Add tree_hash() debugging output

Since tree hashes cause us so much grief, make it easier for us to
figure out what _exactly_ is different between two trees.

src/GitTools.jl

@@ -257,31 +257,43 @@ end
 
 Calculate the git tree hash of a given path.
 """
-function tree_hash(::Type{HashType}, root::AbstractString) where HashType
+function tree_hash(::Type{HashType}, root::AbstractString; debug_out::Union{IO,Nothing} = nothing, indent::Int=0) where HashType
  entries = Tuple{String, Vector{UInt8}, GitMode}[]
- for f in readdir(root)
+ for f in sort(readdir(root; join=true); by = f -> isdir(f) ? f*"/" : f)
  # Skip `.git` directories
  if f == ".git"
  continue
  end
 
- filepath = abspath(root, f)
+ filepath = abspath(f)
  mode = gitmode(filepath)
  if mode == mode_dir
  # If this directory contains no files, then skip it
  contains_files(filepath) || continue
 
  # Otherwise, hash it up!
- hash = tree_hash(HashType, filepath)
+ child_stream = nothing
+ if debug_out !== nothing
+ child_stream = IOBuffer()
+ end
+ hash = tree_hash(HashType, filepath; debug_out=child_stream, indent=indent+1)
+ if debug_out !== nothing
+ indent_str = "| "^indent
+ println(debug_out, "$(indent_str)+ [D] $(basename(filepath)) - $(bytes2hex(hash))")
+ print(debug_out, String(take!(child_stream)))
+ println(debug_out, indent_str)
+ end
  else
  hash = blob_hash(HashType, filepath)
+ if debug_out !== nothing
+ indent_str = "| "^indent
+ mode_str = mode == mode_normal ? "F" : "X"
+ println(debug_out, "$(indent_str)[$(mode_str)] $(basename(filepath)) - $(bytes2hex(hash))")
+ end
  end
  push!(entries, (f, hash, mode))
  end
 
- # Sort entries by name (with trailing slashes for directories)
- sort!(entries, by = ((name, hash, mode),) -> mode == mode_dir ? name*"/" : name)
-
  content_size = 0
  for (n, h, m) in entries
  content_size += ndigits(UInt32(m); base=8) + 1 + sizeof(n) + 1 + sizeof(h)
@@ -296,7 +308,7 @@ function tree_hash(::Type{HashType}, root::AbstractString) where HashType
  end
  return SHA.digest!(ctx)
 end
-tree_hash(root::AbstractString) = tree_hash(SHA.SHA1_CTX, root)
+tree_hash(root::AbstractString; debug_out::Union{IO,Nothing} = nothing) = tree_hash(SHA.SHA1_CTX, root; debug_out)
 
 function check_valid_HEAD(repo)
  try LibGit2.head(repo)