colexec: fixed nullableArgs projection operators

Previously, the `Concat` projection operators on arrays directly copy nulls into
the output without performing the actual projection whenever either argument was
null. This is incorrect because `Concat` operator can actually handle null arguments,
and we want the actual projection result instead. Since currently the only
projection operator that needs `nullableArgs == true` behaviour is
`ConcatDatumDatum`, this PR fixed this by adding a boolean field `nullableArgs`
to the logic for operators with `Datum`, `Datum`. If we later introduce another
projection operation that has nullableArgs == true, we should update this code
accordingly.

Fixes: cockroachdb#83091

Release note (bug fix): Fixed a bug in `Concat` projection operators on arrays
that gave output of nulls when the projection operator can actually handle null
arguments and may result in a non-null output.

pkg/sql/colexec/colbuilder/execplan.go

@@ -1991,7 +1991,7 @@ func planProjectionOperators(
 		}
 		return planProjectionExpr(
 			ctx, evalCtx, t.Operator, t.ResolvedType(), t.TypedLeft(), t.TypedRight(),
-			columnTypes, input, acc, factory, t.Fn.Fn, nil /* cmpExpr */, releasables,
+			columnTypes, input, acc, factory, t.Fn.Fn, nil /* cmpExpr */, releasables, t.Fn.NullableArgs,
 		)
 	case *tree.CaseExpr:
 		allocator := colmem.NewAllocator(ctx, acc, factory)
@@ -2143,7 +2143,7 @@ func planProjectionOperators(
 	case *tree.ComparisonExpr:
 		return planProjectionExpr(
 			ctx, evalCtx, t.Operator, t.ResolvedType(), t.TypedLeft(), t.TypedRight(),
-			columnTypes, input, acc, factory, nil /* binFn */, t, releasables,
+			columnTypes, input, acc, factory, nil /* binFn */, t, releasables, t.Fn.NullableArgs,
 		)
 	case tree.Datum:
 		op, err = projectDatum(t)
@@ -2310,6 +2310,7 @@ func planProjectionExpr(
 	binFn tree.TwoArgFn,
 	cmpExpr *tree.ComparisonExpr,
 	releasables *[]execinfra.Releasable,
+	nullableArgs bool,
 ) (op colexecop.Operator, resultIdx int, typs []*types.T, err error) {
 	if err := checkSupportedProjectionExpr(left, right); err != nil {
 		return nil, resultIdx, typs, err
@@ -2346,7 +2347,7 @@ func planProjectionExpr(
 		// appended to the input batch.
 		op, err = colexecproj.GetProjectionLConstOperator(
 			allocator, typs, left.ResolvedType(), outputType, projOp, input,
-			rightIdx, lConstArg, resultIdx, evalCtx, binFn, cmpExpr,
+			rightIdx, lConstArg, resultIdx, evalCtx, binFn, cmpExpr, nullableArgs,
 		)
 	} else {
 		var leftIdx int
@@ -2423,7 +2424,7 @@ func planProjectionExpr(
 				// all other projection operators.
 				op, err = colexecproj.GetProjectionRConstOperator(
 					allocator, typs, right.ResolvedType(), outputType, projOp,
-					input, leftIdx, rConstArg, resultIdx, evalCtx, binFn, cmpExpr,
+					input, leftIdx, rConstArg, resultIdx, evalCtx, binFn, cmpExpr, nullableArgs,
 				)
 			}
 		} else {
@@ -2438,7 +2439,7 @@ func planProjectionExpr(
 			resultIdx = len(typs)
 			op, err = colexecproj.GetProjectionOperator(
 				allocator, typs, outputType, projOp, input, leftIdx, rightIdx,
-				resultIdx, evalCtx, binFn, cmpExpr,
+				resultIdx, evalCtx, binFn, cmpExpr, nullableArgs,
 			)
 		}
 	}