Fix duplicate output vector if delayed name removal is disabled (#15975)

Fix duplicate output vector if delayed name removal is disabled

This error is emitted in cleanupMetricLabels, but is skipped if
enableDelayedNameRemoval is false.

This makes it consistent with label_replace

Signed-off-by: Joshua Hesketh <josh@nitrotech.org>

---------

Signed-off-by: Joshua Hesketh <josh@nitrotech.org>
Signed-off-by: Björn Rabenstein <github@rabenste.in>
Co-authored-by: Björn Rabenstein <github@rabenste.in>

promql/functions.go

@@ -1689,6 +1689,9 @@ func (ev *evaluator) evalLabelJoin(ctx context.Context, args parser.Expressions)
 			matrix[i].DropName = el.DropName
 		}
 	}
+	if matrix.ContainsSameLabelset() {
+		ev.errorf("vector cannot contain metrics with the same labelset")
+	}
 
 	return matrix, ws
 }

promql/promqltest/testdata/functions.test

@@ -499,6 +499,8 @@ eval instant at 20s timestamp(metric)
 load 5m
   testmetric{src="a",src1="b",src2="c",dst="original-destination-value"} 0
   testmetric{src="d",src1="e",src2="f",dst="original-destination-value"} 1
+  dup{label="a", this="a"} 1.0
+  dup{label="b", this="a"} 1.0
 
 # label_join joins all src values in order.
 eval instant at 0m label_join(testmetric, "dst", "-", "src", "src1", "src2")
@@ -530,6 +532,9 @@ eval instant at 0m label_join(testmetric1, "dst", ", ", "src", "src1", "src2")
   testmetric1{src="foo",src1="bar",src2="foobar",dst="foo, bar, foobar"} 0
   testmetric1{src="fizz",src1="buzz",src2="fizzbuzz",dst="fizz, buzz, fizzbuzz"} 1
 
+eval_fail instant at 0m label_join(dup, "label", "", "this")
+  expected_fail_message vector cannot contain metrics with the same labelset
+
 clear
 
 # Tests for vector.