feat: extract commit hash from build info

The Go toolchain stores the git commit hash in the binary, which can
then be extracted using `debug.ReadBuildInfo`. The advantage is that the
commit hash is present even on development builds (`go build` etc), and
it simplifies CI _slightly_.

.github/workflows/release.yml

@@ -58,7 +58,6 @@ jobs:
         run: |
           mkdir -p /tmp/out
           docker run --rm \
-            --env COMMIT=${{ github.sha }} \
             --env VERSION=${{ startsWith(github.ref_name, 'v') && github.ref_name || '' }} \
             -v $PWD:/src \
             go-librespot-build-${{ matrix.target }}

Dockerfile.build

@@ -1,6 +1,5 @@
 FROM --platform=linux/amd64 docker.io/golang:1.22.2-bullseye
 
-ENV COMMIT=dev
 ENV VERSION=0.0.0
 
 # Preparations
@@ -56,5 +55,5 @@ ENV CGO_ENABLED=1 PKG_CONFIG_PATH=/tmp/deps/${TARGET}/lib/pkgconfig/ CC=${CC} \
     GOCACHE=/src/.gocache/go-build GOMODCACHE=/src/.gocache/mod
 CMD go build \
     -buildvcs=false \
-    -ldflags="-X github.com/devgianlu/go-librespot.commit=${COMMIT} -X github.com/devgianlu/go-librespot.version=${VERSION}" \
+    -ldflags="-X github.com/devgianlu/go-librespot.version=${VERSION}" \
     -o ./go-librespot${GOOUTSUFFIX} -a ./cmd/daemon

version.go

@@ -3,15 +3,28 @@ package go_librespot
 import (
 	"fmt"
 	"runtime"
+	"runtime/debug"
 	"strings"
 )
 
-var commit, version string
+var version string
+
+// Extract and return the commit hash stored in the binary, if available.
+func commitHash() string {
+	if info, ok := debug.ReadBuildInfo(); ok {
+		for _, setting := range info.Settings {
+			if setting.Key == "vcs.revision" {
+				return setting.Value
+			}
+		}
+	}
+	return ""
+}
 
 func VersionNumberString() string {
 	if len(version) > 0 {
 		return strings.TrimPrefix(version, "v")
-	} else if len(commit) >= 8 {
+	} else if commit := commitHash(); len(commit) >= 8 {
 		return commit[:8]
 	} else {
 		return "dev"
@@ -20,7 +33,7 @@ func VersionNumberString() string {
 
 func SpotifyLikeClientVersion() string {
 	if len(version) > 0 {
-		if len(commit) >= 8 {
+		if commit := commitHash(); len(commit) >= 8 {
 			return fmt.Sprintf("%s.g%s", version, commit[:8])
 		} else {
 			return version