[Bug] FlinkCatalog resolves built-in functions under nonexistent databases

[wuchong]

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Fluss version

main (development)

Please describe the bug 🐞

FlinkCatalog currently ignores the database component when resolving the built-in bitmap functions:

• listFunctions(String dbName) always returns BUILTIN_BITMAP_FUNCTIONS.
• functionExists(ObjectPath) only checks the function name.
• getFunction(ObjectPath) only checks the function name.

As a result, a fully qualified reference can resolve even when its database does not exist:

SELECT fluss_catalog.nonexistent.rb_build(ARRAY[1, 2]);

This is inconsistent with the database-scoped semantics of Flink catalog functions. It also makes it impossible to guarantee that the database component of <catalog>.<database>.<function> identifies an existing database.

The expected behavior is:

• listFunctions(nonexistentDatabase) throws DatabaseNotExistException.
• functionExists(nonexistentDatabase.function) returns false.
• getFunction(nonexistentDatabase.function) throws FunctionNotExistException.
• Built-in functions continue to resolve from every existing database so that unqualified references work with the current Fluss catalog and database.

Solution

Validate the database before listing or resolving built-in functions in FlinkCatalog, and add unit/integration coverage for:

1. Listing and resolving built-in functions from an existing database.
2. Resolving a fully qualified built-in function from a nonexistent database.
3. Calling a built-in function by its unqualified name after switching to a Fluss catalog/database.

[pbanakar]

Hi @wuchong I'll fix it. Working on a PR now.