sql: return expected user-facing error for invalid unnest arguments

[DrewKimball]

Previously, the unnest builtin function could trigger an internal error when passed multiple non array-type arguments. This is because it only checked whether the arguments were NULL when determining whether they were of a valid type. This is not a problem for some types, like INT, because they will prevent the function overloads from being resolved.

However, since TEXT arguments can be cast to ARRAY types, function overload resolution succeeds. Since unnest only checked for NULL, it would assume that the arguments were array types, and attempt to retrieve the (nil) array contents. For the single-argument case this wasn't a problem because nil is used to signal invalid arguments, anyway. However, the multiple-argument case wraps the array contents of each argument type into a tuple, resulting in a tuple-type of nil types. This caused a nil-pointer dereference later down the line.

This patch prevents the internal error by checking directly that the arguments are ARRAY types, to ensure that the array contents are non-nil. If the check fails, the (nil) tree.UnknownReturnType type is returned, which signals an invalid type. That results in an expected, user-facing error instead of an internal error.

The information_schema._pg_expandarray builtin function had a similar vulnerability. This patch fixes that as well.

Fixes #110952

Release note (bug fix): Fixed an edge case in the unnest and information_schema._pg_expandarray builtin functions that could cause an internal error when passed string arguments that could be cast to an array.

[cockroach-teamcity]

This change is 

[yuzefovich]

thanks!

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2)

[michae2]

Nice fix!

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @DrewKimball)

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pkg/sql/logictest/testdata/logic_test/srfs line 1428 at r1 (raw file):

statement error pgcode 42804 pq: could not determine polymorphic type: unnest\(unknown, unknown, unknown\)
SELECT unnest(NULL, NULL, NULL);

Could you add the following testcases as well:

SELECT unnest('{1}'::int[], '{2}', '{3}');
SELECT unnest('{1}'::int[], '{}', '{}');
SELECT unnest('{1}', '{2}', '{3}'::int[]);
SELECT unnest('{}', '{}', '{3}'::int[]);

[DrewKimball]

Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @michae2)

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pkg/sql/logictest/testdata/logic_test/srfs line 1428 at r1 (raw file):

Previously, michae2 (Michael Erickson) wrote…

Could you add the following testcases as well:

SELECT unnest('{1}'::int[], '{2}', '{3}');
SELECT unnest('{1}'::int[], '{}', '{}');
SELECT unnest('{1}', '{2}', '{3}'::int[]);
SELECT unnest('{}', '{}', '{3}'::int[]);

Done.

[DrewKimball]

TFTRs!

bors r+

[craig]

Build failed (retrying...):

• Bazel Essential CI (Cockroach)

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

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