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CiStrings.indexOf (the case-insensitive Strings.CI.indexOf) bails out only when startPos > endLimit, where endLimit = str.length() - searchStr.length() + 1.
For an empty search endLimit is str.length() + 1, so a startPos of exactly str.length() + 1 slips past the guard and the empty-search branch returns startPos unchanged.
Repro: Strings.CI.indexOf("abc", "", 4)
Expected: -1 (the class Javadoc documents out-of-range start positions as -1, e.g. Strings.CI.indexOf("abc", "", 9) = -1)
Actual: 4, an index one past the end of a length-3 string
The case-sensitive CS.indexOf delegates to String.indexOf and clamps, so only the hand-rolled CI implementation is affected. Changed the guard to startPos >= endLimit; -1 is returned once startPos passes the last valid empty-match position (str.length()), and every documented example is unchanged.
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Run a successful build using the default Maven goal with mvn; that's mvn on the command line by itself.
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garydgregory
changed the title
fix Strings.CI.indexOf returning out-of-range index for empty search
Fix Strings.CI.indexOf returning out-of-range index for empty search
Jun 30, 2026
garydgregory
changed the title
Fix Strings.CI.indexOf returning out-of-range index for empty search
Fix Strings.CI.indexOf() returning out-of-range index for empty search
Jun 30, 2026
Had a look through the rest of the class. The empty-search paths in lastIndexOf, contains, startsWith/endsWith, equals and the *Any/remove/replace helpers all behave the same for CI and CS.
The one spot left is indexOf with a start position past the end:
CS delegates to String.indexOf, which clamps the start to the length and so keeps matching the empty search; the hand-rolled CI returns -1 once startPos > length. The shared prose says 'a start position greater than the string length only matches an empty search CharSequence', which lines up with the CS side. Want me to make CI clamp to match CS (and drop the CI.indexOf("abc", "", 9) = -1 example), or keep the documented -1?
Had a look through the rest of the class. The empty-search paths in lastIndexOf, contains, startsWith/endsWith, equals and the *Any/remove/replace helpers all behave the same for CI and CS.
The one spot left is indexOf with a start position past the end:
CS delegates to String.indexOf, which clamps the start to the length and so keeps matching the empty search; the hand-rolled CI returns -1 once startPos > length. The shared prose says 'a start position greater than the string length only matches an empty search CharSequence', which lines up with the CS side. Want me to make CI clamp to match CS (and drop the CI.indexOf("abc", "", 9) = -1 example), or keep the documented -1?
@alhudz
Yeah, the reply should be consistent, regardless of case.
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garydgregory
changed the title
CiStrings.indexOf(the case-insensitiveStrings.CI.indexOf) bails out only whenstartPos > endLimit, whereendLimit = str.length() - searchStr.length() + 1.endLimitisstr.length() + 1, so astartPosof exactlystr.length() + 1slips past the guard and the empty-search branch returnsstartPosunchanged.Repro:
Strings.CI.indexOf("abc", "", 4)Expected:
-1(the class Javadoc documents out-of-range start positions as-1, e.g.Strings.CI.indexOf("abc", "", 9) = -1)Actual:
4, an index one past the end of a length-3stringThe case-sensitive
CS.indexOfdelegates toString.indexOfand clamps, so only the hand-rolledCIimplementation is affected. Changed the guard tostartPos >= endLimit;-1is returned oncestartPospasses the last valid empty-match position (str.length()), and every documented example is unchanged.mvn; that'smvnon the command line by itself.