[clang-tools-extra] [clang-tidy] Unsafe CRTP check (PR #82403)

[via cfe-commits]

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+.. title:: clang-tidy - bugprone-unsafe-crtp
+
+bugprone-unsafe-crtp
+====================
+
+Finds CRTP used in an error-prone way.
+
+If the constructor of a class intended to be used in a CRTP is public, then
+it allows users to construct that class on its own.
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isuckatcs wrote:

Quoting [cppreference](https://en.cppreference.com/w/cpp/language/crtp):

> The [Curiously Recurring Template Pattern](https://en.wikipedia.org/wiki/Curiously_Recurring_Template_Pattern) is an idiom in which a class X derives from a class template Y, taking a template parameter Z, where Y is instantiated with Z = X.

What these lines in the documentain say is bad because they break the `Y is instantiated with Z = X` part. It doesn't do what this idiom says it should do, otherwise from the language's point of view it's perfectly legal.

https://github.com/llvm/llvm-project/pull/82403