rchk fixes (#571)

* Avoid the "multiple allocating arguments" pattern

* PROTECT()/UNPROTECT() `val`

* Protect `cli_warn` too

Author: jennybc

src/vroom_chr.cc

@@ -26,12 +26,14 @@ cpp11::strings read_chr(vroom_vec_info* info) {
     for (auto b = col->begin(), e = col->end(); b != e; ++b) {
       auto str = *b;
       auto val = info->locale->encoder_.makeSEXP(str.begin(), str.end(), true);
+      PROTECT(val);
       if (Rf_xlength(val) < str.end() - str.begin()) {
         info->errors->add_error(
             b.index(), col->get_index(), "", "embedded null", b.filename());
       }
 
       SET_STRING_ELT(out, i++, check_na(nas, val));
+      UNPROTECT(1);
     }
   });
 

src/vroom_errors.h

@@ -87,9 +87,10 @@ class vroom_errors {
       have_warned_ = true;
       // it is intentional that we aren't using cpp11::package
       // https://github.com/tidyverse/vroom/commit/984a3e5e37e124feacfec3d184dbeb02eb1145c4
-      static auto cli_warn = Rf_findFun(
-          Rf_install("cli_warn"),
-          Rf_findVarInFrame(R_NamespaceRegistry, Rf_install("cli")));
+      SEXP cli_ns = Rf_findVarInFrame(R_NamespaceRegistry, Rf_install("cli"));
+      PROTECT(cli_ns);
+      SEXP cli_warn = Rf_findFun(Rf_install("cli_warn"), cli_ns);
+      PROTECT(cli_warn);
       cpp11::strings bullets({
         "w"_nm = "One or more parsing issues, call {.fun problems} on your data frame for details, e.g.:",
         " "_nm = "dat <- vroom(...)",
@@ -99,6 +100,7 @@ class vroom_errors {
         bullets,
         Rf_mkString("vroom_parse_issue"));
       Rf_eval(cli_warn_call, R_EmptyEnv);
+      UNPROTECT(2);
     }
   }