Deprecate register and add plugin use (#12607)

# Description

Adds a new keyword, `plugin use`. Unlike `register`, this merely loads
the signatures from the plugin cache file. The file is configurable with
the `--plugin-config` option either to `nu` or to `plugin use` itself,
just like the other `plugin` family of commands. At the REPL, one might
do this to replace `register`:

```nushell
> plugin add ~/.cargo/bin/nu_plugin_foo
> plugin use foo
```

This will not work in a script, because `plugin use` is a keyword and
`plugin add` does not evaluate at parse time (intentionally). This means
we no longer run random binaries during parse.

The `--plugins` option has been added to allow running `nu` with certain
plugins in one step. This is used especially for the `nu_with_plugins!`
test macro, but I'd imagine is generally useful. The only weird quirk is
that it has to be a list, and we don't really do this for any of our
other CLI args at the moment.

`register` now prints a deprecation parse warning.

This should fix #11923, as we now have a complete alternative to
`register`.

# User-Facing Changes

- Add `plugin use` command
- Deprecate `register`
- Add `--plugins` option to `nu` to replace a common use of `register`

# Tests + Formatting

I think I've tested it thoroughly enough and every existing test passes.
Testing nu CLI options and alternate config files is a little hairy and
I wish there were some more generic helpers for this, so this will go on
my TODO list for refactoring.

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

- [ ] Update plugins sections of book
- [ ] Release notes

crates/nu-cmd-plugin/src/commands/plugin/add.rs

@@ -54,7 +54,7 @@ apparent the next time `nu` is next launched with that plugin cache file.
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["plugin", "add", "register", "load", "signature"]
+        vec!["load", "register", "signature"]
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-cmd-plugin/src/commands/plugin/list.rs

@@ -29,6 +29,10 @@ impl Command for PluginList {
         "List installed plugins."
     }
 
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["scope"]
+    }
+
     fn examples(&self) -> Vec<nu_protocol::Example> {
         vec![
             Example {

crates/nu-cmd-plugin/src/commands/plugin/mod.rs

@@ -4,11 +4,13 @@ mod add;
 mod list;
 mod rm;
 mod stop;
+mod use_;
 
 pub use add::PluginAdd;
 pub use list::PluginList;
 pub use rm::PluginRm;
 pub use stop::PluginStop;
+pub use use_::PluginUse;
 
 #[derive(Clone)]
 pub struct PluginCommand;
@@ -28,10 +30,6 @@ impl Command for PluginCommand {
         "Commands for managing plugins."
     }
 
-    fn extra_usage(&self) -> &str {
-        "To load a plugin, see `register`."
-    }
-
     fn run(
         &self,
         engine_state: &EngineState,
@@ -54,6 +52,20 @@ impl Command for PluginCommand {
 
     fn examples(&self) -> Vec<Example> {
         vec![
+            Example {
+                example: "plugin add nu_plugin_inc",
+                description: "Run the `nu_plugin_inc` plugin from the current directory and install its signatures.",
+                result: None,
+            },
+            Example {
+                example: "plugin use inc",
+                description: "
+Load (or reload) the `inc` plugin from the plugin cache file and put its commands in scope.
+The plugin must already be in the cache file at parse time.
+"
+                .trim(),
+                result: None,
+            },
             Example {
                 example: "plugin list",
                 description: "List installed plugins",
@@ -64,11 +76,6 @@ impl Command for PluginCommand {
                 description: "Stop the plugin named `inc`.",
                 result: None,
             },
-            Example {
-                example: "plugin add nu_plugin_inc",
-                description: "Run the `nu_plugin_inc` plugin from the current directory and install its signatures.",
-                result: None,
-            },
             Example {
                 example: "plugin rm inc",
                 description: "Remove the installed signatures for the `inc` plugin.",

crates/nu-cmd-plugin/src/commands/plugin/rm.rs

@@ -51,7 +51,7 @@ fixed with `plugin add`.
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["plugin", "rm", "remove", "delete", "signature"]
+        vec!["remove", "delete", "signature"]
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-cmd-plugin/src/commands/plugin/use_.rs

@@ -0,0 +1,81 @@
+use nu_engine::command_prelude::*;
+
+#[derive(Clone)]
+pub struct PluginUse;
+
+impl Command for PluginUse {
+    fn name(&self) -> &str {
+        "plugin use"
+    }
+
+    fn usage(&self) -> &str {
+        "Load a plugin from the plugin cache file into scope."
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build(self.name())
+            .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .named(
+                "plugin-config",
+                SyntaxShape::Filepath,
+                "Use a plugin cache file other than the one set in `$nu.plugin-path`",
+                None,
+            )
+            .required(
+                "name",
+                SyntaxShape::String,
+                "The name of the plugin to load (not the filename)",
+            )
+            .category(Category::Plugin)
+    }
+
+    fn extra_usage(&self) -> &str {
+        r#"
+This command is a parser keyword. For details, check:
+  https://www.nushell.sh/book/thinking_in_nu.html
+
+The plugin definition must be available in the plugin cache file at parse time.
+Run `plugin add` first in the REPL to do this, or from a script consider
+preparing a plugin cache file and passing `--plugin-config`, or using the
+`--plugin` option to `nu` instead.
+
+If the plugin was already loaded, this will reload the latest definition from
+the cache file into scope.
+"#
+        .trim()
+    }
+
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["add", "register", "scope"]
+    }
+
+    fn is_parser_keyword(&self) -> bool {
+        true
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        _call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        Ok(PipelineData::empty())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Load the commands for the `query` plugin from $nu.plugin-path",
+                example: r#"plugin use query"#,
+                result: None,
+            },
+            Example {
+                description:
+                    "Load the commands for the `query` plugin from a custom plugin cache file",
+                example: r#"plugin use --plugin-config local-plugins.msgpackz query"#,
+                result: None,
+            },
+        ]
+    }
+}

crates/nu-cmd-plugin/src/commands/register.rs

@@ -35,12 +35,17 @@ impl Command for Register {
     }
 
     fn extra_usage(&self) -> &str {
-        r#"This command is a parser keyword. For details, check:
-  https://www.nushell.sh/book/thinking_in_nu.html"#
+        r#"
+Deprecated in favor of `plugin add` and `plugin use`.
+
+This command is a parser keyword. For details, check:
+  https://www.nushell.sh/book/thinking_in_nu.html
+"#
+        .trim()
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["plugin", "add", "register"]
+        vec!["add"]
     }
 
     fn is_parser_keyword(&self) -> bool {

crates/nu-cmd-plugin/src/default_context.rs

@@ -12,11 +12,12 @@ pub fn add_plugin_command_context(mut engine_state: EngineState) -> EngineState
         }
 
         bind_command!(
-            PluginCommand,
             PluginAdd,
+            PluginCommand,
             PluginList,
             PluginRm,
             PluginStop,
+            PluginUse,
             Register,
         );
 

crates/nu-command/tests/format_conversions/nuon.rs

@@ -479,5 +479,5 @@ fn read_code_should_fail_rather_than_panic() {
     let actual = nu!(cwd: "tests/fixtures/formats", pipeline(
         r#"open code.nu | from nuon"#
     ));
-    assert!(actual.err.contains("error when parsing"))
+    assert!(actual.err.contains("Error when loading"))
 }

crates/nu-parser/src/parse_keywords.rs

@@ -71,6 +71,7 @@ pub const UNALIASABLE_PARSER_KEYWORDS: &[&[u8]] = &[
     b"source",
     b"where",
     b"register",
+    b"plugin use",
 ];
 
 /// Check whether spans start with a parser keyword that can be aliased
@@ -93,11 +94,14 @@ pub fn is_unaliasable_parser_keyword(working_set: &StateWorkingSet, spans: &[Spa
 /// This is a new more compact method of calling parse_xxx() functions without repeating the
 /// parse_call() in each function. Remaining keywords can be moved here.
 pub fn parse_keyword(working_set: &mut StateWorkingSet, lite_command: &LiteCommand) -> Pipeline {
+    let orig_parse_errors_len = working_set.parse_errors.len();
+
     let call_expr = parse_call(working_set, &lite_command.parts, lite_command.parts[0]);
 
-    // if err.is_some() {
-    //     return (Pipeline::from_vec(vec![call_expr]), err);
-    // }
+    // If an error occurred, don't invoke the keyword-specific functionality
+    if working_set.parse_errors.len() > orig_parse_errors_len {
+        return Pipeline::from_vec(vec![call_expr]);
+    }
 
     if let Expression {
         expr: Expr::Call(call),
@@ -121,6 +125,8 @@ pub fn parse_keyword(working_set: &mut StateWorkingSet, lite_command: &LiteComma
             "overlay hide" => parse_overlay_hide(working_set, call),
             "overlay new" => parse_overlay_new(working_set, call),
             "overlay use" => parse_overlay_use(working_set, call),
+            #[cfg(feature = "plugin")]
+            "plugin use" => parse_plugin_use(working_set, call),
             _ => Pipeline::from_vec(vec![call_expr]),
         }
     } else {
@@ -1946,7 +1952,7 @@ pub fn parse_module_file_or_dir(
     let cwd = working_set.get_cwd();
 
     let module_path =
-        if let Some(path) = find_in_dirs(&module_path_str, working_set, &cwd, LIB_DIRS_VAR) {
+        if let Some(path) = find_in_dirs(&module_path_str, working_set, &cwd, Some(LIB_DIRS_VAR)) {
             path
         } else {
             working_set.error(ParseError::ModuleNotFound(path_span, module_path_str));
@@ -3402,7 +3408,7 @@ pub fn parse_source(working_set: &mut StateWorkingSet, lite_command: &LiteComman
                     }
                 };
 
-                if let Some(path) = find_in_dirs(&filename, working_set, &cwd, LIB_DIRS_VAR) {
+                if let Some(path) = find_in_dirs(&filename, working_set, &cwd, Some(LIB_DIRS_VAR)) {
                     if let Some(contents) = path.read(working_set) {
                         // Add the file to the stack of files being processed.
                         if let Err(e) = working_set.files.push(path.clone().path_buf(), spans[1]) {
@@ -3546,11 +3552,13 @@ pub fn parse_where(working_set: &mut StateWorkingSet, lite_command: &LiteCommand
     }
 }
 
+/// `register` is deprecated and will be removed in 0.94. Use `plugin add` and `plugin use` instead.
 #[cfg(feature = "plugin")]
 pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteCommand) -> Pipeline {
-    use nu_plugin::{get_signature, PersistentPlugin, PluginDeclaration};
+    use nu_plugin::{get_signature, PluginDeclaration};
     use nu_protocol::{
-        engine::Stack, ErrSpan, PluginCacheItem, PluginIdentity, PluginSignature, RegisteredPlugin,
+        engine::Stack, ErrSpan, ParseWarning, PluginCacheItem, PluginIdentity, PluginSignature,
+        RegisteredPlugin,
     };
 
     let spans = &lite_command.parts;
@@ -3561,7 +3569,7 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
     // Maybe this is not necessary but it is a sanity check
     if working_set.get_span_contents(spans[0]) != b"register" {
         working_set.error(ParseError::UnknownState(
-            "internal error: Wrong call name for parse plugin function".into(),
+            "internal error: Wrong call name for 'register' function".into(),
             span(spans),
         ));
         return garbage_pipeline(spans);
@@ -3609,6 +3617,16 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
         }
     };
 
+    // Now that the call is parsed, add the deprecation warning
+    working_set
+        .parse_warnings
+        .push(ParseWarning::DeprecatedWarning {
+            old_command: "register".into(),
+            new_suggestion: "use `plugin add` and `plugin use`".into(),
+            span: call.head,
+            url: "https://www.nushell.sh/book/plugins.html".into(),
+        });
+
     // Extracting the required arguments from the call and keeping them together in a tuple
     let arguments = call
         .positional_nth(0)
@@ -3619,7 +3637,8 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
                 .coerce_into_string()
                 .map_err(|err| err.wrap(working_set, call.head))?;
 
-            let Some(path) = find_in_dirs(&filename, working_set, &cwd, PLUGIN_DIRS_VAR) else {
+            let Some(path) = find_in_dirs(&filename, working_set, &cwd, Some(PLUGIN_DIRS_VAR))
+            else {
                 return Err(ParseError::RegisteredFileNotFound(filename, expr.span));
             };
 
@@ -3695,27 +3714,8 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
         // Create the plugin identity. This validates that the plugin name starts with `nu_plugin_`
         let identity = PluginIdentity::new(path, shell).err_span(path_span)?;
 
-        // Find garbage collection config
-        let gc_config = working_set
-            .get_config()
-            .plugin_gc
-            .get(identity.name())
-            .clone();
-
-        // Add it to the working set
-        let plugin = working_set.find_or_create_plugin(&identity, || {
-            Arc::new(PersistentPlugin::new(identity.clone(), gc_config.clone()))
-        });
-
-        // Downcast the plugin to `PersistentPlugin` - we generally expect this to succeed. The
-        // trait object only exists so that nu-protocol can contain plugins without knowing anything
-        // about their implementation, but we only use `PersistentPlugin` in practice.
-        let plugin: Arc<PersistentPlugin> = plugin.as_any().downcast().map_err(|_| {
-            ParseError::InternalError(
-                "encountered unexpected RegisteredPlugin type".into(),
-                spans[0],
-            )
-        })?;
+        let plugin = nu_plugin::add_plugin_to_working_set(working_set, &identity)
+            .map_err(|err| err.wrap(working_set, call.head))?;
 
         let signatures = signature.map_or_else(
             || {
@@ -3731,8 +3731,6 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
                     )
                 })?;
 
-                plugin.set_gc_config(&gc_config);
-
                 let signatures = get_signature(plugin.clone(), get_envs).map_err(|err| {
                     log::warn!("Error getting signatures: {err:?}");
                     ParseError::LabeledError(
@@ -3776,6 +3774,100 @@ pub fn parse_register(working_set: &mut StateWorkingSet, lite_command: &LiteComm
     }])
 }
 
+#[cfg(feature = "plugin")]
+pub fn parse_plugin_use(working_set: &mut StateWorkingSet, call: Box<Call>) -> Pipeline {
+    use nu_protocol::{FromValue, PluginCacheFile};
+
+    let cwd = working_set.get_cwd();
+
+    if let Err(err) = (|| {
+        let name = call
+            .positional_nth(0)
+            .map(|expr| {
+                eval_constant(working_set, expr)
+                    .and_then(Spanned::<String>::from_value)
+                    .map_err(|err| err.wrap(working_set, call.head))
+            })
+            .expect("required positional should have been checked")?;
+
+        let plugin_config = call
+            .named_iter()
+            .find(|(arg_name, _, _)| arg_name.item == "plugin-config")
+            .map(|(_, _, expr)| {
+                let expr = expr
+                    .as_ref()
+                    .expect("--plugin-config arg should have been checked already");
+                eval_constant(working_set, expr)
+                    .and_then(Spanned::<String>::from_value)
+                    .map_err(|err| err.wrap(working_set, call.head))
+            })
+            .transpose()?;
+
+        // Find the actual plugin config path location. We don't have a const/env variable for this,
+        // it either lives in the current working directory or in the script's directory
+        let plugin_config_path = if let Some(custom_path) = &plugin_config {
+            find_in_dirs(&custom_path.item, working_set, &cwd, None).ok_or_else(|| {
+                ParseError::FileNotFound(custom_path.item.clone(), custom_path.span)
+            })?
+        } else {
+            ParserPath::RealPath(
+                working_set
+                    .permanent_state
+                    .plugin_path
+                    .as_ref()
+                    .ok_or_else(|| ParseError::LabeledErrorWithHelp {
+                        error: "Plugin cache file not set".into(),
+                        label: "can't load plugin without cache file".into(),
+                        span: call.head,
+                        help:
+                            "pass --plugin-config to `plugin use` when $nu.plugin-path is not set"
+                                .into(),
+                    })?
+                    .to_owned(),
+            )
+        };
+
+        let file = plugin_config_path.open(working_set).map_err(|err| {
+            ParseError::LabeledError(
+                "Plugin cache file can't be opened".into(),
+                err.to_string(),
+                plugin_config.as_ref().map(|p| p.span).unwrap_or(call.head),
+            )
+        })?;
+
+        // The file is now open, so we just have to parse the contents and find the plugin
+        let contents = PluginCacheFile::read_from(file, Some(call.head))
+            .map_err(|err| err.wrap(working_set, call.head))?;
+
+        let plugin_item = contents
+            .plugins
+            .iter()
+            .find(|plugin| plugin.name == name.item)
+            .ok_or_else(|| ParseError::PluginNotFound {
+                name: name.item.clone(),
+                name_span: name.span,
+                plugin_config_span: plugin_config.as_ref().map(|p| p.span),
+            })?;
+
+        // Now add the signatures to the working set
+        nu_plugin::load_plugin_cache_item(working_set, plugin_item, Some(call.head))
+            .map_err(|err| err.wrap(working_set, call.head))?;
+
+        Ok(())
+    })() {
+        working_set.error(err);
+    }
+
+    let call_span = call.span();
+
+    Pipeline::from_vec(vec![Expression {
+        expr: Expr::Call(call),
+        span: call_span,
+        ty: Type::Nothing,
+        custom_completion: None,
+    }])
+}
+
 pub fn find_dirs_var(working_set: &StateWorkingSet, var_name: &str) -> Option<VarId> {
     working_set
         .find_variable(format!("${}", var_name).as_bytes())
@@ -3799,13 +3891,13 @@ pub fn find_in_dirs(
     filename: &str,
     working_set: &StateWorkingSet,
     cwd: &str,
-    dirs_var_name: &str,
+    dirs_var_name: Option<&str>,
 ) -> Option<ParserPath> {
     pub fn find_in_dirs_with_id(
         filename: &str,
         working_set: &StateWorkingSet,
         cwd: &str,
-        dirs_var_name: &str,
+        dirs_var_name: Option<&str>,
     ) -> Option<ParserPath> {
         // Choose whether to use file-relative or PWD-relative path
         let actual_cwd = working_set
@@ -3845,8 +3937,10 @@ pub fn find_in_dirs(
         }
 
         // Look up relative path from NU_LIB_DIRS
-        working_set
-            .get_variable(find_dirs_var(working_set, dirs_var_name)?)
+        dirs_var_name
+            .as_ref()
+            .and_then(|dirs_var_name| find_dirs_var(working_set, dirs_var_name))
+            .map(|var_id| working_set.get_variable(var_id))?
             .const_val
             .as_ref()?
             .as_list()
@@ -3868,7 +3962,7 @@ pub fn find_in_dirs(
         filename: &str,
         working_set: &StateWorkingSet,
         cwd: &str,
-        dirs_env: &str,
+        dirs_env: Option<&str>,
     ) -> Option<PathBuf> {
         // Choose whether to use file-relative or PWD-relative path
         let actual_cwd = working_set
@@ -3882,7 +3976,9 @@ pub fn find_in_dirs(
             let path = Path::new(filename);
 
             if path.is_relative() {
-                if let Some(lib_dirs) = working_set.get_env_var(dirs_env) {
+                if let Some(lib_dirs) =
+                    dirs_env.and_then(|dirs_env| working_set.get_env_var(dirs_env))
+                {
                     if let Ok(dirs) = lib_dirs.as_list() {
                         for lib_dir in dirs {
                             if let Ok(dir) = lib_dir.to_path() {

crates/nu-parser/src/parser.rs

@@ -5149,12 +5149,24 @@ pub fn parse_expression(working_set: &mut StateWorkingSet, spans: &[Span]) -> Ex
             #[cfg(feature = "plugin")]
             b"register" => {
                 working_set.error(ParseError::BuiltinCommandInPipeline(
-                    "plugin".into(),
+                    "register".into(),
                     spans[0],
                 ));
 
                 parse_call(working_set, &spans[pos..], spans[0])
             }
+            #[cfg(feature = "plugin")]
+            b"plugin" => {
+                if spans.len() > 1 && working_set.get_span_contents(spans[1]) == b"use" {
+                    // only 'plugin use' is banned
+                    working_set.error(ParseError::BuiltinCommandInPipeline(
+                        "plugin use".into(),
+                        spans[0],
+                    ));
+                }
+
+                parse_call(working_set, &spans[pos..], spans[0])
+            }
 
             _ => parse_call(working_set, &spans[pos..], spans[0]),
         }
@@ -5286,6 +5298,20 @@ pub fn parse_builtin_commands(
         b"where" => parse_where(working_set, lite_command),
         #[cfg(feature = "plugin")]
         b"register" => parse_register(working_set, lite_command),
+        // Only "plugin use" is a keyword
+        #[cfg(feature = "plugin")]
+        b"plugin"
+            if lite_command
+                .parts
+                .get(1)
+                .is_some_and(|span| working_set.get_span_contents(*span) == b"use") =>
+        {
+            if let Some(redirection) = lite_command.redirection.as_ref() {
+                working_set.error(redirecting_builtin_error("plugin use", redirection));
+                return garbage_pipeline(&lite_command.parts);
+            }
+            parse_keyword(working_set, lite_command)
+        }
         _ => {
             let element = parse_pipeline_element(working_set, lite_command);
 

crates/nu-parser/src/parser_path.rs

@@ -103,17 +103,33 @@ impl ParserPath {
         }
     }
 
-    pub fn read<'a>(&'a self, working_set: &'a StateWorkingSet) -> Option<Vec<u8>> {
+    pub fn open<'a>(
+        &'a self,
+        working_set: &'a StateWorkingSet,
+    ) -> std::io::Result<Box<dyn std::io::Read + 'a>> {
         match self {
-            ParserPath::RealPath(p) => std::fs::read(p).ok(),
+            ParserPath::RealPath(p) => {
+                std::fs::File::open(p).map(|f| Box::new(f) as Box<dyn std::io::Read>)
+            }
             ParserPath::VirtualFile(_, file_id) => working_set
                 .get_contents_of_file(*file_id)
-                .map(|bytes| bytes.to_vec()),
+                .map(|bytes| Box::new(bytes) as Box<dyn std::io::Read>)
+                .ok_or(std::io::ErrorKind::NotFound.into()),
 
-            ParserPath::VirtualDir(..) => None,
+            ParserPath::VirtualDir(..) => Err(std::io::ErrorKind::NotFound.into()),
         }
     }
 
+    pub fn read<'a>(&'a self, working_set: &'a StateWorkingSet) -> Option<Vec<u8>> {
+        self.open(working_set)
+            .and_then(|mut reader| {
+                let mut vec = vec![];
+                reader.read_to_end(&mut vec)?;
+                Ok(vec)
+            })
+            .ok()
+    }
+
     pub fn from_virtual_path(
         working_set: &StateWorkingSet,
         name: &str,

crates/nu-plugin/src/lib.rs

@@ -78,10 +78,11 @@ pub use serializers::{json::JsonSerializer, msgpack::MsgPackSerializer};
 // Used by other nu crates.
 #[doc(hidden)]
 pub use plugin::{
-    create_plugin_signature, get_signature, load_plugin_cache_item, load_plugin_file,
-    serve_plugin_io, EngineInterfaceManager, GetPlugin, Interface, InterfaceManager,
-    PersistentPlugin, PluginDeclaration, PluginExecutionCommandContext, PluginExecutionContext,
-    PluginInterface, PluginInterfaceManager, PluginSource, ServePluginError,
+    add_plugin_to_working_set, create_plugin_signature, get_signature, load_plugin_cache_item,
+    load_plugin_file, serve_plugin_io, EngineInterfaceManager, GetPlugin, Interface,
+    InterfaceManager, PersistentPlugin, PluginDeclaration, PluginExecutionCommandContext,
+    PluginExecutionContext, PluginInterface, PluginInterfaceManager, PluginSource,
+    ServePluginError,
 };
 #[doc(hidden)]
 pub use protocol::{PluginCustomValue, PluginInput, PluginOutput};

crates/nu-plugin/src/plugin/interface/plugin.rs

@@ -748,9 +748,9 @@ impl PluginInterface {
                     PluginCall::CustomValueOp(val, _) => Some(val.span),
                 },
                 help: Some(format!(
-                    "the plugin may have experienced an error. Try registering the plugin again \
+                    "the plugin may have experienced an error. Try loading the plugin again \
                         with `{}`",
-                    self.state.source.identity.register_command(),
+                    self.state.source.identity.use_command(),
                 )),
                 inner: vec![],
             })?;

crates/nu-plugin/src/plugin/mod.rs

@@ -25,7 +25,7 @@ use nu_engine::documentation::get_flags_section;
 use nu_protocol::{
     ast::Operator, engine::StateWorkingSet, report_error_new, CustomValue, IntoSpanned,
     LabeledError, PipelineData, PluginCacheFile, PluginCacheItem, PluginCacheItemData,
-    PluginIdentity, PluginSignature, ShellError, Span, Spanned, Value,
+    PluginIdentity, PluginSignature, RegisteredPlugin, ShellError, Span, Spanned, Value,
 };
 use thiserror::Error;
 
@@ -942,7 +942,7 @@ pub fn load_plugin_cache_item(
     working_set: &mut StateWorkingSet,
     plugin: &PluginCacheItem,
     span: Option<Span>,
-) -> Result<(), ShellError> {
+) -> Result<Arc<PersistentPlugin>, ShellError> {
     let identity =
         PluginIdentity::new(plugin.filename.clone(), plugin.shell.clone()).map_err(|_| {
             ShellError::GenericError {
@@ -960,39 +960,54 @@ pub fn load_plugin_cache_item(
 
     match &plugin.data {
         PluginCacheItemData::Valid { commands } => {
-            // Find garbage collection config for the plugin
-            let gc_config = working_set
-                .get_config()
-                .plugin_gc
-                .get(identity.name())
-                .clone();
+            let plugin = add_plugin_to_working_set(working_set, &identity)?;
 
-            // Add it to / get it from the working set
-            let plugin = working_set.find_or_create_plugin(&identity, || {
-                Arc::new(PersistentPlugin::new(identity.clone(), gc_config.clone()))
-            });
-
-            // Downcast the plugin to `PersistentPlugin` - we generally expect this to succeed.
-            // The trait object only exists so that nu-protocol can contain plugins without knowing
-            // anything about their implementation, but we only use `PersistentPlugin` in practice.
-            let plugin: Arc<PersistentPlugin> =
-                plugin
-                    .as_any()
-                    .downcast()
-                    .map_err(|_| ShellError::NushellFailed {
-                        msg: "encountered unexpected RegisteredPlugin type".into(),
-                    })?;
+            // Ensure that the plugin is reset. We're going to load new signatures, so we want to
+            // make sure the running plugin reflects those new signatures, and it's possible that it
+            // doesn't.
+            plugin.reset()?;
 
             // Create the declarations from the commands
             for signature in commands {
                 let decl = PluginDeclaration::new(plugin.clone(), signature.clone());
                 working_set.add_decl(Box::new(decl));
             }
-            Ok(())
+            Ok(plugin)
         }
         PluginCacheItemData::Invalid => Err(ShellError::PluginCacheDataInvalid {
             plugin_name: identity.name().to_owned(),
-            register_command: identity.register_command(),
+            span,
+            add_command: identity.add_command(),
         }),
     }
 }
+
+#[doc(hidden)]
+pub fn add_plugin_to_working_set(
+    working_set: &mut StateWorkingSet,
+    identity: &PluginIdentity,
+) -> Result<Arc<PersistentPlugin>, ShellError> {
+    // Find garbage collection config for the plugin
+    let gc_config = working_set
+        .get_config()
+        .plugin_gc
+        .get(identity.name())
+        .clone();
+
+    // Add it to / get it from the working set
+    let plugin = working_set.find_or_create_plugin(identity, || {
+        Arc::new(PersistentPlugin::new(identity.clone(), gc_config.clone()))
+    });
+
+    plugin.set_gc_config(&gc_config);
+
+    // Downcast the plugin to `PersistentPlugin` - we generally expect this to succeed.
+    // The trait object only exists so that nu-protocol can contain plugins without knowing
+    // anything about their implementation, but we only use `PersistentPlugin` in practice.
+    plugin
+        .as_any()
+        .downcast()
+        .map_err(|_| ShellError::NushellFailed {
+            msg: "encountered unexpected RegisteredPlugin type".into(),
+        })
+}

crates/nu-protocol/src/ast/expression.rs

@@ -108,6 +108,13 @@ impl Expression {
         }
     }
 
+    pub fn as_filepath(&self) -> Option<(String, bool)> {
+        match &self.expr {
+            Expr::Filepath(string, quoted) => Some((string.clone(), *quoted)),
+            _ => None,
+        }
+    }
+
     pub fn as_import_pattern(&self) -> Option<ImportPattern> {
         match &self.expr {
             Expr::ImportPattern(pattern) => Some(*pattern.clone()),

crates/nu-protocol/src/errors/parse_error.rs

@@ -439,6 +439,19 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::file_not_found))]
     FileNotFound(String, #[label("File not found: {0}")] Span),
 
+    #[error("Plugin not found")]
+    #[diagnostic(
+        code(nu::parser::plugin_not_found),
+        help("plugins need to be added to the plugin cache file before your script is run (see `plugin add`)"),
+    )]
+    PluginNotFound {
+        name: String,
+        #[label("Plugin not found: {name}")]
+        name_span: Span,
+        #[label("in this cache file")]
+        plugin_config_span: Option<Span>,
+    },
+
     #[error("Invalid literal")] // <problem> in <entity>.
     #[diagnostic()]
     InvalidLiteral(String, String, #[label("{0} in {1}")] Span),
@@ -544,6 +557,7 @@ impl ParseError {
             ParseError::SourcedFileNotFound(_, s) => *s,
             ParseError::RegisteredFileNotFound(_, s) => *s,
             ParseError::FileNotFound(_, s) => *s,
+            ParseError::PluginNotFound { name_span, .. } => *name_span,
             ParseError::LabeledError(_, _, s) => *s,
             ParseError::ShellAndAnd(s) => *s,
             ParseError::ShellOrOr(s) => *s,

crates/nu-protocol/src/errors/parse_warning.rs

@@ -5,19 +5,21 @@ use thiserror::Error;
 
 #[derive(Clone, Debug, Error, Diagnostic, Serialize, Deserialize)]
 pub enum ParseWarning {
-    #[error("Deprecated: {0}")]
-    DeprecatedWarning(
-        String,
-        String,
-        #[label = "`{0}` is deprecated and will be removed in 0.90. Please use `{1}` instead, more info: https://www.nushell.sh/book/custom_commands.html"]
-        Span,
-    ),
+    #[error("Deprecated: {old_command}")]
+    #[diagnostic(help("for more info: {url}"))]
+    DeprecatedWarning {
+        old_command: String,
+        new_suggestion: String,
+        #[label("`{old_command}` is deprecated and will be removed in 0.94. Please {new_suggestion} instead")]
+        span: Span,
+        url: String,
+    },
 }
 
 impl ParseWarning {
     pub fn span(&self) -> Span {
         match self {
-            ParseWarning::DeprecatedWarning(_, _, s) => *s,
+            ParseWarning::DeprecatedWarning { span, .. } => *span,
         }
     }
 }

crates/nu-protocol/src/errors/shell_error.rs

@@ -750,17 +750,19 @@ pub enum ShellError {
         span: Span,
     },
 
-    /// The cached plugin data (in `$nu.plugin-path`) for a plugin is invalid.
+    /// The cached plugin data for a plugin is invalid.
     ///
     /// ## Resolution
     ///
-    /// `register` the plugin again to update the data, or remove it.
+    /// `plugin add` the plugin again to update the data, or remove it with `plugin rm`.
     #[error("The cached plugin data for `{plugin_name}` is invalid")]
     #[diagnostic(code(nu::shell::plugin_cache_data_invalid))]
     PluginCacheDataInvalid {
         plugin_name: String,
-        #[help("try registering the plugin again with `{}`")]
-        register_command: String,
+        #[label("plugin `{plugin_name}` loaded here")]
+        span: Option<Span>,
+        #[help("the format in the plugin cache file is not compatible with this version of Nushell.\n\nTry adding the plugin again with `{}`")]
+        add_command: String,
     },
 
     /// A plugin failed to load.

crates/nu-protocol/src/plugin/identity.rs

@@ -1,11 +1,10 @@
 use std::path::{Path, PathBuf};
 
-use crate::{ParseError, Spanned};
+use crate::{ParseError, ShellError, Spanned};
 
-/// Error when an invalid plugin filename was encountered. This can be converted to [`ParseError`]
-/// if a span is added.
+/// Error when an invalid plugin filename was encountered.
 #[derive(Debug, Clone)]
-pub struct InvalidPluginFilename;
+pub struct InvalidPluginFilename(PathBuf);
 
 impl std::fmt::Display for InvalidPluginFilename {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
@@ -23,6 +22,18 @@ impl From<Spanned<InvalidPluginFilename>> for ParseError {
     }
 }
 
+impl From<Spanned<InvalidPluginFilename>> for ShellError {
+    fn from(error: Spanned<InvalidPluginFilename>) -> ShellError {
+        ShellError::GenericError {
+            error: format!("Invalid plugin filename: {}", error.item.0.display()),
+            msg: "not a valid plugin filename".into(),
+            span: Some(error.span),
+            help: Some("valid Nushell plugin filenames must start with `nu_plugin_`".into()),
+            inner: vec![],
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct PluginIdentity {
     /// The filename used to start the plugin
@@ -35,17 +46,25 @@ pub struct PluginIdentity {
 
 impl PluginIdentity {
     /// Create a new plugin identity from a path to plugin executable and shell option.
+    ///
+    /// The `filename` must be an absolute path. Canonicalize before trying to construct the
+    /// [`PluginIdentity`].
     pub fn new(
         filename: impl Into<PathBuf>,
         shell: Option<PathBuf>,
     ) -> Result<PluginIdentity, InvalidPluginFilename> {
-        let filename = filename.into();
+        let filename: PathBuf = filename.into();
+
+        // Must pass absolute path.
+        if filename.is_relative() {
+            return Err(InvalidPluginFilename(filename));
+        }
 
         let name = filename
             .file_stem()
             .map(|stem| stem.to_string_lossy().into_owned())
             .and_then(|stem| stem.strip_prefix("nu_plugin_").map(|s| s.to_owned()))
-            .ok_or(InvalidPluginFilename)?;
+            .ok_or_else(|| InvalidPluginFilename(filename.clone()))?;
 
         Ok(PluginIdentity {
             filename,
@@ -89,30 +108,42 @@ impl PluginIdentity {
             .expect("fake plugin identity path is invalid")
     }
 
-    /// A command that could be used to register the plugin, for suggesting in errors.
-    pub fn register_command(&self) -> String {
+    /// A command that could be used to add the plugin, for suggesting in errors.
+    pub fn add_command(&self) -> String {
         if let Some(shell) = self.shell() {
             format!(
-                "register --shell '{}' '{}'",
+                "plugin add --shell '{}' '{}'",
                 shell.display(),
                 self.filename().display(),
             )
         } else {
-            format!("register '{}'", self.filename().display())
+            format!("plugin add '{}'", self.filename().display())
         }
     }
+
+    /// A command that could be used to reload the plugin, for suggesting in errors.
+    pub fn use_command(&self) -> String {
+        format!("plugin use '{}'", self.name())
+    }
 }
 
 #[test]
 fn parses_name_from_path() {
     assert_eq!("test", PluginIdentity::new_fake("test").name());
     assert_eq!("test_2", PluginIdentity::new_fake("test_2").name());
+    let absolute_path = if cfg!(windows) {
+        r"C:\path\to\nu_plugin_foo.sh"
+    } else {
+        "/path/to/nu_plugin_foo.sh"
+    };
     assert_eq!(
         "foo",
-        PluginIdentity::new("nu_plugin_foo.sh", Some("sh".into()))
+        PluginIdentity::new(absolute_path, Some("sh".into()))
             .expect("should be valid")
             .name()
     );
+    // Relative paths should be invalid
+    PluginIdentity::new("nu_plugin_foo.sh", Some("sh".into())).expect_err("should be invalid");
     PluginIdentity::new("other", None).expect_err("should be invalid");
     PluginIdentity::new("", None).expect_err("should be invalid");
 }

crates/nu-test-support/src/macros.rs

@@ -235,7 +235,6 @@ macro_rules! nu_with_plugins {
 
 use crate::{Outcome, NATIVE_PATH_ENV_VAR};
 use std::ffi::OsStr;
-use std::fmt::Write;
 use std::{
     path::Path,
     process::{Command, Stdio},
@@ -340,17 +339,17 @@ where
 
     crate::commands::ensure_plugins_built();
 
-    let registrations: String = plugins
+    let plugin_paths_quoted: Vec<String> = plugins
         .iter()
-        .fold(String::new(), |mut output, plugin_name| {
+        .map(|plugin_name| {
             let plugin = with_exe(plugin_name);
             let plugin_path = nu_path::canonicalize_with(&plugin, &test_bins)
                 .unwrap_or_else(|_| panic!("failed to canonicalize plugin {} path", &plugin));
             let plugin_path = plugin_path.to_string_lossy();
-            let _ = write!(output, "register {plugin_path};");
-            output
-        });
-    let commands = format!("{registrations}{command}");
+            escape_quote_string(plugin_path.into_owned())
+        })
+        .collect();
+    let plugins_arg = format!("[{}]", plugin_paths_quoted.join(","));
 
     let target_cwd = crate::fs::in_directory(&cwd);
     // In plugin testing, we need to use installed nushell to drive
@@ -362,13 +361,15 @@ where
     let process = match setup_command(&executable_path, &target_cwd)
         .envs(envs)
         .arg("--commands")
-        .arg(commands)
+        .arg(command)
         .arg("--config")
         .arg(temp_config_file)
         .arg("--env-config")
         .arg(temp_env_config_file)
         .arg("--plugin-config")
         .arg(temp_plugin_file)
+        .arg("--plugins")
+        .arg(plugins_arg)
         .stdout(Stdio::piped())
         .stderr(Stdio::piped())
         .spawn()