Result from format_args! cannot be center-aligned within another format string

[ColinFinck]

I can do println!("{:=^80}", " TEST ") to pretty-print a center-aligned header within equality signs.
However, the alignment is ignored when I do println!("{:=^80}", format_args!(" TEST ")).
I need the latter syntax to further write code like
println!("{:=^80}", format_args!(" TEST {:#016X} ", some_integer)).

I understand that a format_args! result is harder to center-align due to cases where the final width could be unknown. Nevertheless, it should be possible for the compiler to determine the string width in my example cases to let it be center-aligned.

[estebank]

Can't you in this case use println!("{:=^80}", format!(" TEST {:#016X} ", some_integer));?

[ColinFinck]

No, my code must run in a no_std environment without heap allocations.

[steveklabnik]

Triage: not aware of any changes here.