regex: print out final regex in trace mode

This is useful for debugging to see what regex is actually being run.
We put this as a trace since the regex can be quite gnarly. (It is not
pretty printed.)

grep-regex/src/crlf.rs

@@ -34,6 +34,11 @@ impl CRLFMatcher {
         }
         Ok(CRLFMatcher { regex, names })
     }
+
+    /// Return the underlying regex used by this matcher.
+    pub fn regex(&self) -> &Regex {
+        &self.regex
+    }
 }
 
 impl Matcher for CRLFMatcher {

grep-regex/src/matcher.rs

@@ -50,9 +50,12 @@ impl RegexMatcherBuilder {
         if let Some(ref re) = fast_line_regex {
             trace!("extracted fast line regex: {:?}", re);
         }
+
+        let matcher = RegexMatcherImpl::new(&chir)?;
+        trace!("final regex: {:?}", matcher.regex());
         Ok(RegexMatcher {
             config: self.config.clone(),
-            matcher: RegexMatcherImpl::new(&chir)?,
+            matcher: matcher,
             fast_line_regex: fast_line_regex,
             non_matching_bytes: non_matching_bytes,
         })
@@ -370,6 +373,15 @@ impl RegexMatcherImpl {
             Ok(RegexMatcherImpl::Standard(StandardMatcher::new(expr)?))
         }
     }
+
+    /// Return the underlying regex object used.
+    fn regex(&self) -> &Regex {
+        match *self {
+            RegexMatcherImpl::Word(ref x) => x.regex(),
+            RegexMatcherImpl::CRLF(ref x) => x.regex(),
+            RegexMatcherImpl::Standard(ref x) => &x.regex,
+        }
+    }
 }
 
 // This implementation just dispatches on the internal matcher impl except

grep-regex/src/word.rs

@@ -55,6 +55,11 @@ impl WordMatcher {
         }
         Ok(WordMatcher { regex, names, locs })
     }
+
+    /// Return the underlying regex used by this matcher.
+    pub fn regex(&self) -> &Regex {
+        &self.regex
+    }
 }
 
 impl Matcher for WordMatcher {