morningman opened a new pull request, #69025:
URL: https://github.com/apache/doris/pull/69025
### What problem does this PR solve?
Issue Number: None
Related PR: #68968
Problem Summary:
**In short.** FE constant folding cast a VARBINARY constant to a string type
as the hex text of its bytes, while BE keeps the bytes. Every folded expression
that takes a VARBINARY constant through such a cast returned a different result
from the same expression evaluated by BE, including `hex()` and `to_base64()`
of a VARBINARY constant. This came up while testing #68968.
**Background.** `hex()` and `to_base64()` only have string signatures, so a
VARBINARY argument reaches them through an implicit `CAST(... AS VARCHAR)`. BE
implements `CAST(VARBINARY AS VARCHAR/STRING)` by keeping the bytes as they
are. When the argument is a constant, `FoldConstantRuleOnFE` folds that cast
with `Literal.checkedCastTo`, which builds the string from
`VarBinaryLiteral.castValueToString()`; that method returned `toString()`, the
base16 text of the bytes.
**The problem, and what it cost.**
| Query | folded on FE (master) | evaluated by BE
(`debug_skip_fold_constant=true`) / with this PR |
|---|---|---|
| `SELECT hex(cast('abc' AS varbinary(16)))` | `363136323633` | `616263` |
| `SELECT to_base64(cast('abc' AS varbinary(16)))` | `NjE2MjYz` | `YWJj` |
| `SELECT length(cast(cast('abc' AS varbinary(16)) AS string))` | 6 | 3 |
| `SELECT hex(X'FF')` | `4646` | `FF` |
The plan shows the difference: master sends `hex('616263')` to BE, while
with folding disabled it sends `hex(CAST(X'616263' AS varchar(65533)))`. The
same wrong value appears for a column read from a constant subquery or a view.
**How this PR fixes it.**
- `VarBinaryLiteral.castValueToString()` decodes the bytes as UTF-8
(`CodingErrorAction.REPORT`), so the folded string carries exactly the bytes BE
keeps; valid UTF-8 round-trips unchanged when the literal is sent to BE.
- Bytes that are not valid UTF-8 cannot be carried by an FE string literal,
so `castValueToString()` throws an `AnalysisException` for them.
`FoldConstantRuleOnFE.visitCast` turns only a `CastException` into NULL and
returns any other failing cast unfolded, so BE evaluates it (`hex(X'FF')` is
`FF`). A direct caller of `checkedCastTo` gets the exception.
**Results.** With this PR, every query in the table returns the BE result
whether or not constant folding is enabled, on a local cluster. The FE UT fails
when `castValueToString()` returns the hex text again (`expected: <'abc'> but
was: <'616263'>`). The existing `.out` of
`external_table_p0/dialect_compatible/sql/presto/scalar/TestVarbinaryFunctions`
already expects the BE values (`YWJj` for `to_base64(CAST('abc' AS
VARBINARY))`).
### Release note
Fix wrong results of constant expressions that cast a VARBINARY value to a
string, including `hex()` and `to_base64()` of a VARBINARY constant.
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [x] Regression test
-
`query_p0/sql_functions/binary_functions/test_varbinary_cast_fold`: `hex()`,
`to_base64()`, `length()` and casts of VARBINARY constants (valid UTF-8,
multi-byte, `X'FF'`, empty), run with constant folding on and off; the two
result blocks match. `.out` generated by the script.
- [x] Unit Test
- `FoldConstantTest.testCastVarBinaryToStringFold`: the cast folds
to the bytes for ASCII and multi-byte UTF-8, and stays unfolded for `X'FF'`.
- [ ] 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.
- [x] Yes. <!-- Explain the behavior change -->
- A folded cast of a VARBINARY constant to a string type returns its
bytes instead of their hex text, as BE does.
- Does this need documentation?
- [x] 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
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