From 7b34b1da9bdb88c0e72ed860e518e9407ac3524a Mon Sep 17 00:00:00 2001
From: Jason Williams <jase.williams@gmail.com>
Date: Mon, 13 Aug 2018 23:12:54 +0100
Subject: [PATCH] adding lexer updates

---
 src/lib/syntax/lexer.rs | 137 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 126 insertions(+), 11 deletions(-)

diff --git a/src/lib/syntax/lexer.rs b/src/lib/syntax/lexer.rs
index ab7ad88ace..3b5d63d083 100644
--- a/src/lib/syntax/lexer.rs
+++ b/src/lib/syntax/lexer.rs
@@ -1,7 +1,42 @@
+use std::char::from_u32;
+use std::error;
+use std::fmt;
+use std::iter::Peekable;
 use std::str::Chars;
 use syntax::ast::punc::Punctuator;
 use syntax::ast::token::{Token, TokenData};
 
+// Defining an error type
+#[derive(Debug, Clone)]
+pub struct LexerError {
+    details: String,
+}
+impl LexerError {
+    fn new(msg: &str) -> LexerError {
+        LexerError {
+            details: msg.to_string(),
+        }
+    }
+}
+
+impl fmt::Display for LexerError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.details)
+    }
+}
+
+// This is important for other errors to wrap this one.
+impl error::Error for LexerError {
+    fn description(&self) -> &str {
+        &self.details
+    }
+
+    fn cause(&self) -> Option<&error::Error> {
+        // Generic error, underlying cause isn't tracked.
+        None
+    }
+}
+
 /// A javascript Lexer
 pub struct Lexer<'a> {
     // The list fo tokens generated so far
@@ -11,7 +46,7 @@ pub struct Lexer<'a> {
     // the current column number in the script
     column_number: u64,
     // The full string
-    buffer: Chars<'a>,
+    buffer: Peekable<Chars<'a>>,
 }
 
 impl<'a> Lexer<'a> {
@@ -20,7 +55,7 @@ impl<'a> Lexer<'a> {
             tokens: Vec::new(),
             line_number: 1,
             column_number: 0,
-            buffer: buffer.chars(),
+            buffer: buffer.chars().peekable(),
         }
     }
     /// Push tokens onto the token queue
@@ -34,19 +69,99 @@ impl<'a> Lexer<'a> {
         self.push_token(TokenData::TPunctuator(punc));
     }
 
-    fn next(&mut self) -> Option<char> {
-        self.buffer.next()
+    fn next(&mut self) -> Result<char, LexerError> {
+        self.buffer.next().ok_or(LexerError::new("next failed"))
+    }
+
+    fn preview_next(&mut self) -> Result<&char, ()> {
+        // ok_or converts Option to a Result
+        self.buffer.peek().ok_or(())
     }
 
-    pub fn lex(&mut self) {
+    fn next_is(&mut self, peek: char) -> Result<bool, ()> {
+        let result = try!(self.preview_next()) == &peek;
+        if result {
+            self.buffer.next();
+        }
+        Ok(result)
+    }
+
+    pub fn lex(&mut self) -> Result<(), LexerError> {
         loop {
-            let ch = self.next();
+            let ch = match self.next() {
+                Ok(ch) => ch,
+                Err(LexerError) => return Err(LexerError),
+            };
+            self.column_number += 1;
             match ch {
-                Some(c) => {
-                    println!("{}", c);
-                }
-                None => {
-                    break;
+                '"' | '\'' => {
+                    let mut buf = String::new();
+                    loop {
+                        match self.next()? {
+                            '\'' if ch == '\'' => {
+                                break;
+                            }
+                            '"' if ch == '"' => {
+                                break;
+                            }
+                            '\\' => {
+                                let escape = self.next()?;
+                                if escape != '\n' {
+                                    let escaped_ch = match escape {
+                                        'n' => '\n',
+                                        'r' => '\r',
+                                        't' => '\t',
+                                        'b' => '\x08',
+                                        'f' => '\x0c',
+                                        '0' => '\0',
+                                        'x' => {
+                                            let mut nums = String::with_capacity(2);
+                                            for _ in 0u8..2 {
+                                                nums.push(self.next()?);
+                                            }
+                                            self.column_number += 2;
+                                            let as_num = match u64::from_str_radix(&nums, 16) {
+                                                Ok(v) => v,
+                                                Err(e) => 0,
+                                            };
+                                            match from_u32(as_num as u32) {
+                                                Some(v) => v,
+                                                None => panic!(
+                                                    "{}:{}: {} is not a valid unicode scalar value",
+                                                    self.line_number, self.column_number, as_num
+                                                ),
+                                            }
+                                        }
+                                        'u' => {
+                                            let mut nums = String::new();
+                                            for _ in 0u8..4 {
+                                                nums.push(self.next()?);
+                                            }
+                                            self.column_number += 4;
+                                            let as_num = match u64::from_str_radix(&nums, 16) {
+                                                Ok(v) => v,
+                                                Err(e) => 0,
+                                            };
+                                            match from_u32(as_num as u32) {
+                                                Some(v) => v,
+                                                None => panic!(
+                                                    "{}:{}: {} is not a valid unicode scalar value",
+                                                    self.line_number, self.column_number, as_num
+                                                ),
+                                            }
+                                        }
+                                        '\'' | '"' => escape,
+                                        _ => panic!(
+                                            "{}:{}: Invalid escape `{}`",
+                                            self.line_number, self.column_number, ch
+                                        ),
+                                    };
+                                    buf.push(escaped_ch);
+                                }
+                            }
+                            ch => buf.push(ch),
+                        }
+                    }
                 }
             }
         }