Allow folding with tables. (#2538)

crates/nu-cli/src/commands/is_empty.rs

@@ -50,9 +50,16 @@ async fn is_empty(
     args: CommandArgs,
     registry: &CommandRegistry,
 ) -> Result<OutputStream, ShellError> {
+    let name_tag = args.call_info.name_tag.clone();
     let registry = registry.clone();
     let (IsEmptyArgs { rest }, input) = args.process(&registry).await?;
 
+    if input.is_empty() {
+        return Ok(OutputStream::one(ReturnSuccess::value(
+            UntaggedValue::boolean(true).into_value(name_tag),
+        )));
+    }
+
     Ok(input
         .map(move |value| {
             let value_tag = value.tag();
@@ -72,7 +79,6 @@ async fn is_empty(
                     (_, _) => IsEmptyFor::Value,
                 }
             } else {
-                // let no_args = vec![];
                 let mut arguments = rest.iter().rev();
                 let replacement_if_true = match arguments.next() {
                     Some(arg) => arg.clone(),

crates/nu-cli/src/commands/reduce.rs

@@ -138,7 +138,19 @@ async fn reduce(
                 let row = each::make_indexed_item(input.0 + ioffset, input.1);
 
                 async {
-                    let f = acc?.into_vec().await[0].clone();
+                    let values = acc?.drain_vec().await;
+
+                    let f = if values.len() == 1 {
+                        let value = values
+                            .get(0)
+                            .ok_or_else(|| ShellError::unexpected("No value to update with"))?;
+                        value.clone()
+                    } else if values.is_empty() {
+                        UntaggedValue::nothing().into_untagged_value()
+                    } else {
+                        UntaggedValue::table(&values).into_untagged_value()
+                    };
+
                     scope.vars.insert(String::from("$acc"), f);
                     process_row(block, Arc::new(scope), context, row).await
                 }
@@ -154,9 +166,20 @@ async fn reduce(
                 let context = Arc::clone(&context);
 
                 async {
-                    scope
-                        .vars
-                        .insert(String::from("$acc"), acc?.into_vec().await[0].clone());
+                    let values = acc?.drain_vec().await;
+
+                    let f = if values.len() == 1 {
+                        let value = values
+                            .get(0)
+                            .ok_or_else(|| ShellError::unexpected("No value to update with"))?;
+                        value.clone()
+                    } else if values.is_empty() {
+                        UntaggedValue::nothing().into_untagged_value()
+                    } else {
+                        UntaggedValue::table(&values).into_untagged_value()
+                    };
+
+                    scope.vars.insert(String::from("$acc"), f);
                     process_row(block, Arc::new(scope), context, row).await
                 }
             })

crates/nu-cli/tests/commands/is_empty.rs

@@ -40,8 +40,7 @@ fn adds_value_provided_for_columns_that_are_empty() {
                 [
                     {"boost": 1, "check": []},
                     {"boost": 1, "check": ""},
-                    {"boost": 1, "check": {}},
-                    {"boost": null, "check": ["" {} [] ""]}
+                    {"boost": 1, "check": {}}
                 ]
 
             "#,
@@ -58,7 +57,7 @@ fn adds_value_provided_for_columns_that_are_empty() {
             "#
         ));
 
-        assert_eq!(actual.out, "8");
+        assert_eq!(actual.out, "6");
     })
 }
 
@@ -72,8 +71,7 @@ fn value_emptiness_check() {
                     "are_empty": [
                         {"check": []},
                         {"check": ""},
-                        {"check": {}},
-                        {"check": ["" {} [] ""]}
+                        {"check": {}}
                     ]
                 }
             "#,
@@ -91,6 +89,6 @@ fn value_emptiness_check() {
             "#
         ));
 
-        assert_eq!(actual.out, "4");
+        assert_eq!(actual.out, "3");
     })
 }

crates/nu-cli/tests/commands/reduce.rs

@@ -62,6 +62,26 @@ fn reduce_numbered_example() {
     assert_eq!(actual.out, "1");
 }
 
+#[test]
+fn folding_with_tables() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo [10 20 30 40]
+        | reduce -f [] {
+            with-env [value $it] {
+              echo $acc | append $(= 10 * $(= $nu.env.value | str to-int))
+            }
+          }
+        | math sum
+        | echo $it
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "1000");
+}
+
 #[test]
 fn error_reduce_fold_type_mismatch() {
     let actual = nu!(

crates/nu-protocol/src/value.rs

@@ -385,12 +385,10 @@ impl Value {
                 value: UntaggedValue::Primitive(p),
                 ..
             } => p.is_empty(),
-            t
-            @
             Value {
-                value: UntaggedValue::Table(_),
+                value: UntaggedValue::Table(rows),
                 ..
-            } => t.table_entries().all(|row| row.is_empty()),
+            } => rows.is_empty(),
             r
             @
             Value {