EXPLAIN SYNTAX with old analyzer ignores SQL SECURITY DEFINER for parameterized views

[pamarcos]

Description

EXPLAIN SYNTAX with the old analyzer does not preserve SQL SECURITY DEFINER
semantics for parameterized views. A restricted user can successfully query a
SQL SECURITY DEFINER parameterized view, but EXPLAIN SYNTAX for the same
query fails with ACCESS_DENIED because it checks privileges on the underlying
table as the invoker.

This is reproducible in 26.4.2.10-stable.

Reproduction

Run setup as default:

DROP DATABASE IF EXISTS repro_definer_explain SYNC;
DROP USER IF EXISTS repro_definer_user;

CREATE DATABASE repro_definer_explain;

CREATE TABLE repro_definer_explain.secret_table
(
    x UInt64
)
ENGINE = Memory;

INSERT INTO repro_definer_explain.secret_table VALUES (42);

CREATE USER repro_definer_user;

CREATE VIEW repro_definer_explain.definer_pv
DEFINER = CURRENT_USER SQL SECURITY DEFINER AS
SELECT x
FROM repro_definer_explain.secret_table
WHERE x = {v:UInt64};

GRANT SELECT ON repro_definer_explain.definer_pv TO repro_definer_user;

Run as repro_definer_user:

SELECT * FROM repro_definer_explain.secret_table;

This correctly fails with ACCESS_DENIED.

Run as repro_definer_user:

SELECT * FROM repro_definer_explain.definer_pv(v = 42);

This correctly returns:

42

Run as repro_definer_user:

EXPLAIN SYNTAX
SELECT * FROM repro_definer_explain.definer_pv(v = 42)
SETTINGS allow_experimental_analyzer = 1;

This succeeds in 26.4.2.10-stable and returns the unexpanded parameterized
view call.

Run as repro_definer_user:

EXPLAIN SYNTAX
SELECT * FROM repro_definer_explain.definer_pv(v = 42)
SETTINGS allow_experimental_analyzer = 0;

This fails:

Code: 497. DB::Exception: repro_definer_user: Not enough privileges. To execute
this query, it's necessary to have the grant SELECT ON
repro_definer_explain.secret_table: While processing SELECT * FROM
`repro_definer_explain.definer_pv`(v = 42) SETTINGS allow_experimental_analyzer = 0.
(ACCESS_DENIED)

Expected behavior

EXPLAIN SYNTAX should respect the same SQL SECURITY DEFINER semantics as
query execution. If repro_definer_user can execute
SELECT * FROM repro_definer_explain.definer_pv(v = 42), the corresponding
EXPLAIN SYNTAX should not require direct SELECT privileges on
repro_definer_explain.secret_table.

Notes

The issue appears specific to the old analyzer path. The analyzer path in
26.4.2.10-stable does not reproduce this access-denied behavior because it
does not expand the parameterized view in EXPLAIN SYNTAX.