nh: move checks to a dedicated module; validate nix setup

Author: NotAShelf

src/check.rs

@@ -0,0 +1,95 @@
+use std::cmp::Ordering;
+
+use color_eyre::{eyre, Result};
+use semver::Version;
+
+use crate::util;
+
+/// Verifies if the installed Nix version meets requirements
+///
+/// # Returns
+///
+/// * `Result<()>` - Ok if version requirements are met, error otherwise
+pub fn check_nix_version() -> Result<()> {
+    let version = util::get_nix_version()?;
+    let is_lix_binary = util::is_lix()?;
+
+    let min_version = if is_lix_binary { "2.91.0" } else { "2.26.1" };
+
+    let current = Version::parse(&version)?;
+    let required = Version::parse(min_version)?;
+
+    match current.cmp(&required) {
+        Ordering::Less => {
+            let binary_name = if is_lix_binary { "Lix" } else { "Nix" };
+            Err(eyre::eyre!(
+                "{} version {} is too old. Minimum required version is {}",
+                binary_name,
+                version,
+                min_version
+            ))
+        }
+        _ => Ok(()),
+    }
+}
+
+/// Verifies if the required experimental features are enabled
+///
+/// # Returns
+///
+/// * `Result<()>` - Ok if all required features are enabled, error otherwise
+pub fn check_nix_features() -> Result<()> {
+    let mut required_features = vec!["nix-command", "flakes"];
+
+    // Lix still uses repl-flake, which is removed in the latest version of Nix.
+    if util::is_lix()? {
+        required_features.push("repl-flake");
+    }
+
+    if !util::has_all_experimental_features(&required_features)? {
+        return Err(eyre::eyre!(
+            "Missing required experimental features. Please enable: {}",
+            required_features.join(", ")
+        ));
+    }
+
+    Ok(())
+}
+
+/// Handles environment variable setup and returns if a warning should be shown
+///
+/// # Returns
+///
+/// * `Result<bool>` - True if a warning should be shown about the FLAKE variable, false otherwise
+pub fn setup_environment() -> Result<bool> {
+    let mut do_warn = false;
+
+    if let Ok(f) = std::env::var("FLAKE") {
+        // Set NH_FLAKE if it's not already set
+        if std::env::var("NH_FLAKE").is_err() {
+            std::env::set_var("NH_FLAKE", f);
+
+            // Only warn if FLAKE is set and we're using it to set NH_FLAKE
+            // AND none of the command-specific env vars are set
+            if std::env::var("NH_OS_FLAKE").is_err()
+                && std::env::var("NH_HOME_FLAKE").is_err()
+                && std::env::var("NH_DARWIN_FLAKE").is_err()
+            {
+                do_warn = true;
+            }
+        }
+    }
+
+    Ok(do_warn)
+}
+
+/// Runs all necessary checks for Nix functionality
+///
+/// # Returns
+///
+/// * `Result<()>` - Ok if all checks pass, error otherwise
+pub fn verify_nix_environment() -> Result<()> {
+    check_nix_version()?;
+    check_nix_features()?;
+    Ok(())
+}

src/main.rs

@@ -1,3 +1,4 @@
+mod check;
 mod clean;
 mod commands;
 mod completion;
@@ -20,22 +21,7 @@ const NH_VERSION: &str = env!("CARGO_PKG_VERSION");
 const NH_REV: Option<&str> = option_env!("NH_REV");
 
 fn main() -> Result<()> {
-    let mut do_warn = false;
-    if let Ok(f) = std::env::var("FLAKE") {
-        // Set NH_FLAKE if it's not already set
-        if std::env::var("NH_FLAKE").is_err() {
-            std::env::set_var("NH_FLAKE", f);
-
-            // Only warn if FLAKE is set and we're using it to set NH_FLAKE
-            // AND none of the command-specific env vars are set
-            if std::env::var("NH_OS_FLAKE").is_err()
-                && std::env::var("NH_HOME_FLAKE").is_err()
-                && std::env::var("NH_DARWIN_FLAKE").is_err()
-            {
-                do_warn = true;
-            }
-        }
-    }
+    let do_warn = check::setup_environment()?;
 
     let args = <crate::interface::Main as clap::Parser>::parse();
     crate::logging::setup_logging(args.verbose)?;
@@ -48,9 +34,13 @@ fn main() -> Result<()> {
         );
     }
 
+    // Verify the Nix environment before running commands
+    check::verify_nix_environment()?;
+
     args.command.run()
 }
 
+/// Self-elevates the current process by re-executing it with sudo
 fn self_elevate() -> ! {
     use std::os::unix::process::CommandExt;
 

src/util.rs

@@ -1,34 +1,11 @@
-extern crate semver;
-
+use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::str;
 
 use color_eyre::{eyre, Result};
-use semver::Version;
 use tempfile::TempDir;
 
-/// Compares two semantic versions and returns their order.
-///
-/// This function takes two version strings, parses them into `semver::Version` objects, and compares them.
-/// It returns an `Ordering` indicating whether the current version is less than, equal to, or
-/// greater than the target version.
-///
-/// # Arguments
-///
-/// * `current` - A string slice representing the current version.
-/// * `target` - A string slice representing the target version to compare against.
-///
-/// # Returns
-///
-/// * `Result<std::cmp::Ordering>` - The comparison result.
-pub fn compare_semver(current: &str, target: &str) -> Result<std::cmp::Ordering> {
-    let current = Version::parse(current)?;
-    let target = Version::parse(target)?;
-
-    Ok(current.cmp(&target))
-}
-
 /// Retrieves the installed Nix version as a string.
 ///
 /// This function executes the `nix --version` command, parses the output to extract the version string,
@@ -59,6 +36,19 @@ pub fn get_nix_version() -> Result<String> {
     Err(eyre::eyre!("Failed to extract version"))
 }
 
+/// Determines if the Nix binary is actually Lix
+///
+/// # Returns
+///
+/// * `Result<bool>` - True if the binary is Lix, false if it's standard Nix
+pub fn is_lix() -> Result<bool> {
+    let output = Command::new("nix").arg("--version").output()?;
+    let output_str = str::from_utf8(&output.stdout)?.to_lowercase();
+
+    Ok(output_str.contains("lix"))
+}
+
+/// Represents an object that may be a temporary path
 pub trait MaybeTempPath: std::fmt::Debug {
     fn get_path(&self) -> &Path;
 }
@@ -75,6 +65,11 @@ impl MaybeTempPath for (PathBuf, TempDir) {
     }
 }
 
+/// Gets the hostname of the current system
+///
+/// # Returns
+///
+/// * `Result<String>` - The hostname as a string or an error
 pub fn get_hostname() -> Result<String> {
     #[cfg(not(target_os = "macos"))]
     {
@@ -102,3 +97,47 @@ pub fn get_hostname() -> Result<String> {
         Ok(name.to_string())
     }
 }
+
+/// Retrieves all enabled experimental features in Nix.
+///
+/// This function executes the `nix config show experimental-features` command and returns
+/// a HashSet of the enabled features.
+///
+/// # Returns
+///
+/// * `Result<HashSet<String>>` - A HashSet of enabled experimental features or an error.
+pub fn get_nix_experimental_features() -> Result<HashSet<String>> {
+    let output = Command::new("nix")
+        .args(["config", "show", "experimental-features"])
+        .output()?;
+
+    if !output.status.success() {
+        return Err(eyre::eyre!(
+            "Failed to get experimental features: {}",
+            String::from_utf8_lossy(&output.stderr)
+        ));
+    }
+
+    let output_str = str::from_utf8(&output.stdout)?;
+    let enabled_features: HashSet<String> =
+        output_str.split_whitespace().map(String::from).collect();
+
+    Ok(enabled_features)
+}
+
+/// Checks if all specified experimental features are enabled in Nix.
+///
+/// # Arguments
+///
+/// * `features` - A slice of string slices representing the features to check for.
+///
+/// # Returns
+///
+/// * `Result<bool>` - True if all specified features are enabled, false otherwise.
+pub fn has_all_experimental_features(features: &[&str]) -> Result<bool> {
+    let enabled_features = get_nix_experimental_features()?;
+    let features_set: HashSet<String> = features.iter().map(|&s| s.to_string()).collect();
+
+    // Check if features_set is a subset of enabled_features
+    Ok(features_set.is_subset(&enabled_features))
+}