Check DISPLAY environment variable in default_backend

This patch changes the default_backend to also check the DISPLAY
environment variable.  If it is set, there probably is a X server
running, so we try to use the zenity backend.  Otherwise, the dialog
backend is used.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/backends/mod.rs b/src/backends/mod.rs
index 20cb8c1..f5af7ef 100644
--- a/src/backends/mod.rs
+++ b/src/backends/mod.rs
@@ -7,6 +7,9 @@ mod zenity;
 pub use crate::backends::dialog::Dialog;
 pub use crate::backends::zenity::Zenity;
 
+use std::env;
+use std::path;
+
 use crate::Result;
 
 /// A dialog backend.
@@ -32,6 +35,17 @@ pub trait Backend {
     fn show_question(&self, question: &super::Question) -> Result<super::Choice>;
 }
 
+pub(crate) fn is_available(name: &str) -> bool {
+    if let Ok(path) = env::var("PATH") {
+        for part in path.split(":") {
+            if path::Path::new(part).join(name).exists() {
+                return true;
+            }
+        }
+    }
+    false
+}
+
 pub(crate) fn from_str(s: &str) -> Option<Box<dyn Backend>> {
     match s.to_lowercase().as_ref() {
         "dialog" => Some(Box::new(Dialog::new())),