@groeneai can you confirm no other issues happen with the eval function for every other explain statement, or sql statement?

Confirmed, and measured: 80 eval shapes on two binaries built from the same tree with only this line differing, one process per shape, debug builds, so a LOGICAL_ERROR aborts and cannot be missed. Coverage is all 10 ASTExplainQuery::ExplainKind values with their option flags, both AST based arms over non-SELECT and nested tops, and 21 statements with no EXPLAIN at all (full list below).

• On master 27 of the 80 abort, every one with the same Logical error: 'Incorrect table expression' thrown at StorageView.cpp:666 in replaceWithSubquery. With this PR: zero, no logical error in any shape.
• Only two arms reach that code at all: EXPLAIN AST optimize = 1 (any graph), and EXPLAIN SYNTAX when the top level is not a plain SELECT (measured: INSERT and CREATE TABLE ... AS SELECT). Plain EXPLAIN SYNTAX SELECT, the other eight kinds and every statement without EXPLAIN never reach it, on either binary.
• No second error class turned up. Every non-OK result is identical on both binaries and is a deliberate check: eval in an expression context Code: 46, eval inside eval Code: 36, eval as an argument of remote/cluster Code: 1, materialized view from a table function Code: 397, PREWHERE on a View Code: 182, EXPLAIN WHATIF wants a MergeTree table Code: 48, EXPLAIN TABLE OVERRIDE eval(...) Code: 80, the setting off Code: 344. EXPLAIN SYNTAX of CREATE MATERIALIZED VIEW or of ALTER is Code: 62 from the EXPLAIN parser, with or without eval (checked both).
• The change is inert outside the throwing path: of the shapes that already worked, stdout is byte identical on 49 of the 50 I diffed, and the exception is EXPLAIN ANALYZE, whose output carries timings and differs the same way between two runs of the same binary.
• The other places that hard code this name list need nothing for eval: QueryAnalyzer has such a list for view and merge as an argument of another table function, which eval can never be (Code: 1), and ASTFunction::appendColumnNameImpl lists the table functions that cannot be used as an expression, which eval reaches as an unknown function first (Code: 46).

EXPLAIN kinds, each with its option flags (optimize, graph, oneline, run_query_tree_passes, run_passes, json, indexes, actions, header, compact): AST, SYNTAX, QUERY TREE, PLAN, PIPELINE, ESTIMATE, ANALYZE, WHATIF, TABLE OVERRIDE, CURRENT TRANSACTION.

AST based arms over: INSERT, INSERT INTO FUNCTION, CREATE TABLE AS SELECT, CREATE VIEW AS SELECT, CREATE MATERIALIZED VIEW AS SELECT, UNION, CTE, IN, scalar subquery, subquery, JOIN with eval on either or both sides, comma join, DISTINCT with GROUP BY and ORDER BY, FINAL, SAMPLE, PREWHERE, ARRAY JOIN, eval nested in view / viewIfPermitted / remote, eval inside eval, eval((SELECT ...)), query level SETTINGS, and the fuzzer query from the CI fatal log. Controls: the same shapes with view, merge and numbers.

Without EXPLAIN: SELECT, count, ordered multi row read, JOIN, IN, CTE, subquery, INSERT SELECT, CREATE TABLE AS SELECT, CREATE VIEW then SELECT from it, CREATE MATERIALIZED VIEW, DESCRIBE, remote, cluster, eval nested in view and viewIfPermitted, expression context, FINAL, PREWHERE, and the experimental setting turned off.

Aborting on master, passing with this PR:

EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST graph = 1, optimize = 1 SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST graph = 1, optimize = 1 SELECT DISTINCT * FROM eval((SELECT toLowCardinality('SELECT 5 AS lc') LIMIT 539));
EXPLAIN AST optimize = 1 INSERT INTO t SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN SYNTAX INSERT INTO t SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST optimize = 1 CREATE TABLE t ENGINE = Memory AS SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN SYNTAX CREATE TABLE t ENGINE = Memory AS SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST optimize = 1 CREATE VIEW v AS SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') UNION ALL SELECT 6 AS x;
EXPLAIN AST optimize = 1 SELECT * FROM (SELECT * FROM eval('SELECT 5 AS x'));
EXPLAIN AST optimize = 1 WITH c AS (SELECT * FROM eval('SELECT 5 AS x')) SELECT * FROM c;
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') WHERE x IN (SELECT * FROM eval('SELECT 5 AS y'));
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') AS a JOIN numbers(1) AS n ON 1;
EXPLAIN AST optimize = 1 SELECT * FROM numbers(1) AS n JOIN eval('SELECT 5 AS x') AS a ON 1;
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') AS a JOIN eval('SELECT 5 AS x') AS b USING (x);
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') AS a, eval('SELECT 6 AS y') AS b;
EXPLAIN AST optimize = 1 SELECT DISTINCT x FROM eval('SELECT 5 AS x') GROUP BY x ORDER BY x LIMIT 1;
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') FINAL;
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') SAMPLE 1 / 2;
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') PREWHERE x > 1;
EXPLAIN AST optimize = 1 SELECT a FROM eval('SELECT [1, 2] AS arr') ARRAY JOIN arr AS a;
EXPLAIN AST optimize = 1 SELECT * FROM eval((SELECT 'SELECT 5 AS x'));
EXPLAIN AST optimize = 1 CREATE MATERIALIZED VIEW mv ENGINE = Memory AS SELECT * FROM eval('SELECT 5 AS x');
EXPLAIN AST optimize = 1 SELECT (SELECT count() FROM eval('SELECT 5 AS x'));
EXPLAIN AST optimize = 1 INSERT INTO FUNCTION null('x UInt8') SELECT * FROM eval('SELECT 5 AS x');
SELECT count() FROM (EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x'));
EXPLAIN AST optimize = 1 SELECT * FROM eval('SELECT 5 AS x') SETTINGS max_threads = 1;

Tell me if you want any of these pinned in the test, I kept it to five cases for a one line fix.

@groeneai Kept it to five cases for a one line fix.