Re: [RFC PATCH 19/21] usage API: use C99 macros for {usage,usagef,die,error,warning,die}*()

> 
> It might be a good change to remove the "fmt" key from the "error"
> events as a follow-up change. As these few examples from running the
> test suite show it's sometimes redundant (same as the "msg"), rather
> useless (just a "%s"), or something we could now mostly aggregate by
> file/line instead of the normalized printf format:
> 
>        1 file":"builtin/gc.c","line":1391,"msg":"'bogus' is not a valid task","fmt":"'%s' is not a valid task"}
>        1 file":"builtin/for-each-ref.c","line":89,"msg":"format: %(then) atom used more than once","fmt":"%s"}
>        1 file":"builtin/fast-import.c","line":411,"msg":"Garbage after mark: N :202 :302x","fmt":"Garbage after mark: %s"}
> 
> "Mostly" here assumes that it would be OK if the aggregation changed
> between git versions, which may be what all users of trace2 want. The
> change that introduced the "fmt" code was ee4512ed481 (trace2: create
> new combined trace facility, 2019-02-22), and the documentation change
> was e544221d97a (trace2: Documentation/technical/api-trace2.txt,
> 2019-02-22).
> 
> Both are rather vague on what problem "fmt" solved exactly, aside from
> the obvious one of it being impossible to do meaningful aggregations
> due to the "file" and "line" being the same everywhere, which isn't
> the case now.
> 
> In any case, let's leave "fmt" be for now, the above summary was given
> in case it's interesting to remove it in the future, e.g. to save
> space in trace2 payloads.