rustup-init: --default-host is broken under cygwin

[abr-egn]

Verification

• I searched for recent similar issues at https://github.com/rust-lang/rustup/issues?q=is%3Aissue and found no duplicates.
• I am on the latest version of Rustup according to https://github.com/rust-lang/rustup/tags and am still able to reproduce my issue.

Problem

Attempting to pass a value for --default-host to rustup-init.sh will fail with the following error:

error: error: the argument '--default-host <DEFAULT_HOST>' cannot be used multiple times

It looks like #4497 is the cause; that will prepend a --default-host=$_arch unconditionally when running on a windows host.

Steps

On a cygwin host:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- --default-host=x86_64-pc-windows-msvc

Possible Solution(s)

No response

Notes

No response

Rustup version

rustup-init 1.29.0 (28d1352db 2026-03-05)

Installed toolchains

n/a

OS version

CYGWIN_NT-10.0-20348 3.6.6-1.x86_64 x86_64 Cygwin

[rami3l]

@abr-egn Thanks for reporting! It was my fault when updating the script to think that two --default-host occurrences will give priority over the latter. I'll work on a fix real soon.