feat: move messages to its own trait

Resolves #53

genealogos-cli/Cargo.toml

@@ -21,7 +21,7 @@ cyclonedx-bom.workspace = true
 env_logger.workspace = true
 indicatif.workspace = true
 indicatif-log-bridge.workspace = true
-genealogos = { workspace = true, features = [ "backend_handle_messages", "clap" ] }
+genealogos = { workspace = true, features = [ "clap" ] }
 nixtract.workspace = true
 
 [features]

genealogos-cli/src/main.rs

@@ -7,7 +7,7 @@ use std::path;
 use clap::Parser;
 
 use genealogos::args;
-use genealogos::backend::{Backend, BackendHandle};
+use genealogos::backend::{Backend, BackendHandle, BackendHandleMessages};
 
 /// `cli` application for processing data files and generating CycloneDX output
 #[derive(Parser, Debug)]
@@ -57,7 +57,7 @@ fn main() -> Result<()> {
     };
 
     // Initialize the backend and get access to the status update messages
-    let (mut backend, handle) = *args.backend.get_backend()?;
+    let (mut backend, handle) = *args.backend.get_backend_messages()?;
 
     // Set backend options
     backend.include_narinfo(args.include_narinfo);

genealogos/Cargo.toml

@@ -35,10 +35,6 @@ default = []
 # It disables all tests that require a working internet connection.
 nix = []
 
-# The messages function of the `BanendHandle` trait violates object safety.
-# For those users of the library that don't need to use this trait as an object, and would like access to the `messages` function, this feature should be enabled.
-backend_handle_messages = []
-
 clap = [ "args", "dep:clap" ]
 rocket = [ "args", "dep:rocket" ]
 

genealogos/src/args.rs

@@ -8,7 +8,7 @@ use std::str::FromStr as _;
 #[cfg(feature = "clap")]
 use std::sync::OnceLock;
 
-use crate::backend::{Backend, BackendHandle};
+use crate::backend::{Backend, BackendHandle, BackendHandleMessages};
 use crate::bom::Bom;
 use crate::error::*;
 
@@ -26,7 +26,13 @@ pub enum BackendArg {
 }
 
 impl BackendArg {
+    /// Get a backend and handle that is object safe
     pub fn get_backend(&self) -> Result<Box<(impl Backend, impl BackendHandle)>> {
+        self.get_backend_messages()
+    }
+
+    /// Get a backend and handle that is not object safe and implements the `messages` function
+    pub fn get_backend_messages(&self) -> Result<Box<(impl Backend, impl BackendHandleMessages)>> {
         match self {
             BackendArg::Nixtract => Ok(Box::new(crate::backend::nixtract_backend::Nixtract::new())),
         }

genealogos/src/backend/mod.rs

@@ -211,10 +211,15 @@ pub trait BackendHandle {
     /// Gets all messages that were produced since the previous call to this function
     fn new_messages(&self) -> Result<Vec<Message>>;
 
-    /// Gets an iterator over all messages
-    #[cfg(feature = "backend_handle_messages")]
-    fn messages(&self) -> Result<impl Iterator<Item = Message>>;
-
     /// Gets an upper bound to the number of different ids to expect in the messages
     fn max_index(&self) -> usize;
 }
+
+/// `BackendHandleMessages` is a trait that defines additional behaviour of a backend handle.
+///
+/// This trait is seperate from the `BackendHandle` trait because it can't be made int a trait object.
+/// BackendHandle is a supertrait of this trait.
+pub trait BackendHandleMessages: BackendHandle {
+    /// Gets an iterator over all messages
+    fn messages(&self) -> Result<impl Iterator<Item = Message>>;
+}

genealogos/src/backend/nixtract_backend.rs

@@ -114,17 +114,18 @@ impl super::BackendHandle for NixtractHandle {
         Ok(messages)
     }
 
-    #[cfg(feature = "backend_handle_messages")]
+    fn max_index(&self) -> usize {
+        rayon::current_num_threads()
+    }
+}
+
+impl super::BackendHandleMessages for NixtractHandle {
     fn messages(&self) -> crate::Result<impl Iterator<Item = super::Message>> {
         Ok(self.receiver.iter().map(|m| super::Message {
             index: m.id,
             content: m.to_string(),
         }))
     }
-
-    fn max_index(&self) -> usize {
-        rayon::current_num_threads()
-    }
 }
 
 impl<T> From<T> for Model