sql: gate functions in views and descriptor expressions in mixed-version state

[ajwerner]

Describe the problem

Cockroach stores sql expressions in a number of places: views, default expressions, computed expressions, index predicates, on update expressions etc. These expressions may invoke functions. Functions (and probably other syntactic elements) can be introduced in new versions. Unfortunately, there's no code which exists today to validate that an expression uses only functions or syntax that is available at the current version. This is a problem in a mixed-version state where the gateway processing the SQL is using code newer than the current active cluster version.

To Reproduce

Let's consider the following in the v20.2 <-> v21.1 mixed state. Node 1 is running 21.1, other are running 20.2. soundex is a new function in 21.1.

root@localhost:26257/defaultdb> CREATE TABLE foo (i INT PRIMARY KEY, j STRING DEFAULT (soundex('a')));
CREATE TABLE

Other node:

root@localhost:26259/defaultdb> INSERT INTO foo(i) VALUES (1);
ERROR: unknown function: soundex()
SQLSTATE: 42883

Expected behavior

We should probably prevent the creation of this table.

Additional context

This seems to not be so bad. The entity is unusable for writes, but things aren't really worse than that.

This was noted by @nvanbenschoten in #70204 (comment).

Jira issue: CRDB-10077

[RichardJCai]

@otan also mentioned that this is also applicable to if we change the implementation of a builtin.

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