Use distro-aware fallback for WSL UNC makefile reads

Author: jgabry

R/path.R

@@ -267,17 +267,65 @@ latest_cmdstan_installed <- function(installs_path) {
   latest_cmdstan
 }
 
+is_wsl_unc_path <- function(path) {
+  is.character(path) &&
+    length(path) == 1 &&
+    !is.na(path) &&
+    startsWith(repair_path(path), "//wsl$/")
+}
+
+# Extract the distro name from a WSL UNC path like //wsl$/Ubuntu-22.04/...
+wsl_unc_distro_name <- function(path) {
+  sub("^//wsl\\$/([^/]+).*$", "\\1", repair_path(path))
+}
+
+# Convert a WSL UNC path to the corresponding Linux path within the distro.
+wsl_unc_path_to_linux <- function(path) {
+  sub("^//wsl\\$/[^/]+", "", repair_path(path))
+}
+
+read_lines_direct <- function(path) {
+  tryCatch(
+    suppressWarnings(readLines(path, warn = FALSE)),
+    error = function(e) NULL
+  )
+}
+
+# Fall back to reading through `wsl` when Windows R can't read a WSL UNC path.
+read_lines_via_wsl <- function(path) {
+  file_contents <- processx::run(
+    command = "wsl",
+    args = c("-d", wsl_unc_distro_name(path), "cat", wsl_unc_path_to_linux(path)),
+    error_on_status = FALSE
+  )
+  if (file_contents$status != 0) {
+    return(NULL)
+  }
+  if (!nzchar(file_contents$stdout)) {
+    return(character(0))
+  }
+  con <- textConnection(file_contents$stdout)
+  on.exit(close(con), add = TRUE)
+  readLines(con, warn = FALSE)
+}
+
+# Preserve existing direct reads and only use the WSL fallback when needed.
+read_lines_with_wsl_fallback <- function(path) {
+  file_contents <- read_lines_direct(path)
+  if (!is.null(file_contents) || !is_wsl_unc_path(path)) {
+    return(file_contents)
+  }
+  read_lines_via_wsl(path)
+}
+
 
 #' Find the version of CmdStan from makefile
 #' @noRd
 #' @param path Path to installation.
 #' @return Version number as a string.
 read_cmdstan_version <- function(path) {
   makefile_path <- file.path(path, "makefile")
-  makefile <- tryCatch(
-    suppressWarnings(readLines(makefile_path, warn = FALSE)),
-    error = function(e) NULL
-  )
+  makefile <- read_lines_with_wsl_fallback(makefile_path)
   if (is.null(makefile)) {
     warning(
       "Can't find CmdStan makefile to detect version number. ",

tests/testthat/test-path.R

@@ -221,6 +221,52 @@ test_that("CmdStan version helpers handle invalid inputs", {
   expect_false(is_supported_cmdstan_version("not-a-version"))
 })
 
+test_that("WSL UNC path helpers work", {
+  wsl_path <- "//wsl$/Ubuntu-22.04/root/.cmdstan/cmdstan-2.38.0"
+  expect_true(is_wsl_unc_path(wsl_path))
+  expect_false(is_wsl_unc_path(PATH))
+  expect_equal(wsl_unc_distro_name(wsl_path), "Ubuntu-22.04")
+  expect_equal(
+    wsl_unc_path_to_linux(file.path(wsl_path, "makefile")),
+    "/root/.cmdstan/cmdstan-2.38.0/makefile"
+  )
+})
+
+test_that("read_cmdstan_version() prefers direct reads for UNC paths", {
+  wsl_path <- "//wsl$/Ubuntu-22.04/root/.cmdstan/cmdstan-2.38.0"
+  local_mocked_bindings(
+    read_lines_direct = function(path) {
+      expect_equal(
+        path,
+        file.path(wsl_path, "makefile")
+      )
+      "CMDSTAN_VERSION := 2.38.0"
+    },
+    read_lines_via_wsl = function(path) {
+      stop("WSL fallback should not be used when direct reads succeed.")
+    }
+  )
+  expect_equal(read_cmdstan_version(wsl_path), "2.38.0")
+})
+
+test_that("read_cmdstan_version() falls back to distro-aware WSL reads", {
+  wsl_path <- "//wsl$/Ubuntu-22.04/root/.cmdstan/cmdstan-2.38.0"
+  local_mocked_bindings(
+    read_lines_direct = function(path) {
+      expect_equal(
+        path,
+        file.path(wsl_path, "makefile")
+      )
+      NULL
+    },
+    read_lines_via_wsl = function(path) {
+      expect_equal(path, file.path(wsl_path, "makefile"))
+      "CMDSTAN_VERSION := 2.38.0"
+    }
+  )
+  expect_equal(read_cmdstan_version(wsl_path), "2.38.0")
+})
+
 test_that("cmdstan_ext() works", {
   if (os_is_windows() && !os_is_wsl()) {
     expect_identical(cmdstan_ext(), ".exe")