feat: add coerce_arguments flag to UDTFs to allow skipping automatic …

[evangelisilva]

UDTF Argument Coercion Suppression

Which issue does this PR close?

Closes #20293.

Rationale for this change

Currently, User-Defined Table Functions (UDTFs) in DataFusion automatically undergo argument coercion and simplification before being passed to the function creator. This process happens against an empty schema (DFSchema::empty()).

If a UDTF uses arguments that contain identifiers (e.g., scan_with(index=['a', 'b'])), the simplifier fails with a Schema error: No field named index because it attempts to resolve index as a column reference. This prevents UDTFs from implementing custom argument parsing logic that relies on identifiers or complex expressions.

What changes are included in this PR?

1. Modified TableFunctionImpl trait: Added a new method coerce_arguments(&self) -> bool that defaults to true. This allows UDTF authors to opt-out of automatic coercion.
2. Updated TableFunction struct: Exposed coerce_arguments on the wrapper struct.
3. Updated SessionContextProvider: Modified the SQL planner integration in session_state.rs to check the coerce_arguments flag. If false, the raw Expr arguments are passed directly to the UDTF creator without modification.
4. Unit Tests: Added comprehensive tests in session_state.rs to verify both the default behavior (automatic coercion/failure on identifiers) and the new suppressed behavior (allowing identifiers).

Are these changes tested?

Yes. I've added a new test module udtf_tests in datafusion/core/src/execution/session_state.rs containing:

• test_udtf_no_coercion: Verifies that identifiers survive when coercion is disabled.
• test_udtf_default_coercion: Verifies that the existing behavior (failing on identifiers) is preserved by default to ensure no regressions.

Are there any user-facing changes?

Yes. There is a new method on the TableFunctionImpl trait. However, because it has a default implementation that returns true, it is backward compatible and will not break existing UDTF implementations. UDTF authors who need the new behavior simply need to override this method.

cc: @askalt @alamb