Thanks for reporting. Updating the rust package now, after it is done compiling (takes a while).

Updated! The version reported is now:
rustc 1.0.0 (built 2015-06-01)

Please remove the parameter.
It not only changes the version information, but also disables all unstable features.

For example, you have built rust with ffi support, but you also disable rust's libc usage because it is an unstable feature, this is quite odd.

But then, arch's stable Rust version 1.0.0 will be behave different to all other distributions, and different to the official release.
You can use Rust nightly or beta for unstable features. Or you could silence the linter to report unstable features as an error.

Enabling unstable features does not seem to be the right way to go.

All unstable features are disabled by default, but we can only use them in dev-channel.
Even the examples in the official rust documentation contain ton of unstable features such as core, convert, simd...
Moreover, you can't build rust itself by a stable-channel release. Just try to build rust with '--enbale-local-rust'

By the way, I try to find rust in other distributions' official repositories but has no result.
http://packages.ubuntu.com/search?keywords=Rust
https://packages.debian.org/search?keywords=rust&searchon=names&suite=all&section=all
https://admin.fedoraproject.org/pkgdb/packages/rust*/

There also has some personal builds, none of them add this parameter
https://build.opensuse.org/package/view_file/devel:languages:rust/rust/rust.spec?expand=1
https://launchpad.net/~hansjorg/+archive/ubuntu/rust/+packages
https://github.com/Alexpux/MINGW-packages/blob/master/mingw-w64-rust/PKGBUILD

One last brief comment on that: If you remove "--release-channel=stable" the Rust 1.0 version in Arch will be different than the official release. This will lead to some confusion (which is not necessary): https://users.rust-lang.org/t/stable-versions-of-source-and-linux-binary-differ/1561/4
The reasons why you still have unstable examples in the official docs (which do not compile using the official release, too): https://github.com/rust-lang/rust/issues/25863

I see understand why this bothers to you. But why don't you just use nightly or multirust?

To the package maintainers: Feel free to set this to the dev-channel again, I will not reopen this issue.
But keep in mind there are good reasons against it and that next Rust release is in about two weeks.

Official Arch Linux packages are in general supposed to be the latest release version, not the latest development version. Keeping the stable channel, for now.
If this is problematic, please hear what the rust developers has to say about the issue and re-open this bug-report, and I'll change the channel back to dev if that is what they recommend.

Thanks for caring about the rust package.