don't use table compaction in to nuon if not a table (#4671)

* don't use table compaction in to nuon if not a table

* Make a proper nuon conversion test

* more nuon tests

crates/nu-command/src/formats/to/nuon.rs

@@ -65,7 +65,7 @@ fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
         Value::Int { val, .. } => Ok(format!("{}", *val)),
         Value::List { vals, .. } => {
             let headers = get_columns(vals);
-            if vals.iter().all(|x| x.columns() == headers) {
+            if !headers.is_empty() && vals.iter().all(|x| x.columns() == headers) {
                 // Table output
                 let headers_output = headers.join(", ");
 

crates/nu-command/tests/format_conversions/mod.rs

@@ -5,6 +5,7 @@ mod html;
 mod ics;
 mod json;
 mod markdown;
+mod nuon;
 mod ods;
 mod sqlite;
 mod ssv;

crates/nu-command/tests/format_conversions/nuon.rs

@@ -0,0 +1,104 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn to_nuon_correct_compaction() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            open appveyor.yml 
+            | to nuon 
+            | str length 
+            | $in > 500
+        "#
+    ));
+
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn to_nuon_list_of_numbers() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            [1, 2, 3, 4]
+            | to nuon
+            | from nuon
+            | $in == [1, 2, 3, 4]
+        "#
+    ));
+
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn to_nuon_list_of_strings() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            [abc, xyz, def]
+            | to nuon
+            | from nuon
+            | $in == [abc, xyz, def]
+        "#
+    ));
+
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn to_nuon_table() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            [[my, columns]; [abc, xyz], [def, ijk]]
+            | to nuon
+            | from nuon
+            | $in == [[my, columns]; [abc, xyz], [def, ijk]]
+        "#
+    ));
+
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn to_nuon_bool() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            $false
+            | to nuon
+            | from nuon
+        "#
+    ));
+
+    assert_eq!(actual.out, "false");
+}
+
+#[test]
+fn to_nuon_negative_int() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            -1
+            | to nuon
+            | from nuon
+        "#
+    ));
+
+    assert_eq!(actual.out, "-1");
+}
+
+#[test]
+fn to_nuon_records() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            {name: "foo bar", age: 100, height: 10}
+            | to nuon
+            | from nuon
+            | $in == {name: "foo bar", age: 100, height: 10}
+        "#
+    ));
+
+    assert_eq!(actual.out, "true");
+}