GH-37761: [R] Argument names ignored in schema supplied as in_type argument to register_scalar_function()

[thisisnic]

Rationale for this change

No validation/warning makes it easy for incorrectly specified UDFs to appear to work...but they don't!

What changes are included in this PR?

Validation

Are these changes tested?

Yeah

Are there any user-facing changes?

I guess if they have incorrectly specified UDFs, yeah

AI usage

All of it, we talked tho

• GitHub Issue: [R] Argument names ignored in schema supplied as in_type argument to register_scalar_function() #37761

[github-actions]

⚠️ GitHub issue #37761 has been automatically assigned in GitHub to PR creator.

[Copilot]

🟡 Changes recommended

Validation still bypasses explicitly declared arguments when a function also includes ....

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Pull request overview

Adds validation to ensure named UDF input schemas match function argument names.

Changes:

• Implements argument-name validation.
• Adds regression tests and snapshots.
• Updates documentation.

File summaries

File	Description
r/tests/testthat/test-udf.R	Adds validation tests.
r/tests/testthat/_snaps/udf.md	Records validation output.
r/R/udf.R	Implements argument-name validation.
r/man/register_scalar_function.Rd	Documents naming requirements.

Review details

Files not reviewed (1)

• r/man/register_scalar_function.Rd: Generated file

• Files reviewed: 3/4 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🔵 Needs a closer look

Two moderate validation gaps remain in r/R/udf.R.

Review details

Files not reviewed (1)

• r/man/register_scalar_function.Rd: Generated file

Suppressed comments (2)

r/R/udf.R:171

• When a later kernel has more fields than fun, indexing fun_arg_names past its length yields NA; any() then returns NA and isTRUE() suppresses the mismatch. For example, function(context, x) with list(schema(x = int32()), schema(x = int32(), y = int32())) passes this new name check and produces an invalid arrow_scalar_function; treat named positions beyond fun_arg_names as mismatches (and add a regression test).

        isTRUE(any(nzchar(nms) & nms != fun_arg_names[seq_along(nms)]))

r/R/udf.R:166

• Because the name check is gated by !fun_formals_have_dots, any function with ... bypasses it—even function(context, x, ...), where x is a fixed positional argument. For example, schema(blah = int32()) is still silently accepted for that function, so the bug this PR targets remains for mixed fixed/ellipsis formals. Restrict the exemption to the ellipsis portion and validate explicit formals before it.

  if (!fun_formals_have_dots) {
    fun_arg_names <- names(formals(fun))[-1]

• Files reviewed: 3/4 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The validation is correctly implemented and documented, and the added tests/snapshots cover the new behavior and expected error messaging.

Review details

Files not reviewed (1)

• r/man/register_scalar_function.Rd: Generated file

• Files reviewed: 3/4 changed files
• Comments generated: 0 new
• Review effort level: Lite

[jonkeane]

Looks good