Fixes #14185.

This fix suppresses dead_code warnings from code generated by regex! when
the result of regex! is unused. Correct behavior should be a single
unused variable warning.

Regression tests are included for both `let` and `static` bound regex!
values.

src/libregex_macros/lib.rs

@@ -142,11 +142,20 @@ impl<'a> NfaGen<'a> {
         let regex = self.original.as_slice();
 
         quote_expr!(self.cx, {
+// When `regex!` is bound to a name that is not used, we have to make sure
+// that dead_code warnings don't bubble up to the user from the generated
+// code. Therefore, we suppress them by allowing dead_code. The effect is that
+// the user is only warned about *their* unused variable/code, and not the
+// unused code generated by regex!. See #14185 for an example.
+#[allow(dead_code)]
 static CAP_NAMES: &'static [Option<&'static str>] = &$cap_names;
+
+#[allow(dead_code)]
 fn exec<'t>(which: ::regex::native::MatchKind, input: &'t str,
             start: uint, end: uint) -> Vec<Option<uint>> {
     #![allow(unused_imports)]
     #![allow(unused_mut)]
+
     use regex::native::{
         MatchKind, Exists, Location, Submatches,
         StepState, StepMatchEarlyReturn, StepMatch, StepContinue,