Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 282 insertions, 0 deletions

diff --git a/third_party/rust/regex/src/backtrack.rs b/third_party/rust/regex/src/backtrack.rs
new file mode 100644
index 0000000000..4d83856ca0
--- /dev/null
+++ b/third_party/rust/regex/src/backtrack.rs
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+// This is the backtracking matching engine. It has the same exact capability
+// as the full NFA simulation, except it is artificially restricted to small
+// regexes on small inputs because of its memory requirements.
+//
+// In particular, this is a *bounded* backtracking engine. It retains worst
+// case linear time by keeping track of the states that it has visited (using a
+// bitmap). Namely, once a state is visited, it is never visited again. Since a
+// state is keyed by `(instruction index, input index)`, we have that its time
+// complexity is `O(mn)` (i.e., linear in the size of the search text).
+//
+// The backtracking engine can beat out the NFA simulation on small
+// regexes/inputs because it doesn't have to keep track of multiple copies of
+// the capture groups. In benchmarks, the backtracking engine is roughly twice
+// as fast as the full NFA simulation. Note though that its performance doesn't
+// scale, even if you're willing to live with the memory requirements. Namely,
+// the bitset has to be zeroed on each execution, which becomes quite expensive
+// on large bitsets.
+
+use crate::exec::ProgramCache;
+use crate::input::{Input, InputAt};
+use crate::prog::{InstPtr, Program};
+use crate::re_trait::Slot;
+
+type Bits = u32;
+
+const BIT_SIZE: usize = 32;
+const MAX_SIZE_BYTES: usize = 256 * (1 << 10); // 256 KB
+
+/// Returns true iff the given regex and input should be executed by this
+/// engine with reasonable memory usage.
+pub fn should_exec(num_insts: usize, text_len: usize) -> bool {
+    // Total memory usage in bytes is determined by:
+    //
+    //   ((len(insts) * (len(input) + 1) + bits - 1) / bits) * (size_of(u32))
+    //
+    // The actual limit picked is pretty much a heuristic.
+    // See: https://github.com/rust-lang/regex/issues/215
+    let size = ((num_insts * (text_len + 1) + BIT_SIZE - 1) / BIT_SIZE) * 4;
+    size <= MAX_SIZE_BYTES
+}
+
+/// A backtracking matching engine.
+#[derive(Debug)]
+pub struct Bounded<'a, 'm, 'r, 's, I> {
+    prog: &'r Program,
+    input: I,
+    matches: &'m mut [bool],
+    slots: &'s mut [Slot],
+    m: &'a mut Cache,
+}
+
+/// Shared cached state between multiple invocations of a backtracking engine
+/// in the same thread.
+#[derive(Clone, Debug)]
+pub struct Cache {
+    jobs: Vec<Job>,
+    visited: Vec<Bits>,
+}
+
+impl Cache {
+    /// Create new empty cache for the backtracking engine.
+    pub fn new(_prog: &Program) -> Self {
+        Cache { jobs: vec![], visited: vec![] }
+    }
+}
+
+/// A job is an explicit unit of stack space in the backtracking engine.
+///
+/// The "normal" representation is a single state transition, which corresponds
+/// to an NFA state and a character in the input. However, the backtracking
+/// engine must keep track of old capture group values. We use the explicit
+/// stack to do it.
+#[derive(Clone, Copy, Debug)]
+enum Job {
+    Inst { ip: InstPtr, at: InputAt },
+    SaveRestore { slot: usize, old_pos: Option<usize> },
+}
+
+impl<'a, 'm, 'r, 's, I: Input> Bounded<'a, 'm, 'r, 's, I> {
+    /// Execute the backtracking matching engine.
+    ///
+    /// If there's a match, `exec` returns `true` and populates the given
+    /// captures accordingly.
+    pub fn exec(
+        prog: &'r Program,
+        cache: &ProgramCache,
+        matches: &'m mut [bool],
+        slots: &'s mut [Slot],
+        input: I,
+        start: usize,
+        end: usize,
+    ) -> bool {
+        let mut cache = cache.borrow_mut();
+        let cache = &mut cache.backtrack;
+        let start = input.at(start);
+        let mut b = Bounded { prog, input, matches, slots, m: cache };
+        b.exec_(start, end)
+    }
+
+    /// Clears the cache such that the backtracking engine can be executed
+    /// on some input of fixed length.
+    fn clear(&mut self) {
+        // Reset the job memory so that we start fresh.
+        self.m.jobs.clear();
+
+        // Now we need to clear the bit state set.
+        // We do this by figuring out how much space we need to keep track
+        // of the states we've visited.
+        // Then we reset all existing allocated space to 0.
+        // Finally, we request more space if we need it.
+        //
+        // This is all a little circuitous, but doing this using unchecked
+        // operations doesn't seem to have a measurable impact on performance.
+        // (Probably because backtracking is limited to such small
+        // inputs/regexes in the first place.)
+        let visited_len =
+            (self.prog.len() * (self.input.len() + 1) + BIT_SIZE - 1)
+                / BIT_SIZE;
+        self.m.visited.truncate(visited_len);
+        for v in &mut self.m.visited {
+            *v = 0;
+        }
+        if visited_len > self.m.visited.len() {
+            let len = self.m.visited.len();
+            self.m.visited.reserve_exact(visited_len - len);
+            for _ in 0..(visited_len - len) {
+                self.m.visited.push(0);
+            }
+        }
+    }
+
+    /// Start backtracking at the given position in the input, but also look
+    /// for literal prefixes.
+    fn exec_(&mut self, mut at: InputAt, end: usize) -> bool {
+        self.clear();
+        // If this is an anchored regex at the beginning of the input, then
+        // we're either already done or we only need to try backtracking once.
+        if self.prog.is_anchored_start {
+            return if !at.is_start() { false } else { self.backtrack(at) };
+        }
+        let mut matched = false;
+        loop {
+            if !self.prog.prefixes.is_empty() {
+                at = match self.input.prefix_at(&self.prog.prefixes, at) {
+                    None => break,
+                    Some(at) => at,
+                };
+            }
+            matched = self.backtrack(at) || matched;
+            if matched && self.prog.matches.len() == 1 {
+                return true;
+            }
+            if at.pos() >= end {
+                break;
+            }
+            at = self.input.at(at.next_pos());
+        }
+        matched
+    }
+
+    /// The main backtracking loop starting at the given input position.
+    fn backtrack(&mut self, start: InputAt) -> bool {
+        // N.B. We use an explicit stack to avoid recursion.
+        // To avoid excessive pushing and popping, most transitions are handled
+        // in the `step` helper function, which only pushes to the stack when
+        // there's a capture or a branch.
+        let mut matched = false;
+        self.m.jobs.push(Job::Inst { ip: 0, at: start });
+        while let Some(job) = self.m.jobs.pop() {
+            match job {
+                Job::Inst { ip, at } => {
+                    if self.step(ip, at) {
+                        // Only quit if we're matching one regex.
+                        // If we're matching a regex set, then mush on and
+                        // try to find other matches (if we want them).
+                        if self.prog.matches.len() == 1 {
+                            return true;
+                        }
+                        matched = true;
+                    }
+                }
+                Job::SaveRestore { slot, old_pos } => {
+                    if slot < self.slots.len() {
+                        self.slots[slot] = old_pos;
+                    }
+                }
+            }
+        }
+        matched
+    }
+
+    fn step(&mut self, mut ip: InstPtr, mut at: InputAt) -> bool {
+        use crate::prog::Inst::*;
+        loop {
+            // This loop is an optimization to avoid constantly pushing/popping
+            // from the stack. Namely, if we're pushing a job only to run it
+            // next, avoid the push and just mutate `ip` (and possibly `at`)
+            // in place.
+            if self.has_visited(ip, at) {
+                return false;
+            }
+            match self.prog[ip] {
+                Match(slot) => {
+                    if slot < self.matches.len() {
+                        self.matches[slot] = true;
+                    }
+                    return true;
+                }
+                Save(ref inst) => {
+                    if let Some(&old_pos) = self.slots.get(inst.slot) {
+                        // If this path doesn't work out, then we save the old
+                        // capture index (if one exists) in an alternate
+                        // job. If the next path fails, then the alternate
+                        // job is popped and the old capture index is restored.
+                        self.m.jobs.push(Job::SaveRestore {
+                            slot: inst.slot,
+                            old_pos,
+                        });
+                        self.slots[inst.slot] = Some(at.pos());
+                    }
+                    ip = inst.goto;
+                }
+                Split(ref inst) => {
+                    self.m.jobs.push(Job::Inst { ip: inst.goto2, at });
+                    ip = inst.goto1;
+                }
+                EmptyLook(ref inst) => {
+                    if self.input.is_empty_match(at, inst) {
+                        ip = inst.goto;
+                    } else {
+                        return false;
+                    }
+                }
+                Char(ref inst) => {
+                    if inst.c == at.char() {
+                        ip = inst.goto;
+                        at = self.input.at(at.next_pos());
+                    } else {
+                        return false;
+                    }
+                }
+                Ranges(ref inst) => {
+                    if inst.matches(at.char()) {
+                        ip = inst.goto;
+                        at = self.input.at(at.next_pos());
+                    } else {
+                        return false;
+                    }
+                }
+                Bytes(ref inst) => {
+                    if let Some(b) = at.byte() {
+                        if inst.matches(b) {
+                            ip = inst.goto;
+                            at = self.input.at(at.next_pos());
+                            continue;
+                        }
+                    }
+                    return false;
+                }
+            }
+        }
+    }
+
+    fn has_visited(&mut self, ip: InstPtr, at: InputAt) -> bool {
+        let k = ip * (self.input.len() + 1) + at.pos();
+        let k1 = k / BIT_SIZE;
+        let k2 = usize_to_u32(1 << (k & (BIT_SIZE - 1)));
+        if self.m.visited[k1] & k2 == 0 {
+            self.m.visited[k1] |= k2;
+            false
+        } else {
+            true
+        }
+    }
+}
+
+fn usize_to_u32(n: usize) -> u32 {
+    if (n as u64) > (::std::u32::MAX as u64) {
+        panic!("BUG: {} is too big to fit into u32", n)
+    }
+    n as u32
+}