allow compact to also compact empty strings (#10912)

# Description

This change allows `compact` to also compact things with empty strings,
empty lists, and empty records if the `--empty` switch is used. Let's
add a quality-of-life improvement here to just compact all this mess. If
this is a bad idea, please cite examples demonstrating why.

```
❯ [[name position]; [Francis Lead] [Igor TechLead] [Aya null]] | compact position
╭#┬─name──┬position╮
│0│Francis│Lead    │
│1│Igor   │TechLead│
╰─┴───────┴────────╯
❯ [[name position]; [Francis Lead] [Igor TechLead] [Aya ""]] | compact position --empty
╭#┬─name──┬position╮
│0│Francis│Lead    │
│1│Igor   │TechLead│
╰─┴───────┴────────╯
❯ [1, null, 2, "", 3, [], 4, {}, 5] | compact
╭─┬─────────────────╮
│0│                1│
│1│                2│
│2│                 │
│3│                3│
│4│[list 0 items]   │
│5│                4│
│6│{record 0 fields}│
│7│                5│
╰─┴─────────────────╯
❯ [1, null, 2, "", 3, [], 4, {}, 5] | compact --empty
╭─┬─╮
│0│1│
│1│2│
│2│3│
│3│4│
│4│5│
╰─┴─╯
```

# User-Facing Changes
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crates/nu-command/src/filters/compact.rs

@@ -27,6 +27,11 @@ impl Command for Compact {
                     Type::List(Box::new(Type::Any)),
                 ),
             ])
+            .switch(
+                "empty",
+                "also compact empty items like \"\", {}, and []",
+                Some('e'),
+            )
             .rest(
                 "columns",
                 SyntaxShape::Any,
@@ -46,18 +51,19 @@ impl Command for Compact {
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        compact(engine_state, stack, call, input)
+        let empty = call.has_flag("empty");
+        compact(engine_state, stack, call, input, empty)
     }
 
     fn examples(&self) -> Vec<Example> {
         vec![
             Example {
-                description: "Filter out all records where 'Hello' is null (returns nothing)",
+                description: "Filter out all records where 'Hello' is null",
                 example: r#"[["Hello" "World"]; [null 3]] | compact Hello"#,
                 result: Some(Value::test_list(vec![])),
             },
             Example {
-                description: "Filter out all records where 'World' is null (Returns the table)",
+                description: "Filter out all records where 'World' is null",
                 example: r#"[["Hello" "World"]; [null 3]] | compact World"#,
                 result: Some(Value::test_list(vec![Value::test_record(record! {
                     "Hello" => Value::nothing(Span::test_data()),
@@ -65,13 +71,24 @@ impl Command for Compact {
                 })])),
             },
             Example {
-                description: "Filter out all instances of nothing from a list (Returns [1,2])",
+                description: "Filter out all instances of null from a list",
                 example: r#"[1, null, 2] | compact"#,
                 result: Some(Value::test_list(vec![
                     Value::test_int(1),
                     Value::test_int(2),
                 ])),
             },
+            Example {
+                description: "Filter out all instances of null and empty items from a list",
+                example: r#"[1, null, 2, "", 3, [], 4, {}, 5] | compact --empty"#,
+                result: Some(Value::test_list(vec![
+                    Value::test_int(1),
+                    Value::test_int(2),
+                    Value::test_int(3),
+                    Value::test_int(4),
+                    Value::test_int(5),
+                ])),
+            },
         ]
     }
 }
@@ -81,6 +98,7 @@ pub fn compact(
     stack: &mut Stack,
     call: &Call,
     input: PipelineData,
+    compact_empties: bool,
 ) -> Result<PipelineData, ShellError> {
     let columns: Vec<String> = call.rest(engine_state, stack, 0)?;
     let metadata = input.metadata();
@@ -90,7 +108,7 @@ pub fn compact(
                 match item {
                     // Nothing is filtered out
                     Value::Nothing { .. } => false,
-                    Value::Record { .. } => {
+                    Value::Record { val, .. } => {
                         for column in columns.iter() {
                             match item.get_data_by_key(column) {
                                 None => return false,
@@ -98,12 +116,35 @@ pub fn compact(
                                     if let Value::Nothing { .. } = x {
                                         return false;
                                     }
+                                    if compact_empties {
+                                        if let Value::String { val, .. } = x {
+                                            if val.is_empty() {
+                                                return false;
+                                            }
+                                        }
+                                    }
                                 }
                             }
                         }
+
+                        if compact_empties && val.is_empty() {
+                            return false;
+                        }
                         // No defined columns contained Nothing
                         true
                     }
+                    Value::List { vals, .. } => {
+                        if compact_empties && vals.is_empty() {
+                            return false;
+                        }
+                        true
+                    }
+                    Value::String { val, .. } => {
+                        if compact_empties && val.is_empty() {
+                            return false;
+                        }
+                        true
+                    }
                     // Any non-Nothing, non-record should be kept
                     _ => true,
                 }