fail to load value that is a Dict during precompile

[Roger-luo]

one can create a package to test this, the Project.toml looks like following

name = "PkgModule"
uuid = "81468456-a077-41e9-90c9-0e047517ca6f"
authors = ["Roger-Luo <rogerluo.rl18@gmail.com> and contributors"]
version = "0.1.0"

[deps]
Preferences = "21216c6a-2e73-6563-6e65-726566657250"

[compat]
julia = "1.6.1"

[extras]
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[preferences.PkgModule.color]
name = "light_blue"

[targets]
test = ["Test"]

the src/PkgModule.jl looks like this

module PkgModule

using Preferences

# uncomment the following to reproduce error
# const color = @load_preference("color")
# const color = load_preference(PkgModule, "color")

end

while I'm expecting color to be loaded as a Dict, but I'm getting

julia> using PkgModule
[ Info: Precompiling PkgModule [81468456-a077-41e9-90c9-0e047517ca6f]
fatal: error thrown and no exception handler available.
TypeError(func=:typeassert, context="", expected=Union{Nothing, String}, got=Base.Dict{String, Any}(slots=Array{UInt8, (16,)}[0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00], keys=Array{String, (16,)}[
  #<null>,
  "name",
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>], vals=Array{Any, (16,)}[
  #<null>,
  "light_blue",
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>,
  #<null>], ndel=0, count=1, age=0x0000000000000001, idxfloor=2, maxprobe=0))
jl_type_error_rt at /buildworker/worker/package_linux64/build/src/rtutils.c:119
jl_type_error at /buildworker/worker/package_linux64/build/src/rtutils.c:127
get_preferences_hash at ./loading.jl:1662
get_preferences_hash at ./loading.jl:1671
jfptr_get_preferences_hash_50003.clone_1 at /home/roger/.ion/packages/julia-1.6/julia-1.6.1/lib/julia/sys.so (unknown line)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2237 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2419
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1703 [inlined]
write_dependency_list at /buildworker/worker/package_linux64/build/src/dump.c:1150 [inlined]
jl_save_incremental at /buildworker/worker/package_linux64/build/src/dump.c:2139
jl_write_compiler_output at /buildworker/worker/package_linux64/build/src/precompile.c:65
jl_atexit_hook at /buildworker/worker/package_linux64/build/src/init.c:211
repl_entrypoint at /buildworker/worker/package_linux64/build/src/jlapi.c:703
main at /buildworker/worker/package_linux64/build/cli/loader_exe.c:51
__libc_start_main at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
_start at /home/roger/.ion/packages/julia-1.6/julia-1.6.1/bin/julia (unknown line)
ERROR: Failed to precompile PkgModule [81468456-a077-41e9-90c9-0e047517ca6f] to /home/roger/.julia/compiled/v1.6/PkgModule/jl_84dbrq.
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:33
  [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::Base.TTY, internal_stdout::Base.TTY)
    @ Base ./loading.jl:1360
  [3] compilecache(pkg::Base.PkgId, path::String)
    @ Base ./loading.jl:1306
  [4] _require(pkg::Base.PkgId)
    @ Base ./loading.jl:1021
  [5] require(uuidkey::Base.PkgId)
    @ Base ./loading.jl:914
  [6] require(into::Module, mod::Symbol)
    @ Base ./loading.jl:901
  [7] eval
    @ ./boot.jl:360 [inlined]
  [8] eval
    @ ./Base.jl:39 [inlined]
  [9] repleval(m::Module, code::Expr, #unused#::String)
    @ VSCodeServer ~/.vscode-server/extensions/julialang.language-julia-1.2.5/scripts/packages/VSCodeServer/src/repl.jl:149

however, this works with using Preference in the REPL

julia> using Preferences

julia> load_preference(PkgModule, "color")
Dict{String, Any} with 1 entry:
  "name" => "light_blue"

[Roger-luo]

versioninfo

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: AMD Ryzen 9 3900X 12-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, znver2)

[Roger-luo]

It seems to be caused by JuliaLang/julia#38285