Backend trait refactors

- Refactor the confusing/bodgy consts backend macro to use a single
  `BackendInfo` struct
- Combine `supports_as_dependency()` and the `switches_dependency` into a single `Option` type as that is a better representation as it is an optional backend feature.
- Add more types like `Packages`, `Sections` for uniformity.
- Added a crate-private prelude and switches all imports to use a
  prelude glob import (excluding functions because it's nice to only be
  importing types)
- Refactored Backend section name in logging by implementing Display for
  `AnyBackend` that just prints the `section`

crates/pacdef/src/backend/mod.rs

@@ -1,23 +1,53 @@
 pub mod actual;
 pub mod backend_trait;
-pub mod macros;
 mod root;
 pub mod todo_per_backend;
 
-use crate::backend::backend_trait::Switches;
-use crate::backend::backend_trait::Text;
-use crate::Group;
-use crate::Groups;
-use crate::Package;
-use anyhow::Result;
-use backend_trait::Backend;
-use std::collections::HashSet;
+use std::fmt::Display;
 
-use self::actual::{
-    fedora::Fedora, flatpak::Flatpak, python::Python, rust::Rust, rustup::Rustup, void::Void,
-};
+use crate::prelude::*;
+use anyhow::{Context, Result};
 
-#[derive(Debug)]
+// A backend with its associated managed packages
+pub struct ManagedBackend {
+    /// All managed packages for this backend, i.e. all packages
+    /// under the corresponding section in all group files.
+    pub packages: Packages,
+    pub any_backend: AnyBackend,
+}
+impl ManagedBackend {
+    /// Get unmanaged packages, sorted alphabetically.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the backend fails to get the explicitly installed packages.
+    pub fn get_unmanaged_packages_sorted(&self) -> Result<Vec<Package>> {
+        let installed = self
+            .any_backend
+            .get_explicitly_installed_packages()
+            .context("could not get explicitly installed packages")?;
+        let mut diff: Vec<_> = installed.difference(&self.packages).cloned().collect();
+        diff.sort_unstable();
+        Ok(diff)
+    }
+
+    /// Get missing packages, sorted alphabetically.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the backend fails to get the installed packages.
+    pub fn get_missing_packages_sorted(&self) -> Result<Vec<Package>> {
+        let installed = self
+            .any_backend
+            .get_all_installed_packages()
+            .context("could not get installed packages")?;
+        let mut diff: Vec<_> = self.packages.difference(&installed).cloned().collect();
+        diff.sort_unstable();
+        Ok(diff)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 #[enum_dispatch::enum_dispatch(Backend)]
 pub enum AnyBackend {
     #[cfg(feature = "arch")]
@@ -31,22 +61,44 @@ pub enum AnyBackend {
     Rustup(Rustup),
     Void(Void),
 }
-
 impl AnyBackend {
     /// Returns an iterator of every variant of backend.
-    pub fn iter() -> impl Iterator<Item = Self> {
+    pub fn all(config: &Config) -> impl Iterator<Item = Self> {
         vec![
             #[cfg(feature = "arch")]
-            Self::Arch(actual::arch::Arch::new()),
+            Self::Arch(actual::arch::Arch::new(config)),
             #[cfg(feature = "debian")]
             Self::Debian(actual::debian::Debian::new()),
-            Self::Flatpak(Flatpak::new()),
+            Self::Flatpak(Flatpak::new(config)),
             Self::Fedora(Fedora::new()),
-            Self::Python(Python::new()),
+            Self::Python(Python::new(config)),
             Self::Rust(Rust::new()),
             Self::Rustup(Rustup::new()),
             Self::Void(Void::new()),
         ]
         .into_iter()
     }
+
+    pub fn from_section(section: &str, config: &Config) -> Result<Self> {
+        match section {
+            #[cfg(feature = "arch")]
+            "arch" => Ok(Self::Arch(actual::arch::Arch::new(config))),
+            #[cfg(feature = "debian")]
+            "debian" => Ok(Self::Debian(actual::debian::Debian::new())),
+            "flatpak" => Ok(Self::Flatpak(Flatpak::new(config))),
+            "fedora" => Ok(Self::Fedora(Fedora::new())),
+            "python" => Ok(Self::Python(Python::new(config))),
+            "rust" => Ok(Self::Rust(Rust::new())),
+            "rustup" => Ok(Self::Rustup(Rustup::new())),
+            "void" => Ok(Self::Void(Void::new())),
+            _ => Err(anyhow::anyhow!(
+                "no matching backend for the section: {section}"
+            )),
+        }
+    }
+}
+impl Display for AnyBackend {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.backend_info().section)
+    }
 }