Add format command

Cargo.toml

@@ -137,6 +137,10 @@ path = "src/plugins/insert.rs"
 name = "nu_plugin_edit"
 path = "src/plugins/edit.rs"
 
+[[bin]]
+name = "nu_plugin_format"
+path = "src/plugins/format.rs"
+
 [[bin]]
 name = "nu_plugin_parse"
 path = "src/plugins/parse.rs"

src/data/base.rs

@@ -422,7 +422,7 @@ impl Tagged<Value> {
         }
     }
 
-    pub(crate) fn as_string(&self) -> Result<String, ShellError> {
+    pub fn as_string(&self) -> Result<String, ShellError> {
         match &self.item {
             Value::Primitive(Primitive::String(s)) => Ok(s.clone()),
             Value::Primitive(Primitive::Boolean(x)) => Ok(format!("{}", x)),

src/plugins/format.rs

@@ -0,0 +1,128 @@
+use nu::{
+    serve_plugin, CallInfo, Plugin, Primitive, ReturnSuccess, ReturnValue, ShellError, Signature,
+    SyntaxShape, Tagged, TaggedItem, Value,
+};
+
+use nom::{
+    bytes::complete::{tag, take_while},
+    IResult,
+};
+
+#[derive(Debug)]
+enum FormatCommand {
+    Text(String),
+    Column(String),
+}
+
+fn format(input: &str) -> IResult<&str, Vec<FormatCommand>> {
+    let mut output = vec![];
+
+    let mut loop_input = input;
+    loop {
+        let (input, before) = take_while(|c| c != '{')(loop_input)?;
+        if before.len() > 0 {
+            output.push(FormatCommand::Text(before.to_string()));
+        }
+        if input != "" {
+            // Look for column as we're now at one
+            let (input, _) = tag("{")(input)?;
+            let (input, column) = take_while(|c| c != '}')(input)?;
+            let (input, _) = tag("}")(input)?;
+
+            output.push(FormatCommand::Column(column.to_string()));
+            loop_input = input;
+        } else {
+            loop_input = input;
+        }
+        if loop_input == "" {
+            break;
+        }
+    }
+
+    Ok((loop_input, output))
+}
+
+struct Format {
+    commands: Vec<FormatCommand>,
+}
+
+impl Format {
+    fn new() -> Self {
+        Format { commands: vec![] }
+    }
+}
+
+impl Plugin for Format {
+    fn config(&mut self) -> Result<Signature, ShellError> {
+        Ok(Signature::build("format")
+            .desc("Format columns into a string using a simple pattern")
+            .required(
+                "pattern",
+                SyntaxShape::Any,
+                "the pattern to match. Eg) \"{foo}: {bar}\"",
+            )
+            .filter())
+    }
+    fn begin_filter(&mut self, call_info: CallInfo) -> Result<Vec<ReturnValue>, ShellError> {
+        if let Some(args) = call_info.args.positional {
+            match &args[0] {
+                Tagged {
+                    item: Value::Primitive(Primitive::String(pattern)),
+                    ..
+                } => {
+                    let format_pattern = format(&pattern).unwrap();
+                    self.commands = format_pattern.1
+                }
+                Tagged { tag, .. } => {
+                    return Err(ShellError::labeled_error(
+                        "Unrecognized type in params",
+                        "expected a string",
+                        tag,
+                    ));
+                }
+            }
+        }
+        Ok(vec![])
+    }
+
+    fn filter(&mut self, input: Tagged<Value>) -> Result<Vec<ReturnValue>, ShellError> {
+        match &input {
+            Tagged {
+                item: Value::Row(dict),
+                ..
+            } => {
+                let mut output = String::new();
+
+                for command in &self.commands {
+                    match command {
+                        FormatCommand::Text(s) => {
+                            output.push_str(s);
+                        }
+                        FormatCommand::Column(c) => {
+                            match dict.entries.get(c) {
+                                Some(c) => match c.as_string() {
+                                    Ok(v) => output.push_str(&v),
+                                    _ => return Ok(vec![]),
+                                },
+                                None => {
+                                    // This row doesn't match, so don't emit anything
+                                    return Ok(vec![]);
+                                }
+                            }
+                        }
+                    }
+                }
+
+                return Ok(vec![ReturnSuccess::value(
+                    Value::string(output).tagged_unknown(),
+                )]);
+            }
+            _ => {}
+        }
+        Ok(vec![])
+    }
+}
+
+fn main() {
+    serve_plugin(&mut Format::new());
+}

tests/tests.rs

@@ -57,7 +57,7 @@ fn insert_plugin() {
 }
 
 #[test]
-fn read_plugin() {
+fn parse_plugin() {
     let actual = nu!(
         cwd: "tests/fixtures/formats", h::pipeline(
         r#"
@@ -72,6 +72,21 @@ fn read_plugin() {
     assert_eq!(actual, "StupidLongName");
 }
 
+#[test]
+fn format_plugin() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", h::pipeline(
+        r#"
+        open cargo_sample.toml
+            | get package
+            | format "{name} has license {license}"
+            | echo $it
+        "#
+    ));
+
+    assert_eq!(actual, "nu has license ISC");
+}
+
 #[test]
 fn prepend_plugin() {
     let actual = nu!(