Add a onepass dfa matcher.

Cargo.toml

@@ -114,6 +114,11 @@ name = "backtrack-bytes"
 path = "tests/test_crates_regex.rs"
 name = "crates-regex"
 
+# Run the test suite on the onepass engine.
+[[test]]
+path = "tests/test_onepass.rs"
+name = "onepass"
+
 [profile.release]
 debug = true
 

regex-syntax/src/hir/interval.rs

@@ -309,6 +309,11 @@ impl<I: Interval> IntervalSet<I> {
         }
         true
     }
+
+    /// Returns true iff this class is empty.
+    pub fn is_empty(&self) -> bool {
+        self.ranges.is_empty()
+    }
 }
 
 /// An iterator over intervals.

regex-syntax/src/hir/mod.rs

@@ -797,6 +797,16 @@ impl ClassUnicode {
     pub fn symmetric_difference(&mut self, other: &ClassUnicode) {
         self.set.symmetric_difference(&other.set);
     }
+
+    /// Returns true iff this character class contains no characters.
+    ///
+    /// This should never be true for a character class which was
+    /// constructed by the regex parser, but a notion of character
+    /// class emptiness can be useful for code that wants to
+    /// programmatically generate character classes.
+    pub fn is_empty(&self) -> bool {
+        self.set.is_empty()
+    }
 }
 
 /// An iterator over all ranges in a Unicode character class.
@@ -998,6 +1008,16 @@ impl ClassBytes {
     pub fn is_all_ascii(&self) -> bool {
         self.set.intervals().last().map_or(true, |r| r.end <= 0x7F)
     }
+
+    /// Returns true iff this character class contains no characters.
+    ///
+    /// This should never be true for a character class which was
+    /// constructed by the regex parser, but a notion of character
+    /// class emptiness can be useful for code that wants to
+    /// programmatically generate character classes.
+    pub fn is_empty(&self) -> bool {
+        self.set.is_empty()
+    }
 }
 
 /// An iterator over all ranges in a byte character class.