38 files declare their use of DrupalDateTime

Announcement.php in core/modules/announcements_feed/src/Announcement.php
CommentForm.php in core/modules/comment/src/CommentForm.php
CommentPreviewTest.php in core/modules/comment/tests/src/Functional/CommentPreviewTest.php
DateElementBase.php in core/lib/Drupal/Core/Datetime/Element/DateElementBase.php
Datelist.php in core/lib/Drupal/Core/Datetime/Element/Datelist.php
DatelistElementFormTest.php in core/tests/Drupal/KernelTests/Core/Datetime/DatelistElementFormTest.php
DateRangeFieldItemList.php in core/modules/datetime_range/src/Plugin/Field/FieldType/DateRangeFieldItemList.php
DateRangeFieldTest.php in core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
DateRangeWidgetBase.php in core/modules/datetime_range/src/Plugin/Field/FieldWidget/DateRangeWidgetBase.php
Datetime.php in core/lib/Drupal/Core/Datetime/Element/Datetime.php
DateTimeComputed.php in core/modules/datetime/src/DateTimeComputed.php
DateTimeCustomFormatter.php in core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeCustomFormatter.php
DateTimeDefaultFormatter.php in core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeDefaultFormatter.php
DatetimeElementFormTest.php in core/tests/Drupal/KernelTests/Core/Datetime/DatetimeElementFormTest.php
DateTimeFieldItemList.php in core/modules/datetime/src/Plugin/Field/FieldType/DateTimeFieldItemList.php
DateTimeFieldTest.php in core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
DateTimeFormatterBase.php in core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
DateTimeFormInjectionTest.php in core/modules/datetime/tests/src/Kernel/DateTimeFormInjectionTest.php
DateTimeInterface.php in core/lib/Drupal/Core/TypedData/Type/DateTimeInterface.php
DateTimeIso8601.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/DateTimeIso8601.php
DateTimeIso8601NormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/DateTimeIso8601NormalizerTest.php
DateTimeNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/DateTimeNormalizerTest.php
DateTimeRangeTrait.php in core/modules/datetime_range/src/DateTimeRangeTrait.php
DateTimeTimeAgoFormatter.php in core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeTimeAgoFormatter.php
DateTimeWidgetBase.php in core/modules/datetime/src/Plugin/Field/FieldWidget/DateTimeWidgetBase.php
DrupalDateTimeTest.php in core/modules/system/tests/src/Functional/Datetime/DrupalDateTimeTest.php
DrupalDateTimeTest.php in core/tests/Drupal/Tests/Core/Datetime/DrupalDateTimeTest.php
EarlyDateTest.php in core/modules/taxonomy/tests/src/Functional/EarlyDateTest.php
FilterDateTest.php in core/modules/datetime/tests/src/Functional/Views/FilterDateTest.php
FormTestDisabledElementsForm.php in core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php
ForumBlockTest.php in core/modules/forum/tests/src/Functional/ForumBlockTest.php
Timestamp.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Timestamp.php
TimestampAgoFormatter.php in core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
TimestampDatetimeWidget.php in core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
TimestampNormalizerTest.php in core/modules/serialization/tests/src/Unit/Normalizer/TimestampNormalizerTest.php
TimestampTest.php in core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
TimezoneTest.php in core/tests/Drupal/KernelTests/Core/Datetime/Element/TimezoneTest.php
TypedDataTest.php in core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php

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