From 2bb7537602d7572035fcc5b61fff9369fb04f2c4 Mon Sep 17 00:00:00 2001
From: Brian Picciano <me@mediocregopher.com>
Date: Thu, 19 Dec 2024 11:51:37 +0100
Subject: [PATCH] Automatically include 'git describe' output in version text

---
 default.nix | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/default.nix b/default.nix
index 44fac61..2063e75 100644
--- a/default.nix
+++ b/default.nix
@@ -3,7 +3,7 @@
   hostSystem ? buildSystem,
   pkgsNix ? (import ./nix/pkgs.nix),
 
-  revision ? "dev",
+  revision ? null,
   releaseName ? "dev",
 }: let
 
@@ -20,12 +20,22 @@
 
 in rec {
 
-  version = pkgs.stdenv.mkDerivation {
+  version = let
+    revisionFile = if builtins.isNull revision
+      then pkgsNative.stdenv.mkDerivation {
+        name = "revision.txt";
+        nativeBuildInputs = [ pkgsNative.git ];
+        src = ./.git;
+        phases = [ "installPhase" ];
+        installPhase = ''
+          git -c safe.directory='*' -C $src describe --tags > $out
+        '';
+      }
+      else pkgsNative.writeText "revision.txt" revision;
+  in pkgs.stdenv.mkDerivation {
     name = "isle-version";
 
-    inherit buildSystem hostSystem revision releaseName;
-
-    nativeBuildInputs = [ pkgsNative.git ];
+    inherit buildSystem hostSystem revisionFile releaseName;
 
     goVersion = pkgs.go.version;
     garageVersion = garageNix.version;
@@ -36,13 +46,13 @@ in rec {
 
       versionFile=version
 
-      echo "Release:         $releaseName"    >> "$versionFile"
-      echo "Platform:        $hostSystem"     >> "$versionFile"
-      echo "Git Revision:    $revision"       >> "$versionFile"
-      echo "Go Version:      $goVersion"      >> "$versionFile"
-      echo "Garage Version:  $garageVersion"  >> "$versionFile"
-      echo "NixPkgs Version: $nixpkgsVersion" >> "$versionFile"
-      echo "Build Platform:  $buildSystem"    >> "$versionFile"
+      echo "Release:         $releaseName"         >> "$versionFile"
+      echo "Platform:        $hostSystem"          >> "$versionFile"
+      echo "Git Revision:    $(cat $revisionFile)" >> "$versionFile"
+      echo "Go Version:      $goVersion"           >> "$versionFile"
+      echo "Garage Version:  $garageVersion"       >> "$versionFile"
+      echo "NixPkgs Version: $nixpkgsVersion"      >> "$versionFile"
+      echo "Build Platform:  $buildSystem"         >> "$versionFile"
 
       mkdir -p "$out"/share
       cp "$versionFile" "$out"/share