Serialize query AST to JSON. (#11123)

**What this PR does / why we need it**:
This introduces the visitor pattern to serialize the LogQL AST to JSON.
We've chose this pattern because it will be more flexible one the AST is
encoded into Protobuf and an actual queryplan.

**Checklist**
- [ ] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [ ] Documentation added
- [x] Tests updated
- [ ] `CHANGELOG.md` updated
- [ ] If the change is worth mentioning in the release notes, add
`add-to-release-notes` label
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/setup/upgrade/_index.md`
- [ ] For Helm chart changes bump the Helm chart version in
`production/helm/loki/Chart.yaml` and update
`production/helm/loki/CHANGELOG.md` and
`production/helm/loki/README.md`. [Example
PR](d10549e)
- [ ] If the change is deprecating or removing a configuration option,
update the `deprecated-config.yaml` and `deleted-config.yaml` files
respectively in the `tools/deprecated-config-checker` directory.
[Example
PR](0d4416a)

pkg/logql/log/ip.go

@@ -78,39 +78,41 @@ func (f *IPLineFilter) filterTy(line []byte, ty labels.MatchType) bool {
 
 type IPLabelFilter struct {
 	ip *ipFilter
-	ty LabelFilterType
+	Ty LabelFilterType
 
-	// if used as label matcher, this holds the identifier label name.
+	// if used as Label matcher, this holds the identifier Label name.
 	// e.g: (|remote_addr = ip("xxx")). Here labelName is `remote_addr`
-	label string
+	Label string
 
 	// patError records if given pattern is invalid.
 	patError error
 
-	// local copy of pattern to display it in errors, even though pattern matcher fails because of invalid pattern.
-	pattern string
+	// local copy of Pattern to display it in errors, even though Pattern matcher fails because of invalid Pattern.
+	Pattern string
 }
 
 // NewIPLabelFilter is used to construct ip filter as label filter for the given `label`.
-func NewIPLabelFilter(pattern string, label string, ty LabelFilterType) *IPLabelFilter {
+func NewIPLabelFilter(pattern, label string, ty LabelFilterType) *IPLabelFilter {
 	ip, err := newIPFilter(pattern)
 	return &IPLabelFilter{
 		ip:       ip,
-		label:    label,
-		ty:       ty,
+		Label:    label,
+		Ty:       ty,
 		patError: err,
-		pattern:  pattern,
+		Pattern:  pattern,
 	}
 }
 
 // `Process` implements `Stage` interface
 func (f *IPLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([]byte, bool) {
-	return line, f.filterTy(line, f.ty, lbs)
+	return line, f.filterTy(line, f.Ty, lbs)
 }
 
+func (f *IPLabelFilter) isLabelFilterer() {}
+
 // `RequiredLabelNames` implements `Stage` interface
 func (f *IPLabelFilter) RequiredLabelNames() []string {
-	return []string{f.label}
+	return []string{f.Label}
 }
 
 // PatternError will be used `labelFilter.Stage()` method so that, if the given pattern is wrong
@@ -124,7 +126,7 @@ func (f *IPLabelFilter) filterTy(_ []byte, ty LabelFilterType, lbs *LabelsBuilde
 		// why `true`?. if there's an error only the string matchers can filter out.
 		return true
 	}
-	input, ok := lbs.Get(f.label)
+	input, ok := lbs.Get(f.Label)
 	if !ok {
 		// we have not found the label.
 		return false
@@ -146,11 +148,11 @@ func (f *IPLabelFilter) filterTy(_ []byte, ty LabelFilterType, lbs *LabelsBuilde
 // `String` implements fmt.Stringer inteface, by which also implements `LabelFilterer` inteface.
 func (f *IPLabelFilter) String() string {
 	eq := "=" // LabelFilterEqual -> "==", we don't want in string representation of ip label filter.
-	if f.ty == LabelFilterNotEqual {
+	if f.Ty == LabelFilterNotEqual {
 		eq = LabelFilterNotEqual.String()
 	}
 
-	return fmt.Sprintf("%s%sip(%q)", f.label, eq, f.pattern) // label filter
+	return fmt.Sprintf("%s%sip(%q)", f.Label, eq, f.Pattern) // label filter
 }
 
 // ipFilter search for IP addresses of given `pattern` in the given `line`.

pkg/logql/log/label_filter.go

@@ -54,23 +54,28 @@ func (f LabelFilterType) String() string {
 }
 
 // LabelFilterer can filter extracted labels.
+//
+//sumtype:decl
 type LabelFilterer interface {
 	Stage
 	fmt.Stringer
+
+	// Seal trait
+	isLabelFilterer()
 }
 
 type BinaryLabelFilter struct {
 	Left  LabelFilterer
 	Right LabelFilterer
-	and   bool
+	And   bool
 }
 
 // NewAndLabelFilter creates a new LabelFilterer from a and binary operation of two LabelFilterer.
 func NewAndLabelFilter(left LabelFilterer, right LabelFilterer) *BinaryLabelFilter {
 	return &BinaryLabelFilter{
 		Left:  left,
 		Right: right,
-		and:   true,
+		And:   true,
 	}
 }
 
@@ -84,16 +89,18 @@ func NewOrLabelFilter(left LabelFilterer, right LabelFilterer) *BinaryLabelFilte
 
 func (b *BinaryLabelFilter) Process(ts int64, line []byte, lbs *LabelsBuilder) ([]byte, bool) {
 	line, lok := b.Left.Process(ts, line, lbs)
-	if !b.and && lok {
+	if !b.And && lok {
 		return line, true
 	}
 	line, rok := b.Right.Process(ts, line, lbs)
-	if !b.and {
+	if !b.And {
 		return line, lok || rok
 	}
 	return line, lok && rok
 }
 
+func (b *BinaryLabelFilter) isLabelFilterer() {}
+
 func (b *BinaryLabelFilter) RequiredLabelNames() []string {
 	var names []string
 	names = append(names, b.Left.RequiredLabelNames()...)
@@ -105,7 +112,7 @@ func (b *BinaryLabelFilter) String() string {
 	var sb strings.Builder
 	sb.WriteString("( ")
 	sb.WriteString(b.Left.String())
-	if b.and {
+	if b.And {
 		sb.WriteString(" , ")
 	} else {
 		sb.WriteString(" or ")
@@ -122,6 +129,9 @@ type NoopLabelFilter struct {
 func (NoopLabelFilter) Process(_ int64, line []byte, _ *LabelsBuilder) ([]byte, bool) {
 	return line, true
 }
+
+func (NoopLabelFilter) isLabelFilterer() {}
+
 func (NoopLabelFilter) RequiredLabelNames() []string { return []string{} }
 
 func (f NoopLabelFilter) String() string {
@@ -197,6 +207,8 @@ func (d *BytesLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([]
 	}
 }
 
+func (d *BytesLabelFilter) isLabelFilterer() {}
+
 func (d *BytesLabelFilter) RequiredLabelNames() []string {
 	return []string{d.Name}
 }
@@ -207,7 +219,7 @@ func (d *BytesLabelFilter) String() string {
 			return -1
 		}
 		return r
-	}, humanize.Bytes(d.Value))
+	}, humanize.Bytes(d.Value)) // TODO: discuss whether this should just be bytes, B, to be more accurate.
 	return fmt.Sprintf("%s%s%s", d.Name, d.Type, b)
 }
 
@@ -262,6 +274,8 @@ func (d *DurationLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder)
 	}
 }
 
+func (d *DurationLabelFilter) isLabelFilterer() {}
+
 func (d *DurationLabelFilter) RequiredLabelNames() []string {
 	return []string{d.Name}
 }
@@ -323,6 +337,8 @@ func (n *NumericLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) (
 
 }
 
+func (n *NumericLabelFilter) isLabelFilterer() {}
+
 func (n *NumericLabelFilter) RequiredLabelNames() []string {
 	return []string{n.Name}
 }
@@ -348,7 +364,7 @@ func NewStringLabelFilter(m *labels.Matcher) LabelFilterer {
 		return &NoopLabelFilter{m}
 	}
 
-	return &lineFilterLabelFilter{
+	return &LineFilterLabelFilter{
 		Matcher: m,
 		filter:  f,
 	}
@@ -358,18 +374,20 @@ func (s *StringLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([
 	return line, s.Matches(labelValue(s.Name, lbs))
 }
 
+func (s *StringLabelFilter) isLabelFilterer() {}
+
 func (s *StringLabelFilter) RequiredLabelNames() []string {
 	return []string{s.Name}
 }
 
-// lineFilterLabelFilter filters the desired label using an optimized line filter
-type lineFilterLabelFilter struct {
+// LineFilterLabelFilter filters the desired label using an optimized line filter
+type LineFilterLabelFilter struct {
 	*labels.Matcher
 	filter Filterer
 }
 
 // overrides the matcher.String() function in case there is a regexpFilter
-func (s *lineFilterLabelFilter) String() string {
+func (s *LineFilterLabelFilter) String() string {
 	if unwrappedFilter, ok := s.filter.(regexpFilter); ok {
 		rStr := unwrappedFilter.String()
 		str := fmt.Sprintf("%s%s`%s`", s.Matcher.Name, s.Matcher.Type, rStr)
@@ -378,12 +396,14 @@ func (s *lineFilterLabelFilter) String() string {
 	return s.Matcher.String()
 }
 
-func (s *lineFilterLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([]byte, bool) {
+func (s *LineFilterLabelFilter) Process(_ int64, line []byte, lbs *LabelsBuilder) ([]byte, bool) {
 	v := labelValue(s.Name, lbs)
 	return line, s.filter.Filter(unsafeGetBytes(v))
 }
 
-func (s *lineFilterLabelFilter) RequiredLabelNames() []string {
+func (s *LineFilterLabelFilter) isLabelFilterer() {}
+
+func (s *LineFilterLabelFilter) RequiredLabelNames() []string {
 	return []string{s.Name}
 }