morningman opened a new pull request, #66769:
URL: https://github.com/apache/doris/pull/66769
### What problem does this PR solve?
Related PR: #66732, #66712
Problem Summary:
`schema_per_db_scanner.h` gives its `unique_ptr` member a default member
initializer:
```cpp
std::unique_ptr<Block> _fetched_block = nullptr;
```
That initializer makes gcc instantiate `~unique_ptr<Block>()` in **every**
translation unit that
includes the header, and the instantiation needs `Block` to be a complete
type. None of the seven
`SchemaPerDbScanner` subclasses include `core/block/block.h`, so each of
them fails to compile with
g++ 15:
```
In instantiation of 'void std::default_delete<_Tp>::operator()(_Tp*) const
[with _Tp = doris::Block]':
bits/unique_ptr.h:399:17: required from 'std::unique_ptr<_Tp,
_Dp>::~unique_ptr() [with _Tp = doris::Block]'
schema_per_db_scanner.h:68:45: required from here
68 | std::unique_ptr<Block> _fetched_block = nullptr;
| ^~~~~~~
bits/unique_ptr.h:91:23: error: invalid application of 'sizeof' to
incomplete type 'doris::Block'
```
Declaring the destructor out of line -- which the header already does --
does not help: the default
member initializer is what marks `~unique_ptr<Block>()` as used. clang does
not instantiate the
destructor there, which is why only the gcc build reports it.
`SchemaScanner::_data_block` has the
same type and the same forward-declared `Block` and is fine, because it has
no initializer.
Dropping the `= nullptr` leaves the member null just the same, and costs
nothing at build time --
the alternative, including `core/block/block.h` from the header, would pull
that closure into seven
more translation units.
Note that the failure is currently masked on master: since #66712 turned
`ENABLE_UNITY_BUILD` on by
default, all of `information_schema` is merged into a single unity TU, and
`schema_per_db_scanner.cpp` in that TU includes `core/block/block.h`, so
`Block` ends up complete for
its neighbours. Building with `ENABLE_UNITY_BUILD=OFF` still fails, as does
any file that later opts
out via `SKIP_UNITY_BUILD_INCLUSION`.
### Release note
None
### Check List (For Author)
- Test
- [x] No need to test or manual test. Explain why:
- [x] This is a refactor/code format and no logic has been changed.
Verified as a build fix instead: reproduced the exact diagnostic with g++
15.2 on a reduced case
and confirmed it compiles clean after removing the initializer, then
re-checked the real
translation units (`schema_key_column_usage_scanner.cpp`,
`schema_partitions_scanner.cpp`,
`schema_table_options_scanner.cpp`, `schema_per_db_scanner.cpp`) against
the edited header.
- Behavior changed:
- [x] No.
- Does this need documentation?
- [x] No.
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