Wrong symlink to non-existent priv and include dirs on Windows

[emtenet]

When app directories are copied into the _build directory symlinks are created to for the include, priv & source directories. https://github.com/erlang/rebar3/blob/master/src/rebar_prv_compile.erl#L204

If the source directory does not exist (for example apps/myapp/priv) then a "file" symlink is created rather than a "directory" symlink.

If the source directory is created in the future, the symlink is not usable as either a directory or a file.

This can be reproduced with:

> rebar3 new release myrel
> cd myrel
> rebar3 compile
> mkdir apps\myrel\priv
> dir _build\default\lib\myrel
<DIR> .rebar3
<DIR> ebin
<SYMLINK> include [c:/Source/Erlang/myrel/apps/myrel/include]
<SYMLINK> priv [c:/Source/Erlang/myrel/apps/myrel/priv]
<SYMLINKD> src [c:/Source/Erlang/myrel/apps/myrel/src]
> rebar3 release
===> Verifying dependencies...
===> Compiling myrel
===> Starting relx build process ...
===> Resolving OTP Applications from directories:
          c:/Source/Erlang/myrel/_build/default/lib
          c:/Source/Erlang/myrel/apps
          c:/Program Files/erl7.3/lib
===> error (eio) accessing file c:/Source/Erlang/myrel/_build/default/lib/myrel/priv

This behavior is on Windows, in a non-Administrator user account that has the SeCreateSymbolicLinkPrivilege

[emtenet]

The decision to make a "file" symlink rather than a "directory" symlink is made in the erlang runtime. https://github.com/erlang/otp/blob/maint/erts/emulator/drivers/win32/win_efile.c#L2019-L2023

[emtenet]

Perhaps rebar_file_utils:symlink_or_copy/2 could be split into two separate functions: symlink_or_copy_dir/2 and symlink_or_copy_file/2. (A quick search of rebar3 sources suggests that the second variation is not needed at this time)

symlink_or_copy_dir/2 could then check the existence of the source directory and use something other than file:make_symlink/2 such as rebar_file_utils:win32_symlink/2 (which creates a JUNCTION) or a SYMLINKD equivalent that uses the MKLINK /D option.

[emtenet]

I have done some work in erlware/relx#472 relating to symlinks on Windows. These two projects seem to have shared common Windows symlink code in the past but have since received their own fixes to common problems.

[ferd]

Ah, this probably explains the problems with #1171

[Taure]

They share codes and if I remember right there was something that I tried to solve. And relx was using old copy for windows. Old copy have the 256 chars restriction in paths.

What I could see in relx issue was that there is a logic error. Will look into that. If you want I can try to give some of my ideas about this.

If I have time I can try to solve this.

[ferd]

This issue has been reported as happening on OSX as well.

[talentdeficit]

i believe the osx issue may be slightly different and may be caused by filelib:ensure_dir/1 failing to create a missing directory because of the existence of a symlink to a non-existent directory

[goertzenator]

The situation described by @talentdeficit is happening to me on linux.