Extra Generators: Deprecate in favor of file-api
The "extra" generator approach is left from a time when CMake did not have widespread adoption. These days many IDEs are CMake-aware and try to provide some level of integration. The cmake-file-api(7) was added to support them. See tracking issue #18398 (closed) for its addition. The file-api offers a stable way for IDEs to load information about CMake-generated build trees. Its implementation is mature and fully covered by the test suite (with verification of output content).
Each extra generator requires code to traverse the CMake internal representation of the code model and to generate an external IDE's project file format (which may change across versions of that IDE). This requires a lot of maintenance. Furthermore it is hard to test extra generators since the output files affect interactive environments. As a result there are many open issues related to extra generators being incomplete, poorly maintained, or simply buggy.
Therefore I propose that we deprecate extra generators in favor of working with IDE developers to use the file-api.