nix_rs(nix_eval): Don't capture stderr (#298)

Resolves #209 

PRs filed tangential to this:
- NixOS/nix#11652

---------

Co-authored-by: Sridhar Ratnakumar <srid@srid.ca>

crates/nix_rs/CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog
 
 ## Unreleased
+
+- **`eval::nix_eval`**
+  - Display evaluation progress
+  - Decrease logging verbosity
 - **`flake::schema`**
   - Don't hardcode flake schema types
 - **`config`**

crates/nix_rs/src/command.rs

@@ -175,20 +175,22 @@ impl NixCmd {
     }
 
     /// Run Nix with given [Command] customizations, while also tracing the command being run.
-    pub async fn run_with<F>(&self, f: F) -> Result<(), CommandError>
+    ///
+    /// Return the stdout bytes returned by [tokio::process::Child::wait_with_output]. In order to capture stdout, you must call `cmd.stdout(Stdio::piped());` inside the handler.
+    pub async fn run_with<F>(&self, f: F) -> Result<Vec<u8>, CommandError>
     where
         F: FnOnce(&mut Command),
     {
         let mut cmd = self.command();
         f(&mut cmd);
         trace_cmd(&cmd);
-        let status = cmd.spawn()?.wait().await?;
-        if status.success() {
-            Ok(())
+        let out = cmd.spawn()?.wait_with_output().await?;
+        if out.status.success() {
+            Ok(out.stdout)
         } else {
             Err(CommandError::ProcessFailed {
                 stderr: None,
-                exit_code: status.code(),
+                exit_code: out.status.code(),
             })
         }
     }

crates/nix_rs/src/copy.rs

@@ -28,5 +28,6 @@ pub async fn nix_copy(
     cmd.run_with(|cmd| {
         cmd.args(args);
     })
-    .await
+    .await?;
+    Ok(())
 }

crates/nix_rs/src/flake/command.rs

@@ -26,7 +26,8 @@ pub async fn run(
             cmd.args([url.to_string(), "--".to_string()]);
             cmd.args(args);
         })
-        .await
+        .await?;
+    Ok(())
 }
 
 /// Run `nix develop` on the given flake devshell.
@@ -42,7 +43,8 @@ pub async fn develop(
             cmd.args(["develop".to_string(), url.to_string(), "-c".to_string()]);
             cmd.args(command);
         })
-        .await
+        .await?;
+    Ok(())
 }
 
 /// Run `nix build`

crates/nix_rs/src/flake/eval.rs

@@ -1,4 +1,6 @@
 //! Work with `nix eval`
+use std::process::Stdio;
+
 use crate::command::{CommandError, NixCmd, NixCmdError};
 
 use super::{command::FlakeOptions, url::FlakeUrl};
@@ -13,10 +15,13 @@ where
     T: serde::de::DeserializeOwned,
 {
     let stdout = nixcmd
-        .run_with_returning_stdout(|cmd| {
+        .run_with(|cmd| {
+            cmd.stdout(Stdio::piped());
             cmd.args(["eval", "--json"]);
             opts.use_in_command(cmd);
             cmd.arg(url.to_string());
+            // Avoid Nix from dumping logs related to `--override-input` use. Yes, this requires *double* use of `--quiet`. Also, `-qq` won't work until https://github.com/NixOS/nix/pull/11652
+            cmd.args(["--quiet", "--quiet"]);
         })
         .await?;
     let v = serde_json::from_slice::<T>(&stdout)?;