This only deprecates the default value of ‘injection’, so we can turn it off by default.
There is a plan on eventually deprecating the injection itself, but that will come later, after the revamp of register to add projections (probably in next version) and adding a way for actions to cleanly and purposefully set variables.
Long story about set_fact:
set_fact was initially named set_var but this was misleading and set_host_scoped_var was … too long. So after many discussions set_fact was the name of compromise, misleading one as it did not ‘set a fact’, but a higher priority hope scoped variable with higher priority than facts. Eventually cacheable was added to allow for it also to be stored in the cache … but what really happens under the hood is that 2 variables get created, the aforementioned host scoped variable with higher precedence AND an actual fact, both set to the same value. The fact, gets cached and has ‘fact level precedence’ once retrieved from the cache, in subsequent runs, as in the ‘current’ run the host scoped variable will still exist and have the higher precedence.