Add nuon format for fun (#4401)

* Add nuon format for fun

* more fun

* More nuon fixes, allow comments, improve errors

crates/nu-command/src/formats/to/mod.rs

@@ -4,6 +4,7 @@ mod delimited;
 mod html;
 mod json;
 mod md;
+mod nuon;
 mod toml;
 mod tsv;
 mod url;
@@ -17,6 +18,7 @@ pub use command::To;
 pub use html::ToHtml;
 pub use json::ToJson;
 pub use md::ToMd;
+pub use nuon::ToNuon;
 pub use tsv::ToTsv;
 pub use xml::ToXml;
 pub use yaml::ToYaml;

crates/nu-command/src/formats/to/nuon.rs

@@ -0,0 +1,98 @@
+use nu_protocol::ast::{Call, RangeInclusion};
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, Value,
+};
+
+#[derive(Clone)]
+pub struct ToNuon;
+
+impl Command for ToNuon {
+    fn name(&self) -> &str {
+        "to nuon"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("to nuon").category(Category::Experimental)
+    }
+
+    fn usage(&self) -> &str {
+        "Converts table data into Nuon (Nushell Object Notation) text."
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, ShellError> {
+        Ok(Value::String {
+            val: to_nuon(call, input)?,
+            span: call.head,
+        }
+        .into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Outputs a nuon string representing the contents of this table",
+            example: "[1 2 3] | to nuon",
+            result: Some(Value::test_string("[1, 2, 3]")),
+        }]
+    }
+}
+
+fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
+    match v {
+        Value::Binary { .. } => Err(ShellError::UnsupportedInput("binary".into(), span)),
+        Value::Block { .. } => Err(ShellError::UnsupportedInput("block".into(), span)),
+        Value::Bool { val, .. } => {
+            if *val {
+                Ok("$true".to_string())
+            } else {
+                Ok("$false".to_string())
+            }
+        }
+        Value::CellPath { .. } => Err(ShellError::UnsupportedInput("cellpath".to_string(), span)),
+        Value::CustomValue { .. } => Err(ShellError::UnsupportedInput("custom".to_string(), span)),
+        Value::Date { .. } => Err(ShellError::UnsupportedInput("date".to_string(), span)),
+        Value::Duration { val, .. } => Ok(format!("{}ns", *val)),
+        Value::Error { .. } => Err(ShellError::UnsupportedInput("error".to_string(), span)),
+        Value::Filesize { val, .. } => Ok(format!("{}b", *val)),
+        Value::Float { val, .. } => Ok(format!("{}", *val)),
+        Value::Int { val, .. } => Ok(format!("{}", *val)),
+        Value::List { vals, .. } => {
+            let mut collection = vec![];
+            for val in vals {
+                collection.push(value_to_string(val, span)?);
+            }
+            Ok(format!("[{}]", collection.join(", ")))
+        }
+        Value::Nothing { .. } => Ok("$nothing".to_string()),
+        Value::Range { val, .. } => Ok(format!(
+            "{}..{}{}",
+            value_to_string(&val.from, span)?,
+            if val.inclusion == RangeInclusion::RightExclusive {
+                "<"
+            } else {
+                ""
+            },
+            value_to_string(&val.to, span)?
+        )),
+        Value::Record { cols, vals, .. } => {
+            let mut collection = vec![];
+            for (col, val) in cols.iter().zip(vals) {
+                collection.push(format!("\"{}\": {}", col, value_to_string(val, span)?));
+            }
+            Ok(format!("{{{}}}", collection.join(", ")))
+        }
+        Value::String { val, .. } => Ok(format!("\"{}\"", val)),
+    }
+}
+
+fn to_nuon(call: &Call, input: PipelineData) -> Result<String, ShellError> {
+    let v = input.into_value(call.head);
+
+    value_to_string(&v, call.head)
+}