Plugins: Plugins loader pipeline (#71438)

* discovery

* flesh out

* add docs

* remove unused func

* bootstrap stage

* fix docs

* update docs

* undo unnecessary changes

* add end tag

* update doc

* fix linter

* fix

* tidy

* update docs

* add class to filter func

* apply PR feedback

* fix test

pkg/plugins/manager/pipeline/bootstrap/bootstrap.go

@@ -0,0 +1,78 @@
+package bootstrap
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/plugins/config"
+	"github.com/grafana/grafana/pkg/plugins/log"
+	"github.com/grafana/grafana/pkg/plugins/manager/loader/assetpath"
+	"github.com/grafana/grafana/pkg/plugins/manager/signature"
+)
+
+// Bootstrapper is responsible for the Bootstrap stage of the plugin loader pipeline.
+type Bootstrapper interface {
+	Bootstrap(ctx context.Context, src plugins.PluginSource, bundles []*plugins.FoundBundle) ([]*plugins.Plugin, error)
+}
+
+// ConstructFunc is the function used for the Construct step of the Bootstrap stage.
+type ConstructFunc func(ctx context.Context, src plugins.PluginSource, bundles []*plugins.FoundBundle) ([]*plugins.Plugin, error)
+
+// DecorateFunc is the function used for the Decorate step of the Bootstrap stage.
+type DecorateFunc func(ctx context.Context, p *plugins.Plugin) (*plugins.Plugin, error)
+
+// Bootstrap implements the Bootstrapper interface.
+//
+// The Bootstrap stage is made up of the following steps (in order):
+// - Construct: Create the initial plugin structs based on the plugin(s) found in the Discovery stage.
+// - Decorate: Decorate the plugins with additional metadata.
+//
+// The Construct step is implemented by the ConstructFunc type.
+//
+// The Decorate step is implemented by the DecorateFunc type.
+type Bootstrap struct {
+	constructStep ConstructFunc
+	decorateSteps []DecorateFunc
+	log           log.Logger
+}
+
+type Opts struct {
+	ConstructFunc ConstructFunc
+	DecorateFuncs []DecorateFunc
+}
+
+// New returns a new Bootstrap stage.
+func New(cfg *config.Cfg, opts Opts) *Bootstrap {
+	if opts.ConstructFunc == nil {
+		opts.ConstructFunc = DefaultConstructFunc(signature.DefaultCalculator(), assetpath.DefaultService(cfg))
+	}
+
+	if len(opts.DecorateFuncs) == 0 {
+		opts.DecorateFuncs = DefaultDecorateFuncs
+	}
+
+	return &Bootstrap{
+		constructStep: opts.ConstructFunc,
+		decorateSteps: opts.DecorateFuncs,
+		log:           log.New("plugins.bootstrap"),
+	}
+}
+
+// Bootstrap will execute the Construct and Decorate steps of the Bootstrap stage.
+func (b *Bootstrap) Bootstrap(ctx context.Context, src plugins.PluginSource, found []*plugins.FoundBundle) ([]*plugins.Plugin, error) {
+	ps, err := b.constructStep(ctx, src, found)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, p := range ps {
+		for _, decorator := range b.decorateSteps {
+			p, err = decorator(ctx, p)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return ps, nil
+}