Bidirectional communication and streams for plugins (#11911)

crates/nu-protocol/src/plugin_signature.rs

@@ -6,7 +6,7 @@ use crate::engine::Command;
 use crate::{BlockId, Category, Flag, PositionalArg, SyntaxShape, Type};
 
 /// A simple wrapper for Signature that includes examples.
-#[derive(Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct PluginSignature {
     pub sig: Signature,
     pub examples: Vec<PluginExample>,

crates/nu-protocol/src/shell_error.rs

@@ -774,6 +774,54 @@ pub enum ShellError {
     #[diagnostic(code(nu::shell::plugin_failed_to_decode))]
     PluginFailedToDecode { msg: String },
 
+    /// A custom value cannot be sent to the given plugin.
+    ///
+    /// ## Resolution
+    ///
+    /// Custom values can only be used with the plugin they came from. Use a command from that
+    /// plugin instead.
+    #[error("Custom value `{name}` cannot be sent to plugin")]
+    #[diagnostic(code(nu::shell::custom_value_incorrect_for_plugin))]
+    CustomValueIncorrectForPlugin {
+        name: String,
+        #[label("the `{dest_plugin}` plugin does not support this kind of value")]
+        span: Span,
+        dest_plugin: String,
+        #[help("this value came from the `{}` plugin")]
+        src_plugin: Option<String>,
+    },
+
+    /// The plugin failed to encode a custom value.
+    ///
+    /// ## Resolution
+    ///
+    /// This is likely a bug with the plugin itself. The plugin may have tried to send a custom
+    /// value that is not serializable.
+    #[error("Custom value failed to encode")]
+    #[diagnostic(code(nu::shell::custom_value_failed_to_encode))]
+    CustomValueFailedToEncode {
+        msg: String,
+        #[label("{msg}")]
+        span: Span,
+    },
+
+    /// The plugin failed to encode a custom value.
+    ///
+    /// ## Resolution
+    ///
+    /// This may be a bug within the plugin, or the plugin may have been updated in between the
+    /// creation of the custom value and its use.
+    #[error("Custom value failed to decode")]
+    #[diagnostic(code(nu::shell::custom_value_failed_to_decode))]
+    #[diagnostic(help(
+        "the plugin may have been updated and no longer support this custom value"
+    ))]
+    CustomValueFailedToDecode {
+        msg: String,
+        #[label("{msg}")]
+        span: Span,
+    },
+
     /// I/O operation interrupted.
     ///
     /// ## Resolution

crates/nu-protocol/src/value/mod.rs

@@ -164,7 +164,6 @@ pub enum Value {
         #[serde(rename = "span")]
         internal_span: Span,
     },
-    #[serde(skip_serializing)]
     CustomValue {
         val: Box<dyn CustomValue>,
         // note: spans are being refactored out of Value