fix(packages): return empty Chef dependencies instead of null (#40237) (#40242)

Backport #40237 by @Shadow0Bit

Fixes #40230

Cookbooks without dependencies are served with `"dependencies": null`
from the universe and version metadata endpoints. This happens because
`omitempty` drops the empty map when the metadata is stored. Chef
clients iterate over this value and Policyfile resolution crashes.

Supermarket returns `{}` for these cookbooks, Gitea now does too. The
fix checks whether dependencies are `nil` while building response,
returns an empty map if true. This way cookbooks that are already stored
are covered without a re-upload.

Tested with the Chef integration test and `chef-cli install`.

Assisted by Claude Code (claude-opus-5-5).

Co-authored-by: rafał przypek <58443512+Shadow0Bit@users.noreply.github.com>

modules/util/slice.go

@@ -77,3 +77,10 @@ func SliceNilAsEmpty[T any](a []T) []T {
 	}
 	return a
 }
+
+func MapNilAsEmpty[K comparable, V any](m map[K]V) map[K]V {
+	if m == nil {
+		return map[K]V{}
+	}
+	return m
+}

routers/api/packages/chef/chef.go

@@ -71,7 +71,7 @@ func PackagesUniverse(ctx *context.Context) {
 			LocationType: "opscode",
 			LocationPath: baseURL,
 			DownloadURL:  fmt.Sprintf("%s/cookbooks/%s/versions/%s/download", baseURL, url.PathEscape(pd.Package.Name), pd.Version.Version),
-			Dependencies: packages_model.DescriptorMetadata[*chef_module.Metadata](pd).Dependencies,
+			Dependencies: util.MapNilAsEmpty(packages_model.DescriptorMetadata[*chef_module.Metadata](pd).Dependencies),
 		}
 	}
 
@@ -250,7 +250,7 @@ func PackageVersionMetadata(ctx *context.Context) {
 		Cookbook:        baseURL,
 		File:            fmt.Sprintf("%s/versions/%s/download", baseURL, pd.Version.Version),
 		License:         metadata.License,
-		Dependencies:    metadata.Dependencies,
+		Dependencies:    util.MapNilAsEmpty(metadata.Dependencies),
 	})
 }
 

tests/integration/api_packages_chef_test.go

@@ -360,6 +360,7 @@ nwIDAQAB
 		assert.Equal(t, "opscode", info.LocationType)
 		assert.Equal(t, setting.AppURL+root[1:], info.LocationPath)
 		assert.Equal(t, fmt.Sprintf("%s%s/cookbooks/%s/versions/%s/download", setting.AppURL, root[1:], packageName, packageVersion), info.DownloadURL)
+		assert.Equal(t, map[string]string{}, info.Dependencies)
 	})
 
 	t.Run("Search", func(t *testing.T) {
@@ -516,6 +517,7 @@ nwIDAQAB
 		assert.Equal(t, packageVersion, result.Version)
 		assert.Equal(t, packageURL, result.Cookbook)
 		assert.Equal(t, fmt.Sprintf("%s/versions/%s/download", packageURL, packageVersion), result.File)
+		assert.Equal(t, map[string]string{}, result.Dependencies)
 	})
 
 	t.Run("Delete", func(t *testing.T) {