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…lumns (apache#26893) ## Which issue does this PR close? - Closes apache#26866. ## Rationale for this change `DESCRIBE`, `SHOW COLUMNS` and `information_schema.columns` show the storage type of a column, even if the column has a registered extension type. For example, a UUID column is shown as `FixedSizeBinary(16)`. Extension types can already customize how their values are formatted, but not how their type is named. With the canonical extension types registered, `DESCRIBE` of a table with a UUID column `u` and a plain column `i` now shows: ``` u UUID YES i Int32 NO ``` Before, the first row was `u FixedSizeBinary(16) YES`. ## What changes are included in this PR? - New method `DFExtensionType::display_name(&self) -> Option<Cow<'_, str>>`. The default returns `None`, which means that the storage type is shown, as before. A name can be static, borrowed from the type or computed from its metadata, so parameterized names are possible. - New function `datafusion_expr::extension_types::append_field_type_display_name(registry, field, builder)`. It appends the display name of the registered extension type of the field to a `StringBuilder`, or else the storage type. It also appends the storage type if the extension type is not registered or cannot be created from the field metadata, so that `DESCRIBE` does not fail on such a column. - `InformationSchemaColumnsBuilder`, which `DESCRIBE`, `SHOW COLUMNS` and `information_schema.columns` share, uses this function with the registry from `with_extension_type_registry`. - `InformationSchemaProvider::with_extension_type_registry` passes the session registry to that builder. The physical planner and `SessionState` set it where they create the provider. - `DFUuid` returns `UUID` and `DFJson` returns `JSON`. The other canonical extension types keep showing their storage type. I was not sure which names to use for them (for example for tensors, whose names would depend on the metadata) and am happy to add them here or in a follow-up. The canonical extension types are not registered in a default session, so the default output does not change. ## What is the testing strategy for this PR? - `extension_type_names.slt` registers the canonical extension types and a table with columns of registered types with and without a display name, of an unregistered extension type and of a plain type. It checks `DESCRIBE`, `information_schema.columns`, `SHOW COLUMNS` and a view. - A unit test for `append_field_type_display_name`, including the fallbacks. ## Are there any user-facing changes? Yes, sessions that register extension types with a display name, such as the canonical `arrow.uuid` and `arrow.json`, show that name in `DESCRIBE`, `SHOW COLUMNS` and `information_schema.columns`. There are no breaking API changes: the new trait method has a default implementation. --------- Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> (cherry picked from commit 608ac9c)
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## branch-56 #27057 +/- ##
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Coverage 83.25% 83.26%
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Files 1169 1169
Lines 474294 474386 +92
Branches 474294 474386 +92
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+ Hits 394887 395002 +115
+ Misses 55485 55462 -23
Partials 23922 23922
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Which issue does this PR close?
56.0.0(Oct/Nov 2026) #24461branch-56