[Fix] OR statements not being evaluated as part of nested line filters (

grafana#11735)

**What this PR does / why we need it**:
When nester line filters were being evaluated, the `OR` statements in
right expressions were omitted and only `LineFilters` were returned.
Resulting in only first value being returned.
It can be reproduced in stringer unit test failing with, 
```
Error Trace:	/Users/poyzannur/workspace/loki/pkg/logql/syntax/ast_test.go:535
        	Error:      	Not equal: 
        	            	expected: "{app=\"foo\"} |= \"foo\" or \"bar\" |= \"baz\" or \"bal\""
        	            	actual  : "{app=\"foo\"} |= \"foo\" or \"bar\" |= \"baz\""
```

We now return the `OR` expression as part of nested line filters. Thanks
a million to @ashwanthgoli for help with debugging, and extra unit test.

**Which issue(s) this PR fixes**:
Fixes https://github.com/grafana/support-escalations/issues/9042

**Special notes for your reviewer**:

**Checklist**
- [x] 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](grafana@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](grafana@0d4416a)

pkg/logql/syntax/ast.go

@@ -353,6 +353,8 @@ func newNestedLineFilterExpr(left *LineFilterExpr, right *LineFilterExpr) *LineF
 	return &LineFilterExpr{
 		Left:       left,
 		LineFilter: right.LineFilter,
+		Or:         right.Or,
+		IsOrChild:  right.IsOrChild,
 	}
 }
 

pkg/logql/syntax/ast_test.go

@@ -383,6 +383,13 @@ func Test_FilterMatcher(t *testing.T) {
 			},
 			[]linecheck{{"foo", true}, {"bar", true}, {"none", false}},
 		},
+		{
+			`{app="foo"} |= "foo" or "bar" |= "buzz" or "fizz"`,
+			[]*labels.Matcher{
+				mustNewMatcher(labels.MatchEqual, "app", "foo"),
+			},
+			[]linecheck{{"foo buzz", true}, {"bar fizz", true}, {"foo", false}, {"bar", false}, {"none", false}},
+		},
 		{
 			`{app="foo"} != "foo" or "bar"`,
 			[]*labels.Matcher{
@@ -496,6 +503,14 @@ func TestStringer(t *testing.T) {
 			in:  `{app="foo"} |~ "foo" or "bar" or "baz"`,
 			out: `{app="foo"} |~ "foo" or "bar" or "baz"`,
 		},
+		{
+			in:  `{app="foo"} |= "foo" or "bar" |= "buzz" or "fizz"`,
+			out: `{app="foo"} |= "foo" or "bar" |= "buzz" or "fizz"`,
+		},
+		{
+			out: `{app="foo"} |= "foo" or "bar" |~ "buzz|fizz"`,
+			in:  `{app="foo"} |= "foo" or "bar" |~ "buzz|fizz"`,
+		},
 		{
 			in:  `{app="foo"} |= ip("127.0.0.1") or "foo"`,
 			out: `{app="foo"} |= ip("127.0.0.1") or "foo"`,

pkg/logql/syntax/parser_test.go

@@ -3138,6 +3138,41 @@ var ParseTestCases = []struct {
 			},
 		},
 	},
+	{
+		in: `{app="foo"} |= "foo" or "bar" |= "buzz" or "fizz"`,
+		exp: &PipelineExpr{
+			Left: newMatcherExpr([]*labels.Matcher{mustNewMatcher(labels.MatchEqual, "app", "foo")}),
+			MultiStages: MultiStageExpr{
+				&LineFilterExpr{
+					Left: newOrLineFilter(
+						&LineFilterExpr{
+							LineFilter: LineFilter{
+								Ty:    labels.MatchEqual,
+								Match: "foo",
+							},
+						},
+						&LineFilterExpr{
+							LineFilter: LineFilter{
+								Ty:    labels.MatchEqual,
+								Match: "bar",
+							},
+						}),
+					LineFilter: LineFilter{
+						Ty:    labels.MatchEqual,
+						Match: "buzz",
+					},
+					Or: &LineFilterExpr{
+						LineFilter: LineFilter{
+							Ty:    labels.MatchEqual,
+							Match: "fizz",
+						},
+						IsOrChild: true,
+					},
+					IsOrChild: false,
+				},
+			},
+		},
+	},
 }
 
 func TestParse(t *testing.T) {