Pub-build fails if PUB_CACHE is in a different drive (windows)

[DartBot]

<img src="https://avatars.githubusercontent.com/u/2049220?v=3" align="left" width="96" height="96"hspace="10"> Issue by sigmundch
Originally opened as dart-lang/sdk#21365

---

Here is an example from one of our package bots:

http://chromegw.corp.google.com/i/client.dart.packages/builders/packages-windows-googleapis_auth/builds/62/steps/Pub%20build/logs/stdio

The failure was that the PUB_CACHE was by default on C:, but the package was on E:\

Clearly the packages symlinks from pub-get were broken, but I was expecting pub-serve/pub-build to work regardless.

If it can't be fixed, we should consider providing an error message to help users debug/fix it.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

---

Assigning to Bob, since he has a Windows machine on which he can reproduce this.

---

Set owner to @munificent.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="48" height="48"hspace="10"> Comment by munificent

---

Unfortunately, symlinks cannot span drives on Windows. Even though pub build and serve don't require the symlinks, they do implicitly run pub get first, which does create them.

We can't change the behavior here, but I agree a better error message would help.

[nex3]

I'm closing this out, since we're close to a solution for #727 anyway.