Fix sharding of vector and time functions

Functions `vector` and `time` can't be sharded, as they produce same set
of series (with zero labels) and can't be concatenated later.

Additionally, functions that have a default `time()` argument,
like `month()`, were not propagating the shardeability checks properly.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

pkg/frontend/querymiddleware/astmapper/parallel.go

@@ -29,6 +29,21 @@ var NonParallelFuncs = []string{
 	"histogram_quantile",
 	"sort_desc",
 	"sort",
+	"time",
+	"vector",
+}
+
+// FuncsWithDefaultTimeArg is the list of functions that extract date information from a variadic list of params,
+// which defaults to be just time() otherwise.
+var FuncsWithDefaultTimeArg = []string{
+	"day_of_month",
+	"day_of_week",
+	"day_of_year",
+	"days_in_month",
+	"hour",
+	"minute",
+	"month",
+	"year",
 }
 
 // CanParallelize tests if a subtree is parallelizable.
@@ -81,7 +96,7 @@ func CanParallelize(node parser.Node, logger log.Logger) bool {
 			return false
 		}
 
-		for _, e := range n.Args {
+		for _, e := range argsWithDefaults(n) {
 			if !CanParallelize(e, logger) {
 				return false
 			}
@@ -133,6 +148,28 @@ func ParallelizableFunc(f parser.Function) bool {
 	return true
 }
 
+// argsWithDefaults returns the arguments of the call, including the omitted defaults.
+func argsWithDefaults(call *parser.Call) parser.Expressions {
+	for _, fn := range FuncsWithDefaultTimeArg {
+		if fn == call.Func.Name && len(call.Args) == 0 {
+			return parser.Expressions{
+				&parser.Call{Func: parser.Functions["time"]},
+			}
+		}
+	}
+	return call.Args
+}
+
+// VariadicDateFunc retuns true if .
+func VariadicDateFunc(f parser.Function) bool {
+	for _, v := range NonParallelFuncs {
+		if v == f.Name {
+			return false
+		}
+	}
+	return true
+}
+
 func noAggregates(n parser.Node) bool {
 	hasAggregates, _ := anyNode(n, isAggregateExpr)
 	return !hasAggregates

pkg/frontend/querymiddleware/astmapper/parallel_test.go

@@ -196,3 +196,24 @@ func TestCanParallel_String(t *testing.T) {
 		})
 	}
 }
+
+func TestFunctionsWithDefaultsIsUpToDate(t *testing.T) {
+	for name, f := range parser.Functions {
+		t.Run(name, func(t *testing.T) {
+			if f.Variadic == 0 {
+				return
+			}
+			if f.Name == "label_join" {
+				// label_join has no defaults, it just accepts any number of labels
+				return
+			}
+			if f.Name == "round" {
+				// round has a default value for the second scalar value, which is not relevant for sharding purposes.
+				return
+			}
+
+			// Rest of the functions with known defaults are functions with a default time() argument.
+			require.Containsf(t, FuncsWithDefaultTimeArg, name, "Function %q has variable arguments, and it's not in the list of functions with default time() argument.")
+		})
+	}
+}

pkg/frontend/querymiddleware/astmapper/sharding_test.go

@@ -446,6 +446,16 @@ func TestShardSummer(t *testing.T) {
 				`)`,
 			expectedShardedQueries: 6,
 		},
+		{
+			in:                     `vector(1) > 0 and vector(1)`,
+			out:                    `vector(1) > 0 and vector(1)`,
+			expectedShardedQueries: 0,
+		},
+		{
+			in:                     `sum(foo) > 0 and vector(1)`,
+			out:                    `sum(` + concatShards(3, `sum(foo{__query_shard__="x_of_y"})`) + `) > 0 and vector(1)`,
+			expectedShardedQueries: 3,
+		},
 	} {
 		tt := tt
 

pkg/frontend/querymiddleware/querysharding_test.go

@@ -447,6 +447,38 @@ func TestQueryShardingCorrectness(t *testing.T) {
 			expectedShardedQueries: 0,
 			noRangeQuery:           true,
 		},
+		"day_of_month() >= 1 and day_of_month()": {
+			query:                  `day_of_month() >= 1 and day_of_month()`,
+			expectedShardedQueries: 0,
+		},
+		"month() >= 1 and month()": {
+			query:                  `month() >= 1 and month()`,
+			expectedShardedQueries: 0,
+		},
+		"vector(1) > 0 and vector(1)": {
+			query:                  `vector(1) > 0 and vector(1)`,
+			expectedShardedQueries: 0,
+		},
+		"sum(metric_counter) > 0 and vector(1)": {
+			query:                  `sum(metric_counter) > 0 and vector(1)`,
+			expectedShardedQueries: 1,
+		},
+		"vector(1)": {
+			query:                  `vector(1)`,
+			expectedShardedQueries: 0,
+		},
+		"time()": {
+			query:                  `vector()`,
+			expectedShardedQueries: 0,
+		},
+		"month(sum(metric_counter))": {
+			query:                  `month(sum(metric_counter))`,
+			expectedShardedQueries: 1, // Sharded because the contents of `sum()` is sharded.
+		},
+		"month(sum(metric_counter)) > 0 and vector(1)": {
+			query:                  `month(sum(metric_counter)) > 0 and vector(1)`,
+			expectedShardedQueries: 1, // Sharded because the contents of `sum()` is sharded.
+		},
 	}
 
 	series := make([]*promql.StorageSeries, 0, numSeries+(numHistograms*len(histogramBuckets)))