https://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines/pro-type-member-init.html
The check flags user-defined constructor definitions that do not initialize all fields that would be left in an undefined state by default construction, e.g. builtins, pointers and record types without user-provided default constructors containing at least one such type. If these fields aren’t initialized, the constructor will leave some of the memory in an undefined state.
Have been multiple calls to add this, i.e #26762 (comment).
Also related to #26296.