Refactor: extract 'get the embedded filesystem' to a separate function

The global `scriptFS` variable was too easy to access, which caused an
issue where the mandatory `"scripts"` subdirectory was not passed.
Accessing via a getter function that hides this requirement prevents this.

internal/manager/job_compilers/job_compilers.go

@@ -61,7 +61,7 @@ func Load(ts TimeService) (*Service, error) {
 	staticFileLoader := func(path string) ([]byte, error) {
 		// TODO: this should try different filesystems, once we allow loading from
 		// disk as well.
-		content, err := loadScriptBytes(scriptsFS, path)
+		content, err := loadScriptBytes(getEmbeddedScriptFS(), path)
 		if err != nil {
 			// The 'require' module uses this to try different variations of the path
 			// in order to find it (without .js, with .js, etc.), so don't log any of

internal/manager/job_compilers/scripts.go

@@ -3,7 +3,6 @@ package job_compilers
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 import (
-	"embed"
 	"fmt"
 	"io"
 	"io/fs"
@@ -15,18 +14,10 @@ import (
 	"github.com/rs/zerolog/log"
 )
 
-//go:embed scripts
-var scriptsFS embed.FS
-
 // loadScripts iterates over all JavaScript files, compiles them, and stores the
 // result into `s.compilers`.
 func (s *Service) loadScripts() error {
-	scriptsSubFS, err := fs.Sub(scriptsFS, "scripts")
-	if err != nil {
-		return fmt.Errorf("failed to find embedded 'scripts' directory: %w", err)
-	}
-
-	compilers, err := loadScriptsFrom(scriptsSubFS)
+	compilers, err := loadScriptsFrom(getEmbeddedScriptFS())
 	if err != nil {
 		return err
 	}

internal/manager/job_compilers/scripts_embedded.go

@@ -0,0 +1,28 @@
+package job_compilers
+
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+)
+
+// Scripts from the `./scripts` subdirectory are embedded into the executable
+// here. Note that accessing these files still requires explicit use of the
+// `scripts/` subdirectory, which is abstracted away by `getEmbeddedScriptFS()`.
+// It is recommended to use that function to get the embedded scripts
+// filesystem.
+
+//go:embed scripts
+var _embeddedScriptsFS embed.FS
+
+// getEmbeddedScriptFS returns the `fs.FS` interface that allows access to the
+// embedded job compiler scripts.
+func getEmbeddedScriptFS() fs.FS {
+	scriptsSubFS, err := fs.Sub(_embeddedScriptsFS, "scripts")
+	if err != nil {
+		panic(fmt.Sprintf("failed to find embedded 'scripts' directory: %v", err))
+	}
+	return scriptsSubFS
+}

internal/manager/job_compilers/scripts_test.go

@@ -1,9 +1,12 @@
 package job_compilers
 
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 import (
 	"os"
 	"testing"
 
+	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -27,6 +30,39 @@ func TestLoadScriptsFrom_on_disk_js(t *testing.T) {
 	assert.Equal(t, expectKeys, keys(compilers))
 }
 
+func TestLoadScriptsFrom_embedded(t *testing.T) {
+	compilers, err := loadScriptsFrom(getEmbeddedScriptFS())
+
+	assert.NoError(t, err)
+	expectKeys := map[string]bool{
+		"echo-sleep-test":       true,
+		"simple-blender-render": true,
+	}
+	assert.Equal(t, expectKeys, keys(compilers))
+}
+
+func BenchmarkLoadScripts_fromEmbedded(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+
+	embeddedFS := getEmbeddedScriptFS()
+	for i := 0; i < b.N; i++ {
+		compilers, err := loadScriptsFrom(embeddedFS)
+		assert.NoError(b, err)
+		assert.NotEmpty(b, compilers)
+	}
+}
+
+func BenchmarkLoadScripts_fromDisk(b *testing.B) {
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+
+	onDiskFS := os.DirFS("scripts-for-unittest")
+	for i := 0; i < b.N; i++ {
+		compilers, err := loadScriptsFrom(onDiskFS)
+		assert.NoError(b, err)
+		assert.NotEmpty(b, compilers)
+	}
+}
+
 // keys returns the set of keys of the mapping.
 func keys[K comparable, V any](mapping map[K]V) map[K]bool {
 	keys := map[K]bool{}