BLI: add function for changing working directory

Add `BLI_change_working_dir(path)` to change the current working directory.

This change is required for adding USDZ support to Blender. When exporting to that format, we are required to do a weird change of directory because of a quirk with the USD library's USDZ functionality. If an absolute filepath is passed into the `UsdUtilsCreateNewUsdzPackage` function, the USDZ archive will store that full path.

macOS uses `NSFileManager` through some new Mac-only wrapper functions.

Ref #99807

Pull Request #104525

source/blender/blenlib/BLI_fileops.h

@@ -142,6 +142,18 @@ double BLI_dir_free_space(const char *dir) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL(
  */
 char *BLI_current_working_dir(char *dir, size_t maxncpy) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL();
 eFileAttributes BLI_file_attributes(const char *path);
+/**
+ * Changes the current working directory to the provided path.
+ *
+ * Usage of this function is strongly discouraged as it is not thread safe. It will likely cause
+ * issues if there is an operation on another thread that does not expect the current working
+ * directory to change. This has been added to support USDZ export, which has a problematic
+ * "feature" described in this issue https://projects.blender.org/blender/blender/issues/99807. It
+ * will be removed if it is possible to resolve that issue upstream in the USD library.
+ *
+ * \return true on success, false otherwise.
+ */
+bool BLI_change_working_dir(const char *dir);
 
 /** \} */
 

source/blender/blenlib/intern/storage.c

@@ -54,11 +54,36 @@
 #include "BLI_linklist.h"
 #include "BLI_path_util.h"
 #include "BLI_string.h"
+#include "BLI_threads.h"
 #include "BLI_utildefines.h"
 
+#if !defined(__APPLE__)
+/* The implementation for Apple lives in storage_apple.mm.*/
+bool BLI_change_working_dir(const char *dir)
+{
+  BLI_assert(BLI_thread_is_main());
+
+  if (!BLI_is_dir(dir)) {
+    return false;
+  }
+#  if defined(WIN32)
+  wchar_t wdir[FILE_MAX];
+  if (conv_utf_8_to_16(dir, wdir, ARRAY_SIZE(wdir)) != 0) {
+    return false;
+  }
+  return _wchdir(wdir) == 0;
+#  else
+  int result = chdir(dir);
+  if (result == 0) {
+    BLI_setenv("PWD", dir);
+  }
+  return result == 0;
+#  endif
+}
+
 char *BLI_current_working_dir(char *dir, const size_t maxncpy)
 {
-#if defined(WIN32)
+#  if defined(WIN32)
   wchar_t path[MAX_PATH];
   if (_wgetcwd(path, MAX_PATH)) {
     if (BLI_strncpy_wchar_as_utf8(dir, path, maxncpy) != maxncpy) {
@@ -66,7 +91,7 @@ char *BLI_current_working_dir(char *dir, const size_t maxncpy)
     }
   }
   return NULL;
-#else
+#  else
   const char *pwd = BLI_getenv("PWD");
   if (pwd) {
     size_t srclen = BLI_strnlen(pwd, maxncpy);
@@ -77,8 +102,9 @@ char *BLI_current_working_dir(char *dir, const size_t maxncpy)
     return NULL;
   }
   return getcwd(dir, maxncpy);
-#endif
+#  endif
 }
+#endif /* !defined (__APPLE__) */
 
 double BLI_dir_free_space(const char *dir)
 {

source/blender/blenlib/intern/storage_apple.mm

@@ -13,6 +13,8 @@
 
 #include "BLI_fileops.h"
 #include "BLI_path_util.h"
+#include "BLI_string.h"
+
 
 /* Extended file attribute used by OneDrive to mark placeholder files. */
 static const char *ONEDRIVE_RECALLONOPEN_ATTRIBUTE = "com.microsoft.OneDrive.RecallOnOpen";
@@ -185,3 +187,27 @@ const char *BLI_expand_tilde(const char *path_with_tilde)
   }
   return path_expanded;
 }
+
+char *BLI_current_working_dir(char *dir, const size_t maxncpy) {
+  /* Can't just copy to the *dir pointer, as [path getCString gets grumpy.*/
+  static char path_expanded[PATH_MAX];
+  @autoreleasepool {
+    NSString *path = [[NSFileManager defaultManager] currentDirectoryPath];
+    const size_t length = maxncpy > PATH_MAX ? PATH_MAX : maxncpy;
+    [path getCString:path_expanded maxLength:length encoding:NSUTF8StringEncoding];
+    BLI_strncpy(dir, path_expanded, maxncpy);
+    return path_expanded;
+  }
+}
+
+bool BLI_change_working_dir(const char* dir) {
+  @autoreleasepool {
+    NSString* path = [[NSString alloc] initWithUTF8String: dir];
+    if ([[NSFileManager defaultManager] changeCurrentDirectoryPath: path] == YES) {
+      return false;
+    }
+    else {
+      return true;
+    }
+  }
+}

source/blender/blenlib/tests/BLI_fileops_test.cc

@@ -1,11 +1,27 @@
 /* SPDX-License-Identifier: Apache-2.0 */
-
-#include "BLI_fileops.hh"
-
 #include "testing/testing.h"
 
+#include "BLI_fileops.hh"
+#include "BLI_path_util.h"
+#include "BLI_string.h"
+#include "BLI_threads.h"
+
 namespace blender::tests {
 
+class ChangeWorkingDirectoryTest : public testing::Test {
+ public:
+  std::string test_temp_dir;
+
+  void TearDown() override
+  {
+    if (!test_temp_dir.empty()) {
+      BLI_delete(test_temp_dir.c_str(), true, false);
+    }
+
+    BLI_threadapi_exit();
+  }
+};
+
 TEST(fileops, fstream_open_string_filename)
 {
   const std::string test_files_dir = blender::tests::flags_test_asset_dir();
@@ -37,4 +53,43 @@ TEST(fileops, fstream_open_charptr_filename)
   /* Reading the file not tested here. That's deferred to `std::fstream` anyway. */
 }
 
+TEST_F(ChangeWorkingDirectoryTest, change_working_directory)
+{
+  /* Must use because BLI_change_working_dir() checks that we are on the main thread. */
+  BLI_threadapi_init();
+
+  char original_wd[FILE_MAX];
+  if (!BLI_current_working_dir(original_wd, FILE_MAX)) {
+    FAIL() << "unable to get the current working directory";
+  }
+
+  const std::string temp_file_name(std::tmpnam(nullptr));
+  test_temp_dir = temp_file_name + "_новый";
+
+  if (BLI_exists(test_temp_dir.c_str())) {
+    BLI_delete(test_temp_dir.c_str(), true, false);
+  }
+
+  ASSERT_FALSE(BLI_change_working_dir(test_temp_dir.c_str()))
+      << "changing directory to a non-existent directory is expected to fail.";
+
+  ASSERT_TRUE(BLI_dir_create_recursive(test_temp_dir.c_str()))
+      << "temporary directory should have been created successfully.";
+
+  ASSERT_TRUE(BLI_change_working_dir(test_temp_dir.c_str()))
+      << "temporary directory should succeed changing directory.";
+
+  char cwd[FILE_MAX];
+  if (!BLI_current_working_dir(cwd, FILE_MAX)) {
+    FAIL() << "unable to get the current working directory";
+  }
+
+  ASSERT_EQ(BLI_path_cmp_normalized(cwd, test_temp_dir.c_str()), 0)
+      << "the path of the current working directory should equal the path of the temporary "
+         "directory that was created.";
+
+  ASSERT_TRUE(BLI_change_working_dir(original_wd))
+      << "changing directory back to the original working directory should succeed.";
+}
+
 }  // namespace blender::tests