fix: better error when cwd is gone (#370)

If external command invocation fails, then check if the current working directory no longer exists; in that case, report a more specific error message.

brush-core/src/commands.rs

@@ -442,7 +442,15 @@ pub(crate) fn execute_external_command(
                 sys::terminal::move_self_to_foreground()?;
             }
 
-            if context.shell.options.sh_mode {
+            if !context.shell.working_dir.exists() {
+                // We may have failed because the working directory doesn't exist.
+                writeln!(
+                    stderr,
+                    "{}: working directory does not exist: {}",
+                    context.shell.shell_name.as_ref().unwrap_or(&String::new()),
+                    context.shell.working_dir.display()
+                )?;
+            } else if context.shell.options.sh_mode {
                 writeln!(
                     stderr,
                     "{}: {}: {}: not found",

brush-shell/tests/cases/simple_commands.yaml

@@ -25,3 +25,15 @@ cases:
     stdin: |
       ./non-existent-command 2>/dev/null
       echo "Result: $?"
+
+  - name: "Simple command with non-existent cwd"
+    # N.B. We intentionally fail here because there's no safe way to pick an
+    # alternate working directory that we are okay with. To our knowledge,
+    # there's no easy way to hold onto the current working directory past
+    # its deletion.
+    known_failure: true
+    stdin: |
+      mkdir test-dir
+      cd test-dir
+      rmdir $(pwd)
+      ls