branch: externals/relint
commit 09ef3dfa9c31317bf508ab18eb0d8f1e31c0b568
Author: Mattias Engdegård <matti...@acm.org>
Commit: Mattias Engdegård <matti...@acm.org>
Describe the new xr wrapped subsumption warning
---
README | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/README b/README
index 944e665..3ca9499 100644
--- a/README
+++ b/README
@@ -122,6 +122,17 @@ skip-syntax-backward.
so the a* could be removed without changing the meaning of the
regexp.
+ - First/last item in repetition subsumes last/first item (wrapped)
+
+ The first and last items in a repeated sequence, being effectively
+ adjacent, match a superset or subset of each other, which makes
+ for an unexpected inefficiency. For example, \(?:a*c[ab]+\)* can
+ be seen as a*c[ab]+a*c[ab]+... where the [ab]+a* in the middle is
+ a slow way of writing [ab]+ which is made worse by the outer
+ repetition. The general remedy is to move the subsumed item out of
+ the repeated sequence, resulting in a*\(?:c[ab]+\)* in the example
+ above.
+
- Uncounted repetition
The construct A\{,\} repeats A zero or more times which was
