I used
stack bench --profile --ba +RTS -hy -l
and this reported the error:
stack: the flag -hy requires the program to be built with -prof
I am confused by this as I thought stack bench --profile does build with -prof
I had no problem with
stack bench --profile --ba +RTS -hc -l
presumably because that does not require a build with -prof
Can anyone tell me what I am missing here?
(I am using Stack Version 3.1.1)
Looks like you are passing the +RTS options to the stack executable itself, rather than to the executable you are trying to profile. Try using -- to separate arguments to stack from arguments to the profiled executable. (I’m not a Stack user, so I’m not completely sure that works for stack bench, but if it doesn’t you should be able to use stack exec which does.)
Many thanks.
This worked as expected
stack bench --profile --ba ‘+RTS -hy -l’
I think you have found a gap in Stack’s online documentation.
The stack executable is built by GHC with option -rtsopts, equivalent to -rtsopts=some. (That is not yet documented.) That means that the RTS extracts the command-line arguments bracketed between +RTS and -RTS as its own, as described here: 5.7. Runtime system (RTS) options — Glasgow Haskell Compiler 9.10.1 User's Guide.
As you have found, quoting the argument to --ba stops the RTS from taking +RTS -hy -l for itself.
EDIT: Stack’s documentation is now updated: Commands - The Haskell Tool Stack