diff options
Diffstat (limited to 'vendor/regex-automata/src/dfa.rs')
| -rw-r--r-- | vendor/regex-automata/src/dfa.rs | 363 |
1 files changed, 363 insertions, 0 deletions
diff --git a/vendor/regex-automata/src/dfa.rs b/vendor/regex-automata/src/dfa.rs new file mode 100644 index 000000000..43de3461f --- /dev/null +++ b/vendor/regex-automata/src/dfa.rs @@ -0,0 +1,363 @@ +use state_id::StateID; + +/// A trait describing the interface of a deterministic finite automaton (DFA). +/// +/// Every DFA has exactly one start state and at least one dead state (which +/// may be the same, as in the case of an empty DFA). In all cases, a state +/// identifier of `0` must be a dead state such that `DFA::is_dead_state(0)` +/// always returns `true`. +/// +/// Every DFA also has zero or more match states, such that +/// `DFA::is_match_state(id)` returns `true` if and only if `id` corresponds to +/// a match state. +/// +/// In general, users of this trait likely will only need to use the search +/// routines such as `is_match`, `shortest_match`, `find` or `rfind`. The other +/// methods are lower level and are used for walking the transitions of a DFA +/// manually. In particular, the aforementioned search routines are implemented +/// generically in terms of the lower level transition walking routines. +pub trait DFA { + /// The representation used for state identifiers in this DFA. + /// + /// Typically, this is one of `u8`, `u16`, `u32`, `u64` or `usize`. + type ID: StateID; + + /// Return the identifier of this DFA's start state. + fn start_state(&self) -> Self::ID; + + /// Returns true if and only if the given identifier corresponds to a match + /// state. + fn is_match_state(&self, id: Self::ID) -> bool; + + /// Returns true if and only if the given identifier corresponds to a dead + /// state. When a DFA enters a dead state, it is impossible to leave and + /// thus can never lead to a match. + fn is_dead_state(&self, id: Self::ID) -> bool; + + /// Returns true if and only if the given identifier corresponds to either + /// a dead state or a match state, such that one of `is_match_state(id)` + /// or `is_dead_state(id)` must return true. + /// + /// Depending on the implementation of the DFA, this routine can be used + /// to save a branch in the core matching loop. Nevertheless, + /// `is_match_state(id) || is_dead_state(id)` is always a valid + /// implementation. + fn is_match_or_dead_state(&self, id: Self::ID) -> bool; + + /// Returns true if and only if this DFA is anchored. + /// + /// When a DFA is anchored, it is only allowed to report matches that + /// start at index `0`. + fn is_anchored(&self) -> bool; + + /// Given the current state that this DFA is in and the next input byte, + /// this method returns the identifier of the next state. The identifier + /// returned is always valid, but it may correspond to a dead state. + fn next_state(&self, current: Self::ID, input: u8) -> Self::ID; + + /// Like `next_state`, but its implementation may look up the next state + /// without memory safety checks such as bounds checks. As such, callers + /// must ensure that the given identifier corresponds to a valid DFA + /// state. Implementors must, in turn, ensure that this routine is safe + /// for all valid state identifiers and for all possible `u8` values. + unsafe fn next_state_unchecked( + &self, + current: Self::ID, + input: u8, + ) -> Self::ID; + + /// Returns true if and only if the given bytes match this DFA. + /// + /// This routine may short circuit if it knows that scanning future input + /// will never lead to a different result. In particular, if a DFA enters + /// a match state or a dead state, then this routine will return `true` or + /// `false`, respectively, without inspecting any future input. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`DenseDFA`](enum.DenseDFA.html). + /// + /// ``` + /// use regex_automata::{DFA, DenseDFA}; + /// + /// # fn example() -> Result<(), regex_automata::Error> { + /// let dfa = DenseDFA::new("foo[0-9]+bar")?; + /// assert_eq!(true, dfa.is_match(b"foo12345bar")); + /// assert_eq!(false, dfa.is_match(b"foobar")); + /// # Ok(()) }; example().unwrap() + /// ``` + #[inline] + fn is_match(&self, bytes: &[u8]) -> bool { + self.is_match_at(bytes, 0) + } + + /// Returns the first position at which a match is found. + /// + /// This routine stops scanning input in precisely the same circumstances + /// as `is_match`. The key difference is that this routine returns the + /// position at which it stopped scanning input if and only if a match + /// was found. If no match is found, then `None` is returned. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`DenseDFA`](enum.DenseDFA.html). + /// + /// ``` + /// use regex_automata::{DFA, DenseDFA}; + /// + /// # fn example() -> Result<(), regex_automata::Error> { + /// let dfa = DenseDFA::new("foo[0-9]+")?; + /// assert_eq!(Some(4), dfa.shortest_match(b"foo12345")); + /// + /// // Normally, the end of the leftmost first match here would be 3, + /// // but the shortest match semantics detect a match earlier. + /// let dfa = DenseDFA::new("abc|a")?; + /// assert_eq!(Some(1), dfa.shortest_match(b"abc")); + /// # Ok(()) }; example().unwrap() + /// ``` + #[inline] + fn shortest_match(&self, bytes: &[u8]) -> Option<usize> { + self.shortest_match_at(bytes, 0) + } + + /// Returns the end offset of the longest match. If no match exists, + /// then `None` is returned. + /// + /// Implementors of this trait are not required to implement any particular + /// match semantics (such as leftmost-first), which are instead manifest in + /// the DFA's topology itself. + /// + /// In particular, this method must continue searching even after it + /// enters a match state. The search should only terminate once it has + /// reached the end of the input or when it has entered a dead state. Upon + /// termination, the position of the last byte seen while still in a match + /// state is returned. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`DenseDFA`](enum.DenseDFA.html). By default, a dense DFA uses + /// "leftmost first" match semantics. + /// + /// Leftmost first match semantics corresponds to the match with the + /// smallest starting offset, but where the end offset is determined by + /// preferring earlier branches in the original regular expression. For + /// example, `Sam|Samwise` will match `Sam` in `Samwise`, but `Samwise|Sam` + /// will match `Samwise` in `Samwise`. + /// + /// Generally speaking, the "leftmost first" match is how most backtracking + /// regular expressions tend to work. This is in contrast to POSIX-style + /// regular expressions that yield "leftmost longest" matches. Namely, + /// both `Sam|Samwise` and `Samwise|Sam` match `Samwise` when using + /// leftmost longest semantics. + /// + /// ``` + /// use regex_automata::{DFA, DenseDFA}; + /// + /// # fn example() -> Result<(), regex_automata::Error> { + /// let dfa = DenseDFA::new("foo[0-9]+")?; + /// assert_eq!(Some(8), dfa.find(b"foo12345")); + /// + /// // Even though a match is found after reading the first byte (`a`), + /// // the leftmost first match semantics demand that we find the earliest + /// // match that prefers earlier parts of the pattern over latter parts. + /// let dfa = DenseDFA::new("abc|a")?; + /// assert_eq!(Some(3), dfa.find(b"abc")); + /// # Ok(()) }; example().unwrap() + /// ``` + #[inline] + fn find(&self, bytes: &[u8]) -> Option<usize> { + self.find_at(bytes, 0) + } + + /// Returns the start offset of the longest match in reverse, by searching + /// from the end of the input towards the start of the input. If no match + /// exists, then `None` is returned. In other words, this has the same + /// match semantics as `find`, but in reverse. + /// + /// # Example + /// + /// This example shows how to use this method with a + /// [`DenseDFA`](enum.DenseDFA.html). In particular, this routine + /// is principally useful when used in conjunction with the + /// [`dense::Builder::reverse`](dense/struct.Builder.html#method.reverse) + /// configuration knob. In general, it's unlikely to be correct to use both + /// `find` and `rfind` with the same DFA since any particular DFA will only + /// support searching in one direction. + /// + /// ``` + /// use regex_automata::{dense, DFA}; + /// + /// # fn example() -> Result<(), regex_automata::Error> { + /// let dfa = dense::Builder::new().reverse(true).build("foo[0-9]+")?; + /// assert_eq!(Some(0), dfa.rfind(b"foo12345")); + /// # Ok(()) }; example().unwrap() + /// ``` + #[inline] + fn rfind(&self, bytes: &[u8]) -> Option<usize> { + self.rfind_at(bytes, bytes.len()) + } + + /// Returns the same as `is_match`, but starts the search at the given + /// offset. + /// + /// The significance of the starting point is that it takes the surrounding + /// context into consideration. For example, if the DFA is anchored, then + /// a match can only occur when `start == 0`. + #[inline] + fn is_match_at(&self, bytes: &[u8], start: usize) -> bool { + if self.is_anchored() && start > 0 { + return false; + } + + let mut state = self.start_state(); + if self.is_match_or_dead_state(state) { + return self.is_match_state(state); + } + for &b in bytes[start..].iter() { + state = unsafe { self.next_state_unchecked(state, b) }; + if self.is_match_or_dead_state(state) { + return self.is_match_state(state); + } + } + false + } + + /// Returns the same as `shortest_match`, but starts the search at the + /// given offset. + /// + /// The significance of the starting point is that it takes the surrounding + /// context into consideration. For example, if the DFA is anchored, then + /// a match can only occur when `start == 0`. + #[inline] + fn shortest_match_at(&self, bytes: &[u8], start: usize) -> Option<usize> { + if self.is_anchored() && start > 0 { + return None; + } + + let mut state = self.start_state(); + if self.is_match_or_dead_state(state) { + return if self.is_dead_state(state) { None } else { Some(start) }; + } + for (i, &b) in bytes[start..].iter().enumerate() { + state = unsafe { self.next_state_unchecked(state, b) }; + if self.is_match_or_dead_state(state) { + return if self.is_dead_state(state) { + None + } else { + Some(start + i + 1) + }; + } + } + None + } + + /// Returns the same as `find`, but starts the search at the given + /// offset. + /// + /// The significance of the starting point is that it takes the surrounding + /// context into consideration. For example, if the DFA is anchored, then + /// a match can only occur when `start == 0`. + #[inline] + fn find_at(&self, bytes: &[u8], start: usize) -> Option<usize> { + if self.is_anchored() && start > 0 { + return None; + } + + let mut state = self.start_state(); + let mut last_match = if self.is_dead_state(state) { + return None; + } else if self.is_match_state(state) { + Some(start) + } else { + None + }; + for (i, &b) in bytes[start..].iter().enumerate() { + state = unsafe { self.next_state_unchecked(state, b) }; + if self.is_match_or_dead_state(state) { + if self.is_dead_state(state) { + return last_match; + } + last_match = Some(start + i + 1); + } + } + last_match + } + + /// Returns the same as `rfind`, but starts the search at the given + /// offset. + /// + /// The significance of the starting point is that it takes the surrounding + /// context into consideration. For example, if the DFA is anchored, then + /// a match can only occur when `start == bytes.len()`. + #[inline(never)] + fn rfind_at(&self, bytes: &[u8], start: usize) -> Option<usize> { + if self.is_anchored() && start < bytes.len() { + return None; + } + + let mut state = self.start_state(); + let mut last_match = if self.is_dead_state(state) { + return None; + } else if self.is_match_state(state) { + Some(start) + } else { + None + }; + for (i, &b) in bytes[..start].iter().enumerate().rev() { + state = unsafe { self.next_state_unchecked(state, b) }; + if self.is_match_or_dead_state(state) { + if self.is_dead_state(state) { + return last_match; + } + last_match = Some(i); + } + } + last_match + } +} + +impl<'a, T: DFA> DFA for &'a T { + type ID = T::ID; + + #[inline] + fn start_state(&self) -> Self::ID { + (**self).start_state() + } + + #[inline] + fn is_match_state(&self, id: Self::ID) -> bool { + (**self).is_match_state(id) + } + + #[inline] + fn is_match_or_dead_state(&self, id: Self::ID) -> bool { + (**self).is_match_or_dead_state(id) + } + + #[inline] + fn is_dead_state(&self, id: Self::ID) -> bool { + (**self).is_dead_state(id) + } + + #[inline] + fn is_anchored(&self) -> bool { + (**self).is_anchored() + } + + #[inline] + fn next_state(&self, current: Self::ID, input: u8) -> Self::ID { + (**self).next_state(current, input) + } + + #[inline] + unsafe fn next_state_unchecked( + &self, + current: Self::ID, + input: u8, + ) -> Self::ID { + (**self).next_state_unchecked(current, input) + } +} |