Failure to install ghc from bindist

[alt-romes]

Initially reported by a user here: https://discourse.haskell.org/t/ghc-9-12-3-rc3-is-now-available/13391/4

The user attempted to install 9.12.3-rc2 using:

ghcup install ghc-9.12.3-rc3 --url https://downloads.haskell.org/ghc/9.12.3-rc3/ghc-9.12.2.20251209-aarch64-apple-darwin.tar.gz

Which failed with

[ Info  ] Unpacking: ghc-9.12.2.20251209-aarch64-apple-darwin.tar.gz to /Users/vanessa/.ghcup/tmp/ghcup-959bbdefb415be95
[ Info  ] Installing GHC (this may take a while)
[ ghc-configure ] checking build system type… aarch64-apple-darwin2…
[ ghc-configure ] checking host system type… aarch64-apple-darwin24…
[ ghc-configure ] checking target system type… Invalid configuratio…
[ ghc-configure ] configure: error: /bin/sh ./config.sub ghc failed

[ Error ] [GHCup-00841] Process “sh” with arguments [“./configure”,
[ …   ]                              “–prefix=/Users/vanessa/.ghcup/ghc/ghc-9.12.3-rc3”,
[ …   ]                              “–target=ghc”, “–disable-ld-override”] failed with exit code 1.
[ Error ] Also check the logs in /Users/vanessa/.ghcup/logs

> cat ~/.ghcup/logs/ghc-configure.log
checking build system type… aarch64-apple-darwin24.6.0
checking host system type… aarch64-apple-darwin24.6.0
checking target system type… Invalid configuration ‘ghc’: machine ‘ghc-unknown’ not recognized
configure: error: /bin/sh ./config.sub ghc failed

I was able to reproduce this error on a clean VM with only ghcup installed. This also failed when trying to install ghc-9.12.3-rc2.

On that same VM, I then tried to install from the bindist manually, using:

curl -LO https://downloads.haskell.org/ghc/9.12.3-rc3/ghc-9.12.2.20251209-aarch64-apple-darwin.tar.gz
tar xzf ghc-9.12.2.20251209-aarch64-apple-darwin.tar.gz
cd ghc-9.12.2.20251209-aarch64-apple-darwin
./configure --prefix=$(pwd)/here
make install
./here/bin/ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.12.2.20251209

And that succeeded without trouble.

I suspect the installation failure may be a bug with the way GHCup configures the bindist, hence this ticket.

[wz1000]

--target=ghc might be the problem.

[hasufell]

Yes, the invocation is wrong.

Always use ghcup install ghc --url <url> <version>

ghcup install <version> is a legacy command that we keep around for backswards compat. You can see in your log that we warn about it even. It'll parse your version identifier as a cross compiler.