default to file completion after first command, add command option for completions (#6257)

* remove unnecessary FlatShape

* add test

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

@@ -11,6 +11,7 @@ pub struct CommandCompletion {
     engine_state: Arc<EngineState>,
     flattened: Vec<(Span, FlatShape)>,
     flat_shape: FlatShape,
+    force_completion_after_space: bool,
 }
 
 impl CommandCompletion {
@@ -19,11 +20,13 @@ impl CommandCompletion {
         _: &StateWorkingSet,
         flattened: Vec<(Span, FlatShape)>,
         flat_shape: FlatShape,
+        force_completion_after_space: bool,
     ) -> Self {
         Self {
             engine_state,
             flattened,
             flat_shape,
+            force_completion_after_space,
         }
     }
 
@@ -81,9 +84,6 @@ impl CommandCompletion {
         match_algorithm: MatchAlgorithm,
     ) -> Vec<Suggestion> {
         let partial = working_set.get_span_contents(span);
-        if partial.is_empty() {
-            return Vec::new();
-        }
 
         let filter_predicate = |command: &[u8]| match_algorithm.matches_u8(command, partial);
 
@@ -209,6 +209,10 @@ impl Completer for CommandCompletion {
             || ((span.end - span.start) == 0)
         {
             // we're in a gap or at a command
+            if working_set.get_span_contents(span).is_empty() && !self.force_completion_after_space
+            {
+                return vec![];
+            }
             self.complete_commands(
                 working_set,
                 span,

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

@@ -215,6 +215,26 @@ impl NuCompleter {
                             }
                         }
 
+                        // specially check if it is currently empty - always complete commands
+                        if flat_idx == 0 && working_set.get_span_contents(new_span).is_empty() {
+                            let mut completer = CommandCompletion::new(
+                                self.engine_state.clone(),
+                                &working_set,
+                                flattened.clone(),
+                                // flat_idx,
+                                FlatShape::String,
+                                true,
+                            );
+                            return self.process_completion(
+                                &mut completer,
+                                &working_set,
+                                prefix,
+                                new_span,
+                                offset,
+                                pos,
+                            );
+                        }
+
                         // Completions that depends on the previous expression (e.g: use, source)
                         if flat_idx > 0 {
                             if let Some(previous_expr) = flattened.get(flat_idx - 1) {
@@ -302,6 +322,7 @@ impl NuCompleter {
                                     flattened.clone(),
                                     // flat_idx,
                                     flat_shape.clone(),
+                                    false,
                                 );
 
                                 let mut out: Vec<_> = self.process_completion(

crates/nu-cli/tests/completions.rs

@@ -625,3 +625,36 @@ fn run_external_completion(block: &str, input: &str) -> Vec<Suggestion> {
 
     completer.complete(&input, input.len())
 }
+
+#[test]
+fn unknown_command_completion() {
+    let (_, _, engine, stack) = new_engine();
+
+    let mut completer = NuCompleter::new(std::sync::Arc::new(engine), stack);
+
+    let target_dir = "thiscommanddoesnotexist ";
+    let suggestions = completer.complete(target_dir, target_dir.len());
+
+    #[cfg(windows)]
+    let expected_paths: Vec<String> = vec![
+        "nushell".to_string(),
+        "test_a\\".to_string(),
+        "test_b\\".to_string(),
+        "another\\".to_string(),
+        "custom_completion.nu".to_string(),
+        ".hidden_file".to_string(),
+        ".hidden_folder\\".to_string(),
+    ];
+    #[cfg(not(windows))]
+    let expected_paths: Vec<String> = vec![
+        "nushell".to_string(),
+        "test_a/".to_string(),
+        "test_b/".to_string(),
+        "another/".to_string(),
+        "custom_completion.nu".to_string(),
+        ".hidden_file".to_string(),
+        ".hidden_folder/".to_string(),
+    ];
+
+    match_suggestions(expected_paths, suggestions)
+}