Error when code has reserved keywords

.gitattributes

@@ -0,0 +1,2 @@
+* text=auto eol=lf
+*.rda binary

R/utils.R

@@ -950,6 +950,32 @@ compile_functions <- function(env, verbose = FALSE, global = FALSE) {
     prep_fun_cpp(funs[ind], fun_end, env$hpp_code)
   })
 
+  reserved_names <- unique(
+    unlist(
+      lapply(stan_funs, function(stan_fun) {
+        regmatches(
+          stan_fun,
+          gregexpr("(?<=_stan_)[[:alnum:]_]+", stan_fun, perl = TRUE)
+        )[[1]]
+      }),
+      use.names = FALSE
+    )
+  )
+
+  if (length(reserved_names) > 0) {
+    stop(
+      paste0(
+        "expose_functions() can't expose this Stan function because the function ",
+        "name and/or one or more argument names use a reserved keyword ",
+        "(typically in the C++ toolchain used to compile Stan). Please rename ",
+        "the function/arguments in your Stan functions block and try again. ",
+        "Conflicting names: ",
+        paste(reserved_names, collapse = ", ")
+      ),
+      call. = FALSE
+    )
+  }
+
   env$fun_names <- sapply(seq_len(length(funs) - 1), function(ind) {
     get_function_name(funs[ind], funs[ind + 1], env$hpp_code)
   })

tests/testthat/test-model-expose-functions.R

@@ -380,6 +380,86 @@ test_that("Overloaded functions give meaningful errors", {
                "Overloaded functions are currently not able to be exposed to R! The following overloaded functions were found: fun1, fun3")
 })
 
+reserved_names_msg <- function(names) {
+  paste(
+    "expose_functions() can't expose this Stan function because the function",
+    "name and/or one or more argument names use a reserved keyword",
+    "(typically in the C++ toolchain used to compile Stan). Please rename",
+    "the function/arguments in your Stan functions block and try again.",
+    paste("Conflicting names:", paste(names, collapse = ", "))
+  )
+}
+
+test_that("Reserved names in Stan code give the same error", {
+  stan_file <- write_stan_file(
+    "
+  functions {
+    real min(real max, real class) {
+      return max - class;
+    }
+  }
+  "
+  )
+
+  funmod <- cmdstan_model(stan_file, force_recompile = TRUE)
+  expect_error(
+    funmod$expose_functions(),
+    reserved_names_msg(c("min", "max", "class")),
+    fixed = TRUE
+  )
+})
+
+test_that("Multiple reserved C++ keywords in Stan code give the same error", {
+  stan_file <- write_stan_file(
+    "
+  functions {
+    real template(real class, real namespace, real private) {
+      return class + namespace + private;
+    }
+  }
+  "
+  )
+
+  funmod <- cmdstan_model(stan_file, force_recompile = TRUE)
+  expect_error(
+    funmod$expose_functions(),
+    reserved_names_msg(c("template", "class", "namespace", "private")),
+    fixed = TRUE
+  )
+})
+
+test_that("Reserved keywords in Stan function bodies are allowed", {
+  stan_file <- write_stan_file(
+    "
+  functions {
+    real add_one(real x) {
+      real class = 1;
+      return x + class;
+    }
+  }
+  "
+  )
+
+  funmod <- cmdstan_model(stan_file, force_recompile = TRUE)
+  expect_no_error(funmod$expose_functions())
+  expect_equal(funmod$functions$add_one(2), 3)
+})
+
+test_that("Stan code with no reserved names exposes functions", {
+  stan_file <- write_stan_file(
+    "
+  functions {
+    real add_pair(real left, real right) {
+      return left + right;
+    }
+  }
+  "
+  )
+
+  funmod <- cmdstan_model(stan_file, force_recompile = TRUE)
+  expect_no_error(funmod$expose_functions())
+})
+
 test_that("Exposing external functions errors before v2.32", {
   fake_cmdstan_version("2.26.0")