TRY_CONVERT

[robozmey]

Extension TRY_CONVERT adds function TRY_CONVERT

TRY_CONVERT was made to use like TRY_CAST from SQL-Server

Due polymorphism have strange signature (some_type, anyelement) -> anyelement

First parament is SOURCE_VALUE

Second parameter is DEFAULT_VALUE::TARGET_TYPE

TRY_CONVERT('42'::text, NULL::int2) -- returns 42::int2
TRY_CONVERT('42d'::text, NULL::int2) -- returns NULL::int2
TRY_CONVERT('42d'::text, 1234::int2) -- returns 1234::int2

We cannot have (any1, any2) -> any2 signature with different anyelement types, but we can create multiple (_, any) -> any functions in contrib/try_convert/try_convert--1.0.sql or use select add_type_for_try_convert('date'::regtype); to add types.

In init we can add all supported types, but with add_type_for_try_convert user can add whatever type he wants

ERROR HANDLING

Error handles by PG_TRY() PG_CATCH()

But better way is use "soft" error handling from Postgres 17 (postgres/postgres@ccff2d2) it also realising OPENGPDB (open-gpdb/gpdb@21be368). Of course it needs to convert datatype function to support "soft" error handling

Fixes #ISSUE_Number

What does this PR do?

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

Test Plan

• Unit tests added/updated
• Integration tests added/updated
• Passed make installcheck
• Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• Requested review from cloudberry committers

Additional Context

CI Skip Instructions

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[gfphoenix78]

What if the source or target type is invalid?

[robozmey]

All will happend like in

cloudberry/src/backend/parser/parse_coerce.c

Line 3151 in e601fb6

if (OidIsValid(sourceTypeId))

(My conversion algorithm duplicates internal one)

We will look in pg_cast table - will find nothing, will try to get TypeCategory and will get assert in TypeCategory(targetTypeId)

[gfphoenix78]

Better add else branch here.

[gfphoenix78]

Why is the error handling undetermined?

[tuhaihe]

Suggested change

	TRY_CONVERT is Greenplum extension, which adds function for error-safe type cast like [TRY_CAST from SQL-Server](https://learn.microsoft.com/ru-ru/sql/t-sql/functions/try-cast-transact-sql?view=sql-server-ver16)
	TRY_CONVERT is Greenplum/Cloudberry extension, which adds function for error-safe type cast like [TRY_CAST from SQL-Server](https://learn.microsoft.com/ru-ru/sql/t-sql/functions/try-cast-transact-sql?view=sql-server-ver16)

[tuhaihe]

Suggested change

	Greenplum function polymorphism accept to have polymorphic functions only one any type in signature.
	Greenplum/Cloudberry function polymorphism accept to have polymorphic functions only one any type in signature.

[tuhaihe]

Hi @robozmey thanks for your updates! Now the license headers look good to me. Please make sure these files are originally created by our community members, not cherry-picked or copied from other projects.

Before merging, welcome to squash your commits into one and revise the commit message body, you can take this template as a reference.