Keep plugins persistently running in the background (#12064)

# Description
This PR uses the new plugin protocol to intelligently keep plugin
processes running in the background for further plugin calls.

Running plugins can be seen by running the new `plugin list` command,
and stopped by running the new `plugin stop` command.

This is an enhancement for the performance of plugins, as starting new
plugin processes has overhead, especially for plugins in languages that
take a significant amount of time on startup. It also enables plugins
that have persistent state between commands, making the migration of
features like dataframes and `stor` to plugins possible.

Plugins are automatically stopped by the new plugin garbage collector,
configurable with `$env.config.plugin_gc`:

```nushell
  $env.config.plugin_gc = {
      # Configuration for plugin garbage collection
      default: {
          enabled: true # true to enable stopping of inactive plugins
          stop_after: 10sec # how long to wait after a plugin is inactive to stop it
      }
      plugins: {
          # alternate configuration for specific plugins, by name, for example:
          #
          # gstat: {
          #     enabled: false
          # }
      }
  }
```

If garbage collection is enabled, plugins will be stopped after
`stop_after` passes after they were last active. Plugins are counted as
inactive if they have no running plugin calls. Reading the stream from
the response of a plugin call is still considered to be activity, but if
a plugin holds on to a stream but the call ends without an active
streaming response, it is not counted as active even if it is reading
it. Plugins can explicitly disable the GC as appropriate with
`engine.set_gc_disabled(true)`.

The `version` command now lists plugin names rather than plugin
commands. The list of plugin commands is accessible via `plugin list`.

Recommend doing this together with #12029, because it will likely force
plugin developers to do the right thing with mutability and lead to less
unexpected behavior when running plugins nested / in parallel.

# User-Facing Changes
- new command: `plugin list`
- new command: `plugin stop`
- changed command: `version` (now lists plugin names, rather than
commands)
- new config: `$env.config.plugin_gc`
- Plugins will keep running and be reused, at least for the configured
GC period
- Plugins that used mutable state in weird ways like `inc` did might
misbehave until fixed
- Plugins can disable GC if they need to
- Had to change plugin signature to accept `&EngineInterface` so that
the GC disable feature works. #12029 does this anyway, and I'm expecting
(resolvable) conflicts with that

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

Because there is some specific OS behavior required for plugins to not
respond to Ctrl-C directly, I've developed against and tested on both
Linux and Windows to ensure that works properly.

# After Submitting
I think this probably needs to be in the book somewhere

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

@@ -1,5 +1,3 @@
-use std::path::Path;
-
 use crate::{ast::Call, Alias, BlockId, Example, PipelineData, ShellError, Signature};
 
 use super::{EngineState, Stack, StateWorkingSet};
@@ -91,8 +89,14 @@ pub trait Command: Send + Sync + CommandClone {
         false
     }
 
-    // Is a plugin command (returns plugin's path, type of shell if the declaration is a plugin)
-    fn is_plugin(&self) -> Option<(&Path, Option<&Path>)> {
+    /// Is a plugin command
+    fn is_plugin(&self) -> bool {
+        false
+    }
+
+    /// The identity of the plugin, if this is a plugin command
+    #[cfg(feature = "plugin")]
+    fn plugin_identity(&self) -> Option<&crate::PluginIdentity> {
         None
     }
 
@@ -118,7 +122,7 @@ pub trait Command: Send + Sync + CommandClone {
             self.is_parser_keyword(),
             self.is_known_external(),
             self.is_alias(),
-            self.is_plugin().is_some(),
+            self.is_plugin(),
         ) {
             (true, false, false, false, false, false) => CommandType::Builtin,
             (true, true, false, false, false, false) => CommandType::Custom,

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

@@ -23,6 +23,9 @@ use std::sync::{
 
 type PoisonDebuggerError<'a> = PoisonError<MutexGuard<'a, Box<dyn Debugger>>>;
 
+#[cfg(feature = "plugin")]
+use crate::RegisteredPlugin;
+
 pub static PWD_ENV: &str = "PWD";
 
 #[derive(Clone, Debug)]
@@ -113,6 +116,8 @@ pub struct EngineState {
     pub table_decl_id: Option<usize>,
     #[cfg(feature = "plugin")]
     pub plugin_signatures: Option<PathBuf>,
+    #[cfg(feature = "plugin")]
+    plugins: Vec<Arc<dyn RegisteredPlugin>>,
     config_path: HashMap<String, PathBuf>,
     pub history_enabled: bool,
     pub history_session_id: i64,
@@ -171,6 +176,8 @@ impl EngineState {
             table_decl_id: None,
             #[cfg(feature = "plugin")]
             plugin_signatures: None,
+            #[cfg(feature = "plugin")]
+            plugins: vec![],
             config_path: HashMap::new(),
             history_enabled: true,
             history_session_id: 0,
@@ -255,14 +262,27 @@ impl EngineState {
         self.scope.active_overlays.append(&mut activated_ids);
 
         #[cfg(feature = "plugin")]
-        if delta.plugins_changed {
-            let result = self.update_plugin_file();
-
-            if result.is_ok() {
-                delta.plugins_changed = false;
+        if !delta.plugins.is_empty() {
+            // Replace plugins that overlap in identity.
+            for plugin in std::mem::take(&mut delta.plugins) {
+                if let Some(existing) = self
+                    .plugins
+                    .iter_mut()
+                    .find(|p| p.identity() == plugin.identity())
+                {
+                    // Stop the existing plugin, so that the new plugin definitely takes over
+                    existing.stop()?;
+                    *existing = plugin;
+                } else {
+                    self.plugins.push(plugin);
+                }
             }
+        }
 
-            return result;
+        #[cfg(feature = "plugin")]
+        if delta.plugins_changed {
+            // Update the plugin file with the new signatures.
+            self.update_plugin_file()?;
         }
 
         Ok(())
@@ -274,6 +294,8 @@ impl EngineState {
         stack: &mut Stack,
         cwd: impl AsRef<Path>,
     ) -> Result<(), ShellError> {
+        let mut config_updated = false;
+
         for mut scope in stack.env_vars.drain(..) {
             for (overlay_name, mut env) in scope.drain() {
                 if let Some(env_vars) = self.env_vars.get_mut(&overlay_name) {
@@ -285,6 +307,7 @@ impl EngineState {
                             let mut new_record = v.clone();
                             let (config, error) = new_record.into_config(&self.config);
                             self.config = config;
+                            config_updated = true;
                             env_vars.insert(k, new_record);
                             if let Some(e) = error {
                                 return Err(e);
@@ -303,6 +326,12 @@ impl EngineState {
         // TODO: better error
         std::env::set_current_dir(cwd)?;
 
+        if config_updated {
+            // Make plugin GC config changes take effect immediately.
+            #[cfg(feature = "plugin")]
+            self.update_plugin_gc_configs(&self.config.plugin_gc);
+        }
+
         Ok(())
     }
 
@@ -465,6 +494,11 @@ impl EngineState {
         None
     }
 
+    #[cfg(feature = "plugin")]
+    pub fn plugins(&self) -> &[Arc<dyn RegisteredPlugin>] {
+        &self.plugins
+    }
+
     #[cfg(feature = "plugin")]
     pub fn update_plugin_file(&self) -> Result<(), ShellError> {
         use std::io::Write;
@@ -490,8 +524,9 @@ 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, shell) = decl.is_plugin().expect("plugin should have file name");
-                    let mut file_name = path
+                    let identity = decl.plugin_identity().expect("plugin should have identity");
+                    let mut file_name = identity
+                        .filename()
                         .to_str()
                         .expect("path was checked during registration as a str")
                         .to_string();
@@ -518,8 +553,8 @@ impl EngineState {
                     serde_json::to_string_pretty(&sig_with_examples)
                         .map(|signature| {
                             // Extracting the possible path to the shell used to load the plugin
-                            let shell_str = shell
-                                .as_ref()
+                            let shell_str = identity
+                                .shell()
                                 .map(|path| {
                                     format!(
                                         "-s {}",
@@ -558,6 +593,14 @@ impl EngineState {
             })
     }
 
+    /// Update plugins with new garbage collection config
+    #[cfg(feature = "plugin")]
+    fn update_plugin_gc_configs(&self, plugin_gc: &crate::PluginGcConfigs) {
+        for plugin in &self.plugins {
+            plugin.set_gc_config(plugin_gc.get(plugin.identity().name()));
+        }
+    }
+
     pub fn num_files(&self) -> usize {
         self.files.len()
     }
@@ -650,7 +693,7 @@ impl EngineState {
         let mut unique_plugin_decls = HashMap::new();
 
         // Make sure there are no duplicate decls: Newer one overwrites the older one
-        for decl in self.decls.iter().filter(|d| d.is_plugin().is_some()) {
+        for decl in self.decls.iter().filter(|d| d.is_plugin()) {
             unique_plugin_decls.insert(decl.name(), decl);
         }
 
@@ -733,6 +776,12 @@ impl EngineState {
     }
 
     pub fn set_config(&mut self, conf: Config) {
+        #[cfg(feature = "plugin")]
+        if conf.plugin_gc != self.config.plugin_gc {
+            // Make plugin GC config changes take effect immediately.
+            self.update_plugin_gc_configs(&conf.plugin_gc);
+        }
+
         self.config = conf;
     }
 
@@ -841,7 +890,7 @@ impl EngineState {
                 (
                     signature,
                     decl.examples(),
-                    decl.is_plugin().is_some(),
+                    decl.is_plugin(),
                     decl.get_block_id().is_some(),
                     decl.is_parser_keyword(),
                 )

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

@@ -2,6 +2,12 @@ use super::{usage::Usage, Command, EngineState, OverlayFrame, ScopeFrame, Virtua
 use crate::ast::Block;
 use crate::{Module, Variable};
 
+#[cfg(feature = "plugin")]
+use std::sync::Arc;
+
+#[cfg(feature = "plugin")]
+use crate::RegisteredPlugin;
+
 /// A delta (or change set) between the current global state and a possible future global state. Deltas
 /// can be applied to the global state to update it to contain both previous state and the state held
 /// within the delta.
@@ -17,6 +23,8 @@ pub struct StateDelta {
     pub scope: Vec<ScopeFrame>,
     #[cfg(feature = "plugin")]
     pub(super) plugins_changed: bool, // marks whether plugin file should be updated
+    #[cfg(feature = "plugin")]
+    pub(super) plugins: Vec<Arc<dyn RegisteredPlugin>>,
 }
 
 impl StateDelta {
@@ -40,6 +48,8 @@ impl StateDelta {
             usage: Usage::new(),
             #[cfg(feature = "plugin")]
             plugins_changed: false,
+            #[cfg(feature = "plugin")]
+            plugins: vec![],
         }
     }
 

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

@@ -11,6 +11,12 @@ use core::panic;
 use std::collections::{HashMap, HashSet};
 use std::path::PathBuf;
 
+#[cfg(feature = "plugin")]
+use std::sync::Arc;
+
+#[cfg(feature = "plugin")]
+use crate::{PluginIdentity, RegisteredPlugin};
+
 /// A temporary extension to the global state. This handles bridging between the global state and the
 /// additional declarations and scope changes that are not yet part of the global scope.
 ///
@@ -155,6 +161,28 @@ impl<'a> StateWorkingSet<'a> {
         self.delta.plugins_changed = true;
     }
 
+    #[cfg(feature = "plugin")]
+    pub fn find_or_create_plugin(
+        &mut self,
+        identity: &PluginIdentity,
+        make: impl FnOnce() -> Arc<dyn RegisteredPlugin>,
+    ) -> Arc<dyn RegisteredPlugin> {
+        // Check in delta first, then permanent_state
+        if let Some(plugin) = self
+            .delta
+            .plugins
+            .iter()
+            .chain(self.permanent_state.plugins())
+            .find(|p| p.identity() == identity)
+        {
+            plugin.clone()
+        } else {
+            let plugin = make();
+            self.delta.plugins.push(plugin.clone());
+            plugin
+        }
+    }
+
     pub fn merge_predecl(&mut self, name: &[u8]) -> Option<DeclId> {
         self.move_predecls_to_overlay();