Fix return setting last exit code (#14120)

# Description

Fixes #14113 and #14112.

# Tests + Formatting

Added a test.

crates/nu-cli/src/util.rs

@@ -221,7 +221,7 @@ pub fn eval_source(
             report_shell_error(engine_state, &err);
             let code = err.exit_code();
             stack.set_last_error(&err);
-            code
+            code.unwrap_or(0)
         }
     };
 

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

@@ -32,3 +32,9 @@ fn return_works_in_script_with_def_main() {
     );
     assert!(actual.err.is_empty());
 }
+
+#[test]
+fn return_does_not_set_last_exit_code() {
+    let actual = nu!("hide-env LAST_EXIT_CODE; do --env { return 42 }; $env.LAST_EXIT_CODE?");
+    assert!(matches!(actual.out.as_str(), ""));
+}

crates/nu-protocol/src/engine/stack.rs

@@ -287,8 +287,8 @@ impl Stack {
     pub fn set_last_error(&mut self, error: &ShellError) {
         if let Some(code) = error.external_exit_code() {
             self.set_last_exit_code(code.item, code.span);
-        } else {
-            self.set_last_exit_code(1, Span::unknown());
+        } else if let Some(code) = error.exit_code() {
+            self.set_last_exit_code(code, Span::unknown());
         }
     }
 

crates/nu-protocol/src/errors/shell_error.rs

@@ -1470,8 +1470,11 @@ impl ShellError {
         Some(Spanned { item, span })
     }
 
-    pub fn exit_code(&self) -> i32 {
-        self.external_exit_code().map(|e| e.item).unwrap_or(1)
+    pub fn exit_code(&self) -> Option<i32> {
+        match self {
+            Self::Return { .. } | Self::Break { .. } | Self::Continue { .. } => None,
+            _ => self.external_exit_code().map(|e| e.item).or(Some(1)),
+        }
     }
 
     pub fn into_value(self, span: Span) -> Value {

src/run.rs

@@ -104,7 +104,7 @@ pub(crate) fn run_commands(
 
     if let Err(err) = result {
         report_shell_error(engine_state, &err);
-        std::process::exit(err.exit_code());
+        std::process::exit(err.exit_code().unwrap_or(0));
     }
 }
 
@@ -178,7 +178,7 @@ pub(crate) fn run_file(
 
     if let Err(err) = result {
         report_shell_error(engine_state, &err);
-        std::process::exit(err.exit_code());
+        std::process::exit(err.exit_code().unwrap_or(0));
     }
 }