Add NU config to allow user be able to turn off external completion (#5773)

* 06-07-wsl

* 06-07-linux-issue-with-delete-input

* 06-08-2023

* 06-08-Linux

* commit for merge

* Fix unit test

* format

* clean code

* Add flag to turn off external completion

* change env var to config

* Fix comment

Co-authored-by: Frank Zhang <v-frankz@microsoft.com>

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

@@ -199,12 +199,19 @@ impl Completer for CommandCompletion {
             return subcommands;
         }
 
+        let config = working_set.get_config();
         let commands = if matches!(self.flat_shape, nu_parser::FlatShape::External)
             || matches!(self.flat_shape, nu_parser::FlatShape::InternalCall)
             || ((span.end - span.start) == 0)
         {
             // we're in a gap or at a command
-            self.complete_commands(working_set, span, offset, true, options.match_algorithm)
+            self.complete_commands(
+                working_set,
+                span,
+                offset,
+                config.enable_external_completion,
+                options.match_algorithm,
+            )
         } else {
             vec![]
         };

crates/nu-protocol/src/config.rs

@@ -76,6 +76,7 @@ pub struct Config {
     pub disable_table_indexes: bool,
     pub cd_with_abbreviations: bool,
     pub case_sensitive_completions: bool,
+    pub enable_external_completion: bool,
 }
 
 impl Default for Config {
@@ -107,6 +108,7 @@ impl Default for Config {
             disable_table_indexes: false,
             cd_with_abbreviations: false,
             case_sensitive_completions: false,
+            enable_external_completion: true,
         }
     }
 }
@@ -323,6 +325,13 @@ impl Value {
                             eprintln!("$config.case_sensitive_completions is not a bool")
                         }
                     }
+                    "enable_external_completion" => {
+                        if let Ok(b) = value.as_bool() {
+                            config.enable_external_completion = b;
+                        } else {
+                            eprintln!("$config.enable_external_completion is not a bool")
+                        }
+                    }
                     x => {
                         eprintln!("$config.{} is an unknown config setting", x)
                     }

docs/sample_config/default_config.nu

@@ -219,6 +219,7 @@ let-env config = {
   disable_table_indexes: false # set to true to remove the index column from tables
   cd_with_abbreviations: false # set to true to allow you to do things like cd s/o/f and nushell expand it to cd some/other/folder
   case_sensitive_completions: false # set to true to enable case-sensitive completions
+  enable_external_completion: true # set to false to prevent nushell looking into $env.PATH to find more suggestions, `false` recommended for WSL users as this look up my be very slow
 
   hooks: {
     pre_prompt: [{