[clang-tools-extra] [clang-tidy] Support find for string-like classes in readability-container-contains (PR #157243)

[Nicolas van Kempen via cfe-commits]

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@@ -263,6 +263,11 @@ Changes in existing checks
   <clang-tidy/checks/portability/template-virtual-member-function>` check to
   avoid false positives on pure virtual member functions.
 
+- Improved :doc:`readability-container-contains
+  <clang-tidy/checks/readability/container-contains>` to support string
+  comparisons to ``npos``. Internal changes may cause new rare false positives
+  in non-standard containers.
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nicovank wrote:

Technically, every static analysis is prone to false positives :) In this case, it would need to be particularly weird code. I can only see it happening on _maybe_ a weird pointer or string container but even then, it would probably be a code smell. Hopefully I'm not proven wrong. The benefit of added true positives IMO outweighs the potential false positives.

https://github.com/llvm/llvm-project/pull/157243