app/override: Don't crash on no change

Doing `override reset --all` may be a no-op if there are no overrides
currently applied. But we were trying to always print the tree diff
under the assumption that all override invocations have to result in a
new deployment.

Fix this by using the same default deployment check that `upgrade` does
before printing.

Closes: #1407
Approved by: cgwalters

src/app/rpmostree-override-builtins.c

@@ -83,6 +83,8 @@ handle_override (RPMOSTreeSysroot  *sysroot_proxy,
   g_variant_dict_insert (&dict, "no-overrides", "b", opt_reset_all);
   g_autoptr(GVariant) options = g_variant_ref_sink (g_variant_dict_end (&dict));
 
+  g_autoptr(GVariant) previous_deployment = rpmostree_os_dup_default_deployment (os_proxy);
+
   g_autofree char *transaction_address = NULL;
   if (!rpmostree_update_deployment (os_proxy,
                                     NULL, /* set-refspec */
@@ -110,7 +112,10 @@ handle_override (RPMOSTreeSysroot  *sysroot_proxy,
     }
   else if (!opt_reboot)
     {
-      /* override ops currently always result in a new deployment */
+      /* only print diff if a new deployment was laid down (e.g. reset --all may not) */
+      if (!rpmostree_has_new_default_deployment (os_proxy, previous_deployment))
+        return TRUE;
+
       const char *sysroot_path = rpmostree_sysroot_get_path (sysroot_proxy);
       if (!rpmostree_print_treepkg_diff_from_sysroot_path (sysroot_path,
                                                            cancellable,

tests/vmcheck/test-override-remove.sh

@@ -135,6 +135,8 @@ vm_rpmostree override reset --all
 vm_assert_status_jq \
   '.deployments[0]["base-removals"]|length == 0' \
   '.deployments[0]["requested-base-removals"]|length == 0'
+vm_rpmostree override reset --all |& tee out.txt
+assert_file_has_content out.txt "No change."
 echo "ok override reset --all"
 
 # check that upgrading to a base without foo works