nushell: Set up external completion using fish

tree/.config/nushell/config.nu

@@ -174,11 +174,22 @@ let light_theme = {
     shape_vardecl: purple
 }
 
-# External completer example
-# let carapace_completer = {|spans|
-#     carapace $spans.0 nushell $spans | from json
-# }
+# Use fish for external completion
+let fish_completer = {|spans|
+    # if the current command is an alias, get it's expansion
+    let expanded_alias = (scope aliases | where name == $spans.0 | get -i 0 | get -i expansion)
 
+    # overwrite
+    let spans = (if $expanded_alias != null  {
+        # put the first word of the expanded alias first in the span
+        $spans | skip 1 | prepend ($expanded_alias | split row " " | take 1)
+    } else { $spans })
+
+
+    fish --command $'complete "--do-complete=($spans | str join " ")"'
+    | $"value(char tab)description(char newline)" + $in
+    | from tsv --flexible --no-infer
+}
 
 $env.config = {
     show_banner: false
@@ -259,7 +270,7 @@ $env.config = {
         external: {
             enable: true # set to false to prevent nushell looking into $env.PATH to find more suggestions, `false` recommended for WSL users as this look up may be very slow
             max_results: 100 # setting it lower can improve completion performance at the cost of omitting some options
-            completer: null # check 'carapace_completer' above as an example
+            completer: $fish_completer
         }
     }