feat: enable simpler builtins implemented outside brush (#130)

brush-core/src/builtins.rs

@@ -56,8 +56,8 @@ mod unimp;
 mod unset;
 mod wait;
 
-pub use factory::builtin;
 pub(crate) use factory::get_default_builtins;
+pub use factory::{builtin, simple_builtin, SimpleCommand};
 
 /// Macro to define a struct that represents a shell built-in flag argument that can be
 /// enabled or disabled by specifying an option with a leading '+' or '-' character.
@@ -160,6 +160,14 @@ pub type CommandExecuteFunc = fn(
     Vec<commands::CommandArg>,
 ) -> BoxFuture<'_, Result<BuiltinResult, error::Error>>;
 
+/// Type of a function to retrieve help content for a built-in command.
+///
+/// # Arguments
+///
+/// * `name` - The name of the command.
+/// * `content_type` - The type of content to retrieve.
+pub type CommandContentFunc = fn(&str, ContentType) -> Result<String, error::Error>;
+
 /// Trait implemented by built-in shell commands.
 #[async_trait::async_trait]
 pub trait Command: Parser {
@@ -256,7 +264,7 @@ pub struct Registration {
     pub execute_func: CommandExecuteFunc,
 
     /// Function to retrieve the builtin's content/help text.
-    pub content_func: fn(&str, ContentType) -> Result<String, error::Error>,
+    pub content_func: CommandContentFunc,
 
     /// Has this registration been disabled?
     pub disabled: bool,

brush-core/src/builtins/factory.rs

@@ -9,6 +9,31 @@ use crate::builtins;
 use crate::commands::{self, CommandArg};
 use crate::error;
 
+/// A simple command that can be registered as a built-in.
+pub trait SimpleCommand {
+    /// Returns the content of the built-in command.
+    fn get_content(name: &str, content_type: builtins::ContentType)
+        -> Result<String, error::Error>;
+
+    /// Executes the built-in command.
+    fn execute(
+        context: commands::ExecutionContext<'_>,
+        args: &[&str],
+    ) -> Result<builtins::BuiltinResult, error::Error>;
+}
+
+/// Returns a built-in command registration, given an implementation of the
+/// `SimpleCommand` trait.
+pub fn simple_builtin<B: SimpleCommand + Send + Sync>() -> builtins::Registration {
+    builtins::Registration {
+        execute_func: exec_simple_builtin::<B>,
+        content_func: B::get_content,
+        disabled: false,
+        special_builtin: false,
+        declaration_builtin: false,
+    }
+}
+
 /// Returns a built-in command registration, given an implementation of the
 /// `Command` trait.
 pub fn builtin<B: builtins::Command + Send + Sync>() -> builtins::Registration {
@@ -58,6 +83,31 @@ fn get_builtin_content<T: builtins::Command + Send + Sync>(
     T::get_content(name, content_type)
 }
 
+fn exec_simple_builtin<T: SimpleCommand + Send + Sync>(
+    context: commands::ExecutionContext<'_>,
+    args: Vec<CommandArg>,
+) -> BoxFuture<'_, Result<builtins::BuiltinResult, error::Error>> {
+    Box::pin(async move { exec_simple_builtin_impl::<T>(context, args).await })
+}
+
+#[allow(clippy::unused_async)]
+async fn exec_simple_builtin_impl<T: SimpleCommand + Send + Sync>(
+    context: commands::ExecutionContext<'_>,
+    args: Vec<CommandArg>,
+) -> Result<builtins::BuiltinResult, error::Error> {
+    let plain_args: Vec<_> = args
+        .into_iter()
+        .map(|arg| match arg {
+            CommandArg::String(s) => s,
+            CommandArg::Assignment(a) => a.to_string(),
+        })
+        .collect();
+
+    let plain_args: Vec<_> = plain_args.iter().map(AsRef::as_ref).collect();
+
+    T::execute(context, plain_args.as_slice())
+}
+
 fn exec_builtin<T: builtins::Command + Send + Sync>(
     context: commands::ExecutionContext<'_>,
     args: Vec<CommandArg>,