Error reporting on File in dart:io

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 9b7093daff51e3fe6336ad217173c90e1ee9c5e3..44fe08d50fd338a775857094995528450ff0ad1f 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -106,6 +106,13 @@ off_t File::Length() {
 
 
 File* File::Open(const char* name, FileOpenMode mode) {
+  struct stat st;
+  if (TEMP_FAILURE_RETRY(stat(name, &st)) == 0) {
+    if (!S_ISREG(st.st_mode)) {
+      errno = (S_ISDIR(st.st_mode)) ? EISDIR : ENOENT;
+      return false;
+    }
+  }
   int flags = O_RDONLY;
   if ((mode & kWrite) != 0) {
     flags = (O_RDWR | O_CREAT);
@@ -185,6 +192,15 @@ char* File::GetCanonicalPath(const char* pathname) {
 
 
 char* File::GetContainingDirectory(char* pathname) {
+  struct stat st;
+  if (TEMP_FAILURE_RETRY(stat(pathname, &st)) == 0) {
+    if (!S_ISREG(st.st_mode)) {
+      errno = (S_ISDIR(st.st_mode)) ? EISDIR : ENOENT;
+      return NULL;
+    }
+  } else {
+    return NULL;
+  }
   char* path = NULL;
   do {
     path = dirname(pathname);