Fix invalid ESC escape sequence parsing

This strictens the ESC escape sequence parser to prevent invalid
intermediates from being ignored. Previously the parser would just look
at the first intermediate without validating that the rest of them is
empty.

If an escape like `\e(#0` is used now, it will no longer be accepted as
`\e(0` since the intermediate `#` is also present.

2 files changed, 23 insertions, 22 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e98ae125..37f208af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -37,6 +37,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - No live config update when starting Alacritty with a broken configuration file
 - PTY not drained to the end with the `--hold` flag enabled
 - High CPU usage on BSD with live config reload enabled
+- Alacritty not discarding invalid escape sequences starting with ESC
 
 ### Removed
 
diff --git a/alacritty_terminal/src/ansi.rs b/alacritty_terminal/src/ansi.rs
index 4c50495c..21f0ec45 100644
--- a/alacritty_terminal/src/ansi.rs
+++ b/alacritty_terminal/src/ansi.rs
@@ -1131,12 +1131,12 @@ where
         }
 
         macro_rules! configure_charset {
-            ($charset:path, $intermediate:expr) => {{
-                let index: CharsetIndex = match $intermediate {
-                    Some(b'(') => CharsetIndex::G0,
-                    Some(b')') => CharsetIndex::G1,
-                    Some(b'*') => CharsetIndex::G2,
-                    Some(b'+') => CharsetIndex::G3,
+            ($charset:path, $intermediates:expr) => {{
+                let index: CharsetIndex = match $intermediates {
+                    [b'('] => CharsetIndex::G0,
+                    [b')'] => CharsetIndex::G1,
+                    [b'*'] => CharsetIndex::G2,
+                    [b'+'] => CharsetIndex::G3,
                     _ => {
                         unhandled!();
                         return;
@@ -1146,27 +1146,27 @@ where
             }};
         }
 
-        match (byte, intermediates.get(0)) {
-            (b'B', intermediate) => configure_charset!(StandardCharset::Ascii, intermediate),
-            (b'D', None) => self.handler.linefeed(),
-            (b'E', None) => {
+        match (byte, intermediates) {
+            (b'B', intermediates) => configure_charset!(StandardCharset::Ascii, intermediates),
+            (b'D', []) => self.handler.linefeed(),
+            (b'E', []) => {
                 self.handler.linefeed();
                 self.handler.carriage_return();
             },
-            (b'H', None) => self.handler.set_horizontal_tabstop(),
-            (b'M', None) => self.handler.reverse_index(),
-            (b'Z', None) => self.handler.identify_terminal(self.writer, None),
-            (b'c', None) => self.handler.reset_state(),
-            (b'0', intermediate) => {
-                configure_charset!(StandardCharset::SpecialCharacterAndLineDrawing, intermediate)
+            (b'H', []) => self.handler.set_horizontal_tabstop(),
+            (b'M', []) => self.handler.reverse_index(),
+            (b'Z', []) => self.handler.identify_terminal(self.writer, None),
+            (b'c', []) => self.handler.reset_state(),
+            (b'0', intermediates) => {
+                configure_charset!(StandardCharset::SpecialCharacterAndLineDrawing, intermediates)
             },
-            (b'7', None) => self.handler.save_cursor_position(),
-            (b'8', Some(b'#')) => self.handler.decaln(),
-            (b'8', None) => self.handler.restore_cursor_position(),
-            (b'=', None) => self.handler.set_keypad_application_mode(),
-            (b'>', None) => self.handler.unset_keypad_application_mode(),
+            (b'7', []) => self.handler.save_cursor_position(),
+            (b'8', [b'#']) => self.handler.decaln(),
+            (b'8', []) => self.handler.restore_cursor_position(),
+            (b'=', []) => self.handler.set_keypad_application_mode(),
+            (b'>', []) => self.handler.unset_keypad_application_mode(),
             // String terminator, do nothing (parser handles as string terminator).
-            (b'\\', None) => (),
+            (b'\\', []) => (),
             _ => unhandled!(),
         }
     }