Make install procedure overwrite existing addons

However, back them up first and restore them if anything goes wrong

bpkg_manager/__init__.py

@@ -195,8 +195,10 @@ class BPKG_OT_install(SubprocMixin, bpy.types.Operator):
         install_path = pathlib.Path(bpy.utils.user_resource('SCRIPTS', 'addons', create=True))
         self.log.debug("Using %s as install path", install_path)
 
+        import addon_utils
+
         proc = multiprocessing.Process(target=subproc.download_and_install,
-                                       args=(self.pipe_subproc, self.package_url, install_path))
+                                       args=(self.pipe_subproc, self.package_url, install_path, addon_utils.paths()))
         return proc
 
     def _subproc_progress(self, progress: subproc.Progress):

bpkg_manager/subproc.py

@@ -4,6 +4,7 @@ All the stuff that needs to run in a subprocess.
 
 import logging
 import pathlib
+import shutil
 
 
 class Message:
@@ -72,6 +73,49 @@ class Aborted(SubprocMessage):
 class InstallException(Exception):
     """Raised when there is an error during installation"""
 
+
+class InplaceBackup:
+    """Utility for moving a file out of the way by appending a '~'"""
+
+    log = logging.getLogger('%s.inplace-backup' % __name__)
+
+    def __init__(self, path: pathlib.Path):
+        self.path = path
+        self.backup()
+
+    def backup(self):
+        """Move 'path' to 'path~'"""
+        self.backup_path = pathlib.Path(str(self.path) + '~')
+        if self.backup_path.exists():
+            self.log.warning("Overwriting existing backup '{}'".format(self.backup_path))
+            self._rm(self.backup_path)
+
+        shutil.move(str(self.path), str(self.backup_path))
+
+    def restore(self):
+        """Move 'path~' to 'path'"""
+        if not self.backup_path:
+            raise RuntimeError("Can't restore file before backing it up")
+
+        if self.path.exists():
+            self.log.warning("Overwriting '{0}' with backup file".format(self.path))
+            self._rm(self.backup_path)
+
+        shutil.move(str(self.backup_path), str(self.path))
+
+    def remove(self):
+        """Remove 'path~'"""
+        self._rm(self.backup_path)
+
+    def _rm(self, path: pathlib.Path):
+        """Just delete whatever is specified by `path`"""
+        if path.is_file():
+            path.unlink()
+        elif path.is_dir():
+            shutil.rmtree(str(path))
+
+
+
 def _download(pipe_to_blender, package_url: str, download_dir: pathlib.Path) -> pathlib.Path:
     """Downloads the given package
 
@@ -133,7 +177,7 @@ def _download(pipe_to_blender, package_url: str, download_dir: pathlib.Path) ->
 
     return local_fpath
 
-def _install(pipe_to_blender, pkgpath: pathlib.Path, dest: pathlib.Path):
+def _install(pipe_to_blender, pkgpath: pathlib.Path, dest: pathlib.Path, searchpaths: list):
     """Extracts/moves package at `pkgpath` to `dest`"""
     import zipfile
 
@@ -178,31 +222,33 @@ def _install(pipe_to_blender, pkgpath: pathlib.Path, dest: pathlib.Path):
                     rootlist.append(f)
             return rootlist
 
-        conflicts = [f for f in root_files(file_to_extract.namelist()) if (dest / f).exists()]
-        if len(conflicts) > 0:
-            # TODO: handle this better than just dumping a list of all files
-            pipe_to_blender.send(FileConflictError("Installation would overwrite: %s" % conflicts, conflicts))
-            raise InstallException
+        conflicts = [dest / f for f in root_files(file_to_extract.namelist()) if (dest / f).exists()]
+        backups = []
+        for conflict in conflicts:
+            backups.append(InplaceBackup(conflict))
 
         try:
             file_to_extract.extractall(str(dest))
         except Exception as err:
+            for backup in backups:
+                backup.restore()
             pipe_to_blender.send(InstallError("Failed to extract zip file to '%s': %s" % (dest, err)))
             raise InstallException from err
 
+        for backup in backups:
+            backup.remove()
+
     else:
         log.debug("Package is pyfile")
         dest_file = (dest / pkgpath.name)
 
         if dest_file.exists():
-            pipe_to_blender.send(FileConflictError("Installation would overwrite %s" % dest_file, [dest_file]))
-            raise InstallException
-
-        import shutil
+            backup = InplaceBackup(dest_file)
 
         try:
             shutil.copyfile(str(pkgpath), str(dest_file))
         except Exception as err:
+            backup.restore()
             pipe_to_blender.send(InstallError("Failed to copy file to '%s': %s" % (dest, err)))
             raise InstallException from err
 
@@ -217,13 +263,15 @@ def _install(pipe_to_blender, pkgpath: pathlib.Path, dest: pathlib.Path):
     return
 
 
-def download_and_install(pipe_to_blender, package_url: str, install_dir: pathlib.Path):
+def download_and_install(pipe_to_blender, package_url: str, install_path: pathlib.Path, search_paths: list):
     """Downloads and installs the given package."""
 
     from . import cache
 
     log = logging.getLogger('%s.download_and_install' % __name__)
 
+    # log.debug(utils.user_resource('SCRIPTS', 'blorp'))
+
     cache_dir = cache.cache_directory('downloads')
     downloaded = _download(pipe_to_blender, package_url, cache_dir)
 
@@ -234,8 +282,10 @@ def download_and_install(pipe_to_blender, package_url: str, install_dir: pathlib
     # Only send success if _install doesn't throw an exception
     # Maybe not the best way to do this? (will also catch exceptions which occur during message sending)
     try:
-        _install(pipe_to_blender, downloaded, install_dir)
+        _install(pipe_to_blender, downloaded, install_path, search_paths)
         pipe_to_blender.send(Success())
+    except InstallException as err:
+        log.debug("InstallException thrown")
     except:
         raise