Warn if an already loaded package is attempted to be loaded from a different path

[KristofferC]

As a use case, let's say I want to try out some Revise version but I forgot that I have Revise loaded in my startup file. With this PR, one gets:

(@v1.9) pkg> activate --temp
  Activating new project at `/tmp/jl_gIUuRd`

(jl_gIUuRd) pkg> add Revise@v3.2
    Updating registry at `~/.julia/registries/General.toml`
   Resolving package versions...
    Updating `/tmp/jl_gIUuRd/Project.toml`
⌃ [295af30f] + Revise v3.2.1
...

julia> using Revise
┌ Warning: Package Revise already loaded from path "/home/kc/.julia/packages/Revise/wjNpr/src/Revise.jl", now attempted to be loaded from "/home/kc/.julia/packages/Revise/xRdlY/src/Revise.jl". This might indicate a change of environment between package loads and can mean that incompatible packages have been loaded.
└ @ Base REPL[2]:21

Oops, thanks Julia for warning me that I in fact did not load the version of the package that I thought I did.

This is a quite common source of confusion, for example, I remember IJulia loading some version of JSON that was incompatible with what many people had in their projects. Since IJulia loads the package into the same session as the user code, this lead to confusing behavior when users had a different JSON loaded than what they thought.

There is a cost to this in that we have to look up the path for the package even when it is already loaded. I have yet to do some benchmarks for this but I doubt it is significant.

I wonder how useful it is to write out the full path in the error message.

[vchuravy]

I think this is a great improvement!

[giordano]

I have yet to do some benchmarks for this but I doubt it is significant.

I may have a system in mind where the impact can be significant...

[KristofferC]

I may have a system in mind where the impact can be significant...

I am not sure, you still have to do the UUID lookup which does a bunch of file system stuff that is checked for the duration of the require call, so the path lookup should be not very expensive. But would be interesting to measure it for sure.

[KristofferC]

I'm not sure this will work well for packages in the sysimage.

[vtjnash]

I wonder if we should move this up a level in the call-stack (to require(::Module, ::Symbol)), nearer to the aforementioned UUID lookup, and to only emit this for the toplevel modules?

[DilumAluthge]

This will need a rebase on master so that it picks up the Buildkite CI config.

[IanButterworth]

Latest demo

% ./julia                    
┌ Info: Precompiling Revise [295af30f-e4ad-537b-8983-00126c2a3abe]
└ @ Base loading.jl:2631
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.11.0-DEV.1149 (2023-12-23)
 _/ |\__'_|_|_|\__'_|  |  kc/check_path_different/02a632aa9a* (fork: 1 commits, 0 days)
|__/                   |

(@v1.11) pkg> activate --temp
  Activating new project at `/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_pPDv9H`

(jl_pPDv9H) pkg> add JET JuliaInterpreter@0.9.25
   Resolving package versions...
    Updating `/private/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_pPDv9H/Project.toml`
  [c3a54625] + JET v0.8.21
⌃ [aa1ae85d] + JuliaInterpreter v0.9.25
    Updating `/private/var/folders/1z/jf841bdj73bdj3vk7kc7f_3w0000gn/T/jl_pPDv9H/Manifest.toml`
...
Precompiling project...
  ✓ JuliaInterpreter
  6 dependencies successfully precompiled in 28 seconds. 32 already precompiled.
  1 dependency precompiled but a different version is currently loaded. Restart julia to access the new version

julia> using JET
[ Info: Precompiling JET [c3a54625-cd67-489e-a8e7-0a5a0ff4e31b]
┌ Warning: JuliaInterpreter [aa1ae85d-cabe-5617-a682-6adf51b2e16a] is already loaded from a different path:
│   loaded:    v0.9.27 "/Users/ian/.julia/packages/JuliaInterpreter/EsH1r/src/JuliaInterpreter.jl"
│   requested: v0.9.25 "/Users/ian/.julia/packages/JuliaInterpreter/ddLm7/src/JuliaInterpreter.jl"
│ This might indicate a change of environment has happened between package loads and can mean that
│ incompatible packages have been loaded. If this happened due to a startup.jl consider starting julia
│ directly in the project via the `--project` arg.
└ @ Base loading.jl:2051

julia>

[IanButterworth]

Now following messages are shorter

julia> using JET
[ Info: Precompiling JET [c3a54625-cd67-489e-a8e7-0a5a0ff4e31b]
┌ Warning: JuliaInterpreter [aa1ae85d-cabe-5617-a682-6adf51b2e16a] is already loaded from a different path:
│   loaded:    v0.9.27 "/Users/ian/.julia/packages/JuliaInterpreter/EsH1r/src/JuliaInterpreter.jl"
│   requested: v0.9.25 "/Users/ian/.julia/packages/JuliaInterpreter/ddLm7/src/JuliaInterpreter.jl"
│ This might indicate a change of environment has happened between package loads and can mean that
│ incompatible packages have been loaded. If this happened due to a startup.jl consider starting julia
│ directly in the project via the `--project` arg.
└ @ Base loading.jl:2018

julia> using OrderedCollections
┌ Warning: OrderedCollections [bac558e1-5e72-5ebc-8fee-abe8a469f55d] is already loaded from a different path:
│   loaded:    v1.6.3 "/Users/ian/.julia/packages/OrderedCollections/9C4Uz/src/OrderedCollections.jl"
│   requested: v1.6.2 "/Users/ian/.julia/packages/OrderedCollections/SInLM/src/OrderedCollections.jl"
└ @ Base loading.jl:2018

julia>