Tar.create: include entries for non-empty directories

Issue #103 points out that omitting directory entries for non-empty
directories can confuse some tools that consume tarballs, including
docker, which applies overly restrictive permissions to directories
which are not explicitly included in a tarball.

This commit changes `Tar.create` and `Tar.rewrite` to produce tarballs
which include explicit directory entries for all (non-root) directories.
This changes Tar.jl's "canonical format", which is, by design one-to-one
with git tree hashes. However, it does not seem like anyone currently
depends on that exact reproducibility and it seems worth making this
change in order to avoid confusing external consumers of our tarballs.

Closes #103.

src/create.jl

@@ -80,24 +80,26 @@ function write_tarball(
     tar_path::String = ".";
     buf::Vector{UInt8} = Vector{UInt8}(undef, DEFAULT_BUFFER_SIZE),
 )
-    w = 0
     hdr, data = callback(sys_path, tar_path)
     if hdr.type == :directory
         data isa Union{Nothing, AbstractDict{<:AbstractString}} ||
             error("callback must return a dict of strings, got: $(repr(data))")
-        data !== nothing && for name in sort!(collect(keys(data)))
-            sys_path′ = data[name]
-            tar_path′ = tar_path == "." ? name : "$tar_path/$name"
-            w += write_tarball(callback, tar, sys_path′, tar_path′, buf=buf)
-        end
     else
         data isa Union{Nothing, AbstractString, IO, Tuple{IO,Integer}} ||
             error("callback must return nothing, string or IO, got: $(repr(data))")
     end
-    if hdr.type != :directory || w == 0
+    w = 0
+    if tar_path != "."
+        w += write_tarball(tar, hdr, data, buf=buf)
+    end
+    data isa AbstractDict && for name in sort!(collect(keys(data)))
+        sys_path′ = data[name]
+        tar_path′ = tar_path == "." ? name : "$tar_path/$name"
+        w += write_tarball(callback, tar, sys_path′, tar_path′, buf=buf)
+    end
+    if tar_path == "." && w == 0
         w += write_tarball(tar, hdr, data, buf=buf)
     end
-    @assert w > 0
     return w
 end
 

test/runtests.jl

@@ -212,6 +212,7 @@ end
     # check rewrite
     tarball′ = Tar.rewrite(tarball)
     @test Tar.list(tarball′) == [
+        Tar.Header("dir", :directory, 0o755, 0, "")
         Tar.Header("dir/file", :file, 0o755, 0, "")
         Tar.Header("file", :file, 0o755, 0, "")
     ]

test/setup.jl

@@ -135,7 +135,7 @@ function make_test_dir(gen_skip::Bool=false)
     return dir
 end
 
-const test_dir_paths = ["dir/file", "empty", "file", "link"]
+const test_dir_paths = ["dir", "dir/file", "empty", "file", "link"]
 Sys.iswindows() && pop!(test_dir_paths)
 
 # uses Tar.list(callback, tarball) API