Highlight help tutor (#838)

* WIP

* Syntax highlight help, add tutor

crates/nu-cli/src/lib.rs

@@ -1,11 +1,13 @@
 mod completions;
 mod errors;
+mod nu_highlight;
 mod prompt;
 mod syntax_highlight;
 mod validation;
 
 pub use completions::NuCompleter;
 pub use errors::CliError;
+pub use nu_highlight::NuHighlight;
 pub use prompt::NushellPrompt;
 pub use syntax_highlight::NuHighlighter;
 pub use validation::NuValidator;

crates/nu-cli/src/nu_highlight.rs

@@ -0,0 +1,63 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Value};
+use reedline::Highlighter;
+
+#[derive(Clone)]
+pub struct NuHighlight;
+
+impl Command for NuHighlight {
+    fn name(&self) -> &str {
+        "nu-highlight"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("nu-highlight").category(Category::Strings)
+    }
+
+    fn usage(&self) -> &str {
+        "Syntax highlight the input string."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let head = call.head;
+
+        let ctrlc = engine_state.ctrlc.clone();
+        let engine_state = engine_state.clone();
+        let config = stack.get_config()?;
+
+        let highlighter = crate::NuHighlighter {
+            engine_state,
+            config,
+        };
+
+        input.map(
+            move |x| match x.as_string() {
+                Ok(line) => {
+                    let highlights = highlighter.highlight(&line);
+
+                    Value::String {
+                        val: highlights.render_simple(),
+                        span: head,
+                    }
+                }
+                Err(err) => Value::Error { error: err },
+            },
+            ctrlc,
+        )
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Describe the type of a string",
+            example: "'let x = 3' | nu-highlight",
+            result: None,
+        }]
+    }
+}