Add an explicit NuGet source for NuGetPush

[daveaglick]

As of NuGet client 3.4.something, performing a NuGet push requires a source to be specified (it used to use a default source if none was provided). See NuGet/Home#2504 for more information.

At first glance, I would assume this should go in NuGetPusher (https://github.com/cake-build/cake/blob/develop/src/Cake.Common/Tools/NuGet/Push/NuGetPusher.cs#L74) as an alternate branch if NuGetPushSettings.Source isn't specified. The bigger question is probably what the default should be...

[daveaglick]

I've confirmed that the previous default was (and should probably continue to be) https://www.nuget.org/api/v2/package. I'll go ahead and write up a PR to get the ball rolling.

[gep13]

@daveaglick I wanted to touch base on this issue.

We, the @cake-build/team have spoken about this at length, and we have come to the decision that we are not going to implement this suggestion. What it comes down to is that there is no real way to cover all the requirements of this "breaking" NuGet change, without inversely affecting build scripts that are already in place.

The approach that we have decided to follow is this:

1. Leave aliases as is
2. Add verbose warning if no source specified
3. Add remarks to docs.

As a result, I am going to go ahead and close the PR that you opened for this issue. If you would like to talk about this some more, then please feel free to reach out to the team.

[daveaglick]

Sounds good - I've already patched my own builds to supply sources on push, so this no longer affects me personally.

Anyone else who has a build script that doesn't supply a source will break when they update NuGet and try to push. I'm guessing at this point most folks have probably already updated NuGet and encountered this if they were going to. The verbose warning should help point out what they need to do to get back up and running.

[gep13]

@daveaglick re-opening this, as I have an open PR that will add documentation for this scenario.

[devlead]

Fixed by #1113