Plugins: Introduce LoadingStrategy for frontend loading logic (#92392)

* do it all

* feat(plugins): move loadingStrategy to ds pluginMeta and add to plugin settings endpoint

* support child plugins and update tests

* use relative path for nested plugins

* feat(plugins): support nested plugins in the plugin loader cache by extracting pluginId from path

* feat(grafana-data): add plugin loading strategy to plugin meta and export

* feat(plugins): pass down loadingStrategy to fe plugin loader

* refactor(plugins): make PluginLoadingStrategy an enum

* feat(plugins): add the loading strategy to the fe plugin loader cache

* feat(plugins): load fe plugin js assets as script tags based on be loadingStrategy

* add more tests

* feat(plugins): add loading strategy to plugin preloader

* feat(plugins): make loadingStrategy a maybe and provide fetch fallback

* test(alerting): update config.apps mocks to include loadingStrategy

* fix format

---------

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>

pkg/services/pluginsintegration/pluginassets/pluginassets.go

@@ -0,0 +1,81 @@
+package pluginassets
+
+import (
+	"context"
+
+	"github.com/Masterminds/semver/v3"
+
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/plugins/pluginscdn"
+	"github.com/grafana/grafana/pkg/services/pluginsintegration/pluginstore"
+	"github.com/grafana/grafana/pkg/setting"
+)
+
+const (
+	CreatePluginVersionCfgKey               = "create_plugin_version"
+	CreatePluginVersionScriptSupportEnabled = "4.15.0"
+)
+
+var (
+	scriptLoadingMinSupportedVersion = semver.MustParse(CreatePluginVersionScriptSupportEnabled)
+)
+
+func ProvideService(cfg *setting.Cfg, cdn *pluginscdn.Service) *Service {
+	return &Service{
+		cfg: cfg,
+		cdn: cdn,
+		log: log.New("pluginassets"),
+	}
+}
+
+type Service struct {
+	cfg *setting.Cfg
+	cdn *pluginscdn.Service
+	log log.Logger
+}
+
+// LoadingStrategy calculates the loading strategy for a plugin.
+// If a plugin has plugin setting `create_plugin_version` >= 4.15.0, set loadingStrategy to "script".
+// If a plugin is not loaded via the CDN and is not Angular, set loadingStrategy to "script".
+// Otherwise, set loadingStrategy to "fetch".
+func (s *Service) LoadingStrategy(_ context.Context, p pluginstore.Plugin) plugins.LoadingStrategy {
+	if pCfg, ok := s.cfg.PluginSettings[p.ID]; ok {
+		if s.compatibleCreatePluginVersion(pCfg) {
+			return plugins.LoadingStrategyScript
+		}
+	}
+
+	// If the plugin has a parent, check the parent's create_plugin_version setting
+	if p.Parent != nil {
+		if pCfg, ok := s.cfg.PluginSettings[p.Parent.ID]; ok {
+			if s.compatibleCreatePluginVersion(pCfg) {
+				return plugins.LoadingStrategyScript
+			}
+		}
+	}
+
+	if !s.cndEnabled(p) && !p.Angular.Detected {
+		return plugins.LoadingStrategyScript
+	}
+
+	return plugins.LoadingStrategyFetch
+}
+
+func (s *Service) compatibleCreatePluginVersion(ps map[string]string) bool {
+	if cpv, ok := ps[CreatePluginVersionCfgKey]; ok {
+		createPluginVer, err := semver.NewVersion(cpv)
+		if err != nil {
+			s.log.Warn("Failed to parse create plugin version setting as semver", "version", cpv, "error", err)
+		} else {
+			if !createPluginVer.LessThan(scriptLoadingMinSupportedVersion) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (s *Service) cndEnabled(p pluginstore.Plugin) bool {
+	return s.cdn.PluginSupported(p.ID) || p.Class == plugins.ClassCDN
+}