fix(completion): an edge case of aliased external head command (nushell#16882)

Fixes this ignored test case:


https://github.com/nushell/nushell/blob/a9263cf13489517b3a185ae1e33ecc41bddedb5f/crates/nu-cli/tests/completions/mod.rs#L2643-L2660

Previously `e<tab>` gets empty results because it dives deep into the
external head expression, `^$env.EDITOR` in this case.

This PR fixes it using the same mechanism as nushell#16876 and nushell#16640

## Release notes summary - What our users need to know

Fixed a bug in aliased external command completion where `alias ea =
^$env.EDITOR /tmp/test.s; e<tab>` gets empty result.

## Tasks after submitting

Author: blindFS

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

@@ -7,7 +7,7 @@ use crate::completions::{
 use nu_color_config::{color_record_to_nustyle, lookup_ansi_color_style};
 use nu_parser::{parse, parse_module_file_or_dir};
 use nu_protocol::{
-    CommandWideCompleter, Completion, Span, Type, Value,
+    CommandWideCompleter, Completion, GetSpan, Span, Type, Value,
     ast::{
         Argument, Block, Expr, Expression, FindMapResult, ListItem, PipelineRedirection,
         RedirectionTarget, Traverse,
@@ -55,14 +55,25 @@ fn find_pipeline_element_by_position<'a>(
         Expr::ExternalCall(head, arguments) => arguments
             .iter()
             .find_map(|arg| arg.expr().find_map(working_set, &closure))
-            .or(head.as_ref().find_map(working_set, &closure))
+            .or_else(|| {
+                // For aliased external_call, the span of original external command head should fail the
+                // contains(pos) check, thus avoiding recursion into its head expression.
+                // See issue #7648 for details.
+                let span = working_set.get_span(head.span_id);
+                if span.contains(pos) {
+                    // This is for complicated external head expressions, e.g. `^(echo<tab> foo)`
+                    head.as_ref().find_map(working_set, &closure)
+                } else {
+                    None
+                }
+            })
             .or(Some(expr))
             .map(FindMapResult::Found)
             .unwrap_or_default(),
         // complete the operator
         Expr::BinaryOp(lhs, _, rhs) => lhs
             .find_map(working_set, &closure)
-            .or(rhs.find_map(working_set, &closure))
+            .or_else(|| rhs.find_map(working_set, &closure))
             .or(Some(expr))
             .map(FindMapResult::Found)
             .unwrap_or_default(),

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

@@ -760,17 +760,13 @@ fn dotnu_completions_const_nu_lib_dirs() {
 }
 
 #[test]
-#[ignore]
 fn external_completer_trailing_space() {
     // https://github.com/nushell/nushell/issues/6378
     let block = "{|spans| $spans}";
     let input = "gh alias ";
 
     let suggestions = run_external_completion(block, input);
-    assert_eq!(3, suggestions.len());
-    assert_eq!("gh", suggestions.first().unwrap().value);
-    assert_eq!("alias", suggestions.get(1).unwrap().value);
-    assert_eq!("", suggestions.get(2).unwrap().value);
+    match_suggestions(&vec!["gh", "alias", ""], &suggestions);
 }
 
 #[test]
@@ -2640,7 +2636,6 @@ fn exact_match_case_insensitive() {
     });
 }
 
-#[ignore = "was reverted, still needs fixing"]
 #[rstest]
 fn alias_offset_bug_7648() {
     let (_, _, mut engine, mut stack) = new_engine();
@@ -2650,16 +2645,15 @@ fn alias_offset_bug_7648() {
     assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack).is_ok());
 
     let mut completer = NuCompleter::new(Arc::new(engine), Arc::new(stack));
+    let suggestions = completer.complete("e", 1);
+    assert!(!suggestions.is_empty());
 
-    // Issue #7648
-    // Nushell crashes when an alias name is shorter than the alias command
-    // and the alias command is a external command
-    // This happens because of offset is not correct.
-    // This crashes before PR #7779
-    let _suggestions = completer.complete("e", 1);
+    // Make sure completion in complicated external head expression still works
+    let input = "^(ls | e";
+    let suggestions = completer.complete(input, input.len());
+    assert!(!suggestions.is_empty());
 }
 
-#[ignore = "was reverted, still needs fixing"]
 #[rstest]
 fn alias_offset_bug_7754() {
     let (_, _, mut engine, mut stack) = new_engine();
@@ -2669,12 +2663,8 @@ fn alias_offset_bug_7754() {
     assert!(support::merge_input(alias.as_bytes(), &mut engine, &mut stack).is_ok());
 
     let mut completer = NuCompleter::new(Arc::new(engine), Arc::new(stack));
-
-    // Issue #7754
-    // Nushell crashes when an alias name is shorter than the alias command
-    // and the alias command contains pipes.
-    // This crashes before PR #7756
-    let _suggestions = completer.complete("ll -a | c", 9);
+    let suggestions = completer.complete("ll -a | c", 9);
+    assert!(!suggestions.is_empty());
 }
 
 #[rstest]