Investigate slow installation (merging file trees) on windows

[hasufell]

https://discord.com/channels/280033776820813825/505370075402862594/1310055203709390858

[andreasabel]

Yes, this is really very slow, on my (old) Windows machine this step takes more than 15min. (Running under git bash.)

After turning off "real-time protection" in the "Windows Security / Virus Protection" things sped up quite a bit: from ghcup getting <1% CPU to getting around 10% CPU.

With real-time protection off, I can get an install done in <8min, which is still longish:

$ time ghcup install ghc 9.8.4
[ Info  ] downloading: https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-0.0.9.yaml as file C:\ghcup\cache\ghcup-0.0.9.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
[ Warn  ] Could not parse version of stray directorystack-2.7.5.exe.tmp
[ Warn  ] New ghc version available. If you want to install this latest version, run 'ghcup install ghc 9.12.1'
[ Warn  ] New cabal version available. If you want to install this latest version, run 'ghcup install cabal 3.14.1.1'
[ Warn  ] New stack version available. If you want to install this latest version, run 'ghcup install stack 3.3.1'
[ Info  ] verifying digest of: gs.exe
[ Info  ] downloading: https://downloads.haskell.org/~ghc/9.8.4/ghc-9.8.4-x86_64-unknown-mingw32.tar.xz as file C:\ghcup\tmp\ghcup-d9c1e195dccae9c8\ghc-9.8.4-x86_64-unknown-mingw32.tar.xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  322M  100  322M    0     0  2839k      0  0:01:56  0:01:56 --:--:-- 3104k
[ Info  ] verifying digest of: ghc-9.8.4-x86_64-unknown-mingw32.tar.xz
[ Info  ] Unpacking: ghc-9.8.4-x86_64-unknown-mingw32.tar.xz to C:\ghcup\tmp\ghcup-2a0f46cb130a58f8
[ Info  ] Installing GHC (this may take a while)
[ Info  ] Merging file tree from "C:\ghcup\tmp\ghcup-2a0f46cb130a58f8\ghc-9.8.4-x86_64-unknown-mingw32" to "C:\ghcup\ghc\9.8.4"
[ Info  ] GHC installation successful

real    7m23.913s
user    0m0.015s
sys     0m0.031s

[FranklinWilson]

Recently had the same experience with very slow 'merging file tree' on my Windows 11 PC.
As andreasabel mentioned, turning off real-time protection (Windows Security -> Virus and threat protection -> manage settings) made all the difference, completed in a matter of seconds.