[clang-tools-extra] [clang-tidy] Add user-defined functions to `bugprone-unsafe-functions` check (PR #106350)

[via cfe-commits]

================
@@ -74,10 +75,50 @@ Both macros have to be defined to suggest replacement functions from *Annex K.*
 ``__STDC_WANT_LIB_EXT1__`` must be defined to ``1`` by the user **before**
 including any system headers.
 
+.. _CustomFunctions:
+
+Custom functions
+----------------
+
+The option `CustomFunctions` allows the user to define custom functions to be
+checked. The format is the following, without newlines:
+
+.. code::
+
+   bugprone-unsafe-functions.CustomFunctions="
+     functionRegex1[, replacement1[, reason1]]; 
+     functionRegex2[, replacement2[, reason2]];
+     ...
+   "
+
+The functions are matched using POSIX extended regular expressions.
+*(Note: The regular expressions do not support negative* ``(?!)`` *matches)*
+
+The `reason` is optional and is used to provide additional information about the
+reasoning behind the replacement. The default reason is `is marked as unsafe`.
+
+If `replacement` is empty, the text `it should not be used` will be shown
+instead of the suggestion for a replacement.
+
+As an example, the configuration `^original$, replacement, is deprecated;`
+will produce the following diagnostic message.
+
+.. code:: c
+  
+   original(); // warning: function 'original' is deprecated; 'replacement' should be used instead.
+   ::std::original(); // no-warning
+   original_function(); // no-warning
+
+If the regular expression contains the character `:`, it is matched against the
+qualified name (i.e. ``std::original``), otherwise the regex is matched against the unqualified name (``original``).
+If the regular expression starts with `::` (or `^::`), it is matched against the
+fully qualified name (``::std::original``).
 
 Options
 -------
 
+.. _option-ReportMoreUnsafeFunctions:
+
----------------
Discookie wrote:

Checked, they aren't needed. Thanks for finding usages for the doc syntax!

https://github.com/llvm/llvm-project/pull/106350