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GH-49073: [C++] Remove the TODO asking to remove check_metadata in compare.cc #49077

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GH-49073: [C++] Remove the TODO asking to remove check_metadata in compare.cc #49077

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2 changes: 1 addition & 1 deletion cpp/src/arrow/compare.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1513,7 +1513,7 @@ bool TypeEquals(const DataType& left, const DataType& right, bool check_metadata
return left_fp == right_fp;
}

// TODO remove check_metadata here?
// Fall back to TypeEqualsVisitor when fingerprints are unavailable.
TypeEqualsVisitor visitor(right, check_metadata);
auto error = VisitTypeInline(left, &visitor);
if (!error.ok()) {
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25 changes: 25 additions & 0 deletions cpp/src/arrow/type_test.cc
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Expand Up @@ -2004,6 +2004,31 @@ TEST(TestNestedType, Equals) {
AssertFieldNotEqual(*u0, *u0_bad);
}

TEST(TestNestedType, FieldMetadataComparisonWithEmptyFingerprints) {
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@HyukjinKwon HyukjinKwon Jan 30, 2026

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This might be too much. I am fine with removing this test case if anyone thinks so. It's more to demonstrate the case of triggering check_metadata.

// Manual ListType with empty fingerprints to force TypeEqualsVisitor path
class EmptyFingerprintListType : public ListType {
public:
using ListType::ListType;

protected:
std::string ComputeFingerprint() const override { return ""; }
std::string ComputeMetadataFingerprint() const override { return ""; }
};

auto metadata1 = key_value_metadata({{"key", "value1"}});
auto metadata2 = key_value_metadata({{"key", "value2"}});
auto field1 = field("item", int32(), true, metadata1);
auto field2 = field("item", int32(), true, metadata2);
auto list1 = std::make_shared<EmptyFingerprintListType>(field1);
auto list2 = std::make_shared<EmptyFingerprintListType>(field2);

ASSERT_TRUE(list1->fingerprint().empty());
ASSERT_TRUE(list1->metadata_fingerprint().empty());

EXPECT_TRUE(list1->Equals(*list2, /* check_metadata = */ false));
EXPECT_FALSE(list1->Equals(*list2, /* check_metadata = */ true));
}

TEST(TestStructType, Basics) {
auto f0_type = int32();
auto f0 = field("f0", f0_type);
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