Prevent people from loading incompatible packages via changing enviroments between loads

[oxinabox]

I think many people have known this is possible for a while.
Because compatibility is checked at package install time on a per enviroment basis.
And because modules are not reloaded (ever), including after changing enviroments.

Today I think I saw this in the wild.

Here is a way to reproduce what i saw posted in Slack:

# julia --startup-file=no

# make for fresh enviroments
rm("a"; recursive=true, force=true); rm("b", recursive=true; force=true);
mkdir("a"); mkdir("b");

using Pkg

Pkg.activate("a")
pkg"add CodeTracking@1"
using CodeTracking  # Load CodeTracking@1

Pkg.activate("b")
pkg"add Revise@2.7.2"
using Revise  # Load Revise, which would load CodeTracking@5.9 but doesn't because CodeTracking@1 is already loaded

# We have now put Revise in an invalid state because 
# Revise@2.7.2 is compatible only with CodeTracking@5.9, 
# and errors if it is used with CodeTracking@1

# Demonstrate the error:
pkg"add Example"
using Example
pkg"dev --local Example"

Revise will then flip-out because the API of CodeTracking is not what it said it was compatible with.

(b) pkg> Revise.LogRecord(Error, evaluation error starting at /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:4, lowered
, Revise_e943ed8b, "/Users/oxinabox/.julia/packages/Revise/tV8FE/src/lowered.jl", 106, (mod=Example, ex=begin
    #= /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:4 =#
    hello(who::String) = begin
            #= /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:9 =#
            "Hello, $(who)"
        end
end)MethodError: Cannot `convert` an object of type Tuple{LineNumberNode,Expr} to an object of type Array{Tuple{LineNumberNode,Expr},
1}
  ...
Stacktrace:
 [1] convert(::Type{Union{Missing, Array{Tuple{LineNumberNode,Expr},1}}}, ::Tuple{LineNumberNode,Expr}) at ./missing.jl:69
 [2] setindex!(::IdDict{Type,Union{Missing, Array{Tuple{LineNumberNode,Expr},1}}}, ::Any, ::Any) at ./abstractdict.jl:585
 [3] add_signature!(::Revise.CodeTrackingMethodInfo, ::Any, ::LineNumberNode) at /Users/oxinabox/.julia/packages/Revise/tV8FE/src/Rev
ise.jl:489)Revise.LogRecord(Error, evaluation error starting at /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:11, lowe
red, Revise_e943ed8b, "/Users/oxinabox/.julia/packages/Revise/tV8FE/src/lowered.jl", 106, (mod=Example, ex=begin
    #= /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:11 =#
    domath(x::Number) = begin
            #= /Users/oxinabox/.julia/packages/Example/aqsx3/src/Example.jl:16 =#
            x + 5
        end

[oxinabox]

cf #37421 (comment)

[timholy]

Also xref #35663

[oxinabox]

I think when activating environments we should first check all loaded packages and if they are not compatible with the environment we should error.

I think in 1.9 that is finally relatively easy as we record the versions of packages when we load them.

[KristofferC]

Alternatively, something like #44329.

[oxinabox]

@timholy is this just plain a duplicate of #35663 ?
So we can close this one?