clean up backend

src/backend/actual/rust.rs

@@ -0,0 +1,67 @@
+use std::collections::HashSet;
+use std::fs::read_to_string;
+use std::path::PathBuf;
+
+use anyhow::{Context, Result};
+use serde_json::Value;
+
+use crate::backend::backend_trait::*;
+use crate::{impl_backend_constants, Group, Package};
+
+pub(crate) struct Rust {
+    pub(crate) packages: HashSet<Package>,
+}
+
+const BINARY: Text = "cargo";
+const SECTION: Text = "rust";
+const SWITCHES_INSTALL: Switches = &["install"];
+const SWITCHES_REMOVE: Switches = &["uninstall"];
+
+impl Backend for Rust {
+    impl_backend_constants!();
+
+    fn get_all_installed_packages(&self) -> Result<HashSet<Package>> {
+        let file = get_crates_file().context("getting path to crates file")?;
+        let content = read_to_string(file).context("reading crates file")?;
+        let json: Value = serde_json::from_str(&content).context("parsing JSON")?;
+        extract_packages(json).context("extracing packages from JSON")
+    }
+
+    fn get_explicitly_installed_packages(&self) -> Result<HashSet<Package>> {
+        self.get_all_installed_packages()
+            .context("getting all installed packages")
+    }
+}
+
+fn extract_packages(json: Value) -> Result<HashSet<Package>> {
+    let result: HashSet<_> = json
+        .get("installs")
+        .context("get 'installs' field from json")?
+        .as_object()
+        .context("getting object")?
+        .into_iter()
+        .map(|(name, _)| name)
+        .map(|name| {
+            name.split_whitespace()
+                .next()
+                .expect("identifier is whitespace-delimited")
+        })
+        .map(|name| Package::try_from(name).expect("name is valid"))
+        .collect();
+    Ok(result)
+}
+
+impl Rust {
+    pub(crate) fn new() -> Self {
+        Self {
+            packages: HashSet::new(),
+        }
+    }
+}
+
+fn get_crates_file() -> Result<PathBuf> {
+    let mut result = crate::path::get_home_dir().context("getting home dir")?;
+    result.push(".cargo");
+    result.push(".crates2.json");
+    Ok(result)
+}