[I] [Bug](function) count_substrings returns wrong result for overlapping pattern boundary [doris]

["hakanuzum (via GitHub)" <gi...@apache.org>]

hakanuzum opened a new issue, #62768:
URL: https://github.com/apache/doris/issues/62768

   ### Search before asking
   - [x] I searched in the issues and found no similar issues.
   
   ### Version
   master (after PR #62262)
   
   ### What happened
   `count_substrings('ccc', 'cc')` returns **2** instead of expected **1** (non-overlapping count).
   
   The regression test `test_string_all.groovy` expects 1, but BE returns 2, causing `cloud_p0` CI failures.
   
   ### Root Cause
   In PR #62262, `function_string.h` was split into `function_string_search.cpp`. The `find_pos()` function checks `pos < str_size` but does not verify `pos + pattern_ref.size <= str_size`, so it matches a pattern that extends beyond the string boundary via `memcmp_small_allow_overflow15`.
   
   ```cpp
   // function_string_search.cpp, find_pos()
   while (pos < str_size &&    // ← should be: pos + pattern_ref.size <= str_size
          memcmp_small_allow_overflow15(...)) {
       pos++;
   }
   ```
   
   For `count_substrings('ccc', 'cc')`:
   - pos=0: matches `cc` at [0,1] → count=1, advance to pos=2
   - pos=2: `pos < str_size` (2 < 3) is true, memcmp reads bytes [2,3] which overflows → false match → count=2
   
   ### Expected behavior
   `count_substrings('ccc', 'cc')` should return **1** (non-overlapping).
   
   ### How to reproduce
   ```sql
   SELECT count_substrings('ccc', 'cc');
   -- Returns: 2
   -- Expected: 1
   ```
   
   ### Anything else
   This causes `qt_count_substrings_53` in `test_string_all.groovy` to fail in CI.
   Introduced by refactoring PR #62262.


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Re: [I] [Bug](function) count_substrings returns wrong result for overlapping pattern boundary [doris]

["HappenLee (via GitHub)" <gi...@apache.org>]

HappenLee closed issue #62768: [Bug](function) count_substrings returns wrong result for overlapping pattern boundary
URL: https://github.com/apache/doris/issues/62768


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