Plugin json (#474)

* json encoder

* thread to pass messages

* description for example

crates/nu-protocol/src/engine/command.rs

@@ -48,8 +48,8 @@ pub trait Command: Send + Sync + CommandClone {
         self.name().contains(' ')
     }
 
-    // Is a plugin command (returns plugin's name if yes)
-    fn is_plugin(&self) -> Option<&PathBuf> {
+    // Is a plugin command (returns plugin's path and encoding if yes)
+    fn is_plugin(&self) -> Option<(&PathBuf, &str)> {
         None
     }
 

crates/nu-protocol/src/engine/engine_state.rs

@@ -230,11 +230,13 @@ impl EngineState {
                 self.plugin_decls().try_for_each(|decl| {
                     // A successful plugin registration already includes the plugin filename
                     // No need to check the None option
-                    let path = decl.is_plugin().expect("plugin should have file name");
+                    let (path, encoding) = decl.is_plugin().expect("plugin should have file name");
                     let file_name = path.to_str().expect("path should be a str");
 
                     serde_json::to_string_pretty(&decl.signature())
-                        .map(|signature| format!("register {} {}\n\n", file_name, signature))
+                        .map(|signature| {
+                            format!("register {} -e {} {}\n\n", file_name, encoding, signature)
+                        })
                         .map_err(|err| ShellError::PluginFailedToLoad(err.to_string()))
                         .and_then(|line| {
                             plugin_file

crates/nu-protocol/src/span.rs

@@ -2,7 +2,7 @@ use miette::SourceSpan;
 use serde::{Deserialize, Serialize};
 
 /// A spanned area of interest, generic over what kind of thing is of interest
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct Spanned<T>
 where
     T: Clone + std::fmt::Debug,