Alternate windows approach

Author: andrjohns

R/utils.R

@@ -740,25 +740,30 @@ with_cmdstan_flags <- function(expr) {
 
   libs <- c("LDLIBS", "LIBSUNDIALS", "TBB_TARGETS", "LDFLAGS_TBB")
   libs <- paste(sapply(libs, get_cmdstan_flags), collapse = " ")
-  if (.Platform$OS.type == "windows") {
+  if (os_is_windows()) {
     libs <- paste(libs, "-fopenmp -lstdc++")
   }
   lib_paths <- c("/stan/lib/stan_math/lib/tbb/",
                  "/stan/lib/stan_math/lib/sundials_6.1.1/lib/")
+  new_makevars <- c(
+    PKG_CPPFLAGS = ifelse(cmdstan_version() <= "2.30.1", "-DCMDSTAN_JSON", ""),
+    PKG_CXXFLAGS = paste(cxxflags, cmdstanr_includes, r_includes, collapse = " "),
+    PKG_LIBS = libs
+  )
+  if (os_is_windows()) {
+    new_makevars <- c(
+      new_makevars,
+      SHLIB_LD = paste0(rtools4x_toolchain_path(),"/gcc"),
+      LOCAL_CPPFLAGS = paste0("-L'",rtools4x_toolchain_path(),"/../include'"),
+      LOCAL_LIBS = paste0("-L'",rtools4x_toolchain_path(),"/../lib'")
+    )
+  }
   withr::with_path(
     c(
       paste0(cmdstan_path(), lib_paths),
       toolchain_PATH_env_var()
     ),
-    withr::with_makevars(
-     c(
-       USE_CXX14 = 1,
-       PKG_CPPFLAGS = ifelse(cmdstan_version() <= "2.30.1", "-DCMDSTAN_JSON", ""),
-       PKG_CXXFLAGS = paste(cxxflags, cmdstanr_includes, r_includes, collapse = " "),
-       PKG_LIBS = libs
-     ),
-     expr
-    )
+    withr::with_makevars(new_makevars, expr)
   )
 }
 
@@ -818,11 +823,16 @@ expose_model_methods <- function(env, force_recompile = FALSE, verbose = FALSE)
   }
 
   methods_dll <- tempfile(fileext = .Platform$dynlib.ext)
+  envvar <- c("current")
+  if (os_is_windows()) {
+    envvar <- c(envvar, "BINPREF" = paste0(rtools4x_toolchain_path(), "/"))
+  }
   with_cmdstan_flags(
     processx::run(
       command = file.path(R.home(component = "bin"), "R"),
       args = c("CMD", "SHLIB", repair_path(model_obj_file), repair_path(precomp_methods_file),
                 "-o", repair_path(methods_dll)),
+      env = envvar,
       echo = verbose || is_verbose_mode(),
       echo_cmd = is_verbose_mode(),
       error_on_status = FALSE