Improve error message for invalid executors (#99)

* Improve error message for invalid executors

* Add test for custom error

mask/src/executor.rs

@@ -18,7 +18,22 @@ pub fn execute_command(cmd: Command, maskfile_path: String) -> Result<ExitStatus
     child = add_utility_variables(child, maskfile_path);
     child = add_flag_variables(child, &cmd);
 
-    child.spawn()?.wait()
+    child
+        .spawn()
+        .map_err(|e| {
+            if e.kind() != ErrorKind::NotFound {
+                return e;
+            }
+            Error::new(
+                ErrorKind::NotFound,
+                format!(
+                    "program '{}' for executor '{}' not in PATH",
+                    child.get_program().to_string_lossy(),
+                    script.executor
+                ),
+            )
+        })?
+        .wait()
 }
 
 fn prepare_command(cmd: &Command) -> process::Command {

mask/tests/supported_runtimes_test.rs

@@ -26,6 +26,28 @@ echo "this won't do anything..."
         .failure();
 }
 
+#[test]
+fn custom_not_found_error_if_program_not_found() {
+    let (_temp, maskfile_path) = common::maskfile(
+        r#"
+## missing
+~~~notfound
+echo "this won't do anything..."
+~~~
+"#,
+    );
+
+    common::run_mask(&maskfile_path)
+        .command("missing")
+        .assert()
+        .code(1)
+        .stderr(contains(format!(
+            "{} program 'notfound' for executor 'notfound' not in PATH",
+            "ERROR:".red()
+        )))
+        .failure();
+}
+
 #[cfg(windows)]
 #[test]
 fn powershell() {