Add functionality to overwrite broken links

This commit adds an option to the extended configuration syntax for
linking files and directories. The relink option is a safe alternative
to forcibly linking that only removes broken symbolic links, so it
cannot result in data loss.

2 files changed, 22 insertions, 10 deletions

diff --git a/README.md b/README.md
index 86f7686..c2c46f3 100644
--- a/README.md
+++ b/README.md
@@ -131,8 +131,9 @@ Link commands support an (optional) extended configuration. In this type of
 configuration, instead of specifying source locations directly, targets are
 mapped to extended configuration dictionaries. These dictionaries map `path` to
 the source path, specify `create` as `true` if the parent directory should be
-created if necessary, and specify `force` as `true` if the file or directory
-should be forcibly linked.
+created if necessary, specify `relink` as `true` if incorrect symbolic links
+should be automatically overwritten, and specify `force` as `true` if the file
+or directory should be forcibly linked.
 
 #### Example
 
@@ -142,7 +143,9 @@ should be forcibly linked.
       create: true
       path: config/terminator/
     ~/.vim: vim/
-    ~/.vimrc: vimrc
+    ~/.vimrc:
+      relink: true
+      path: vimrc
     ~/.zshrc:
       force: true
       path: zshrc
diff --git a/dotbot/executor/linker.py b/dotbot/executor/linker.py
index 9821fe7..f0e94bc 100644
--- a/dotbot/executor/linker.py
+++ b/dotbot/executor/linker.py
@@ -23,11 +23,14 @@ class Linker(Executor):
                 # extended config
                 path = source['path']
                 force = source.get('force', False)
+                relink = source.get('relink', False)
                 create = source.get('create', False)
                 if create:
                     success &= self._create(destination)
                 if force:
-                    success &= self._delete(path, destination)
+                    success &= self._delete(path, destination, force=True)
+                elif relink:
+                    success &= self._delete(path, destination, force=False)
             else:
                 path = source
             success &= self._link(path, destination)
@@ -71,24 +74,30 @@ class Linker(Executor):
                 self._log.lowinfo('Creating directory %s' % parent)
         return success
 
-    def _delete(self, source, path):
+    def _delete(self, source, path, force):
         success = True
         source = os.path.join(self._base_directory, source)
         if ((self._is_link(path) and self._link_destination(path) != source) or
                 (self._exists(path) and not self._is_link(path))):
             fullpath = os.path.expanduser(path)
+            removed = False
             try:
                 if os.path.islink(fullpath):
                     os.unlink(fullpath)
-                elif os.path.isdir(fullpath):
-                    shutil.rmtree(fullpath)
-                else:
-                    os.remove(fullpath)
+                    removed = True
+                elif force:
+                    if os.path.isdir(fullpath):
+                        shutil.rmtree(fullpath)
+                        removed = True
+                    else:
+                        os.remove(fullpath)
+                        removed = True
             except OSError:
                 self._log.warning('Failed to remove %s' % path)
                 success = False
             else:
-                self._log.lowinfo('Removing %s' % path)
+                if removed:
+                    self._log.lowinfo('Removing %s' % path)
         return success
 
     def _link(self, source, link_name):