environment.yml: channel-name::package-name syntax has global effect

[w-hc]

conda version 4.8.3

When I create the following environment.yml

name: temp
channels:
  - defaults
dependencies:
  - python=3
  - numpy
  - conda-forge::av
  - jupyterlab=2.1.4

I expect that conda-forge::av would only introduce conda-forge channel to that single package. Other dependencies should not be able to access anything from conda-forge.
Currently jupyterlab=2.1.4 is not available in the default channel, and so I expect the installation to fail.
In reality however conda would go ahead to fetch jupyterlab=2.1.4 from conda-forge, without notifying me what happened.

I also tried this

name: temp
channels:
  - defaults
dependencies:
  - python=3
  - numpy
  - jupyterlab=2.1.4

In this case, conda-forge does not appear anywhere, and the installation fails as it should.

The desired behavior should be to isolate the effect of the channel specifier to the single line, not exposing it globally.

[w-hc]

#2800, #7202 both refer to this problem. However it seems that isolated per dependency channel is still not there.

[angloyna]

I think we've since updated our jupyterlab on the defaults channel to include v2.1.4, but I was able to reproduce this by adding a different package from conda-forge which doesn't exist in defaults.

[github-actions]

Hi there, thank you for your contribution!

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