Fix stack overflow on parsing deeply nested expressions

Added a maximum expression depth of 64 to the parser and a more helpful error message if it's exceeded

This fixes #788

Changelog: fixed

Author: Keithcat1

ast/src/parser.rs

@@ -50,6 +50,9 @@ pub struct ParseError {
     pub location: Location,
 }
 
+/// The maximum number of nested expressions allowed
+const MAX_DEPTH: u32 = 64;
+
 /// A recursive-descent parser that turns Inko source code into an AST.
 ///
 /// The AST is not a lossless AST. For example, whitespace and comments are not
@@ -60,13 +63,14 @@ pub struct Parser {
     lexer: Lexer,
     peeked: Option<Token>,
     comments: bool,
+    depth: u32,
 }
 
 impl Parser {
     pub fn new(input: Vec<u8>, file: PathBuf) -> Self {
         let lexer = Lexer::new(input);
 
-        Self { file, lexer, comments: false, peeked: None }
+        Self { file, lexer, comments: false, peeked: None, depth: 0 }
     }
 
     pub fn with_comments(input: Vec<u8>, file: PathBuf) -> Self {
@@ -1552,7 +1556,16 @@ impl Parser {
     }
 
     fn expression(&mut self, start: Token) -> Result<Expression, ParseError> {
-        self.boolean_and_or(start)
+        if self.depth == MAX_DEPTH {
+            error!(
+                start.location,
+                "Maximum expression depth of {} exceeded", MAX_DEPTH
+            )
+        }
+        self.depth += 1;
+        let res = self.boolean_and_or(start);
+        self.depth -= 1;
+        res
     }
 
     fn boolean_and_or(