refactor progress

grep/src/literals.rs

@@ -0,0 +1,207 @@
+use std::cmp;
+use std::iter;
+
+use regex::bytes::Regex;
+use syntax::{
+    Expr, Literals, Lit,
+    Repeater,
+};
+
+#[derive(Debug)]
+pub struct LiteralSets {
+    prefixes: Literals,
+    suffixes: Literals,
+    required: Literals,
+}
+
+impl LiteralSets {
+    pub fn create(expr: &Expr) -> Self {
+        let mut required = Literals::empty();
+        union_required(expr, &mut required);
+        LiteralSets {
+            prefixes: expr.prefixes(),
+            suffixes: expr.suffixes(),
+            required: required,
+        }
+    }
+
+    pub fn to_regex(&self) -> Option<Regex> {
+        if self.prefixes.all_complete() && !self.prefixes.is_empty() {
+            // When this is true, the regex engine will do a literal scan.
+            return None;
+        }
+
+        // Out of inner required literals, prefixes and suffixes, which one
+        // is the longest? We pick the longest to do fast literal scan under
+        // the assumption that a longer literal will have a lower false
+        // positive rate.
+        let pre_lcp = self.prefixes.longest_common_prefix();
+        let pre_lcs = self.prefixes.longest_common_suffix();
+        let suf_lcp = self.suffixes.longest_common_prefix();
+        let suf_lcs = self.suffixes.longest_common_suffix();
+
+        let req_lits = self.required.literals();
+        let req = match req_lits.iter().max_by_key(|lit| lit.len()) {
+            None => &[],
+            Some(req) => &***req,
+        };
+
+        let mut lit = pre_lcp;
+        if pre_lcs.len() > lit.len() {
+            lit = pre_lcs;
+        }
+        if suf_lcp.len() > lit.len() {
+            lit = suf_lcp;
+        }
+        if suf_lcs.len() > lit.len() {
+            lit = suf_lcs;
+        }
+        if req.len() > lit.len() {
+            lit = req;
+        }
+        if lit.is_empty() {
+            None
+        } else {
+            // Literals always compile.
+            Some(Regex::new(&bytes_to_regex(lit)).unwrap())
+        }
+    }
+}
+
+fn union_required(expr: &Expr, lits: &mut Literals) {
+    use syntax::Expr::*;
+    match *expr {
+        Literal { ref chars, casei: false } => {
+            let s: String = chars.iter().cloned().collect();
+            lits.cross_add(s.as_bytes());
+        }
+        Literal { casei: true, .. } => {
+            lits.cut();
+        }
+        LiteralBytes { ref bytes, casei: false } => {
+            lits.cross_add(bytes);
+        }
+        LiteralBytes { casei: true, .. } => {
+            lits.cut();
+        }
+        Class(_) => {
+            lits.cut();
+        }
+        ClassBytes(_) => {
+            lits.cut();
+        }
+        Group { ref e, .. } => {
+            union_required(&**e, lits);
+        }
+        Repeat { r: Repeater::ZeroOrOne, .. } => lits.cut(),
+        Repeat { r: Repeater::ZeroOrMore, .. } => lits.cut(),
+        Repeat { ref e, r: Repeater::OneOrMore, .. } => {
+            union_required(&**e, lits);
+            lits.cut();
+        }
+        Repeat { ref e, r: Repeater::Range { min, max }, greedy } => {
+            repeat_range_literals(
+                &**e, min, max, greedy, lits, union_required);
+        }
+        Concat(ref es) if es.is_empty() => {}
+        Concat(ref es) if es.len() == 1 => union_required(&es[0], lits),
+        Concat(ref es) => {
+            for e in es {
+                let mut lits2 = lits.to_empty();
+                union_required(e, &mut lits2);
+                if lits2.is_empty() {
+                    lits.cut();
+                    continue;
+                }
+                if lits2.contains_empty() {
+                    lits.cut();
+                }
+                // if !lits.union(lits2) {
+                if !lits.cross_product(&lits2) {
+                    // If this expression couldn't yield any literal that
+                    // could be extended, then we need to quit. Since we're
+                    // short-circuiting, we also need to freeze every member.
+                    lits.cut();
+                    break;
+                }
+            }
+        }
+        Alternate(ref es) => {
+            alternate_literals(es, lits, union_required);
+        }
+        _ => lits.cut(),
+    }
+}
+
+fn repeat_range_literals<F: FnMut(&Expr, &mut Literals)>(
+    e: &Expr,
+    min: u32,
+    max: Option<u32>,
+    _greedy: bool,
+    lits: &mut Literals,
+    mut f: F,
+) {
+    use syntax::Expr::*;
+
+    if min == 0 {
+        // This is a bit conservative. If `max` is set, then we could
+        // treat this as a finite set of alternations. For now, we
+        // just treat it as `e*`.
+        lits.cut();
+    } else {
+        let n = cmp::min(lits.limit_size(), min as usize);
+        let es = iter::repeat(e.clone()).take(n).collect();
+        f(&Concat(es), lits);
+        if n < min as usize {
+            lits.cut();
+        }
+        if max.map_or(true, |max| min < max) {
+            lits.cut();
+        }
+    }
+}
+
+fn alternate_literals<F: FnMut(&Expr, &mut Literals)>(
+    es: &[Expr],
+    lits: &mut Literals,
+    mut f: F,
+) {
+    let mut lits2 = lits.to_empty();
+    for e in es {
+        let mut lits3 = lits.to_empty();
+        lits3.set_limit_size(lits.limit_size() / 5);
+        f(e, &mut lits3);
+        if lits3.is_empty() || !lits2.union(lits3) {
+            // If we couldn't find suffixes for *any* of the
+            // alternates, then the entire alternation has to be thrown
+            // away and any existing members must be frozen. Similarly,
+            // if the union couldn't complete, stop and freeze.
+            lits.cut();
+            return;
+        }
+    }
+    // All we do at the moment is look for prefixes and suffixes. If both
+    // are empty, then we report nothing. We should be able to do better than
+    // this, but we'll need something more expressive than just a "set of
+    // literals."
+    let lcp = lits2.longest_common_prefix();
+    let lcs = lits2.longest_common_suffix();
+    if !lcp.is_empty() {
+        lits.cross_add(lcp);
+    }
+    lits.cut();
+    if !lcs.is_empty() {
+        lits.add(Lit::empty());
+        lits.add(Lit::new(lcs.to_vec()));
+    }
+}
+
+/// Converts an arbitrary sequence of bytes to a literal suitable for building
+/// a regular expression.
+fn bytes_to_regex(bs: &[u8]) -> String {
+    let mut s = String::with_capacity(bs.len());
+    for &b in bs {
+        s.push_str(&format!("\\x{:02x}", b));
+    }
+    s
+}