SSE/NG: Add expression metadata for EvalMatch (#32213)

- Add the ability to stick metadata attached to a value in expressions. Currently uses Frame.Meta.Custom.
- None of this is consumed by anything yet, so an incremental step.

pkg/expr/mathexp/type_series.go

@@ -97,6 +97,14 @@ func (s Series) SetLabels(ls data.Labels) { s.Frame.Fields[s.ValueIdx].Labels =
 
 func (s Series) GetName() string { return s.Frame.Name }
 
+func (s Series) GetMeta() interface{} {
+	return s.Frame.Meta.Custom
+}
+
+func (s Series) SetMeta(v interface{}) {
+	s.Frame.SetMeta(&data.FrameMeta{Custom: v})
+}
+
 // AsDataFrame returns the underlying *data.Frame.
 func (s Series) AsDataFrame() *data.Frame { return s.Frame }
 

pkg/expr/mathexp/types.go

@@ -30,6 +30,8 @@ type Value interface {
 	Value() interface{}
 	GetLabels() data.Labels
 	SetLabels(data.Labels)
+	GetMeta() interface{}
+	SetMeta(interface{})
 	AsDataFrame() *data.Frame
 }
 
@@ -48,6 +50,14 @@ func (s Scalar) GetLabels() data.Labels { return nil }
 
 func (s Scalar) SetLabels(ls data.Labels) {}
 
+func (s Scalar) GetMeta() interface{} {
+	return s.Frame.Meta.Custom
+}
+
+func (s Scalar) SetMeta(v interface{}) {
+	s.Frame.SetMeta(&data.FrameMeta{Custom: v})
+}
+
 // AsDataFrame returns the underlying *data.Frame.
 func (s Scalar) AsDataFrame() *data.Frame { return s.Frame }
 
@@ -105,3 +115,11 @@ func NewNumber(name string, labels data.Labels) Number {
 		),
 	}
 }
+
+func (n Number) GetMeta() interface{} {
+	return n.Frame.Meta.Custom
+}
+
+func (n Number) SetMeta(v interface{}) {
+	n.Frame.SetMeta(&data.FrameMeta{Custom: v})
+}