df: implement the File column

Implement the "File" column in the `df` output table. Before this
commit, a blank entry appeared in the "File" column for each
row. After this commit, a "-" entry appears when `df` is run with no
positional arguments and the filename appears when run with positional
arguments. For example:

    $ touch a b c && df --output=target,file a b c
    Mounted on File
    /          a
    /          b
    /          c

src/uu/df/src/df.rs

@@ -243,7 +243,10 @@ fn get_all_filesystems(opt: &Options) -> Vec<Filesystem> {
 
     // Convert each `MountInfo` into a `Filesystem`, which contains
     // both the mount information and usage information.
-    mounts.into_iter().filter_map(Filesystem::new).collect()
+    mounts
+        .into_iter()
+        .filter_map(|m| Filesystem::new(m, None))
+        .collect()
 }
 
 /// For each path, get the filesystem that contains that path.

src/uu/df/src/filesystem.rs

@@ -23,6 +23,13 @@ use uucore::fsext::{FsUsage, MountInfo};
 /// space available on the filesystem and the amount of space used.
 #[derive(Debug, Clone)]
 pub(crate) struct Filesystem {
+    /// The file given on the command line if any.
+    ///
+    /// When invoking `df` with a positional argument, it displays
+    /// usage information for the filesystem that contains the given
+    /// file. If given, this field contains that filename.
+    pub file: Option<String>,
+
     /// Information about the mounted device, mount directory, and related options.
     pub mount_info: MountInfo,
 
@@ -66,7 +73,7 @@ where
 
 impl Filesystem {
     // TODO: resolve uuid in `mount_info.dev_name` if exists
-    pub(crate) fn new(mount_info: MountInfo) -> Option<Self> {
+    pub(crate) fn new(mount_info: MountInfo, file: Option<String>) -> Option<Self> {
         let _stat_path = if !mount_info.mount_dir.is_empty() {
             mount_info.mount_dir.clone()
         } else {
@@ -84,7 +91,11 @@ impl Filesystem {
         let usage = FsUsage::new(statfs(_stat_path).ok()?);
         #[cfg(windows)]
         let usage = FsUsage::new(Path::new(&_stat_path));
-        Some(Self { mount_info, usage })
+        Some(Self {
+            mount_info,
+            usage,
+            file,
+        })
     }
 
     /// Find and create the filesystem that best matches a given path.
@@ -107,11 +118,12 @@ impl Filesystem {
     where
         P: AsRef<Path>,
     {
+        let file = path.as_ref().display().to_string();
         let canonicalize = true;
         let mount_info = mount_info_from_path(mounts, path, canonicalize)?;
         // TODO Make it so that we do not need to clone the `mount_info`.
         let mount_info = (*mount_info).clone();
-        Self::new(mount_info)
+        Self::new(mount_info, Some(file))
     }
 }
 

src/uu/df/src/table.rs

@@ -24,6 +24,9 @@ use std::ops::AddAssign;
 /// A row comprises several pieces of information, including the
 /// filesystem device, the mountpoint, the number of bytes used, etc.
 pub(crate) struct Row {
+    /// The filename given on the command-line, if given.
+    file: Option<String>,
+
     /// Name of the device on which the filesystem lives.
     fs_device: String,
 
@@ -73,6 +76,7 @@ pub(crate) struct Row {
 impl Row {
     pub(crate) fn new(source: &str) -> Self {
         Self {
+            file: None,
             fs_device: source.into(),
             fs_type: "-".into(),
             fs_mount: "-".into(),
@@ -101,6 +105,7 @@ impl AddAssign for Row {
         let inodes = self.inodes + rhs.inodes;
         let inodes_used = self.inodes_used + rhs.inodes_used;
         *self = Self {
+            file: None,
             fs_device: "total".into(),
             fs_type: "-".into(),
             fs_mount: "-".into(),
@@ -145,6 +150,7 @@ impl From<Filesystem> for Row {
             ..
         } = fs.usage;
         Self {
+            file: fs.file,
             fs_device: dev_name,
             fs_type,
             fs_mount: mount_dir,
@@ -246,8 +252,9 @@ impl fmt::Display for DisplayRow<'_> {
                 Column::Ipcent => {
                     write!(f, "{0: >5} ", DisplayRow::percentage(self.row.inodes_usage))?;
                 }
-                // TODO Implement this.
-                Column::File => {}
+                Column::File => {
+                    write!(f, "{0: <16}", self.row.file.as_ref().unwrap_or(&"-".into()))?
+                }
                 Column::Fstype => write!(f, "{0: <5} ", self.row.fs_type)?,
                 #[cfg(target_os = "macos")]
                 Column::Capacity => write!(
@@ -406,6 +413,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),
@@ -437,6 +445,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),
@@ -468,6 +477,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),
@@ -499,6 +509,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),
@@ -530,6 +541,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),
@@ -560,6 +572,7 @@ mod tests {
             ..Default::default()
         };
         let row = Row {
+            file: Some("/path/to/file".to_string()),
             fs_device: "my_device".to_string(),
             fs_type: "my_type".to_string(),
             fs_mount: "my_mount".to_string(),

tests/by-util/test_df.rs

@@ -222,4 +222,45 @@ fn test_output_selects_columns() {
     );
 }
 
-// ToDO: more tests...
+// TODO Fix the spacing.
+#[test]
+fn test_output_file_all_filesystems() {
+    // When run with no positional arguments, `df` lets "-" represent
+    // the "File" entry for each row.
+    let output = new_ucmd!()
+        .arg("--output=file")
+        .succeeds()
+        .stdout_move_str();
+    let mut lines = output.lines();
+    assert_eq!(lines.next().unwrap(), "File            ");
+    for line in lines {
+        assert_eq!(line, "-               ");
+    }
+}
+
+// TODO Fix the spacing.
+#[test]
+fn test_output_file_specific_files() {
+    // Create three files.
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.touch("a");
+    at.touch("b");
+    at.touch("c");
+
+    // When run with positional arguments, the filesystems should
+    // appear in the "File" column.
+    let output = ucmd
+        .args(&["--output=file", "a", "b", "c"])
+        .succeeds()
+        .stdout_move_str();
+    let actual: Vec<&str> = output.lines().collect();
+    assert_eq!(
+        actual,
+        vec![
+            "File            ",
+            "a               ",
+            "b               ",
+            "c               "
+        ]
+    );
+}