Add support for +RTS/-RTS flags from GHC

[antew]

Enabling these flags allows for tuning the GHC runtime and can dramatically improve build times when a lot of files have to be recompiled, as well as improving performance on large case statements, the main benefit is reducing the time spent in the garbage collector.

This does require a version of elm-make compiled with the -rtsopts option to allow runtime control, if you try to run it on a version without that enabled you'll get the message:

$ elm-make src/elm/Main.elm +RTS -A128M -N128M -n8m -RTS
elm-make.exe: Most RTS options are disabled. Link with -rtsopts to enable them.

Some further information and related issues here:

• Performance reduced when running on multi-core ( which is by default ) elm-lang/elm-make#159 (comment)
• https://discourse.elm-lang.org/t/repos-with-slow-compile-times-wanted-for-research/662
• GHC option: Enable rtsopts elm-lang/elm-make#179

The current version of elm-make does allow limited RTS options, for instance, you can use +RTS -s -RTS to profile a run.

[rtfeldman]

Cool, thanks @antew!

[rtfeldman]

Published as 4.5.0

[antew]

Thank you @rtfeldman 🎉 🎈 !!

[andys8]

@antew @rtfeldman This will only work for self compiled elm compilers, right? Can we somehow enable the flag in the next version of the compiler? Otherwise the added argument in node-elm-compiler will not work for most of the users, right?

elm-lang/elm-make#164 (comment)