1 files changed, 74 insertions, 0 deletions
diff --git a/third_party/rust/regex-automata/src/dfa/start.rs b/third_party/rust/regex-automata/src/dfa/start.rs
new file mode 100644
index 0000000000..fddc702df5
--- /dev/null
+++ b/third_party/rust/regex-automata/src/dfa/start.rs
@@ -0,0 +1,74 @@
+use core::mem::size_of;
+
+use crate::util::wire::{self, DeserializeError, Endian, SerializeError};
+
+/// The kind of anchored starting configurations to support in a DFA.
+///
+/// Fully compiled DFAs need to be explicitly configured as to which anchored
+/// starting configurations to support. The reason for not just supporting
+/// everything unconditionally is that it can use more resources (such as
+/// memory and build time). The downside of this is that if you try to execute
+/// a search using an [`Anchored`](crate::Anchored) mode that is not supported
+/// by the DFA, then the search will return an error.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum StartKind {
+    /// Support both anchored and unanchored searches.
+    Both,
+    /// Support only unanchored searches. Requesting an anchored search will
+    /// panic.
+    ///
+    /// Note that even if an unanchored search is requested, the pattern itself
+    /// may still be anchored. For example, `^abc` will only match `abc` at the
+    /// start of a haystack. This will remain true, even if the regex engine
+    /// only supported unanchored searches.
+    Unanchored,
+    /// Support only anchored searches. Requesting an unanchored search will
+    /// panic.
+    Anchored,
+}
+
+impl StartKind {
+    pub(crate) fn from_bytes(
+        slice: &[u8],
+    ) -> Result<(StartKind, usize), DeserializeError> {
+        wire::check_slice_len(slice, size_of::<u32>(), "start kind bytes")?;
+        let (n, nr) = wire::try_read_u32(slice, "start kind integer")?;
+        match n {
+            0 => Ok((StartKind::Both, nr)),
+            1 => Ok((StartKind::Unanchored, nr)),
+            2 => Ok((StartKind::Anchored, nr)),
+            _ => Err(DeserializeError::generic("unrecognized start kind")),
+        }
+    }
+
+    pub(crate) fn write_to<E: Endian>(
+        &self,
+        dst: &mut [u8],
+    ) -> Result<usize, SerializeError> {
+        let nwrite = self.write_to_len();
+        if dst.len() < nwrite {
+            return Err(SerializeError::buffer_too_small("start kind"));
+        }
+        let n = match *self {
+            StartKind::Both => 0,
+            StartKind::Unanchored => 1,
+            StartKind::Anchored => 2,
+        };
+        E::write_u32(n, dst);
+        Ok(nwrite)
+    }
+
+    pub(crate) fn write_to_len(&self) -> usize {
+        size_of::<u32>()
+    }
+
+    #[cfg_attr(feature = "perf-inline", inline(always))]
+    pub(crate) fn has_unanchored(&self) -> bool {
+        matches!(*self, StartKind::Both | StartKind::Unanchored)
+    }
+
+    #[cfg_attr(feature = "perf-inline", inline(always))]
+    pub(crate) fn has_anchored(&self) -> bool {
+        matches!(*self, StartKind::Both | StartKind::Anchored)
+    }
+}