add error handling per backend

src/backend/rust.rs

@@ -2,7 +2,7 @@ use std::collections::HashSet;
 use std::fs::read_to_string;
 use std::path::PathBuf;
 
-use anyhow::Result;
+use anyhow::{Context, Result};
 use serde_json::Value;
 
 use super::{Backend, Switches, Text};
@@ -20,28 +20,34 @@ const SWITCHES_REMOVE: Switches = &["uninstall"];
 impl Backend for Rust {
     impl_backend_constants!();
 
-    fn get_all_installed_packages(&self) -> HashSet<Package> {
+    fn get_all_installed_packages(&self) -> Result<HashSet<Package>> {
         let file = get_crates_file().unwrap();
         let content = read_to_string(file).unwrap();
         let json: Value = serde_json::from_str(&content).unwrap();
         extract_packages(json)
     }
 
-    fn get_explicitly_installed_packages(&self) -> HashSet<Package> {
+    fn get_explicitly_installed_packages(&self) -> Result<HashSet<Package>> {
         self.get_all_installed_packages()
     }
 }
 
-fn extract_packages(json: Value) -> HashSet<Package> {
-    json.get("installs")
-        .unwrap()
+fn extract_packages(json: Value) -> Result<HashSet<Package>> {
+    let result: HashSet<_> = json
+        .get("installs")
+        .context("get 'installs' field from json")?
         .as_object()
-        .unwrap()
+        .context("getting object")?
         .into_iter()
         .map(|(name, _)| name)
-        .map(|name| name.split_whitespace().next().unwrap())
-        .filter_map(Package::try_from)
-        .collect()
+        .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 {