From 84fae6e07ef63a4c504573a2e2688e888641a73c Mon Sep 17 00:00:00 2001
From: Reilly Wood <26268125+rgwood@users.noreply.github.com>
Date: Sun, 7 Aug 2022 11:40:41 -0700
Subject: [PATCH] Suggest alternative when command not found (#6256)

* Suggest alternative when command not found

* Add tests for command-not-found suggestions

* Put suggestion in label

* Fix tests
---
 crates/nu-command/src/system/run_external.rs | 39 +++++++++++++++++---
 crates/nu-command/tests/commands/all.rs      |  2 +-
 crates/nu-command/tests/commands/any.rs      |  2 +-
 tests/shell/pipeline/commands/external.rs    | 13 +++++++
 4 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/crates/nu-command/src/system/run_external.rs b/crates/nu-command/src/system/run_external.rs
index 5c08898989..354959548e 100644
--- a/crates/nu-command/src/system/run_external.rs
+++ b/crates/nu-command/src/system/run_external.rs
@@ -2,6 +2,7 @@ use fancy_regex::Regex;
 use itertools::Itertools;
 use nu_engine::env_to_strings;
 use nu_engine::CallExt;
+use nu_protocol::did_you_mean;
 use nu_protocol::engine::{EngineState, Stack};
 use nu_protocol::{ast::Call, engine::Command, ShellError, Signature, SyntaxShape, Value};
 use nu_protocol::{Category, Example, ListStream, PipelineData, RawStream, Span, Spanned};
@@ -157,11 +158,21 @@ impl ExternalCommand {
         }
 
         match child {
-            Err(err) => Err(ShellError::ExternalCommand(
-                "can't run executable".to_string(),
-                err.to_string(),
-                self.name.span,
-            )),
+            Err(err) => {
+                // If we try to run an external but can't, there's a good chance
+                // that the user entered the wrong command name
+                let suggestion = suggest_command(&self.name.item, engine_state);
+                let label = match suggestion {
+                    Some(s) => format!("did you mean '{s}'?"),
+                    None => "can't run executable".into(),
+                };
+
+                Err(ShellError::ExternalCommand(
+                    label,
+                    err.to_string(),
+                    self.name.span,
+                ))
+            }
             Ok(mut child) => {
                 if !input.is_nothing() {
                     let mut engine_state = engine_state.clone();
@@ -513,6 +524,24 @@ impl ExternalCommand {
     }
 }
 
+/// Given an invalid command name, try to suggest an alternative
+fn suggest_command(attempted_command: &str, engine_state: &EngineState) -> Option<String> {
+    let commands = engine_state.get_signatures(false);
+    let command_name_lower = attempted_command.to_lowercase();
+    let search_term_match = commands.iter().find(|sig| {
+        sig.search_terms
+            .iter()
+            .any(|term| term.to_lowercase() == command_name_lower)
+    });
+    match search_term_match {
+        Some(sig) => Some(sig.name.clone()),
+        None => {
+            let command_names: Vec<String> = commands.iter().map(|sig| sig.name.clone()).collect();
+            did_you_mean(&command_names, attempted_command)
+        }
+    }
+}
+
 fn has_unsafe_shell_characters(arg: &str) -> bool {
     let re: Regex = Regex::new(r"[^\w@%+=:,./-]").expect("regex to be valid");
 
diff --git a/crates/nu-command/tests/commands/all.rs b/crates/nu-command/tests/commands/all.rs
index 3882da785a..b597e3f4a4 100644
--- a/crates/nu-command/tests/commands/all.rs
+++ b/crates/nu-command/tests/commands/all.rs
@@ -65,5 +65,5 @@ fn checks_if_all_returns_error_with_invalid_command() {
         "#
     ));
 
-    assert!(actual.err.contains("can't run executable") || actual.err.contains("type_mismatch"));
+    assert!(actual.err.contains("can't run executable") || actual.err.contains("did you mean"));
 }
diff --git a/crates/nu-command/tests/commands/any.rs b/crates/nu-command/tests/commands/any.rs
index a3aad7cfa0..dea2f6cde1 100644
--- a/crates/nu-command/tests/commands/any.rs
+++ b/crates/nu-command/tests/commands/any.rs
@@ -41,5 +41,5 @@ fn checks_if_any_returns_error_with_invalid_command() {
         "#
     ));
 
-    assert!(actual.err.contains("can't run executable") || actual.err.contains("type_mismatch"));
+    assert!(actual.err.contains("can't run executable") || actual.err.contains("did you mean"));
 }
diff --git a/tests/shell/pipeline/commands/external.rs b/tests/shell/pipeline/commands/external.rs
index d48975585b..ee894f562f 100644
--- a/tests/shell/pipeline/commands/external.rs
+++ b/tests/shell/pipeline/commands/external.rs
@@ -107,6 +107,19 @@ fn passes_binary_data_between_externals() {
     )
 }
 
+#[test]
+fn command_not_found_error_suggests_search_term() {
+    // 'distinct' is not a command, but it is a search term for 'uniq'
+    let actual = nu!(cwd: ".", "ls | distinct");
+    assert!(actual.err.contains("uniq"));
+}
+
+#[test]
+fn command_not_found_error_suggests_typo_fix() {
+    let actual = nu!(cwd: ".", "benhcmark { echo 'foo'}");
+    assert!(actual.err.contains("benchmark"));
+}
+
 mod it_evaluation {
     use super::nu;
     use nu_test_support::fs::Stub::{EmptyFile, FileWithContent, FileWithContentToBeTrimmed};