df: show error if specified type doesn't exist

Fixes #3252. As a side effect, "df -H -total" will now fail, too, as
expected.

src/uu/df/src/df.rs

@@ -358,15 +358,20 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     }
 
     let opt = Options::from(&matches).map_err(DfError::OptionsError)?;
-
     // Get the list of filesystems to display in the output table.
     let filesystems: Vec<Filesystem> = match matches.values_of(OPT_PATHS) {
-        None => get_all_filesystems(&opt),
+        None => {
+            let filesystems = get_all_filesystems(&opt);
+
+            if filesystems.is_empty() {
+                return Err(USimpleError::new(1, "No file systems processed"));
+            }
+
+            filesystems
+        }
         Some(paths) => {
             let paths: Vec<&str> = paths.collect();
-            get_named_filesystems(&paths)
-        }
-    };
+            let filesystems = get_named_filesystems(&paths);
 
             // This can happen if paths are given as command-line arguments
             // but none of the paths exist.
@@ -374,6 +379,10 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
                 return Ok(());
             }
 
+            filesystems
+        }
+    };
+
     // The running total of filesystem sizes and usage.
     //
     // This accumulator is computed in case we need to display the

tests/by-util/test_df.rs

@@ -42,6 +42,13 @@ fn test_df_output() {
     assert_eq!(actual, expected);
 }
 
+#[test]
+fn test_total_option_with_single_dash() {
+    // These should fail because `-total` should have two dashes,
+    // not just one.
+    new_ucmd!().arg("-total").fails();
+}
+
 /// Test that the order of rows in the table does not change across executions.
 #[test]
 fn test_order_same() {
@@ -89,7 +96,17 @@ fn test_output_option_without_equals_sign() {
 
 #[test]
 fn test_type_option() {
-    new_ucmd!().args(&["-t", "ext4", "-t", "ext3"]).succeeds();
+    let fs_types = new_ucmd!()
+        .arg("--output=fstype")
+        .succeeds()
+        .stdout_move_str();
+    let fs_type = fs_types.lines().nth(1).unwrap().trim();
+
+    new_ucmd!().args(&["-t", fs_type]).succeeds();
+    new_ucmd!()
+        .args(&["-t", fs_type, "-t", "nonexisting"])
+        .succeeds();
+    new_ucmd!().args(&["-t", "nonexisting"]).fails();
 }
 
 #[test]