Change input/output types in help to a table (#9686)

# Description

Updates `help` to more clearly show input/output types.

Before:


![image](https://github.com/nushell/nushell/assets/547158/5f11ca5c-54a0-414d-b3de-1a8b4dd7fcbd)

After:


![image](https://github.com/nushell/nushell/assets/547158/afc0eb1e-fad8-43b1-9382-c2a0d8e9334e)

# User-Facing Changes

See above

# Tests + Formatting
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crates/nu-command/tests/commands/help.rs

@@ -20,13 +20,11 @@ fn help_commands_length() {
 #[test]
 fn help_shows_signature() {
     let actual = nu!("help str distance");
-    assert!(actual
+    assert!(actual.out.contains("Input/output types"));
-        .out
-        .contains("<string> | str distance <string> -> <int>"));
 
     // don't show signature for parser keyword
     let actual = nu!("help alias");
-    assert!(!actual.out.contains("Signatures"));
+    assert!(!actual.out.contains("Input/output types"));
 }
 
 #[ignore = "TODO: Need to decide how to do help messages of new aliases"]

crates/nu-engine/src/documentation.rs

@@ -3,7 +3,9 @@ use nu_protocol::{
     engine::{EngineState, Stack},
     Example, IntoPipelineData, PipelineData, Signature, Span, SyntaxShape, Value,
 };
-use std::fmt::Write;
+use std::{collections::HashMap, fmt::Write};
+
+use crate::eval_call;
 
 pub fn get_full_help(
     sig: &Signature,
@@ -129,17 +131,6 @@ fn get_documentation(
         }))
     }
 
-    if !is_parser_keyword && !sig.input_output_types.is_empty() {
-        if sig.operates_on_cell_paths() {
-            let _ = writeln!(
-                long_desc,
-                "\n{G}Signatures(Cell paths are supported){RESET}:\n{sig}"
-            );
-        } else {
-            let _ = writeln!(long_desc, "\n{G}Signatures{RESET}:\n{sig}");
-        }
-    }
-
     if !sig.required_positional.is_empty()
         || !sig.optional_positional.is_empty()
         || sig.rest_positional.is_some()
@@ -213,6 +204,46 @@ fn get_documentation(
         }
     }
 
+    if !is_parser_keyword && !sig.input_output_types.is_empty() {
+        if let Some(decl_id) = engine_state.find_decl(b"table", &[]) {
+            // FIXME: we may want to make this the span of the help command in the future
+            let span = Span::unknown();
+            let mut vals = vec![];
+            for (input, output) in &sig.input_output_types {
+                vals.push(Value::Record {
+                    cols: vec!["input".into(), "output".into()],
+                    vals: vec![
+                        Value::string(input.to_string(), span),
+                        Value::string(output.to_string(), span),
+                    ],
+                    span,
+                });
+            }
+
+            let mut caller_stack = Stack::new();
+            if let Ok(result) = eval_call(
+                engine_state,
+                &mut caller_stack,
+                &Call {
+                    decl_id,
+                    head: span,
+                    arguments: vec![],
+                    redirect_stdout: true,
+                    redirect_stderr: true,
+                    parser_info: HashMap::new(),
+                },
+                PipelineData::Value(Value::List { vals, span }, None),
+            ) {
+                if let Ok((str, ..)) = result.collect_string_strict(span) {
+                    let _ = writeln!(long_desc, "\n{G}Input/output types{RESET}:");
+                    for line in str.lines() {
+                        let _ = writeln!(long_desc, "  {line}");
+                    }
+                }
+            }
+        }
+    }
+
     if !examples.is_empty() {
         let _ = write!(long_desc, "\n{G}Examples{RESET}:");
     }

src/tests/test_engine.rs

@@ -55,7 +55,7 @@ fn in_and_if_else() -> TestResult {
 #[test]
 fn help_works_with_missing_requirements() -> TestResult {
     // `each while` is part of the *extra* feature and adds 3 lines
-    let expected_length = if cfg!(feature = "extra") { "66" } else { "63" };
+    let expected_length = if cfg!(feature = "extra") { "70" } else { "67" };
     run_test(r#"each --help | lines | length"#, expected_length)
 }