fix: keep a projection's field names when decorrelating a predicate s… - #26657

…ubquery

A set comparison in a projection without an alias failed with

  Internal error: Assertion failed: compatible: Failed due to a difference in schemas:
  original schema: ... Field { name: "Int64(2) > ALL", data_type: Boolean, nullable: true }
  new schema:      ... Field { name: "CASE WHEN EXISTS THEN Boolean(false) ...", ... }

This rule rebuilds a projection from its expressions, and it preserved the output field
names from `Expr::schema_name()` of the expression it was given. That is not the name the
rebuilt projection uses, for two reasons: `schema_name()` keeps a column's qualifier
(`t.k`) while the field is named after the bare column, and earlier rules rewrite
expressions with `map_expressions`, which keeps the schema but can leave an expression
whose display name no longer matches its field name. `RewriteSetComparison` does exactly
that -- it replaces `x > ALL (..)` with a `CASE WHEN EXISTS ..` -- so this rule rebuilt the
projection under the stale name and the optimizer's "the schema is invariant under
optimization" check failed. `datafusion.optimizer.skip_failed_rules` defaults to false, so
an ordinary query returned an internal error asking the user to file a bug report.

Take the field names from the projection's own schema, and compare them against the name
the rebuilt projection would give the expression -- the bare column name for a column, the
alias name for an alias, the display name otherwise -- so an alias is only added when the
rebuilt name would really differ. Comparing against the schema name alone would alias a
qualified column and lose its qualifier, which breaks the same check from the other side.

Tested with three cases in datafusion/sqllogictest/test_files/subquery.slt, and with
subquery.slt, null_aware_mark_join.slt, prepare.slt and cargo test -p datafusion-optimizer.

…projection-field-name

Only subquery.slt conflicted: upstream and this branch both appended tests at the end of
the file. Kept upstream's new cases and appended this branch's three cases after them.

…projection-field-name

Only subquery.slt conflicted: upstream (apache#25258) and this branch both appended
tests at the end of the file. Kept upstream's new cases and left this branch's
three cases above them.

`Expr::qualified_name` implements and documents exactly the three arms the
local helper had, so the helper was a second copy of the field-naming rule
that a later change to either one could drift from. Zip the projection's
expressions with its schema's field names so the pairing is structural
instead of positional, and say in subquery.slt that the aliased case is a
control rather than a regression test.

Verified on the branch merged with main: subquery.slt, subquery_projection.slt,
null_aware_anti_join.slt, null_aware_mark_join.slt and prepare.slt all exit 0,
and cargo test -p datafusion-optimizer is 951 + 29 + 5 passed, 0 failed.

`RewriteSetComparison` replaces `x > ALL (…)` with a `CASE WHEN EXISTS …`, whose
display name is not the name of the field it produces. Rewriting an expression
without preserving its name therefore changes the output schema, and the
optimizer's "the schema is invariant under optimization" check failed with an
internal error instead of returning the answer.

Wrapping `map_expressions` in a `NamePreserver`, the same way `simplify_exprs`
and `type_coercion` do, fixes it at the rule that introduces the stale name.
That replaces the earlier fix in `DecorrelatePredicateSubquery`, which only
covered projections; this also stops the rule leaving mismatched names inside
`Aggregate` and `Window` nodes.

Adds a fourth sqllogictest case with a qualified column next to the set
comparison, which is the other half of the same check.

Verified: subquery.slt (all four cases), subquery_projection.slt,
subquery_sort.slt, merge_into.slt and null_aware_mark_join.slt pass, and
`cargo test -p datafusion-optimizer` is 951 + 29 + 5 passed, 0 failed.