#14238 Now the file completion is triggered on a custom command after the first parameter. (#14481)

- this PR should close #14238

# Description
Solved as described here (First suggestion):
https://github.com/nushell/nushell/issues/14238#issuecomment-2506387012

Below I make the example from the issue, it shows that the completion
now works past the first parameter.
```
~/Projects/nushell> def list [...args] {                                                                                                  11/30/2024 03:21:24 PM
:::     $args
:::     | each {
:::         open $args
:::     }
::: }
~/Projects/nushell> cd tests/fixtures/completions/                                                                                        11/30/2024 03:25:24 PM
~/Projects/nushell/tests/fixtures/completions| list custom_completion.nu                                                                  11/30/2024 03:25:35 PM
another/               custom_completion.nu   directory_completion/  nushell
test_a/                test_b/                .hidden_file           .hidden_folder/
``` 

# User-Facing Changes
The changes introduced to completions in
`baadaee0163a5066ae73509ff6052962b3422673` now does not return if it did
not find "Operator completions".

This could have impact on more than just custom commands, but it could
be seemed as making everything a bit more robust.

# Tests + Formatting
I ran all of:  
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

# After Submitting
I do not think there is any need to update [the
documentation](https://github.com/nushell/nushell.github.io), right?

---------

Co-authored-by: Daniel Winther Petersen <daniel.winther.petersen@subaio.com>

crates/nu-cli/src/completions/completer.rs

@@ -297,7 +297,7 @@ impl NuCompleter {
                                     let mut completer =
                                         OperatorCompletion::new(pipeline_element.expr.clone());
 
-                                    return self.process_completion(
+                                    let operator_suggestion = self.process_completion(
                                         &mut completer,
                                         &working_set,
                                         prefix,
@@ -305,6 +305,9 @@ impl NuCompleter {
                                         fake_offset,
                                         pos,
                                     );
+                                    if !operator_suggestion.is_empty() {
+                                        return operator_suggestion;
+                                    }
                                 }
                             }
                         }

crates/nu-cli/tests/completions/mod.rs

@@ -357,6 +357,39 @@ fn file_completions() {
     // Match the results
     match_suggestions(&expected_paths, &suggestions);
 
+    // Test completions for the current folder even with parts before the autocomplet
+    let target_dir = format!("cp somefile.txt {dir_str}{MAIN_SEPARATOR}");
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Create the expected values
+    let expected_paths: Vec<String> = vec![
+        folder(dir.join("another")),
+        file(dir.join("custom_completion.nu")),
+        folder(dir.join("directory_completion")),
+        file(dir.join("nushell")),
+        folder(dir.join("test_a")),
+        folder(dir.join("test_b")),
+        file(dir.join(".hidden_file")),
+        folder(dir.join(".hidden_folder")),
+    ];
+
+    #[cfg(windows)]
+    {
+        let separator = '/';
+        let target_dir = format!("cp somefile.txt {dir_str}{separator}");
+        let slash_suggestions = completer.complete(&target_dir, target_dir.len());
+
+        let expected_slash_paths: Vec<String> = expected_paths
+            .iter()
+            .map(|s| s.replace('\\', "/"))
+            .collect();
+
+        match_suggestions(&expected_slash_paths, &slash_suggestions);
+    }
+
+    // Match the results
+    match_suggestions(&expected_paths, &suggestions);
+
     // Test completions for a file
     let target_dir = format!("cp {}", folder(dir.join("another")));
     let suggestions = completer.complete(&target_dir, target_dir.len());
@@ -391,6 +424,75 @@ fn file_completions() {
     match_suggestions(&expected_paths, &suggestions);
 }
 
+#[test]
+fn custom_command_rest_any_args_file_completions() {
+    // Create a new engine
+    let (dir, dir_str, mut engine, mut stack) = new_engine();
+    let command = r#"def list [ ...args: any ] {}"#;
+    assert!(support::merge_input(command.as_bytes(), &mut engine, &mut stack).is_ok());
+
+    // Instantiate a new completer
+    let mut completer = NuCompleter::new(Arc::new(engine), Arc::new(stack));
+
+    // Test completions for the current folder
+    let target_dir = format!("list {dir_str}{MAIN_SEPARATOR}");
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Create the expected values
+    let expected_paths: Vec<String> = vec![
+        folder(dir.join("another")),
+        file(dir.join("custom_completion.nu")),
+        folder(dir.join("directory_completion")),
+        file(dir.join("nushell")),
+        folder(dir.join("test_a")),
+        folder(dir.join("test_b")),
+        file(dir.join(".hidden_file")),
+        folder(dir.join(".hidden_folder")),
+    ];
+
+    // Match the results
+    match_suggestions(&expected_paths, &suggestions);
+
+    // Test completions for the current folder even with parts before the autocomplet
+    let target_dir = format!("list somefile.txt {dir_str}{MAIN_SEPARATOR}");
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Create the expected values
+    let expected_paths: Vec<String> = vec![
+        folder(dir.join("another")),
+        file(dir.join("custom_completion.nu")),
+        folder(dir.join("directory_completion")),
+        file(dir.join("nushell")),
+        folder(dir.join("test_a")),
+        folder(dir.join("test_b")),
+        file(dir.join(".hidden_file")),
+        folder(dir.join(".hidden_folder")),
+    ];
+
+    // Match the results
+    match_suggestions(&expected_paths, &suggestions);
+
+    // Test completions for a file
+    let target_dir = format!("list {}", folder(dir.join("another")));
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    // Create the expected values
+    let expected_paths: Vec<String> = vec![file(dir.join("another").join("newfile"))];
+
+    // Match the results
+    match_suggestions(&expected_paths, &suggestions);
+
+    // Test completions for hidden files
+    let target_dir = format!("list {}", file(dir.join(".hidden_folder").join(".")));
+    let suggestions = completer.complete(&target_dir, target_dir.len());
+
+    let expected_paths: Vec<String> =
+        vec![file(dir.join(".hidden_folder").join(".hidden_subfile"))];
+
+    // Match the results
+    match_suggestions(&expected_paths, &suggestions);
+}
+
 #[cfg(windows)]
 #[test]
 fn file_completions_with_mixed_separators() {