Mryange opened a new pull request, #65456:
URL: https://github.com/apache/doris/pull/65456
### What problem does this PR solve?
When constant folding was disabled, BE rejected casts from null-only arrays
to arrays with a different number of dimensions, although FE constant folding
already supported them. Root cause: the BE array cast checked dimensionality
before recognizing that the source element type represented a NULL literal.
This change allows cross-dimensional array casts when the source nested type
is a NULL literal, while ordinary arrays still require matching dimensions. For
example, `CAST([NULL, NULL] AS ARRAY<ARRAY<INT>>)` now returns `[NULL, NULL]`:
BE casts the two nested NULL values to `Nullable<Array<Int>>` and rebuilds the
outer array with its original offsets.
### Release note
Support casting null-only arrays to array types with different dimensions in
BE.
### 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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