morningman commented on code in PR #67476:
URL: https://github.com/apache/doris/pull/67476#discussion_r3925066255
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be/src/exprs/function/cast/cast_to_variant.h:
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@@ -125,6 +148,9 @@ inline Status cast_from_variant_impl(FunctionContext*
context, Block& block,
return cast_from_generic_to_jsonb(context, finalized_block,
arguments, result,
input_rows_count);
Review Comment:
Deliberately not addressed in this PR: the mechanism is real, but it
predates this change and I could not find a reachable path to it.
`ColumnUInt8::create(col_from.size(), 0)` against a loop over
`input_rows_count` has been there since #50940 (bd3c4539f8b, 2025-07-17), and
`cast_from_generic_to_jsonb` is the shared generic-to-JSONB path for
array/map/struct as well. If `input_rows_count < col_from.size()` were
reachable, `CAST(<array> AS JSON)` would already throw today, independently of
variant.
Reachability is the same question as the prefix half of the sibling comment,
and the answer is the same: every cast entry point passes the full row count
(`vcast_expr.cpp:122`, `:171`), the per-row try_cast path passes a 1-row `cut`
with count 1 (`:236`), `prepare_remove_nullable` forwards the count unchanged
over same-size columns, and const arguments run through a temporary block sized
by its own `rows()`.
If you would like it hardened regardless,
`ColumnUInt8::create(input_rows_count, 0)` is a no-op whenever the sizes agree.
I would rather send that as a separate PR against the shared helper than widen
this one, since it changes a function every generic-to-JSONB cast goes through.
Happy to do that if a maintainer prefers.
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