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Real question, Does that form work? Opening CMD I get:

>set FOO=foo && BAR=bar rustc
'BAR' is not recognized as an internal or external command,
operable program or batch file.

@Eh2406 You need set before each variable.

This doesn't work very well on Windows. The escaping rules of cmd are finicky. For example, set FOO='bar' is embedding the single quotes within the variable (cmd doesn't use single quotes for strings). Also, it is space sensitive, so set FOO=one && BAR=two && rustc... will embed spaces after each variable (FOO is one ). I think avoiding the quotes, and just escaping special characters (like ^") might be an option. And avoid the space between commands (not sure if there's a way to avoid that).

Also, would it be possible to detect the shell and use different syntax? I suspect cmd users are rare (at least I don't know any). Most people I've seen use bash or powershell.

@Eh2406

set FOO=foo && BAR=bar rustc

That was a mistake in my description, I acutally implemented set FOO=foo && set BAR=bar && rustc.

@ehuss

Also, it is space sensitive, so set FOO=one && BAR=two && rustc... will embed spaces after each variable (FOO is one ).

This should be fixed now.

I think avoiding the quotes, and just escaping special characters (like ^") might be an option.

So if I understand you, I should not shell escape the variables and only escape the cmd.exe metacharacters with ^. So "Ben & Jerry's" becomes ^"Ben ^& Jerry^'s^". This seemed to work when I tried it but I'm not sure about this. ProcessBuilder already escapes rustc arguments using shell_escape::escape and doesn't do this (although maybe it should). This article linked from the shell_escape docs seems to indicate that both types of escaping are required.

Also, would it be possible to detect the shell and use different syntax? I suspect cmd users are rare (at least I don't know any). Most people I've seen use bash or powershell.

This is out of scope for me. I have a feeling that the powershell escaping story might be even worse than cmd.exe.

This seemed to work when I tried it but I'm not sure about this.

I am not sure about it, either. However, from my understanding of cmd syntax, it works a bit differently from command-line parsing syntax. It seems to be more reliable to use ^ escaping. I think the argument escaping is probably already correct, since that goes through a different mechanism.

One thing I can't figure out is how to set an empty variable. set FOO= deletes the variable. I don't think cargo has any variables where that would matter, but it doesn't seem quite right.

This is out of scope for me. I have a feeling that the powershell escaping story might be even worse than cmd.exe.

That's fair.

This looks like a great start to me, thanks @mikerite! I agree that we'll probably want powershell syntax eventually, but for now I think it's fine to add this in and iterate from here

@bors: r

📌 Commit e557f66 has been approved by alexcrichton

⌛ Testing commit e557f66 with merge 34320d2...

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 34320d2 to master...