bkietz commented on code in PR #46675:
URL: https://github.com/apache/arrow/pull/46675#discussion_r2152530709
##########
cpp/src/arrow/array/util.cc:
##########
@@ -829,7 +829,17 @@ class RepeatedArrayFactory {
}
Status Visit(const ExtensionType& type) {
- return Status::NotImplemented("construction from scalar of type ",
*scalar_.type);
+ // Retrieve the underlying storage scalar from the ExtensionScalar
+ const auto& ext_scalar = checked_cast<const ExtensionScalar&>(scalar_);
+ const auto& storage_scalar = ext_scalar.value;
+
+ // Create an array from the storage scalar
+ ARROW_ASSIGN_OR_RAISE(auto storage_array,
+ MakeArrayFromScalar(*storage_scalar, length_,
pool_));
+
+ // Wrap the storage array in the ExtensionType
+ out_ = type.MakeArray(storage_array->data());
Review Comment:
For this you want
[WrapArray](https://github.com/apache/arrow/blob/3917b605ef1851ad036fb62856efcc83e32f8580/cpp/src/arrow/extension_type.h#L90-L92);
[SmallintType::MakeArray](https://github.com/apache/arrow/blob/639201bfa412db26ce45e73851432018af6c945e/cpp/src/arrow/testing/gtest_util.cc#L859)
assumes that the argument is a fully correct ArrayData (including
ArrayData::type).
This requirement isn't documented in the declaration of
[ExtensionType::MakeArray](https://github.com/apache/arrow/blob/3917b605ef1851ad036fb62856efcc83e32f8580/cpp/src/arrow/extension_type.h#L71-L73),
so either
- we should add to the doccomment that `The argument must valid data for the
extension type, including its .type member; subclasses are not required to
coerce whatsoever. See also WrapArray`
- we should specify what coercion/validation subclasses are expected to
implement and fix the smallint
@pitrou WDYT?
##########
cpp/src/arrow/array/array_test.cc:
##########
@@ -815,6 +815,23 @@ TEST_F(TestArray, TestMakeArrayFromMapScalar) {
AssertAppendScalar(pool_, std::make_shared<MapScalar>(scalar));
}
+TEST_F(TestArray, TestMakeArrayFromScalar_SmallintExtensionType) {
Review Comment:
Underscores are used in name mangling of gtest cases, so [test case names
should not contain
them](https://google.github.io/googletest/faq.html#why-should-test-suite-names-and-test-names-not-contain-underscore)
```suggestion
TEST_F(TestArray, TestMakeArrayFromScalarSmallintExtensionType) {
```
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