ref(nix): Deduplicate run_nix and run_nix_self_upgrade nix --version checking (#1376)

src/steps/os/unix.rs

@@ -418,6 +418,74 @@ pub fn run_guix(ctx: &ExecutionContext) -> Result<()> {
     Ok(())
 }
 
+struct NixVersion {
+    version_string: String,
+}
+
+impl NixVersion {
+    fn new(ctx: &ExecutionContext, nix: &Path) -> Result<Self> {
+        let version_output = ctx.execute(nix).arg("--version").output_checked_utf8()?;
+
+        debug!(
+            output=%version_output,
+            "`nix --version` output"
+        );
+
+        let version_string = version_output
+            .stdout
+            .lines()
+            .next()
+            .ok_or_else(|| eyre!("`nix --version` output is empty"))?
+            .to_string();
+
+        if version_string.is_empty() {
+            return Err(eyre!("`nix --version` output was empty"));
+        }
+
+        Ok(Self { version_string })
+    }
+
+    fn version(&self) -> Result<Version> {
+        static NIX_VERSION_REGEX: LazyLock<Regex> =
+            LazyLock::new(|| Regex::new(r"^nix \([^)]*\) ([0-9.]+)").expect("Nix version regex always compiles"));
+
+        let captures = NIX_VERSION_REGEX
+            .captures(&self.version_string)
+            .ok_or_else(|| eyre!(output_changed_message!("nix --version", "regex did not match")))?;
+        let raw_version = &captures[1];
+
+        debug!("Raw Nix version: {raw_version}");
+
+        // Nix 2.29.0 outputs "2.29" instead of "2.29.0", so we need to add that if necessary.
+        let corrected_raw_version = if raw_version.chars().filter(|&c| c == '.').count() == 1 {
+            &format!("{raw_version}.0")
+        } else {
+            raw_version
+        };
+
+        debug!("Corrected raw Nix version: {corrected_raw_version}");
+
+        let version = Version::parse(corrected_raw_version)
+            .wrap_err_with(|| output_changed_message!("nix --version", "Invalid version"))?;
+
+        debug!("Nix version: {:?}", version);
+
+        Ok(version)
+    }
+
+    fn is_lix(&self) -> bool {
+        let is_lix = self.version_string.contains("Lix");
+        debug!(?is_lix);
+        is_lix
+    }
+
+    fn is_determinate_nix(&self) -> bool {
+        let is_determinate_nix = self.version_string.contains("Determinate Nix");
+        debug!(?is_determinate_nix);
+        is_determinate_nix
+    }
+}
+
 pub fn run_nix(ctx: &ExecutionContext) -> Result<()> {
     let nix = require("nix")?;
     let nix_channel = require("nix-channel")?;
@@ -447,54 +515,11 @@ pub fn run_nix(ctx: &ExecutionContext) -> Result<()> {
 
     ctx.execute(nix_channel).arg("--update").status_checked()?;
 
-    let mut get_version_cmd = ctx.execute(&nix);
+    let nix_version = NixVersion::new(ctx, &nix)?;
-    get_version_cmd.arg("--version");
-    let get_version_cmd_output = get_version_cmd.output_checked_utf8()?;
-    let get_version_cmd_first_line_stdout = get_version_cmd_output
-        .stdout
-        .lines()
-        .next()
-        .ok_or_else(|| eyre!("`nix --version` output is empty"))?;
-
-    let is_lix = get_version_cmd_first_line_stdout.contains("Lix");
-
-    debug!(
-        output=%get_version_cmd_output,
-        ?is_lix,
-        "`nix --version` output"
-    );
-
-    static NIX_VERSION_REGEX: LazyLock<Regex> =
-        LazyLock::new(|| Regex::new(r"^nix \([^)]*\) ([0-9.]+)").expect("Nix version regex always compiles"));
-
-    if get_version_cmd_first_line_stdout.is_empty() {
-        return Err(eyre!("`nix --version` output was empty"));
-    }
-
-    let captures = NIX_VERSION_REGEX
-        .captures(get_version_cmd_first_line_stdout)
-        .ok_or_else(|| eyre!(output_changed_message!("nix --version", "regex did not match")))?;
-    let raw_version = &captures[1];
-
-    debug!("Raw Nix version: {raw_version}");
-
-    // Nix 2.29.0 outputs "2.29" instead of "2.29.0", so we need to add that if necessary.
-    let corrected_raw_version = if raw_version.chars().filter(|&c| c == '.').count() == 1 {
-        &format!("{raw_version}.0")
-    } else {
-        raw_version
-    };
-
-    debug!("Corrected raw Nix version: {corrected_raw_version}");
-
-    let version = Version::parse(corrected_raw_version)
-        .wrap_err_with(|| output_changed_message!("nix --version", "Invalid version"))?;
-
-    debug!("Nix version: {:?}", version);
 
     // Nix since 2.21.0 uses `--all --impure` rather than `.*` to upgrade all packages.
     // Lix is based on Nix 2.18, so it doesn't!
-    let packages = if version >= Version::new(2, 21, 0) && !is_lix {
+    let packages = if nix_version.version()? >= Version::new(2, 21, 0) && !nix_version.is_lix() {
         vec!["--all", "--impure"]
     } else {
         vec![".*"]
@@ -545,22 +570,9 @@ pub fn run_nix_self_upgrade(ctx: &ExecutionContext) -> Result<()> {
 
     print_separator(t!("Nix (self-upgrade)"));
 
-    let version_output = ctx.execute(&nix).arg("--version").output_checked_utf8()?;
+    let nix_version = NixVersion::new(ctx, &nix)?;
-    let version = version_output
-        .stdout
-        .lines()
-        .next()
-        .ok_or_else(|| eyre!("`nix --version` output is empty"))?;
 
-    let is_determinate_nix = version.contains("Determinate Nix");
+    if nix_version.is_determinate_nix() {
-
-    debug!(
-    output=%version_output,
-    ?is_determinate_nix,
-    "`nix --version` output"
-    );
-
-    if is_determinate_nix {
         let nixd = require("determinate-nixd");
         let nixd = match nixd {
             Err(_) => {