Performance improvement.

The refactoring added `next_is` which takes a `&str` as parameter, while
we only use it with strings of lengths 2 and 3. Replacing this by 2
dedicated methods (which can be added to the trait interface and only
specialized if needed) removes almost all the overhead that was added by
`Input`.

parser/src/buffered_input.rs

@@ -90,10 +90,4 @@ impl<T: Iterator<Item = char>> Input for BufferedInput<T> {
     fn peek_nth(&self, n: usize) -> char {
         self.buffer[n]
     }
-
-    #[inline]
-    fn next_is(&self, pat: &str) -> bool {
-        assert!(self.buffer.len() >= pat.len());
-        self.buffer.iter().zip(pat.chars()).all(|(a, b)| *a == b)
-    }
 }

parser/src/input.rs

@@ -102,10 +102,25 @@ pub trait Input {
         self.peek_nth(n) == c
     }
 
-    /// Return whether the next characters in the input source match the given pattern.
+    /// Return whether the next 2 characters in the input source match the given characters.
     ///
-    /// This function assumes that the next `pat.len()` characters in the input has already been
-    /// fetched through [`Input::lookahead`].
+    /// This function assumes that the next 2 characters in the input has already been fetched
+    /// through [`Input::lookahead`].
+    #[inline]
     #[must_use]
-    fn next_is(&self, pat: &str) -> bool;
+    fn next_2_are(&self, c1: char, c2: char) -> bool {
+        assert!(self.buflen() >= 2);
+        self.peek() == c1 && self.peek_nth(1) == c2
+    }
+
+    /// Return whether the next 3 characters in the input source match the given characters.
+    ///
+    /// This function assumes that the next 3 characters in the input has already been fetched
+    /// through [`Input::lookahead`].
+    #[inline]
+    #[must_use]
+    fn next_3_are(&self, c1: char, c2: char, c3: char) -> bool {
+        assert!(self.buflen() >= 3);
+        self.peek() == c1 && self.peek_nth(1) == c2 && self.peek_nth(2) == c3
+    }
 }

parser/src/scanner.rs

@@ -528,7 +528,7 @@ impl<T: Input> Scanner<T> {
     /// Consume a linebreak (either CR, LF or CRLF), if any. Do nothing if there's none.
     #[inline]
     fn skip_linebreak(&mut self) {
-        if self.input.next_is("\r\n") {
+        if self.input.next_2_are('\r', '\n') {
             // While technically not a blank, this does not matter as `self.leading_whitespace`
             // will be reset by `skip_nl`.
             self.skip_blank();
@@ -597,7 +597,7 @@ impl<T: Input> Scanner<T> {
     /// [`Self::lookahead`] must have been called before calling this function.
     fn next_is_document_start(&self) -> bool {
         assert!(self.input.buflen() >= 4);
-        self.input.next_is("---") && is_blank_or_breakz(self.input.peek_nth(3))
+        self.input.next_3_are('-', '-', '-') && is_blank_or_breakz(self.input.peek_nth(3))
     }
 
     /// Check whether the next characters correspond to an end of document.
@@ -605,7 +605,7 @@ impl<T: Input> Scanner<T> {
     /// [`Self::lookahead`] must have been called before calling this function.
     fn next_is_document_end(&self) -> bool {
         assert!(self.input.buflen() >= 4);
-        self.input.next_is("...") && is_blank_or_breakz(self.input.peek_nth(3))
+        self.input.next_3_are('.', '.', '.') && is_blank_or_breakz(self.input.peek_nth(3))
     }
 
     /// Check whether the next characters correspond to a document indicator.
@@ -615,7 +615,7 @@ impl<T: Input> Scanner<T> {
     fn next_is_document_indicator(&self) -> bool {
         assert!(self.input.buflen() >= 4);
         is_blank_or_breakz(self.input.peek_nth(3))
-            && (self.input.next_is("...") || self.input.next_is("---"))
+            && (self.input.next_3_are('.', '.', '.') || self.input.next_3_are('-', '-', '-'))
     }
 
     /// Insert a token at the given position.