GH-37515: [C++] Remove memory address optimization from `ChunkedArray…

…::Equals(const std::shared_ptr<arrow::ChunkedArray>& other)` if the `ChunkedArray` can have `NaN` values (#37579)

### Rationale for this change

`ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other)` assumes that if the two `ChunkedArray`s share the same memory address, then they must be equal. However, this optimization doesn't take into account that `NaN` values are not considered equal by default. Consequently, this can lead to surprising, inconsistent results from a user's perspective. For example, `ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other)`  and `ChunkedArray::Equals(const ChunkedArray& other)` may return different results.

 The program below illustrates this inconsistency:

```c++
#include <arrow/api.h>
#include <arrow/type.h>

#include <iostream>
#include <math.h>
#include <sstream>

arrow::Result<std::shared_ptr<arrow::ChunkedArray>> make_chunked_array() {
    arrow::NumericBuilder<arrow::DoubleType> builder;
    
    std::shared_ptr<arrow::Array> array;
    ARROW_RETURN_NOT_OK(builder.AppendValues({0, 1, NAN, 2, 4}));
    ARROW_RETURN_NOT_OK(builder.Finish(&array));
    
    return arrow::ChunkedArray::Make({array});
}

int main(int argc, char *argv[])
{
    auto maybe_chunked_array = make_chunked_array();
    if (!maybe_chunked_array.ok()) {
        return -1;
    }
    auto chunked_array = std::move(maybe_chunked_array).ValueUnsafe();
    auto array = chunked_array->chunk(0);
    
    std::stringstream stream;

    stream << "chunked_array contents: ";
    stream << "\n\n";
    stream << chunked_array->ToString();
    stream << "\n\n";
    stream << "chunked_array->Equals(chunked_array): ";
    stream << chunked_array->Equals(chunked_array);
    stream << "chunked_array->Equals(*chunked_array): ";
    stream << chunked_array->Equals(*chunked_array);
    
    std::cout << stream.str() << std::endl;
}
```

Here is the output of this program:

```shell
chunked_array contents: 

[
  [
    0,
    1,
    nan,
    2,
    4
  ]
]

chunked_array->Equals(chunked_array): 1
chunked_array->Equals(*chunked_array): 0
```

### What changes are included in this PR?

Updated `ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other)` to only return `true` early IF:
   - The two share the same address AND
   - They cannot have `NaN` values 

If both of those conditions are not satisfied, `ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other)` will do the element-by-element comparison.

### Are these changes tested?

Yes. I added a new test case called `EqualsSameAddressWithNaNs` to `chunked_array_test.cc`.

### Are there any user-facing changes?

Yes. `ChunkedArray::Equals(const std::shared_ptr<arrow::ChunkedArray>& other)` may return `false` even if the two `ChunkedArray`s have the same memory address. This will only occur if the `ChunkedArray`'s contain `NaN` values.

* Closes: #37515

Authored-by: Sarah Gilmore <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

cpp/src/arrow/chunked_array.cc

@@ -30,6 +30,7 @@
 #include "arrow/pretty_print.h"
 #include "arrow/status.h"
 #include "arrow/type.h"
+#include "arrow/type_traits.h"
 #include "arrow/util/checked_cast.h"
 #include "arrow/util/logging.h"
 
@@ -111,13 +112,30 @@ bool ChunkedArray::Equals(const ChunkedArray& other) const {
       .ok();
 }
 
-bool ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other) const {
-  if (this == other.get()) {
-    return true;
+namespace {
+
+bool mayHaveNaN(const arrow::DataType& type) {
+  if (type.num_fields() == 0) {
+    return is_floating(type.id());
+  } else {
+    for (const auto& field : type.fields()) {
+      if (mayHaveNaN(*field->type())) {
+        return true;
+      }
+    }
   }
+  return false;
+}
+
+}  //  namespace
+
+bool ChunkedArray::Equals(const std::shared_ptr<ChunkedArray>& other) const {
   if (!other) {
     return false;
   }
+  if (this == other.get() && !mayHaveNaN(*type_)) {
+    return true;
+  }
   return Equals(*other.get());
 }
 

cpp/src/arrow/chunked_array_test.cc

@@ -146,6 +146,35 @@ TEST_F(TestChunkedArray, EqualsDifferingMetadata) {
   ASSERT_TRUE(left.Equals(right));
 }
 
+TEST_F(TestChunkedArray, EqualsSameAddressWithNaNs) {
+  auto chunk_with_nan1 = ArrayFromJSON(float64(), "[0, 1, 2, NaN]");
+  auto chunk_without_nan1 = ArrayFromJSON(float64(), "[3, 4, 5]");
+  ArrayVector chunks1 = {chunk_with_nan1, chunk_without_nan1};
+  ASSERT_OK_AND_ASSIGN(auto chunked_array_with_nan1, ChunkedArray::Make(chunks1));
+  ASSERT_FALSE(chunked_array_with_nan1->Equals(chunked_array_with_nan1));
+
+  auto chunk_without_nan2 = ArrayFromJSON(float64(), "[6, 7, 8, 9]");
+  ArrayVector chunks2 = {chunk_without_nan1, chunk_without_nan2};
+  ASSERT_OK_AND_ASSIGN(auto chunked_array_without_nan1, ChunkedArray::Make(chunks2));
+  ASSERT_TRUE(chunked_array_without_nan1->Equals(chunked_array_without_nan1));
+
+  auto int32_array = ArrayFromJSON(int32(), "[0, 1, 2]");
+  auto float64_array_with_nan = ArrayFromJSON(float64(), "[0, 1, NaN]");
+  ArrayVector arrays1 = {int32_array, float64_array_with_nan};
+  std::vector<std::string> fieldnames = {"Int32Type", "Float64Type"};
+  ASSERT_OK_AND_ASSIGN(auto struct_with_nan, StructArray::Make(arrays1, fieldnames));
+  ArrayVector chunks3 = {struct_with_nan};
+  ASSERT_OK_AND_ASSIGN(auto chunked_array_with_nan2, ChunkedArray::Make(chunks3));
+  ASSERT_FALSE(chunked_array_with_nan2->Equals(chunked_array_with_nan2));
+
+  auto float64_array_without_nan = ArrayFromJSON(float64(), "[0, 1, 2]");
+  ArrayVector arrays2 = {int32_array, float64_array_without_nan};
+  ASSERT_OK_AND_ASSIGN(auto struct_without_nan, StructArray::Make(arrays2, fieldnames));
+  ArrayVector chunks4 = {struct_without_nan};
+  ASSERT_OK_AND_ASSIGN(auto chunked_array_without_nan2, ChunkedArray::Make(chunks4));
+  ASSERT_TRUE(chunked_array_without_nan2->Equals(chunked_array_without_nan2));
+}
+
 TEST_F(TestChunkedArray, SliceEquals) {
   random::RandomArrayGenerator gen(42);