unrecognized escape sequences no longer crash the shell

src/error.rs

@@ -23,8 +23,11 @@ pub enum InputError {
     #[error("input record cannot convert to control character because it is an up event")]
     ControlCharactersOnlyGoDownNotUp,
 
-    #[error("bad escape sequence")]
-    BadEscapeSequence,
+    #[error("unrecognized escape sequence: {0}")]
+    BadEscapeSequence(String),
+
+    #[error("fart")]
+    UnexpectedInputRecordDuringEscapeParting,
 }
 
 #[derive(Debug, Error)]

src/input.rs

@@ -4,11 +4,12 @@ use crate::{
     log::*,
 };
 use anyhow::{Context, Result};
+use log::error;
 use std::{
     cell::{RefCell, RefMut},
     collections::VecDeque,
     fmt,
-    rc::Rc,
+    rc::{Rc, Weak},
 };
 use windows::Win32::{Foundation::HANDLE, System::Console};
 
@@ -181,8 +182,13 @@ impl Reader {
         }
 
         if is_escape_start(&record) {
-            let escape = self.next_escape_sequence()?;
-            return Ok(Event::Escape(escape));
+            match self.next_escape_sequence() {
+                Ok(escape) => return Ok(Event::Escape(escape)),
+                Err(e) => {
+                    error!("{e}");
+                    return self.next();
+                }
+            }
         }
 
         let event: Event = record.into();
@@ -239,9 +245,12 @@ impl Reader {
                     panic!();
                 }
             }
-            let c = as_escape_character(&record).ok_or(InputError::BadEscapeSequence)?;
-            if let Some(escape) = self.escapes.step(c) {
-                return Ok(escape);
+            let c = as_escape_character(&record)
+                .ok_or(InputError::UnexpectedInputRecordDuringEscapeParting)?;
+            match self.escapes.step(c) {
+                EscapeStep::Continue => {}
+                EscapeStep::End(escape) => return Ok(escape),
+                EscapeStep::Abort(s) => return Err(InputError::BadEscapeSequence(s).into()),
             }
         }
     }
@@ -333,13 +342,14 @@ impl From<Console::INPUT_RECORD> for Event {
 }
 
 /// A reference to a target node in a prefix tree, used for manipulating the prefix tree
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct EscapeCursor {
     target: Rc<EscapeNode>,
     root: Rc<EscapeNode>,
 }
 
-/// A node in a prefix tree. This prefix tree is used to parse strings into escape sequences
+/// A node in a prefix tree. This prefix tree is used to parse strings into escape sequences. This
+/// prefix tree is special in that there are no values in the intermediate nodes of the tree.
 #[derive(Debug)]
 pub enum EscapeNode {
     Root {
@@ -347,15 +357,18 @@ pub enum EscapeNode {
     },
     Nonterminal {
         c: char,
+        parent: Weak<EscapeNode>,
         children: RefCell<Vec<Rc<EscapeNode>>>,
     },
     Terminal {
         c: char,
+        parent: Weak<EscapeNode>,
         v: Escape,
     },
 }
 
 impl EscapeNode {
+    /// Creates a new prefix tree mapping character sequences to structured escape codes
     pub fn new() -> EscapeCursor {
         let root = Rc::new(EscapeNode::Root {
             children: RefCell::new(Vec::new()),
@@ -382,51 +395,44 @@ impl EscapeNode {
         }
     }
 
-    fn child(&self, c: char) -> Option<Rc<EscapeNode>> {
-        for child in self.children().iter_mut() {
-            if child.char() == c {
-                return Some(Rc::clone(child));
-            }
-        }
-        None
-    }
-
-    fn child_nonterminal(&self, c: char) -> Rc<EscapeNode> {
-        for child in self.children().iter_mut() {
-            if child.char() == c {
-                return Rc::clone(child);
-            }
+    fn parent(&self) -> Option<Rc<EscapeNode>> {
+        match self {
+            EscapeNode::Root { .. } => None,
+            EscapeNode::Nonterminal { parent, .. } => parent.upgrade(),
+            EscapeNode::Terminal { parent, .. } => parent.upgrade(),
         }
-        let child = Rc::new(EscapeNode::Nonterminal {
-            c,
-            children: RefCell::new(Vec::new()),
-        });
-        self.children().push(Rc::clone(&child));
-        child
     }
 
-    fn add_child_terminal(&self, c: char, v: Escape) {
+    fn child(&self, c: char) -> Option<Rc<EscapeNode>> {
         for child in self.children().iter_mut() {
             if child.char() == c {
-                panic!();
+                return Some(Rc::clone(child));
             }
         }
-        let child = Rc::new(EscapeNode::Terminal { c, v });
-        self.children().push(child);
+        None
     }
 }
 
 impl EscapeCursor {
-    fn step(&mut self, c: char) -> Option<Escape> {
-        let child = self.target.child(c)?;
+    /// advances our cursor by one step. We look at the current position and descend the tree into
+    /// the node described by the target character. If that node is a terminal node, we return that
+    /// node's value.
+    fn step(&mut self, c: char) -> EscapeStep {
+        let child = match self.target.child(c) {
+            Some(c) => c,
+            None => {
+                let path = self.path();
+                return EscapeStep::Abort(format!("{path}{c}"));
+            }
+        };
         match child.as_ref() {
             EscapeNode::Terminal { v, .. } => {
                 self.reset();
-                Some(*v)
+                EscapeStep::End(*v)
             }
             _ => {
                 self.target = child;
-                None
+                EscapeStep::Continue
             }
         }
     }
@@ -435,14 +441,36 @@ impl EscapeCursor {
         match self.target.child(c) {
             Some(child) => self.target = child,
             None => {
-                self.target = self.target.child_nonterminal(c);
+                for child in self.target.clone().children().iter() {
+                    if child.char() == c {
+                        self.target = Rc::clone(child);
+                        return;
+                    }
+                }
+                let child = Rc::new(EscapeNode::Nonterminal {
+                    c,
+                    parent: Rc::downgrade(&self.target),
+                    children: RefCell::new(Vec::new()),
+                });
+                self.target.children().push(Rc::clone(&child));
+                self.target = child;
             }
         }
     }
 
     /// adds a terminal node into the tree as a child of the current node
     fn add_terminal(&mut self, c: char, v: Escape) {
-        self.target.add_child_terminal(c, v);
+        for child in self.target.children().iter_mut() {
+            if child.char() == c {
+                panic!();
+            }
+        }
+        let child = Rc::new(EscapeNode::Terminal {
+            c,
+            parent: Rc::downgrade(&self.target),
+            v,
+        });
+        self.target.children().push(child);
     }
 
     /// resets the cursor back to the top of the tree
@@ -467,6 +495,23 @@ impl EscapeCursor {
             self.add_step(c);
         }
     }
+
+    /// renders as a string the path that takes us to the node to which we are currently pointed
+    fn path(&self) -> String {
+        let mut cursor = self.clone();
+        let mut chars = Vec::new();
+        while !cursor.is_at_root() {
+            chars.push(cursor.target.char());
+            cursor.target = cursor.target.parent().unwrap();
+        }
+        chars.iter().rev().collect()
+    }
+}
+
+enum EscapeStep {
+    Continue,
+    Abort(String),
+    End(Escape),
 }
 
 /// generates a prefix tree used for parsing escape sequences