Fix various LastIndexOf bugs when dealing with zero-length target substrings - #34616
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- string.LastIndexOf(string.Empty) shouldn't perform -1 adjustment - MemoryExtensions.LastIndexOf(ROS<char>, string.Empty) shouldn't return 0 - Tighten up some existing unit tests
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area-System.Runtime
breaking-change
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Note to @tarekgh: This PR doesn't have the "avoid validating |
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CC @safern just in case he is touching some of the changed files here. |
tarekgh
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tarekgh
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I like the change and now our behavior is more understandable. only one thing, we need to document this as a breaking change. right? if so, can we ensure this is written so we can point users to the doc when anyone complains? Thanks for clearing this area.
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This issue is marked with a breaking change tag. In theory it should be caught in any pre-release sweep we do to account for such changes in the docs. |
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not related to your changes: IMHO this test (IndexOf_AllSubstrings) is very complex and is trying to test too many test cases at the same time. It would be better to split it into few smaller tests with self-describing names
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Agreed, it's a bit of a bear. Do you have recommendations for how it might naturally be split?
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I think that the two if blocks could become separate tests: value.Length == 0, s.Length == 0
ghost
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Fixes #13382.
Fixes #13383.
string.LastIndexOfandMemoryExtensions.LastIndexOfare inconsistent with how they handle zero-length target strings with variousStringComparisonarguments. In some cases they returnstring.Length - 1. In some cases they returnspan.Length. And in some cases they return0.This PR normalizes the behavior of all of these APIs so that a zero-length target substring is always found at the end of the search space. Since
LastIndexOf's parameters vary significantly fromIndexOf's parameters, I also included a code comment right in front ofstring.IndexOf(string)that explains the concept of "search space" vis-à-vis this particular API.There's also some small comment cleanup throughout the code paths which deal with these checks.
This PR was extracted from #1514 into its own standalone review. This PR addresses only
LastIndexOfand doesn't address the zero-weight code point issue tracked by that PR.