Implement some recommendations from copilot

Author: Dragyx

src/json.rs

@@ -70,7 +70,7 @@ pub fn display_diff(
     size_old,
     size_new,
   })?;
-  print!("{json}");
+  println!("{json}");
   Ok(())
 }
 

src/main.rs

@@ -59,8 +59,7 @@ struct Cli {
   #[arg(long, default_value_t = false, global = true)]
   force_correctness: bool,
 
-  /// Does not display the normal, human readable diff, but rather
-  /// serialized to json
+  /// Outputs the diff in JSON format instead of the normal, human-readable diff.
   ///
   /// Requires the "json" feature.
   #[arg(long, default_value_t = false, global = true)]

src/store.rs

@@ -8,10 +8,6 @@ mod db_lazy;
 mod nix_command;
 mod queries;
 
-pub mod store {
-  pub use crate::store::db_lazy::LazyDBConnection;
-}
-
 use std::{
   fmt::Display,
   iter::Iterator,
@@ -25,13 +21,11 @@ use anyhow::{
 use log::warn;
 use size::Size;
 
-use crate::{
-  StorePath,
-  store::{
-    db_eager::EagerDBConnection,
-    nix_command::CommandBackend,
-    store::LazyDBConnection,
-  },
+use crate::StorePath;
+pub use crate::store::{
+  db_eager::EagerDBConnection,
+  db_lazy::LazyDBConnection,
+  nix_command::CommandBackend,
 };
 /// The normal database connection
 pub const DATABASE_PATH: &str = "file:/nix/var/nix/db/db.sqlite";

src/store/nix_command.rs

@@ -57,7 +57,7 @@ fn nix_command_query<'a>(
 }
 
 impl<'a> StoreBackend<'a> for CommandBackend {
-  /// Does nothing (we spawn a new process everytime).
+  /// Does nothing (we spawn a new process every time).
   fn connect(&mut self) -> Result<()> {
     Ok(())
   }
@@ -80,6 +80,15 @@ impl<'a> StoreBackend<'a> for CommandBackend {
       .arg(path.join("sw"))
       .output()
       .context(anyhow!("Encountered error while executing nix command"))?;
+
+    if !cmd_res.status.success() {
+      let stderr = String::from_utf8_lossy(&cmd_res.stderr);
+      return Err(anyhow!(
+        "nix command exited with non-zero status {}: {}",
+        cmd_res.status,
+        stderr.trim()
+      ));
+    }
     let text = str::from_utf8(&cmd_res.stdout)?;
     if let Some(bytes_text) = text.split_whitespace().last()
       && let Ok(bytes) = bytes_text.parse::<u64>()