The Pkg test suite (specifically, the `test/manifests.jl` tests) should treat the Pkg.jl source code directory as immutable

[Moelf]

tests involve stdlib/v1.7/Pkg/test/manifest/formats/v1.0/Manifest.toml_backup etc. don't work:

open("/cvmfs/sft-nightlies.cern.ch/lcg/nightlies/dev4/Sat/julia/1.7.1/x86_64-centos7-gcc10-opt/share/julia/stdlib/v1.7/Pkg/test/manifest/formats/v1.0/Manifest.toml_backup", 577, 33188): read-only file system (EROFS)

things like:

julia -e "using Pkg; Pkg.add(Revise)"

works because DEPOT_PATH is not touched, the read-only path is appended in LOAD_PATH so it works as expected.

Can we fix tests to use the DEPOT_PATH in cases like this?

[DilumAluthge]

There's no need to look at the user's JULIA_DEPOT_PATH for this.

We just need to fix the Pkg test suite so that it does not try to write to the Pkg source directory during the Pkg test suite. Instead, the tests (specifically, the manifest format tests) need to be fixed so that instead of trying to write to the Pkg source directory, they copy the files over to a temp directory, and do any writing in the temp directory.

To illustrate, the problem is lines like this:

Pkg.jl/test/manifests.jl

Line 13 in b616bb0

cp(env_manifest, string(env_manifest, "_backup"))

@Moelf A few requests:

1. I notice that you encountered this on Julia 1.7. Could you make sure that you are able to reproduce with the latest Julia nightly binaries?
2. Also, it would be great if you could post the full stacktrace.