apacheGH-39860: [C++] Expression ExecuteScalarExpression execute empt…

…y args function with a wrong result (apache#39908)

### Rationale for this change

Try to fix apache#39860.

### What changes are included in this PR?

Deal with the call->arguments.size() == 0's condition in ExecuteScalarExpression when we call some functions
has no arguments, like (random, hash_count ...).

### Are these changes tested?

Yes

### Are there any user-facing changes?

No.
* Closes: apache#39860

Lead-authored-by: hugo.zhang <hugo.zhang@openpie.com>
Co-authored-by: 张回归 <zhanghuigui@zhanghuiguideMacBook-Pro-1681.local>
Signed-off-by: Benjamin Kietzman <bengilgit@gmail.com>

cpp/src/arrow/compute/expression.cc

@@ -761,6 +761,15 @@ Result<Datum> ExecuteScalarExpression(const Expression& expr, const ExecBatch& i
     }
   }
 
+  int64_t input_length;
+  if (!arguments.empty() && all_scalar) {
+    // all inputs are scalar, so use a 1-long batch to avoid
+    // computing input.length equivalent outputs
+    input_length = 1;
+  } else {
+    input_length = input.length;
+  }
+
   auto executor = compute::detail::KernelExecutor::MakeScalar();
 
   compute::KernelContext kernel_context(exec_context, call->kernel);
@@ -772,8 +781,8 @@ Result<Datum> ExecuteScalarExpression(const Expression& expr, const ExecBatch& i
   RETURN_NOT_OK(executor->Init(&kernel_context, {kernel, types, options}));
 
   compute::detail::DatumAccumulator listener;
-  RETURN_NOT_OK(executor->Execute(
-      ExecBatch(std::move(arguments), all_scalar ? 1 : input.length), &listener));
+  RETURN_NOT_OK(
+      executor->Execute(ExecBatch(std::move(arguments), input_length), &listener));
   const auto out = executor->WrapResults(arguments, listener.values());
 #ifndef NDEBUG
   DCHECK_OK(executor->CheckResultType(out, call->function_name.c_str()));

cpp/src/arrow/compute/expression_test.cc

@@ -863,6 +863,25 @@ TEST(Expression, ExecuteCall) {
   ])"));
 }
 
+TEST(Expression, ExecuteCallWithNoArguments) {
+  const int kCount = 10;
+  auto random_options = RandomOptions::FromSeed(/*seed=*/0);
+  ExecBatch input({}, kCount);
+
+  Expression random_expr = call("random", {}, random_options);
+  ASSERT_OK_AND_ASSIGN(random_expr, random_expr.Bind(float64()));
+
+  ASSERT_OK_AND_ASSIGN(Datum actual, ExecuteScalarExpression(random_expr, input));
+  compute::ExecContext* exec_context = default_exec_context();
+  ASSERT_OK_AND_ASSIGN(auto function,
+                       exec_context->func_registry()->GetFunction("random"));
+  ASSERT_OK_AND_ASSIGN(Datum expected,
+                       function->Execute(input, &random_options, exec_context));
+  AssertDatumsEqual(actual, expected, /*verbose=*/true);
+
+  EXPECT_EQ(actual.length(), kCount);
+}
+
 TEST(Expression, ExecuteDictionaryTransparent) {
   ExpectExecute(
       equal(field_ref("a"), field_ref("b")),