Follow Type=Link standard desktop entries with drun (#1168)

* [DRun] Introduce data structure changes for Link desktop entries

From the [freedesktop spec][1]:

> This specification defines 3 types of desktop entries:
> Application (type 1), Link (type 2) and Directory (type 3). To allow
> the addition of new types in the future, implementations should
> ignore desktop entries with an unknown type.

This commit adds an enum to capture these types, and adds `type` to
DRunModeEntry.

  [1]: https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html

part of #1166

* [DRun] Sanity check Link entries and capture the URL

Note that we're introducing some logic that will differ depending on
the Desktop entry type (Application or Link). The logic is:

- if entry is Application type,
  - then Exec is required
  - and the value is saved in .exec
  - and drun_mode_result calls exec_cmd_entry
- if entry is Link type,
  - then URL is required (but is not saved in the DRunModeEntry)
  - and drun_mode_result calls new function launch_link_entry

part of #1166

* [DRun] Launch desktop links via xdg-open

Note that this introduces a new dependency on xdg-open, which may not
be installed. In that case, rofi will display an error dialog
with something like:

  "Failed to execute child process xdg-open (No such file or directory)"

which hopefully is explanatory enough for folks.

part of #1166

* Make drun options comments consistent and add a bit of whitespace

* [DRun] new config option drun-url-launcher for opening links

In previous commit, this was a hard-coded string.

part of #1166

1 files changed, 5 insertions, 1 deletions

diff --git a/include/settings.h b/include/settings.h
index 7c57080d..cecb9c34 100644
--- a/include/settings.h
+++ b/include/settings.h
@@ -119,14 +119,18 @@ typedef struct
     SortingMethod  sorting_method_enum;
     /** Sorting method. */
     char           * sorting_method;
+
     /** Desktop entries to match in drun */
     char           * drun_match_fields;
     /** Only show entries in this category */
     char           * drun_categories;
     /** Desktop entry show actions */
     unsigned int   drun_show_actions;
-    /** Desktop entry show */
+    /** Desktop format display */
     char           * drun_display_format;
+    /** Desktop Link launch command */
+    char           * drun_url_launcher;
+
     /** Search case sensitivity */
     unsigned int   case_sensitive;
     /** Cycle through in the element list */