Why do I need to re-install Plots after updating Julia?

[Jerry]

I just downloaded and installed Julia-1.6.app for macOS (1.6.3 I think), upgrading from 1.5.3. Now when I do using Plots it complains

ERROR: ArgumentError: Package Plots not found in current path: Run import Pkg; Pkg.add(“Plots”) to install the Plots package.

Of course I can do that but (1) should I and (2) why? and (3) is this loading up my drive with a copy of stuff that is already there?

[kristoffer.carlsson]

You can also copy the .julia/environments/v1.5/Project.toml to .julia/environments/v1.6/Project.toml and type pkg> instantiate in the Pkg REPL in the new Julia version.

@Jerry

(2) why?

Different Julia versions can have different packages “installed” (available to load) and a new Julia version starts out empty as it is right now.

@Jerry

is this loading up my drive with a copy of stuff that is already there?

No, all Julia versions share package download locations.

[Mattriks]

Re (3): there is also the very useful function Pkg.gc, which will remove old package & artifact versions, no longer used by any other package.

[Jerry]

Thank you for your kind help.