[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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@@ -318,17 +321,15 @@ void testPrivateContains(CustomMapPrivateContains<int, int> &MyMap,
   if (MyMap2.count(0)) {};
 }
 
-struct MyString {};
-
 struct WeirdNonMatchingContains {
   unsigned count(char) const;
-  bool contains(const MyString&) const;
+  bool contains(const std::string&) const;
 };
 
-void testWeirdNonMatchingContains(WeirdNonMatchingContains &MyMap) {
-  // No warning if there is no `contains` method with the right type.
-  if (MyMap.count('a')) {};
-}
+// False positives: when count/find and contains take different types,
+// the check will suggest an invalid code transformation. These cases
+// should not exist in real code or be rare enough.
+// void f(WeirdNonMatchingContains MyMap) { MyMap.count('a'); }
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nicovank wrote:

Checked a few cases from [this search](https://github.com/search?q=repo%3Allvm%2Fllvm-project+PATH%3Aclang-tools-extra%2Ftest%2Fclang-tidy%2Fcheckers+%22false+positive%22&type=code) and seems like that's right! Changing.

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