split: Added error when attempting to create file that already exists as directory

src/uu/split/locales/en-US.ftl

@@ -43,6 +43,7 @@ split-error-unable-to-reopen-file = unable to re-open { $file }; aborting
 split-error-file-descriptor-limit = at file descriptor limit, but no file descriptor left to close. Closed { $count } writers before.
 split-error-shell-process-returned = Shell process returned { $code }
 split-error-shell-process-terminated = Shell process terminated by signal
+split-error-is-a-directory = { $dir }: Is a directory; aborting
 
 # Help messages for command-line options
 split-help-bytes = put SIZE bytes per output file

src/uu/split/src/platform/unix.rs

@@ -4,8 +4,8 @@
 // file that was distributed with this source code.
 use std::env;
 use std::ffi::OsStr;
-use std::io::Write;
 use std::io::{BufWriter, Error, Result};
+use std::io::{ErrorKind, Write};
 use std::path::Path;
 use std::process::{Child, Command, Stdio};
 use uucore::error::USimpleError;
@@ -139,10 +139,13 @@ pub fn instantiate_current_writer(
                     .create(true)
                     .truncate(true)
                     .open(Path::new(&filename))
-                    .map_err(|_| {
-                        Error::other(
+                    .map_err(|e| match e.kind() {
+                        ErrorKind::IsADirectory => Error::other(
+                            translate!("split-error-is-a-directory", "dir" => filename),
+                        ),
+                        _ => Error::other(
                             translate!("split-error-unable-to-open-file", "file" => filename),
-                        )
+                        ),
                     })?
             } else {
                 // re-open file that we previously created to append to it

src/uu/split/src/platform/windows.rs

@@ -3,8 +3,8 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 use std::ffi::OsStr;
-use std::io::Write;
 use std::io::{BufWriter, Error, Result};
+use std::io::{ErrorKind, Write};
 use std::path::Path;
 use uucore::fs;
 use uucore::translate;
@@ -25,8 +25,13 @@ pub fn instantiate_current_writer(
             .create(true)
             .truncate(true)
             .open(Path::new(&filename))
-            .map_err(|_| {
-                Error::other(translate!("split-error-unable-to-open-file", "file" => filename))
+            .map_err(|e| match e.kind() {
+                ErrorKind::IsADirectory => {
+                    Error::other(translate!("split-error-is-a-directory", "dir" => filename))
+                }
+                _ => {
+                    Error::other(translate!("split-error-unable-to-open-file", "file" => filename))
+                }
             })?
     } else {
         // re-open file that we previously created to append to it

tests/by-util/test_split.rs

@@ -2078,3 +2078,16 @@ fn test_split_non_utf8_additional_suffix() {
         "Expected at least one split file to be created"
     );
 }
+
+#[test]
+#[cfg(target_os = "linux")] // To re-enable on Windows once I work out what goes wrong with it.
+fn test_split_directory_already_exists() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    at.mkdir("xaa"); // For collision with.
+    at.touch("file");
+    ucmd.args(&["file"])
+        .fails_with_code(1)
+        .no_stdout()
+        .stderr_is("split: xaa: Is a directory; aborting\n");
+}