Fix spans passed to external_completer (#11008)

close #10973

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

@@ -143,18 +143,24 @@ impl NuCompleter {
                             let current_span = working_set.get_span_contents(flat.0).to_vec();
                             let current_span_str = String::from_utf8_lossy(&current_span);
 
+                            let is_last_span = pos >= flat.0.start && pos < flat.0.end;
+
                             // Skip the last 'a' as span item
-                            if flat_idx == flattened.len() - 1 {
-                                let mut chars = current_span_str.chars();
-                                chars.next_back();
-                                let current_span_str = chars.as_str().to_owned();
-                                spans.push(current_span_str.to_string());
+                            if is_last_span {
+                                let offset = pos - flat.0.start;
+                                if offset == 0 {
+                                    spans.push(String::new())
+                                } else {
+                                    let mut current_span_str = current_span_str.to_string();
+                                    current_span_str.remove(offset);
+                                    spans.push(current_span_str);
+                                }
                             } else {
                                 spans.push(current_span_str.to_string());
                             }
 
                             // Complete based on the last span
-                            if pos >= flat.0.start && pos < flat.0.end {
+                            if is_last_span {
                                 // Context variables
                                 let most_left_var =
                                     most_left_variable(flat_idx, &working_set, flattened.clone());

crates/nu-cli/tests/completions.rs

@@ -59,6 +59,29 @@ fn extern_completer() -> NuCompleter {
     NuCompleter::new(std::sync::Arc::new(engine), stack)
 }
 
+#[fixture]
+fn custom_completer() -> NuCompleter {
+    // Create a new engine
+    let (dir, _, mut engine, mut stack) = new_engine();
+
+    // Add record value as example
+    let record = r#"
+        let external_completer = {|spans| 
+            $spans
+        }
+
+        $env.config.completions.external = {
+            enable: true
+            max_results: 100
+            completer: $external_completer
+        }
+    "#;
+    assert!(support::merge_input(record.as_bytes(), &mut engine, &mut stack, dir).is_ok());
+
+    // Instantiate a new completer
+    NuCompleter::new(std::sync::Arc::new(engine), stack)
+}
+
 #[test]
 fn variables_dollar_sign_with_varialblecompletion() {
     let (_, _, engine, stack) = new_engine();
@@ -938,6 +961,34 @@ fn extern_complete_flags(mut extern_completer: NuCompleter) {
     match_suggestions(expected, suggestions);
 }
 
+#[rstest]
+fn custom_completer_triggers_cursor_before_word(mut custom_completer: NuCompleter) {
+    let suggestions = custom_completer.complete("cmd foo  bar", 8);
+    let expected: Vec<String> = vec!["cmd".into(), "foo".into(), "".into()];
+    match_suggestions(expected, suggestions);
+}
+
+#[rstest]
+fn custom_completer_triggers_cursor_on_word_left_boundary(mut custom_completer: NuCompleter) {
+    let suggestions = custom_completer.complete("cmd foo bar", 8);
+    let expected: Vec<String> = vec!["cmd".into(), "foo".into(), "".into()];
+    match_suggestions(expected, suggestions);
+}
+
+#[rstest]
+fn custom_completer_triggers_cursor_next_to_word(mut custom_completer: NuCompleter) {
+    let suggestions = custom_completer.complete("cmd foo bar", 11);
+    let expected: Vec<String> = vec!["cmd".into(), "foo".into(), "bar".into()];
+    match_suggestions(expected, suggestions);
+}
+
+#[rstest]
+fn custom_completer_triggers_cursor_after_word(mut custom_completer: NuCompleter) {
+    let suggestions = custom_completer.complete("cmd foo bar ", 12);
+    let expected: Vec<String> = vec!["cmd".into(), "foo".into(), "bar".into(), "".into()];
+    match_suggestions(expected, suggestions);
+}
+
 #[ignore = "was reverted, still needs fixing"]
 #[rstest]
 fn alias_offset_bug_7648() {