Fix linking when using both relink and relative

Prior to this patch, the following config led to incorrect behavior:

    - link:
        ~/.folder/file:
          path: file
          create: true
          relative: true
          relink: true

Prior to the change, running the config the first time would result in
expected behavior. However, running the config for the second time would
result in deletion and re-creation of the link (even when the link is
correct).

This patch improves the interaction of relink and relative, taking
relative paths into account when checking the validity of existing links
in the `_delete()` method.

plugins/link.py

@@ -37,7 +37,7 @@ class Link(dotbot.Plugin):
             if create:
                 success &= self._create(destination)
             if force or relink:
-                success &= self._delete(path, destination, force=force)
+                success &= self._delete(path, destination, relative, force)
             success &= self._link(path, destination, relative)
         if success:
             self._log.info('All links have been set up')
@@ -53,11 +53,10 @@ class Link(dotbot.Plugin):
 
     def _link_destination(self, path):
         '''
-        Returns the absolute path to the destination of the symbolic link.
+        Returns the destination of the symbolic link.
         '''
         path = os.path.expanduser(path)
-        rel_dest = os.readlink(path)
-        return os.path.join(os.path.dirname(path), rel_dest)
+        return os.readlink(path)
 
     def _exists(self, path):
         '''
@@ -79,12 +78,14 @@ class Link(dotbot.Plugin):
                 self._log.lowinfo('Creating directory %s' % parent)
         return success
 
-    def _delete(self, source, path, force):
+    def _delete(self, source, path, relative, force):
         success = True
         source = os.path.join(self._context.base_directory(), source)
+        fullpath = os.path.expanduser(path)
+        if relative:
+            source = self._relative_path(source, fullpath)
         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):
@@ -105,6 +106,14 @@ class Link(dotbot.Plugin):
                     self._log.lowinfo('Removing %s' % path)
         return success
 
+    def _relative_path(self, source, destination):
+        '''
+        Returns the relative path to get to the source file from the
+        destination file.
+        '''
+        destination_dir = os.path.dirname(destination)
+        return os.path.relpath(source, destination_dir)
+
     def _link(self, source, link_name, relative):
         '''
         Links link_name to source.
@@ -112,17 +121,21 @@ class Link(dotbot.Plugin):
         Returns true if successfully linked files.
         '''
         success = False
-        source = os.path.join(self._context.base_directory(), source)
+        destination = os.path.expanduser(link_name)
+        absolute_source = os.path.join(self._context.base_directory(), source)
+        if relative:
+            source = self._relative_path(absolute_source, destination)
+        else:
+            source = absolute_source
         if (not self._exists(link_name) and self._is_link(link_name) and
                 self._link_destination(link_name) != source):
             self._log.warning('Invalid link %s -> %s' %
                 (link_name, self._link_destination(link_name)))
-        elif not self._exists(link_name) and self._exists(source):
+        # we need to use absolute_source below because our cwd is the dotfiles
+        # directory, and if source is relative, it will be relative to the
+        # destination directory
+        elif not self._exists(link_name) and self._exists(absolute_source):
             try:
-                destination = os.path.expanduser(link_name)
-                if relative:
-                    destination_dir = os.path.dirname(destination)
-                    source = os.path.relpath(source, destination_dir)
                 os.symlink(source, destination)
             except OSError:
                 self._log.warning('Linking failed %s -> %s' % (link_name, source))
@@ -136,7 +149,8 @@ class Link(dotbot.Plugin):
         elif self._is_link(link_name) and self._link_destination(link_name) != source:
             self._log.warning('Incorrect link %s -> %s' %
                 (link_name, self._link_destination(link_name)))
-        elif not self._exists(source):
+        # again, we use absolute_source to check for existence
+        elif not self._exists(absolute_source):
             if self._is_link(link_name):
                 self._log.warning('Nonexistent target %s -> %s' %
                     (link_name, source))

test/tests/link-relink-relative-leaves-file.bash

@@ -0,0 +1,32 @@
+test_description='relink relative does not incorrectly relink file'
+. '../test-lib.bash'
+
+test_expect_success 'setup' '
+echo "apple" > ${DOTFILES}/f &&
+echo "grape" > ~/.f
+'
+
+test_expect_success 'run1' '
+run_dotbot <<EOF
+- link:
+    ~/.folder/f:
+      path: f
+      create: true
+      relative: true
+EOF
+'
+
+# these are done in a single block because they run in a subshell, and it
+# wouldn't be possible to access `$mtime` outside of the subshell
+test_expect_success 'test' '
+mtime=$(stat ~/.folder/f | grep Modify)
+run_dotbot <<EOF
+- link:
+    ~/.folder/f:
+      path: f
+      create: true
+      relative: true
+      relink: true
+EOF
+[[ "$mtime" == "$(stat ~/.folder/f | grep Modify)" ]]
+'