Mryange opened a new pull request, #65087:
URL: https://github.com/apache/doris/pull/65087
### What problem does this PR solve?
Column wrappers used `for_each_subcolumn` for both read-only traversal and
mutable subcolumn detachment during COW mutation. These two operations have
different contracts: read-only paths only need `const IColumn&`, while COW
mutation needs to replace child pointer slots.
Root cause: the old mutable callback accepted `IColumn::WrappedPtr&`, but
several composite columns store strongly typed child wrappers, such as nullable
null maps and array/map offsets. That forced ad-hoc move-out and cast-back
bridges, and made read-only callers use mutable traversal or `const_cast`.
This change keeps `for_each_subcolumn` as a const read-only traversal API
and adds `mutate_subcolumns()` for the COW mutation path. Composite columns now
detach children through `mutate_subcolumn` helpers, and read-only recursive
checks use the const traversal directly. A dedicated BE unit test file verifies
that mutating exclusive subcolumns does not introduce extra clones, while
shared subcolumns are still detached.
### Release note
None
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [ ] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [ ] No.
- [ ] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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