Support running batch files without typing their extension (#6278)

* Support running batch files without typing their extension

* suppress warning

crates/nu-command/src/system/run_external.rs

@@ -101,6 +101,7 @@ impl Command for External {
     }
 }
 
+#[derive(Clone)]
 pub struct ExternalCommand {
     pub name: Spanned<String>,
     pub args: Vec<Spanned<String>>,
@@ -121,28 +122,75 @@ impl ExternalCommand {
         let ctrlc = engine_state.ctrlc.clone();
 
         let mut process = self.create_process(&input, false, head)?;
-        let child;
+        // mut is used in the windows branch only, suppress warning on other platforms
+        #[allow(unused_mut)]
+        let mut child;
 
         #[cfg(windows)]
         {
-            // Some common Windows commands are actually built in to cmd.exe, not executables in their own right.
-            // To support those commands, we "shell out" to cmd.exe.
+            // Running external commands on Windows has 2 points of complication:
+            // 1. Some common Windows commands are actually built in to cmd.exe, not executables in their own right.
+            // 2. We need to let users run batch scripts etc. (.bat, .cmd) without typing their extension
+
+            // To support these situations, we have a fallback path that gets run if a command
+            // fails to be run as a normal executable:
+            // 1. "shell out" to cmd.exe if the command is a known cmd.exe internal command
+            // 2. Otherwise, use `which-rs` to look for batch files etc. then run those in cmd.exe
+
+            match process.spawn() {
+                Err(err) => {
+                    // set the default value, maybe we'll override it later
+                    child = Err(err);
 
                     // This has the full list of cmd.exe "internal" commands: https://ss64.com/nt/syntax-internal.html
                     // I (Reilly) went through the full list and whittled it down to ones that are potentially useful:
                     const CMD_INTERNAL_COMMANDS: [&str; 8] = [
                         "ASSOC", "DIR", "ECHO", "FTYPE", "MKLINK", "START", "VER", "VOL",
                     ];
-
                     let command_name_upper = self.name.item.to_uppercase();
-            let use_cmd = CMD_INTERNAL_COMMANDS
+                    let looks_like_cmd_internal = CMD_INTERNAL_COMMANDS
                         .iter()
                         .any(|&cmd| command_name_upper == cmd);
 
-            match process.spawn() {
-                Err(_) => {
-                    let mut fg_process = self.create_process(&input, use_cmd, head)?;
-                    child = fg_process.spawn();
+                    if looks_like_cmd_internal {
+                        let mut cmd_process = self.create_process(&input, true, head)?;
+                        child = cmd_process.spawn();
+                    } else {
+                        #[cfg(feature = "which-support")]
+                        {
+                            // maybe it's a batch file (foo.cmd) and the user typed `foo`. Try to find it with `which-rs`
+                            // TODO: clean this up with an if-let chain once those are stable
+                            if let Ok(path) =
+                                nu_engine::env::path_str(engine_state, stack, self.name.span)
+                            {
+                                if let Some(cwd) = self.env_vars.get("PWD") {
+                                    // append cwd to PATH so `which-rs` looks in the cwd too.
+                                    // this approximates what cmd.exe does.
+                                    let path_with_cwd = format!("{};{}", cwd, path);
+                                    if let Ok(which_path) =
+                                        which::which_in(&self.name.item, Some(path_with_cwd), cwd)
+                                    {
+                                        if let Some(file_name) = which_path.file_name() {
+                                            let file_name_upper =
+                                                file_name.to_string_lossy().to_uppercase();
+                                            if file_name_upper != command_name_upper {
+                                                // which-rs found an executable file with a slightly different name
+                                                // than the one the user tried. Let's try running it
+                                                let mut new_command = self.clone();
+                                                new_command.name = Spanned {
+                                                    item: file_name.to_string_lossy().to_string(),
+                                                    span: self.name.span,
+                                                };
+                                                let mut cmd_process = new_command
+                                                    .create_process(&input, true, head)?;
+                                                child = cmd_process.spawn();
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
                 }
                 Ok(process) => {
                     child = Ok(process);

crates/nu-command/tests/commands/run_external.rs

@@ -1,4 +1,4 @@
-use nu_test_support::fs::Stub::EmptyFile;
+use nu_test_support::fs::Stub::{EmptyFile, FileWithContent};
 use nu_test_support::playground::Playground;
 use nu_test_support::{nu, pipeline};
 
@@ -259,3 +259,60 @@ fn single_quote_does_not_expand_path_glob_windows() {
         assert!(actual.out.contains("D&D_volume_2.txt"));
     });
 }
+
+#[cfg(windows)]
+#[test]
+fn can_run_batch_files() {
+    Playground::setup("run a Windows batch file", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContent(
+            "foo.cmd",
+            r#"
+                @echo off
+                echo Hello World
+            "#,
+        )]);
+
+        let actual = nu!(cwd: dirs.test(), pipeline("foo.cmd"));
+        assert!(actual.out.contains("Hello World"));
+    });
+}
+
+#[cfg(windows)]
+#[test]
+fn can_run_batch_files_without_cmd_extension() {
+    Playground::setup(
+        "run a Windows batch file without specifying the extension",
+        |dirs, sandbox| {
+            sandbox.with_files(vec![FileWithContent(
+                "foo.cmd",
+                r#"
+                @echo off
+                echo Hello World
+            "#,
+            )]);
+
+            let actual = nu!(cwd: dirs.test(), pipeline("foo"));
+            assert!(actual.out.contains("Hello World"));
+        },
+    );
+}
+
+#[cfg(windows)]
+#[test]
+fn can_run_batch_files_without_bat_extension() {
+    Playground::setup(
+        "run a Windows batch file without specifying the extension",
+        |dirs, sandbox| {
+            sandbox.with_files(vec![FileWithContent(
+                "foo.bat",
+                r#"
+                @echo off
+                echo Hello World
+            "#,
+            )]);
+
+            let actual = nu!(cwd: dirs.test(), pipeline("foo"));
+            assert!(actual.out.contains("Hello World"));
+        },
+    );
+}