mv compiler to compiler/

compiler/rustc_lexer/src/cursor.rs

@@ -0,0 +1,84 @@
+use std::str::Chars;
+
+/// Peekable iterator over a char sequence.
+///
+/// Next characters can be peeked via `nth_char` method,
+/// and position can be shifted forward via `bump` method.
+pub(crate) struct Cursor<'a> {
+    initial_len: usize,
+    chars: Chars<'a>,
+    #[cfg(debug_assertions)]
+    prev: char,
+}
+
+pub(crate) const EOF_CHAR: char = '\0';
+
+impl<'a> Cursor<'a> {
+    pub(crate) fn new(input: &'a str) -> Cursor<'a> {
+        Cursor {
+            initial_len: input.len(),
+            chars: input.chars(),
+            #[cfg(debug_assertions)]
+            prev: EOF_CHAR,
+        }
+    }
+
+    /// Returns the last eaten symbol (or `'\0'` in release builds).
+    /// (For debug assertions only.)
+    pub(crate) fn prev(&self) -> char {
+        #[cfg(debug_assertions)]
+        {
+            self.prev
+        }
+
+        #[cfg(not(debug_assertions))]
+        {
+            '\0'
+        }
+    }
+
+    /// Returns nth character relative to the current cursor position.
+    /// If requested position doesn't exist, `EOF_CHAR` is returned.
+    /// However, getting `EOF_CHAR` doesn't always mean actual end of file,
+    /// it should be checked with `is_eof` method.
+    fn nth_char(&self, n: usize) -> char {
+        self.chars().nth(n).unwrap_or(EOF_CHAR)
+    }
+
+    /// Peeks the next symbol from the input stream without consuming it.
+    pub(crate) fn first(&self) -> char {
+        self.nth_char(0)
+    }
+
+    /// Peeks the second symbol from the input stream without consuming it.
+    pub(crate) fn second(&self) -> char {
+        self.nth_char(1)
+    }
+
+    /// Checks if there is nothing more to consume.
+    pub(crate) fn is_eof(&self) -> bool {
+        self.chars.as_str().is_empty()
+    }
+
+    /// Returns amount of already consumed symbols.
+    pub(crate) fn len_consumed(&self) -> usize {
+        self.initial_len - self.chars.as_str().len()
+    }
+
+    /// Returns a `Chars` iterator over the remaining characters.
+    fn chars(&self) -> Chars<'a> {
+        self.chars.clone()
+    }
+
+    /// Moves to the next character.
+    pub(crate) fn bump(&mut self) -> Option<char> {
+        let c = self.chars.next()?;
+
+        #[cfg(debug_assertions)]
+        {
+            self.prev = c;
+        }
+
+        Some(c)
+    }
+}