Clarify error message around on(x) group_left(x)

promql/ast.go

@@ -235,7 +235,7 @@ type VectorMatching struct {
 	// rather than only using them.
 	Ignoring bool
 	// Include contains additional labels that should be included in
-	// the result from the side with the higher cardinality.
+	// the result from the side with the lower cardinality.
 	Include model.LabelNames
 }
 

promql/parse.go

@@ -486,7 +486,7 @@ func (p *parser) expr() Expr {
 		for _, ln := range vecMatching.MatchingLabels {
 			for _, ln2 := range vecMatching.Include {
 				if ln == ln2 && !vecMatching.Ignoring {
-					p.errorf("label %q must not occur in ON and INCLUDE clause at once", ln)
+					p.errorf("label %q must not occur in ON and GROUP clause at once", ln)
 				}
 			}
 		}

promql/parse_test.go

@@ -757,7 +757,7 @@ var testExpr = []struct {
 	}, {
 		input:  `http_requests{group="production"} + on(instance) group_left(job,instance) cpu_count{type="smp"}`,
 		fail:   true,
-		errMsg: "label \"instance\" must not occur in ON and INCLUDE clause at once",
+		errMsg: "label \"instance\" must not occur in ON and GROUP clause at once",
 	}, {
 		input:  "foo + bool bar",
 		fail:   true,