wc: implement files0-from option

When this option is present, the files argument is not processed. This option processes the file list from provided file, splitting them by the ascii NUL (\0) character. When files0-from is '-', the file list is processed from stdin.

tests/by-util/test_wc.rs

@@ -245,3 +245,57 @@ fn test_files_from_pseudo_filesystem() {
     let result = new_ucmd!().arg("-c").arg("/proc/version").succeeds();
     assert_ne!(result.stdout_str(), "0 /proc/version\n");
 }
+
+#[test]
+fn test_files0_disabled_files_argument() {
+    const MSG: &str = "file operands cannot be combined with --files0-from";
+    new_ucmd!()
+        .args(&["--files0-from=files0_list.txt"])
+        .arg("lorem_ipsum.txt")
+        .fails()
+        .stderr_contains(MSG)
+        .stdout_is("");
+}
+
+#[test]
+fn test_files0_from() {
+    new_ucmd!()
+        .args(&["--files0-from=files0_list.txt"])
+        .run()
+        .stdout_is(
+            "  13  109  772 lorem_ipsum.txt\n  18  204 1115 moby_dick.txt\n   5   57  302 \
+             alice_in_wonderland.txt\n  36  370 2189 total\n",
+        );
+}
+
+#[test]
+fn test_files0_from_with_stdin() {
+    new_ucmd!()
+        .args(&["--files0-from=-"])
+        .pipe_in("lorem_ipsum.txt")
+        .run()
+        .stdout_is(" 13 109 772 lorem_ipsum.txt\n");
+}
+
+#[test]
+fn test_files0_from_with_stdin_in_file() {
+    new_ucmd!()
+        .args(&["--files0-from=files0_list_with_stdin.txt"])
+        .pipe_in_fixture("alice_in_wonderland.txt")
+        .run()
+        .stdout_is(
+            "     13     109     772 lorem_ipsum.txt\n     18     204    1115 moby_dick.txt\n      5      57     302 \
+             -\n     36     370    2189 total\n",
+        );
+}
+
+#[test]
+fn test_files0_from_with_stdin_try_read_from_stdin() {
+    const MSG: &str = "when reading file names from stdin, no file name of '-' allowed";
+    new_ucmd!()
+        .args(&["--files0-from=-"])
+        .pipe_in("-")
+        .fails()
+        .stderr_contains(MSG)
+        .stdout_is("");
+}