Make default for mv safer, require -f to overwrite (#6904)

* fix: ✨ "saner" default for mv

fixes #6747

As highlighted in the issue, the default behavior of nu currently
is to overwrite the destination file without notice.
This is not a "standard" expectation users that want this behavior
can create a dedicated alias.

* fix: 📝 edit the comment

* fix: ✨ updated the tests

* fix: 🚧 use --force for case test

crates/nu-command/src/filesystem/mv.rs

@@ -50,8 +50,8 @@ impl Command for Mv {
                 "make mv to be verbose, showing files been moved.",
                 Some('v'),
             )
+            .switch("force", "overwrite the destination.", Some('f'))
             .switch("interactive", "ask user to confirm action", Some('i'))
-            // .switch("force", "suppress error when no file", Some('f'))
             .category(Category::FileSystem)
     }
 
@@ -76,7 +76,7 @@ impl Command for Mv {
         let spanned_destination: Spanned<String> = call.req(engine_state, stack, 1)?;
         let verbose = call.has_flag("verbose");
         let interactive = call.has_flag("interactive");
-        // let force = call.has_flag("force");
+        let force = call.has_flag("force");
 
         let ctrlc = engine_state.ctrlc.clone();
 
@@ -101,12 +101,22 @@ impl Command for Mv {
         //
         // First, the destination exists.
         //  - If a directory, move everything into that directory, otherwise
-        //  - if only a single source, overwrite the file, otherwise
+        //  - if only a single source, and --force (or -f) is provided overwrite the file,
-        //  - error.
+        //  - otherwise error.
         //
         // Second, the destination doesn't exist, so we can only rename a single source. Otherwise
         // it's an error.
 
+        if destination.exists() && !force && !destination.is_dir() && !source.is_dir() {
+            return Err(ShellError::GenericError(
+                "Destination file already exists".into(),
+                "you can use -f, --force to force overwriting the destination".into(),
+                Some(spanned_destination.span),
+                None,
+                Vec::new(),
+            ));
+        }
+
         if (destination.exists() && !destination.is_dir() && sources.len() > 1)
             || (!destination.exists() && sources.len() > 1)
         {

crates/nu-command/tests/commands/move_/mv.rs

@@ -23,7 +23,7 @@ fn moves_a_file() {
 }
 
 #[test]
-fn overwrites_if_moving_to_existing_file() {
+fn overwrites_if_moving_to_existing_file_and_force_provided() {
     Playground::setup("mv_test_2", |dirs, sandbox| {
         sandbox.with_files(vec![EmptyFile("andres.txt"), EmptyFile("jonathan.txt")]);
 
@@ -32,7 +32,7 @@ fn overwrites_if_moving_to_existing_file() {
 
         nu!(
             cwd: dirs.test(),
-            "mv andres.txt jonathan.txt"
+            "mv andres.txt -f jonathan.txt"
         );
 
         assert!(!original.exists());
@@ -207,6 +207,19 @@ fn errors_if_source_doesnt_exist() {
     })
 }
 
+#[test]
+fn error_if_moving_to_existing_file_without_force() {
+    Playground::setup("mv_test_10_0", |dirs, sandbox| {
+        sandbox.with_files(vec![EmptyFile("andres.txt"), EmptyFile("jonathan.txt")]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            "mv andres.txt jonathan.txt"
+        );
+        assert!(actual.err.contains("file already exists"))
+    })
+}
+
 #[test]
 fn errors_if_destination_doesnt_exist() {
     Playground::setup("mv_test_10_1", |dirs, sandbox| {
@@ -438,7 +451,7 @@ fn mv_change_case_of_file() {
 
         nu!(
             cwd: dirs.test(),
-            format!("mv {original_file_name} {new_file_name}")
+            format!("mv {original_file_name} -f {new_file_name}")
         );
 
         // Doing this instead of `Path::exists()` because we need to check file existence in