Derive build version from git tags via VERSION file.

flake.nix reads from VERSION instead of hardcoding; Makefile gains
a version target that syncs VERSION from the latest git tag and
injects it into go build ldflags.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Makefile

@@ -1,4 +1,6 @@
-.PHONY: proto build test lint clean
+VERSION := $(shell git describe --tags --abbrev=0 | sed 's/^v//')
+
+.PHONY: proto build test lint clean version
 
 proto:
 	protoc \
@@ -7,8 +9,11 @@ proto:
 		-I proto \
 		proto/sgard/v1/sgard.proto
 
+version:
+	@echo $(VERSION) > VERSION
+
 build:
-	go build ./...
+	go build -ldflags "-X main.version=$(VERSION)" ./...
 
 test:
 	go test ./...

VERSION

@@ -0,0 +1 @@
+3.1.5

flake.nix

@@ -11,17 +11,20 @@
       let
         pkgs = import nixpkgs { inherit system; };
       in
+      let
+        version = builtins.replaceStrings [ "\n" ] [ "" ] (builtins.readFile ./VERSION);
+      in
       {
         packages = {
-          sgard = pkgs.buildGoModule {
+          sgard = pkgs.buildGoModule rec {
             pname = "sgard";
-            version = "2.1.0";
+            inherit version;
             src = pkgs.lib.cleanSource ./.;
             subPackages = [ "cmd/sgard" "cmd/sgardd" ];
 
             vendorHash = "sha256-Z/Ja4j7YesNYefQQcWWRG2v8WuIL+UNqPGwYD5AipZY=";
 
-            ldflags = [ "-s" "-w" ];
+            ldflags = [ "-s" "-w" "-X main.version=${version}" ];
 
             meta = {
               description = "Shimmering Clarity Gardener: dotfile management";
@@ -29,9 +32,9 @@
             };
           };
 
-          sgard-fido2 = pkgs.buildGoModule {
+          sgard-fido2 = pkgs.buildGoModule rec {
             pname = "sgard-fido2";
-            version = "2.1.0";
+            inherit version;
             src = pkgs.lib.cleanSource ./.;
             subPackages = [ "cmd/sgard" "cmd/sgardd" ];
 
@@ -41,7 +44,7 @@
             nativeBuildInputs = [ pkgs.pkg-config ];
             tags = [ "fido2" ];
 
-            ldflags = [ "-s" "-w" ];
+            ldflags = [ "-s" "-w" "-X main.version=${version}" ];
 
             meta = {
               description = "Shimmering Clarity Gardener: dotfile management (with FIDO2 hardware support)";