Make view source more robust (#12359)

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# Description
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Resolves #11800.

```
~/CodingProjects/nushell> def "url expand" [$urls:any = []]: [string -> string, list -> table] {    
:::   let urls = ($in | default $urls)
:::   def expand-link [] {
:::     http head --redirect-mode manual $in | where name == location | get value.0
:::   }
:::   match ($urls | describe) {
:::     string => { $urls | expand-link }
:::     $type if ($type =~ list) => { $urls | wrap link | insert expanded {|url| $url.link | expand-link}}
:::   }
::: }; view source "url expand"
def "url expand" [ $urls: any = [] ]: [string -> string, list<any> -> table] {
  let urls = ($in | default $urls)
  def expand-link [] {
    http head --redirect-mode manual $in | where name == location | get value.0
  }
  match ($urls | describe) {
    string => { $urls | expand-link }
    $type if ($type =~ list) => { $urls | wrap link | insert expanded {|url| $url.link | expand-link}}
  }
}
```

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

`view source` now 
- adds quotes to commands with spaces
- shows default argument values
- shows type signatures

# Tests + Formatting
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crates/nu-std"` to run the tests for the standard library

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# After Submitting
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crates/nu-command/src/debug/view_source.rs

@@ -1,4 +1,5 @@
 use nu_engine::command_prelude::*;
+use nu_protocol::Config;
 
 use std::fmt::Write;
 
@@ -41,6 +42,7 @@ impl Command for ViewSource {
                     let vec_of_optional = &sig.optional_positional;
                     let rest = &sig.rest_positional;
                     let vec_of_flags = &sig.named;
+                    let type_signatures = &sig.input_output_types;
 
                     if decl.is_alias() {
                         if let Some(alias) = &decl.as_alias() {
@@ -58,13 +60,36 @@ impl Command for ViewSource {
                         if let Some(block_span) = block.span {
                             let contents = engine_state.get_span_contents(block_span);
                             // name of function
-                            let mut final_contents = format!("def {val} [ ");
+                            let mut final_contents = String::new();
+                            if val.contains(' ') {
+                                let _ = write!(&mut final_contents, "def \"{val}\" [");
+                            } else {
+                                let _ = write!(&mut final_contents, "def {val} [");
+                            };
+                            if !vec_of_required.is_empty()
+                                || !vec_of_optional.is_empty()
+                                || vec_of_flags.len() != 1
+                                || rest.is_some()
+                            {
+                                final_contents.push(' ');
+                            }
                             for n in vec_of_required {
                                 let _ = write!(&mut final_contents, "{}: {} ", n.name, n.shape);
-                                // positional argu,emts
+                                // positional arguments
                             }
                             for n in vec_of_optional {
-                                let _ = write!(&mut final_contents, "{}?: {} ", n.name, n.shape);
+                                if let Some(s) = n.default_value.clone() {
+                                    let _ = write!(
+                                        &mut final_contents,
+                                        "{}: {} = {} ",
+                                        n.name,
+                                        n.shape,
+                                        s.to_expanded_string(" ", &Config::default())
+                                    );
+                                } else {
+                                    let _ =
+                                        write!(&mut final_contents, "{}?: {} ", n.name, n.shape);
+                                }
                             }
                             for n in vec_of_flags {
                                 // skip adding the help flag
@@ -87,6 +112,19 @@ impl Command for ViewSource {
                                     rest_arg.name, rest_arg.shape
                                 );
                             }
+                            let len = type_signatures.len();
+                            if len != 0 {
+                                final_contents.push_str("]: [");
+                                let mut c = 0;
+                                for (insig, outsig) in type_signatures {
+                                    c += 1;
+                                    let s = format!("{} -> {}", insig, outsig);
+                                    final_contents.push_str(&s);
+                                    if c != len {
+                                        final_contents.push_str(", ")
+                                    }
+                                }
+                            }
                             final_contents.push_str("] ");
                             final_contents.push_str(&String::from_utf8_lossy(contents));
                             Ok(Value::string(final_contents, call.head).into_pipeline_data())