sysroot: support create and load actions on builder

This splits the builder completion step into separate actions for
creating/loading a sysroot.
It also introduces a roundtrip test over a freshly-created empty
sysroot.

rust-bindings/rust/src/sysroot.rs

@@ -29,8 +29,25 @@ impl SysrootBuilder {
         self
     }
 
-    /// Finalize this builder into a `Sysroot`.
-    pub fn build(self, cancellable: Option<&gio::Cancellable>) -> Result<Sysroot, glib::Error> {
+    /// Load an existing `Sysroot` from disk, finalizing this builder.
+    pub fn load(self, cancellable: Option<&gio::Cancellable>) -> Result<Sysroot, glib::Error> {
+        let sysroot = self.configure_common();
+        sysroot.load(cancellable)?;
+
+        Ok(sysroot)
+    }
+
+    /// Create a new `Sysroot` on disk, finalizing this builder.
+    pub fn create(self, cancellable: Option<&gio::Cancellable>) -> Result<Sysroot, glib::Error> {
+        let sysroot = self.configure_common();
+        sysroot.ensure_initialized(cancellable)?;
+        sysroot.load(cancellable)?;
+
+        Ok(sysroot)
+    }
+
+    /// Perform common configuration steps, returning a not-yet-fully-loaded `Sysroot`.
+    fn configure_common(self) -> Sysroot {
         let sysroot = {
             let opt_file = self.path.map(|p| gio::File::for_path(p));
             Sysroot::new(opt_file.as_ref())
@@ -41,8 +58,50 @@ impl SysrootBuilder {
             sysroot.set_mount_namespace_in_use();
         }
 
-        sysroot.load(cancellable)?;
+        sysroot
+    }
+}
 
-        Ok(sysroot)
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sysroot_create_load_empty() {
+        // Create and load an empty sysroot. Make sure it can be properly
+        // inspected as empty, without panics.
+        let tmpdir = tempfile::tempdir().unwrap();
+
+        let path_created = {
+            let tmp_path = Some(tmpdir.path().to_path_buf());
+            let builder = SysrootBuilder::new().path(tmp_path);
+
+            let sysroot = builder.create(gio::NONE_CANCELLABLE).unwrap();
+
+            assert!(sysroot.fd() >= 0);
+            assert_eq!(sysroot.deployments().len(), 0);
+            assert_eq!(sysroot.booted_deployment(), None);
+            assert_eq!(sysroot.bootversion(), 0);
+            assert_eq!(sysroot.subbootversion(), 0);
+            sysroot.cleanup(gio::NONE_CANCELLABLE).unwrap();
+
+            sysroot.path().unwrap()
+        };
+        let path_loaded = {
+            let tmp_path = Some(tmpdir.path().to_path_buf());
+            let builder = SysrootBuilder::new().path(tmp_path);
+
+            let sysroot = builder.create(gio::NONE_CANCELLABLE).unwrap();
+
+            assert!(sysroot.fd() >= 0);
+            assert_eq!(sysroot.deployments().len(), 0);
+            assert_eq!(sysroot.booted_deployment(), None);
+            assert_eq!(sysroot.bootversion(), 0);
+            assert_eq!(sysroot.subbootversion(), 0);
+            sysroot.cleanup(gio::NONE_CANCELLABLE).unwrap();
+
+            sysroot.path().unwrap()
+        };
+        assert_eq!(path_created.to_string(), path_loaded.to_string());
     }
 }