From 03726178494c8978bf48b9bab15ed9676e7c9196 Mon Sep 17 00:00:00 2001
From: Jonathan Keane <jkeane@gmail.com>
Date: Sun, 14 Jul 2024 08:46:33 -0500
Subject: [PATCH] GH-43194: [R] R_existsVarInFrame isn't available earlier than
 R 4.2 (#43243)

### Rationale for this change

`R_existsVarInFrame` doesn't exist before R 4.2, so we need to fall back to `Rf_findVarInFrame3` if it is not defined.

Resolves #43194

### What changes are included in this PR?

`ifdef`s

### Are these changes tested?

Yes, in our extended CI `test-r-versions`, `test-r-rstudio-r-base-4.1-opensuse155`

### Are there any user-facing changes?

No

* GitHub Issue: #43194

Authored-by: Jonathan Keane <jkeane@gmail.com>
Signed-off-by: Jonathan Keane <jkeane@gmail.com>
---
 r/src/arrow_cpp11.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/r/src/arrow_cpp11.h b/r/src/arrow_cpp11.h
index 5e6a7d5a42fb2..b2ed66b83c3d1 100644
--- a/r/src/arrow_cpp11.h
+++ b/r/src/arrow_cpp11.h
@@ -378,9 +378,17 @@ SEXP to_r6(const std::shared_ptr<T>& ptr, const char* r6_class_name) {
   cpp11::external_pointer<std::shared_ptr<T>> xp(new std::shared_ptr<T>(ptr));
   SEXP r6_class = Rf_install(r6_class_name);
 
+// R_existsVarInFrame doesn't exist before R 4.2, so we need to fall back to
+// Rf_findVarInFrame3 if it is not defined.
+#ifdef R_existsVarInFrame
   if (!R_existsVarInFrame(arrow::r::ns::arrow, r6_class)) {
     cpp11::stop("No arrow R6 class named '%s'", r6_class_name);
   }
+#else
+  if (Rf_findVarInFrame3(arrow::r::ns::arrow, r6_class, FALSE) == R_UnboundValue) {
+    cpp11::stop("No arrow R6 class named '%s'", r6_class_name);
+  }
+#endif
 
   // make call:  <symbol>$new(<x>)
   SEXP call = PROTECT(Rf_lang3(R_DollarSymbol, r6_class, arrow::r::symbols::new_));