long symlinks: libuv stat throws errors where /bin/stat doesn't

[maleadt]

Courtesy of Mads.jl, we have this fun symlink:

❯ ls -lah Mads.jl/examples/model_analysis/models/internal-polynomial.jl
lrwxrwxrwx 1 tim tim 472 May 16 12:15 Mads.jl/examples/model_analysis/models/internal-polynomial.jl -> import Mads
import OrderedCollections

function makemadsmodelrun_internal_polynomial(madsdata::AbstractDict)
	times = Mads.getobstime(madsdata)
	names = Mads.getobskeys(madsdata)
	function madsmodelrun(parameters::AbstractDict) # model run
		f(t) = parameters["a"] * (t ^ parameters["n"]) + parameters["b"] * t + parameters["c"] # a * t^n + b * t + c
		predictions = OrderedCollections.OrderedDict{String, Float64}(zip(names, map(f, times)))
		return predictions
	end
end

Yes, this is a symlink pointing to Julia code instead of to a file containing Julia code. As you can see, ls doesn't care, and /bin/stat works fine as well:

❯ stat Mads.jl/examples/model_analysis/models/internal-polynomial.jl
  File: Mads.jl/examples/model_analysis/models/internal-polynomial.jl -> import Mads
import OrderedCollections

function makemadsmodelrun_internal_polynomial(madsdata::AbstractDict)
	times = Mads.getobstime(madsdata)
	names = Mads.getobskeys(madsdata)
	function madsmodelrun(parameters::AbstractDict) # model run
		f(t) = parameters["a"] * (t ^ parameters["n"]) + parameters["b"] * t + parameters["c"] # a * t^n + b * t + c
		predictions = OrderedCollections.OrderedDict{String, Float64}(zip(names, map(f, times)))
		return predictions
	end
end

  Size: 472       	Blocks: 8          IO Block: 4096   symbolic link
Device: 0,40	Inode: 48188       Links: 1
Access: (0777/lrwxrwxrwx)  Uid: ( 1000/     tim)   Gid: ( 1000/     tim)
Access: 2023-05-16 12:47:44.516243458 +0200
Modify: 2023-05-16 12:15:27.991656675 +0200
Change: 2023-05-16 12:15:27.991656675 +0200
 Birth: 2023-05-16 12:15:27.991656675 +0200

statx(AT_FDCWD, "Mads.jl/examples/model_analysis/models/internal-polynomial.jl", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW|AT_NO_AUTOMOUNT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFLNK|0777, stx_size=472, ...}) = 0

Julia/libuv however don't like this symlink:

❯ julia -e 'stat("Mads.jl/examples/model_analysis/models/internal-polynomial.jl")'
ERROR: IOError: stat("Mads.jl/examples/model_analysis/models/internal-polynomial.jl"): name too long (ENAMETOOLONG)
Stacktrace:
 [1] uv_error
   @ ./libuv.jl:97 [inlined]
 [2] stat(path::String)
   @ Base.Filesystem ./stat.jl:152
 [3] top-level scope
   @ none:1

[pid 17416] statx(AT_FDCWD, "Mads.jl/examples/model_analysis/models/internal-polynomial.jl", AT_STATX_SYNC_AS_STAT, STATX_ALL,  <unfinished ...>
[pid 17416] <... statx resumed>0x7ffc0bb7cc80) = -1 ENAMETOOLONG (File name too long)

Note that the Julia code here is around 500 chars, so nothing near PATH_MAX (4096 on my system). In fact, it looks like the limit is 256 characters:

julia> touch("a"^255)

julia> symlink(path, "foo")

julia> stat("foo")
ERROR: IOError: stat("foo"): name too long (ENAMETOOLONG)

shell> stat foo
  File: foo -> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

I don't particularly care about this 'bug', but PkgEval encountered it in the wild (doing isdir for recursive chmod) and it seemed like a curious mismatch between coreutils and libuv.