syntax: improve literal extraction from certain repetitions

When repetitions didn't have an explicit max value, like in `(ab){2,}`
the literal extractor was producing sub-optimal literals, like `"ab"`
instead of `"abab"`.

Close rust-lang#1032

Author: plusvic

regex-syntax/src/hir/literal.rs

@@ -477,7 +477,7 @@ impl Extractor {
                 }
                 seq
             }
-            hir::Repetition { min, max: Some(max), .. } if min < max => {
+            hir::Repetition { min, .. } => {
                 assert!(min > 0); // handled above
                 let limit =
                     u32::try_from(self.limit_repeat).unwrap_or(u32::MAX);
@@ -491,10 +491,6 @@ impl Extractor {
                 seq.make_inexact();
                 seq
             }
-            hir::Repetition { .. } => {
-                subseq.make_inexact();
-                subseq
-            }
         }
     }
 
@@ -2655,6 +2651,12 @@ mod tests {
             ]),
             e(r"(ab|cd)(ef|gh)(ij|kl)")
         );
+
+        assert_eq!(inexact([E("abab")], [E("abab")]), e(r"(ab){2}"));
+
+        assert_eq!(inexact([I("abab")], [I("abab")]), e(r"(ab){2,3}"));
+
+        assert_eq!(inexact([I("abab")], [I("abab")]), e(r"(ab){2,}"));
     }
 
     #[test]