Dependency cycles lead to repeated attempted pre-compilation and error spew

[topolarity]

Make two packages Foo and Bar that depend on each other:

$ cat Foo/src/Foo.jl
module Foo
using Bar
println("Executing Foo!\n")
end # module Foo
$ cat Bar/src/Bar.jl
module Bar
using Foo
println("Executing Bar!\n")
end # module Bar

pkg> precompile works fine (albeit the warning isn't terribly clear whether this is an issue or not):

┌ Warning: Circular dependency detected. Precompilation will be skipped for:
│   Base.PkgId(Base.UUID("9b094d01-e697-4a76-8fe8-871656a862e0"), "Foo")
│   Base.PkgId(Base.UUID("ed96e9dd-c367-45ab-9d59-befe4c57f37f"), "Bar")
└ @ Base.Precompilation precompilation.jl:562

However actually using either package leads to nested re-precompilation and very verbose error messages:

julia> using Foo
┌ Warning: Circular dependency detected. Precompilation will be skipped for:
│   Base.PkgId(Base.UUID("9b094d01-e697-4a76-8fe8-871656a862e0"), "Foo")
│   Base.PkgId(Base.UUID("ed96e9dd-c367-45ab-9d59-befe4c57f37f"), "Bar")
└ @ Base.Precompilation precompilation.jl:562
[ Info: Precompiling Foo [9b094d01-e697-4a76-8fe8-871656a862e0] (cache misses: include_dependency fsize change (4))
┌ Warning: Module Foo with build ID ffffffff-ffff-ffff-0001-e5501f34bcab is missing from the cache.
│ This may mean Foo [9b094d01-e697-4a76-8fe8-871656a862e0] does not support precompilation but is imported by a module that does.
└ @ Base loading.jl:2497
┌ Info: Skipping precompilation due to precompilable error. Importing Foo [9b094d01-e697-4a76-8fe8-871656a862e0].
└   exception = Error when precompiling module, potentially caused by a __precompile__(false) declaration in the module.
┌ Warning: Circular dependency detected. Precompilation will be skipped for:
│   Base.PkgId(Base.UUID("9b094d01-e697-4a76-8fe8-871656a862e0"), "Foo")
│   Base.PkgId(Base.UUID("ed96e9dd-c367-45ab-9d59-befe4c57f37f"), "Bar")
└ @ Base.Precompilation precompilation.jl:562
[ Info: Precompiling Bar [ed96e9dd-c367-45ab-9d59-befe4c57f37f] (cache misses: include_dependency fsize change (4))
┌ Warning: Module Foo with build ID ffffffff-ffff-ffff-0001-e550421fe669 is missing from the cache.
│ This may mean Foo [9b094d01-e697-4a76-8fe8-871656a862e0] does not support precompilation but is imported by a module that does.
└ @ Base loading.jl:2497
┌ Info: Skipping precompilation due to precompilable error. Importing Bar [ed96e9dd-c367-45ab-9d59-befe4c57f37f].
└   exception = Error when precompiling module, potentially caused by a __precompile__(false) declaration in the module.
Executing Bar!

Executing Foo!

Even worse, this warning spew happens every single time you using either package in a new session.

I believe this is the reason that #55557 took 25 minutes, so it can be a very bad experience depending on where you hit the cycle.

[topolarity]

Perhaps pre-compilation needs to create a "cache" file describing its results even when those results are negative (i.e. package errored, or was in a cycle)