
+fn undo_during_a_command_without_undo_keyword_ends_it_and_undoes() {
+    let mut s = Session::new();
+    s.execute("line", &json!({"points": [[0, 0], [10, 0]]})).unwrap();
+    // LINE at its first point offers no Undo: Ctrl+Z ends it, then undoes the earlier line.
+    s.cmdline("line").unwrap();
+    assert!(s.running.is_some());
+    s.start("u").unwrap();
+    assert!(s.running.is_none());
+    assert!(kinds(&s).is_empty());
+    // TEXT offers no Undo keyword either.
+    s.execute("line", &json!({"points": [[0, 0], [10, 0]]})).unwrap();
+    s.script("TEXT 0,0 5 0 HELLO\n").unwrap();
+    s.start("u").unwrap();
+    assert!(s.running.is_none());
+    assert_eq!(kinds(&s), vec!["Line"]);
+}
+
 #[test]
 fn polar_and_direct_distance() {
     let mut s = Session::new();