SIGINT handling during async functions

[Tycho Kirchner]

Hi,
we found quite some inconsistency and weirdness in the handling of SIGINT's 
during async function calls and were wondering, whether those are expected. All 
calls were executed from a script with jobcontrol turned off (set +m) while 
pressing Ctrl+C shortly afterwards. In summary:
The main INT handler is never executed in foofunc (is that expected?) while the new (default) handler 
either aborts command execution in case of 'foofunc &' or continues execution in case of '{ foofunc; 
} &'. While on 'foofunc &' 'trap -p' at the beginning of foofunc (wrongly) prints the main 
handler, in case of '{ foofunc; } &' it suddenly prints the ignore handler "trap -- '' 
SIGINT" and remains indeed uninterruptible. Thus printing the trap apparently changes bash's 
behavior.

Tested bash versions:
GNU bash, Version 5.1.4(1)-release (x86_64-pc-linux-gnu)
GNU bash, Version 5.2.2(1)-release (x86_64-pc-linux-gnu)
on Debian Bullseye.

Thanks and kind regards
Tycho
____________________________________

t='echo INT ${FUNCNAME[0]-main} >&2'
trap "$t" INT
foofunc(){ sleep 3; echo foo >&2; }
foofunc &
sleep 5
--> INT main
# foofunc INT-handler is reset to default ('foo' is not printed).
# Note that 'trap -p' within foofunc wrongly prints above INT handler.

____________________________________

t='echo INT ${FUNCNAME[0]-main} >&2'
trap "$t" INT
foofunc(){ trap "$t" INT; sleep 3; echo foo >&2; }
foofunc &
sleep 5
--> INT main
INT foofunc
foo
# foofunc custom INT-handler works.
____________________________________

t='echo INT ${FUNCNAME[0]-main} >&2'
trap "$t" INT
foofunc(){ sleep 3; echo foo >&2; }
{ foofunc; } &
sleep 5
--> INT main
foo
# Opposing to 'foofunc &' foo _is_ printed so apparently we have a
# different default trap handler here.
____________________________________

t='echo INT ${FUNCNAME[0]-main} >&2'
trap "$t" INT
foofunc(){ trap -p; sleep 3; echo foo >&2; }
{ foofunc; } &
sleep 5
--> trap -- '' SIGINT
^CINT main
$ foo
# Here, when the trap is printed, INT is reported as "ignored" and foofunc
# becomes indeed uninterruptible. So, 'trap -p' changes bash's behavior.
____________________________________