Cannot build package with Julia 1.5 after saving manifest with Julia 1.6

[eschnett]

I have a project where I ran Pkg.update() with Julia Version 1.6.0-DEV.1722, and committed the resulting Manifest.toml. This fails during CI when I test the package with Julia 1.5 or Julia 1.4. The error is

ERROR: AssertionError: sourcepath !== nothing

in the julia-actions/julia-buildpkg@v1 step. The complete output is available at https://github.com/eschnett/SimplexPoly.jl/runs/1533491897. This error occurs in Pkg.

The complete backtrace is

13
Stacktrace:
14
 [1] is_package_downloaded at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:1670 [inlined]
15
 [2] JuliaLang/julia#12 at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:113 [inlined]
16
 [3] _all(::Pkg.Operations.var"#12#13"{Pkg.Types.Context}, ::Array{Pkg.Types.PackageSpec,1}, ::Colon) at ./reduce.jl:828
17
 [4] #all#638 at ./reducedim.jl:735 [inlined]
18
 [5] all at ./reducedim.jl:735 [inlined]
19
 [6] is_instantiated at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:113 [inlined]
20
 [7] instantiate(::Pkg.Types.Context; manifest::Nothing, update_registry::Bool, verbose::Bool, platform::Pkg.BinaryPlatforms.Linux, kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:828
21
 [8] instantiate(::Pkg.Types.Context) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:795
22
 [9] build(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}, ::Bool) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/Operations.jl:838
23
 [10] build(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}; verbose::Bool, kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:745
24
 [11] #build#69 at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:67 [inlined]
25
 [12] build(; name::Nothing, uuid::Nothing, version::Nothing, url::Nothing, rev::Nothing, path::Nothing, mode::Pkg.Types.PackageMode, subdir::Nothing, kwargs::Base.Iterators.Pairs{Symbol,Bool,Tuple{Symbol},NamedTuple{(:verbose,),Tuple{Bool}}}) at /buildworker/worker/package_linux32/build/usr/share/julia/stdlib/v1.5/Pkg/src/API.jl:80
26
 [13] top-level scope at none:1

I notice that the automatically installed transitive dependencies are very different with Julia 1.5 and Julia 1.6. Julia 1.6 says this during Pkg.update():

  [0dad84c5] + ArgTools
  [56f22d72] + Artifacts
  [8ba89e20] - Distributed
  [f43a241f] + Downloads
  [b27032c2] + LibCURL
  [ca575930] + NetworkOptions
  [fa267f1f] + TOML
  [a4e569a6] + Tar
  [deac9b47] + LibCURL_jll
  [29816b5a] + LibSSH2_jll
  [c8ffd9c3] + MbedTLS_jll
  [14a3606d] + MozillaCACerts_jll
  [83775a58] + Zlib_jll
  [8e850ede] + nghttp2_jll

[KristofferC]

Yeah, this is known. Manifests generated on 1.6 do not work well on 1.5.

[StefanKarpinski]

In general, you should be able to upgrade Julia smoothly, but you cannot necessarily downgrade.

[eschnett]

I was hoping for a proper error message; the assertion errors looks like I triggered a bug.

[StefanKarpinski]

It could be fixed in a 1.5 point release but it's unclear if there will be any more of those. Issue belongs on https://github.com/JuliaLang/Pkg.jl

[DilumAluthge]

Duplicate of #2513