remove --column from length command and remove record processing (#10091)

# Description

This PR removes `record` processing from the `length` command. It just
doesn't make sense to try and get the length of a record. This PR also
removes the `--column` parameter. If you want to list or count columns,
you could use `$table | columns` or `$table | columns | length`.

close #10074 

### Before

![image](https://github.com/nushell/nushell/assets/343840/83488316-3ec4-4c32-9583-00341a71f46f)

### After
Catches records two different ways now.
with the `input_output_types` checker

![image](https://github.com/nushell/nushell/assets/343840/ca67f8b6-359e-4933-ab4d-1b702f8d79cf)

and with additional logic in the command for cases like `echo`

![image](https://github.com/nushell/nushell/assets/343840/99064351-b208-4bd3-bab9-535f97cd7ad4)


# User-Facing Changes
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helps us keep track of breaking changes. -->

# Tests + Formatting
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crates/nu-command/src/filters/length.rs

@@ -1,9 +1,7 @@
-use nu_engine::column::get_columns;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
-    Signature, Span, Type, Value,
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
 };
 
 #[derive(Clone)]
@@ -15,7 +13,7 @@ impl Command for Length {
     }
 
     fn usage(&self) -> &str {
-        "Count the number of elements in the input."
+        "Count the number of items in an input list or rows in a table."
     }
 
     fn signature(&self) -> nu_protocol::Signature {
@@ -24,7 +22,6 @@ impl Command for Length {
                 (Type::List(Box::new(Type::Any)), Type::Int),
                 (Type::Table(vec![]), Type::Int),
             ])
-            .switch("column", "Show the number of columns in a table", Some('c'))
             .category(Category::Filters)
     }
 
@@ -34,18 +31,13 @@ impl Command for Length {
 
     fn run(
         &self,
-        engine_state: &EngineState,
+        _engine_state: &EngineState,
         _stack: &mut Stack,
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        let col = call.has_flag("column");
-        if col {
-            length_col(engine_state, call, input)
-        } else {
         length_row(call, input)
     }
-    }
 
     fn examples(&self) -> Vec<Example> {
         vec![
@@ -55,32 +47,29 @@ impl Command for Length {
                 result: Some(Value::test_int(5)),
             },
             Example {
-                description: "Count the number of columns in a table",
-                example: "[{columnA: A0 columnB: B0}] | length -c",
+                description: "Count the number of rows in a table",
+                example: "[{a:1 b:2}, {a:2 b:3}] | length",
                 result: Some(Value::test_int(2)),
             },
         ]
     }
 }
 
-// this simulates calling input | columns | length
-fn length_col(
-    engine_state: &EngineState,
-    call: &Call,
-    input: PipelineData,
-) -> Result<PipelineData, ShellError> {
-    length_row(
-        call,
-        getcol(engine_state, call.head, input)
-            .expect("getcol() should not fail used in column command"),
-    )
-}
-
 fn length_row(call: &Call, input: PipelineData) -> Result<PipelineData, ShellError> {
     match input {
         PipelineData::Value(Value::Nothing { .. }, ..) => {
             Ok(Value::int(0, call.head).into_pipeline_data())
         }
+        // I added this here because input_output_type() wasn't catching a record
+        // being sent in as input from echo. e.g. "echo {a:1 b:2} | length"
+        PipelineData::Value(Value::Record { span, .. }, ..) => {
+            Err(ShellError::OnlySupportsThisInputType {
+                exp_input_type: "list, and table".into(),
+                wrong_type: "record".into(),
+                dst_span: call.head,
+                src_span: span,
+            })
+        }
         _ => {
             let mut count: i64 = 0;
             // Check for and propagate errors
@@ -95,43 +84,6 @@ fn length_row(call: &Call, input: PipelineData) -> Result<PipelineData, ShellErr
     }
 }
 
-fn getcol(
-    engine_state: &EngineState,
-    span: Span,
-    input: PipelineData,
-) -> Result<PipelineData, ShellError> {
-    match input {
-        PipelineData::Empty => Ok(PipelineData::Empty),
-        PipelineData::Value(
-            Value::List {
-                vals: input_vals,
-                span,
-            },
-            ..,
-        ) => {
-            let input_cols = get_columns(&input_vals);
-            Ok(input_cols
-                .into_iter()
-                .map(move |x| Value::String { val: x, span })
-                .into_pipeline_data(engine_state.ctrlc.clone()))
-        }
-        PipelineData::ListStream(stream, ..) => {
-            let v: Vec<_> = stream.into_iter().collect();
-            let input_cols = get_columns(&v);
-
-            Ok(input_cols
-                .into_iter()
-                .map(move |x| Value::String { val: x, span })
-                .into_pipeline_data(engine_state.ctrlc.clone()))
-        }
-        PipelineData::Value(..) | PipelineData::ExternalStream { .. } => {
-            let cols = vec![];
-            let vals = vec![];
-            Ok(Value::Record { cols, vals, span }.into_pipeline_data())
-        }
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;

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

@@ -40,9 +40,10 @@ fn gets_first_row_when_no_amount_given() {
     Playground::setup("first_test_3", |dirs, sandbox| {
         sandbox.with_files(vec![EmptyFile("caballeros.txt"), EmptyFile("arepas.clu")]);
 
-        let actual = nu!(cwd: dirs.test(), "ls | first | length");
+        // FIXME: We should probably change first to return a one row table instead of a record here
+        let actual = nu!(cwd: dirs.test(), "ls | first | values | length");
 
-        assert_eq!(actual.out, "1");
+        assert_eq!(actual.out, "4");
     })
 }
 

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

@@ -33,9 +33,10 @@ fn gets_last_row_when_no_amount_given() {
     Playground::setup("last_test_2", |dirs, sandbox| {
         sandbox.with_files(vec![EmptyFile("caballeros.txt"), EmptyFile("arepas.clu")]);
 
-        let actual = nu!(cwd: dirs.test(), "ls | last | length");
+        // FIXME: We should probably change last to return a one row table instead of a record here
+        let actual = nu!(cwd: dirs.test(), "ls | last | values | length");
 
-        assert_eq!(actual.out, "1");
+        assert_eq!(actual.out, "4");
     })
 }
 

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

@@ -2,14 +2,21 @@ use nu_test_support::nu;
 
 #[test]
 fn length_columns_in_cal_table() {
-    let actual = nu!("cal | length -c");
+    let actual = nu!("cal | columns | length");
 
     assert_eq!(actual.out, "7");
 }
 
 #[test]
 fn length_columns_no_rows() {
-    let actual = nu!("echo [] | length -c");
+    let actual = nu!("echo [] | length");
 
     assert_eq!(actual.out, "0");
 }
+
+#[test]
+fn length_fails_on_echo_record() {
+    let actual = nu!("echo {a:1 b:2} | length");
+
+    assert_eq!(actual.err.contains("only_supports_this_input_type"), true);
+}

src/tests/test_table_operations.rs

@@ -264,7 +264,7 @@ fn update_will_insert() -> TestResult {
 #[test]
 fn length_for_columns() -> TestResult {
     run_test(
-        r#"[[name,age,grade]; [bill,20,a] [a b c]] | length -c"#,
+        r#"[[name,age,grade]; [bill,20,a] [a b c]] | columns | length"#,
         "3",
     )
 }