darwin: show homebrew diff if available

Author: kiliankoe

CHANGELOG.md

@@ -16,6 +16,13 @@ functionality, under the "Removed" section.
 
 ## Unreleased
 
+### Added
+
+- `nh darwin` now displays Homebrew package changes alongside Nix package
+  changes when using nix-darwin configurations with Homebrew management enabled.
+  This shows formulae, casks, taps, and Mac App Store apps that will be
+  added or removed during a configuration switch.
+
 ### Changed
 
 - Nh checks are now more robust in the sense that unnecessary features will not

Cargo.lock

@@ -27,6 +27,7 @@ path = "src/lib.rs"
 
 [dependencies]
 anstyle = "1.0.0"
+brewdiff = "0.2.0"
 chrono = "0.4.39"
 clap.workspace = true
 clap-verbosity-flag = { version = "3.0.3", features = [ "tracing" ], default-features = false }

Cargo.toml

@@ -11,7 +11,7 @@ use crate::installable::Installable;
 use crate::interface::{DarwinArgs, DarwinRebuildArgs, DarwinReplArgs, DarwinSubcommand, DiffType};
 use crate::nixos::toplevel_for;
 use crate::update::update;
-use crate::util::{get_hostname, print_dix_diff};
+use crate::util::{get_hostname, print_dix_diff, print_homebrew_diff};
 
 const SYSTEM_PROFILE: &str = "/nix/var/nix/profiles/system";
 const CURRENT_PROFILE: &str = "/run/current-system";
@@ -130,6 +130,7 @@ impl DarwinRebuildArgs {
                 target_profile.display()
             );
             let _ = print_dix_diff(&PathBuf::from(CURRENT_PROFILE), &target_profile);
+            let _ = print_homebrew_diff(&PathBuf::from(CURRENT_PROFILE), &target_profile);
         }
 
         if self.common.ask && !self.common.dry && !matches!(variant, Build) {

src/darwin.rs

@@ -31,6 +31,7 @@ impl<W: io::Write> fmt::Write for WriteFmt<W> {
         self.0.write_all(string.as_bytes()).map_err(|_| fmt::Error)
     }
 }
+
 /// Get the Nix variant (cached)
 pub fn get_nix_variant() -> &'static NixVariant {
     NIX_VARIANT.get_or_init(|| {
@@ -320,3 +321,85 @@ pub fn print_dix_diff(old_generation: &Path, new_generation: &Path) -> Result<()
     }
     Ok(())
 }
+
+/// Prints the difference between Homebrew packages in darwin generations.
+///
+/// # Arguments
+///
+/// * `old_generation` - A reference to the path of the old/current generation.
+/// * `new_generation` - A reference to the path of the new generation.
+///
+/// # Returns
+///
+/// Returns `Ok(())` if the operation completed successfully, or an error wrapped in `eyre::Result` if something went wrong.
+/// Silently returns Ok(()) if Homebrew is not available or not configured.
+#[cfg(target_os = "macos")]
+pub fn print_homebrew_diff(_old_generation: &Path, new_generation: &Path) -> Result<()> {
+    if !homebrew_available() {
+        debug!("Homebrew not found, skipping Homebrew diff");
+        return Ok(());
+    }
+
+    // Try to extract the nix-darwin Homebrew intent from the new profile
+    // If this fails, it likely means Homebrew isn't configured in the profile
+    let nix_intent = match brewdiff::extract_nix_darwin_intent(new_generation) {
+        Ok(intent) => intent,
+        Err(e) => {
+            debug!("Could not extract Homebrew intent from profile: {}", e);
+            return Ok(());
+        }
+    };
+
+    if !nix_intent.has_packages() {
+        debug!("No Homebrew packages configured in profile, skipping diff");
+        return Ok(());
+    }
+
+    let mut out = WriteFmt(io::stdout());
+
+    let diff_handle = brewdiff::spawn_homebrew_diff(new_generation.to_path_buf());
+    let diff_data = match diff_handle.join() {
+        Ok(Ok(data)) => data,
+        Ok(Err(e)) => {
+            debug!("Failed to compute Homebrew diff: {}", e);
+            return Ok(());
+        }
+        Err(_) => {
+            debug!("Homebrew diff thread panicked");
+            return Ok(());
+        }
+    };
+
+    if diff_data.has_changes() {
+        // Separator from dix' output
+        println!();
+
+        // Print statistics first to make it clear the details below belong to Homebrew
+        brewdiff::write_homebrew_stats(&mut out, &diff_data)?;
+        brewdiff::display::write_diff(&mut out, &diff_data)?;
+    } else {
+        debug!("No Homebrew package changes detected");
+    }
+
+    Ok(())
+}
+
+/// Checks if Homebrew is available on the system
+#[cfg(target_os = "macos")]
+fn homebrew_available() -> bool {
+    use std::process::Command as StdCommand;
+
+    StdCommand::new("which")
+        .arg("brew")
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .status()
+        .map(|s| s.success())
+        .unwrap_or(false)
+}
+
+/// Stub for non-macOS platforms
+#[cfg(not(target_os = "macos"))]
+pub fn print_homebrew_diff(_old_generation: &Path, _new_generation: &Path) -> Result<()> {
+    Ok(())
+}