progress

src/literals.rs

+use std::cmp;
+use std::iter;
+use std::str;
+
+use regex::quote;
+use regex::bytes::Regex;
+use syntax::{
+    Expr, Literals, Lit,
+    ByteClass, CharClass, Repeater, ClassRange, ByteRange,
+};
+
+#[derive(Debug)]
+pub struct LiteralSets {
+    prefixes: Literals,
+    suffixes: Literals,
+    required: Literals,
+}
+
+#[derive(Debug)]
+pub struct LiteralMatcher {
+    re: Regex,
+}
+
+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_matcher(&self) -> Option<LiteralMatcher> {
+        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 {
+            let s = str::from_utf8(lit).unwrap();
+            Some(LiteralMatcher { re: Regex::new(&quote(s)).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 { ref chars, casei: true } => {
+            for &c in chars {
+                let cls = CharClass::new(vec![
+                    ClassRange { start: c, end: c },
+                ]).case_fold();
+                if !lits.add_char_class(&cls) {
+                    lits.cut();
+                    return;
+                }
+            }
+        }
+        LiteralBytes { ref bytes, casei: false } => {
+            lits.cross_add(bytes);
+        }
+        LiteralBytes { ref bytes, casei: true } => {
+            for &b in bytes {
+                let cls = ByteClass::new(vec![
+                    ByteRange { start: b, end: b },
+                ]).case_fold();
+                if !lits.add_byte_class(&cls) {
+                    lits.cut();
+                    return;
+                }
+            }
+        }
+        Class(ref cls) => {
+            if !lits.add_char_class(cls) {
+                lits.cut();
+            }
+        }
+        ClassBytes(ref cls) => {
+            if !lits.add_byte_class(cls) {
+                lits.cut();
+            }
+        }
+        Group { ref e, .. } => {
+            union_required(&**e, lits);
+        }
+        Repeat { ref e, r: Repeater::ZeroOrOne, .. } => lits.cut(),
+        Repeat { ref e, 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()));
+    }
+}

src/main.rs

@@ -19,6 +19,9 @@ use std::result;
 use docopt::Docopt;
 use regex::bytes::Regex;
 
+use literals::LiteralSets;
+
+mod literals;
 mod nonl;
 
 pub type Result<T> = result::Result<T, Box<Error + Send + Sync>>;
@@ -44,6 +47,9 @@ fn main() {
 
 fn run(args: &Args) -> Result<u64> {
     let expr = try!(parse(&args.arg_pattern));
+    let literals = LiteralSets::create(&expr);
+    // println!("{:?}", literals);
+    // println!("{:?}", literals.to_matcher());
     let re = Regex::new(&expr.to_string()).unwrap();
     if args.arg_file.is_empty() {
         let _stdin = io::stdin();