repo: address issue with fix_symlink() when pointed at directory If target is a directory, simply warn about dangling symlink. Light refactoring to make it easier to follow and add documentation. Example: ``` name: test base: core18 version: '0.1' summary: Single-line description: | Bla Bla grade: stable confinement: strict parts: my-part: # See 'snapcraft plugins' source: stuff plugin: nil stage-packages: - openssl - jq override-build: | # Create some host files to use. mkdir -p /tmp/d1 touch /tmp/f1 ln -sf /tmp/d1 /tmp/sd1 ln -sf /tmp/f1 /tmp/sf1 # Symlink from part install to host files. ln -sf /tmp/d1 $SNAPCRAFT_PART_INSTALL/d1 ln -sf /tmp/f1 $SNAPCRAFT_PART_INSTALL/f1 ln -sf /tmp/sd1 $SNAPCRAFT_PART_INSTALL/sd1 ln -sf /tmp/sf1 $SNAPCRAFT_PART_INSTALL/sf1 ln -sf /tmp/does-not-exist $SNAPCRAFT_PART_INSTALL/does-not-exist # Similar for build dir. touch $SNAPCRAFT_PART_BUILD/file ln -sf $SNAPCRAFT_PART_BUILD/build-file $SNAPCRAFT_PART_INSTALL/build-file ``` Run: ``` $ mkdir stuff s snapcraft $ touch stuff/foo $ snapcraft ``` Previously, with the directories, snapcraft would fail: ``` File "/home/ubuntu/snapcraft/snapcraft/internal/repo/_deb.py", line 427, in unpack_stage_packages cls.normalize(str(install_path)) File "/home/ubuntu/snapcraft/snapcraft/internal/repo/_base.py", line 204, in normalize cls._fix_artifacts(unpackdir) File "/home/ubuntu/snapcraft/snapcraft/internal/repo/_base.py", line 252, in _fix_artifacts cls._fix_symlink(path, unpackdir, root) File "/home/ubuntu/snapcraft/snapcraft/internal/repo/_base.py", line 287, in _fix_symlink if not os.path.exists(target) and not _try_copy_local(path, target): File "/home/ubuntu/snapcraft/snapcraft/internal/repo/_base.py", line 311, in _try_copy_local shutil.copyfile(os.readlink(path), target) File "/usr/lib/python3.6/shutil.py", line 120, in copyfile with open(src, 'rb') as fsrc: ``` Now, the re-build will trigger the following messages: 'build-file' will be a dangling symlink 'does-not-exist' will be a dangling symlink 'd1' will be a dangling symlink 'sd1' will be a dangling symlink' The rebuild is required to activate teh fix_symlink() on the assets already in $SNAPCRAFT_PART_INSTALL. Snapcraft either needs to ensure that these checks are run only on installed files from the deb (the original intention), or as a complete pass on build/stage/prime to ensure consistency. This does not address that. Fixes SNAPCRAFT-2AV Signed-off-by: Chris Patterson <chris.patterson@canonical.com>