Make it more clear that user need MSVC for MSVC versions

[bombless]

cc rust-lang/rust#32283

[bombless]

I checked the msi folder and I feel that I may need a little help for this.
Do you have any idea how this could be done, @brson ?

[bombless]

I guess we can add a warning dialog at the very beginning.
Checking how to do this..

[vadimcn]

I guess we can add a warning dialog at the very beginning.

I think that modifying the download page on rust-lang.org would be both easier and more useful, as the users would have this info before downloading the package. Also, I am not a fan of unconditionally adding extra UI in the installer.

[bombless]

@vadimcn But if you get the installer from some where else, which is normal for us, users from mainland China where network is terrible, you will not see notes from website.
Besides, it could be normal that people never check instructions from website if English is not their mother tongue.

[bombless]

Well I think we can do both way, and make the notice from the installer less annoying than what I considered.

[bombless]

FYI I'm checking this doc https://msdn.microsoft.com/en-us/library/aa243959

[bombless]

It might be possible that we can checked the exit code when we call exec on link.exe, and provide some info there. Say, do our best not to surprise new comers.
I might start from there since I'm more familiar with the rustc repo.

[nagisa]

I don’t think reporting this during installation is not suitable at all. We only really need MSVC toolchain post translation phase, you can still do a lot without MSVC: generating docs, running all stages up-to-translation, perhaps running miri(nterpretator) and so on and on.

Personally it seems to me like the best thing to do would be to just emit a error message when we reach stages dependent on MSVC:

error: MSVC installation could not be detected
help: where to find the MSVC or how to help rustc find it

[retep998]

Perhaps I should add a message to rust-lang/rust#31158 in the case where an MSVC installation could not be detected?

[brson]

Here's what the website says on the subject.

@retep998 I do think it would be appropriate for rustc to generally handle missing linkers better, without teaching it about how to acquire linkers. For example, rustc could easily know before compilation that it is going to fail because the linker doesn't exist. It could do this detection at startup and display a nice message, perhaps even with simple platform-specific advice.

I also think it would be appropriate for the MSVC msis to somewhere indicate that MSVC is required, with a download link. Like @vadimcn I don't think it merits a new dialog, but if it were added as text as the final success message seems ok. No extra clicks, just an important note that they may have missed.

This sort of native toolchain detection is also intended to be part of rustup. Though rustup is primarily intended to deal with cross-compiling, it will similarly be probing for native linkers.

cc @alexcrichton

[retep998]

@brson A really tricky issue is when someone is cross compiling from 64 to 32 or 32 to 64 bit on windows, especially when using build scripts. Right now the only way this works is if rustc is responsible for finding the linker, because link.exe is a single target linker. If you use vcvars or equivalent to set it up then either the build script built for the host or the final binary built for the target will be linked with the wrong linker and stuff will fail. If logic is added higher up then it needs to be able to handle passing the correct linker to the correct rustc invocation.

[bombless]

https://chocolatey.org/packages?q=visualstudio I see that you can install MSVC from Chocolatey. So I think cargo-install can do something similar. Long story short, we can provide a checkbox in the installer to install MSVC automatically.