@@ -145,0 +155,4 @@
+/**
+ * Partial blendfile writing.
+ *
+ * This wrapper around the Main struct is designed to have a very short life span, during which it

@@ -145,0 +158,4 @@
+ * This wrapper around the Main struct is designed to have a very short life span, during which it
+ * will contain independent copies of the IDs that are added to it.
+ *
+ * It also has advanced ways to handle dependencies and libraries for linked IDs.

@@ -145,0 +171,4 @@
+
+ private:
+  /**
+   * The filepath that should be used a root for IDs _added_ to the context, when handling

@@ -145,0 +198,4 @@
+   * context, the added one should be able to 'steal' that session_uid in the context, and
+   * re-assign a new one to the other ID.
+   */
+  void preempt_session_uid_(ID *ctx_id, unsigned int session_uid);

@@ -145,0 +221,4 @@
+   * Ensure that the given library path has a matching Library ID in the context, creating a new
+   * one if needed.
+   */
+  Library *ensure_library_(blender::StringRefNull library_absolute_path);

@@ -145,0 +230,4 @@
+  PartialWriteContext(blender::StringRefNull reference_root_filepath);
+  ~PartialWriteContext();
+  /* Delete regular copy constructor, such that only the default move copy constructor (and
+   * assignement operator) can be used. */

@@ -145,0 +232,4 @@
+  /* Delete regular copy constructor, such that only the default move copy constructor (and
+   * assignement operator) can be used. */
+  PartialWriteContext(const PartialWriteContext &) = delete;
+  PartialWriteContext(PartialWriteContext &&) = default;

@@ -145,0 +242,4 @@
+   * nor hanlded as a regular dependency. Instead, the library is _always_ added to the context
+   * data, and never duplicated. Also, library matching always happens based on absolute filepath.
+   */
+  enum AddIDOptions {

@@ -145,0 +263,4 @@
+     * WARNING: This also means that dependencies like obdata, shapekeys or actions are not
+     * duplicated either.
+     */
+    CLEAR_DEPENDENCIES = 1 << 8,

@@ -145,0 +294,4 @@
+   * \return The pointer to the duplicated ID in the partial write context.
+   */
+  ID *id_add(const ID *id,
+             PartialWriteContext::AddIDOptions options,

@@ -145,0 +342,4 @@
+  /**
+   * Fully empty the partial write context.
+   */
+  void clear(void);

@@ -262,0 +268,4 @@
+/**
+ * Make given \a bmain empty again, and free all runtime mappings.
+ *
+ * \note: Unlike #BKE_main_free, only process the given \a bmain, without handling any potential

@@ -1655,0 +1663,4 @@
+PartialWriteContext::PartialWriteContext(StringRefNull reference_root_filepath)
+    : reference_root_filepath_(reference_root_filepath)
+{
+  memset(&this->bmain, 0, sizeof(this->bmain));

@@ -1655,0 +1666,4 @@
+  memset(&this->bmain, 0, sizeof(this->bmain));
+  BKE_main_init(this->bmain);
+  if (!reference_root_filepath_.empty()) {
+    BLI_strncpy(

@@ -1655,0 +1764,4 @@
+
+void PartialWriteContext::make_local(ID *ctx_id, const int make_local_flags)
+{
+  /* Making an ID local typically resets its session UID, here we want to keep the same value. */

@@ -1655,0 +1833,4 @@
+     */
+    BLI_assert(ctx_root_id->session_uid == id->session_uid);
+    this->ensure_id_user(ctx_root_id, set_fake_user);
+    return ctx_root_id;

@@ -145,0 +252,4 @@
+     * \warning By default, when #ADD_DEPENDENCIES is defined, this will also apply to all
+     * dependencies as well.
+     */
+    MAKE_LOCAL = 1 << 0,

@@ -145,0 +295,4 @@
+   * Options passed to the #id_add method.
+   */
+  struct IDAddOptions {
+    IDAddOperations operations;

@@ -1655,0 +1746,4 @@
+                                   (LIB_ID_CREATE_NO_MAIN | LIB_ID_CREATE_NO_USER_REFCOUNT));
+  ctx_root_id->tag |= LIB_TAG_TEMP_MAIN;
+  if (regenerate_session_uid) {
+    /* Callling #BKE_lib_libblock_session_uid_renew is not needed here, copying already generated a

@@ -704,3 +704,3 @@
   data.id_dst = newid;
   data.flag = flag;
-  BKE_library_foreach_ID_link(bmain, newid, id_copy_libmanagement_cb, &data, IDWALK_NOP);
+  /* When copying an embedded ID, typically at this point its owner ID pinter will still point to

@@ -706,1 +706,3 @@
-  BKE_library_foreach_ID_link(bmain, newid, id_copy_libmanagement_cb, &data, IDWALK_NOP);
+  /* When copying an embedded ID, typically at this point its owner ID pinter will still point to
+   * the owner of the source, this code has no access to its valid (i.e. destination) owner. This
+   * can be added at some point is needed, but currently the #id_copy_libmanagement_cb callback

@@ -195,3 +236,2 @@
+  BLI_assert(copy_buffer.is_valid());
 
-  /* Ensure that there are no old copy tags around */
-  BKE_blendfile_write_partial_begin(bmain_src);

@@ -149,0 +130,4 @@
+                            scene_name,
+                            nullptr,
+                            {blendfile::PartialWriteContext::IDAddOperations::SET_FAKE_USER}));
+  id_fake_user_set(&scene_dst->id);

@@ -187,0 +193,4 @@
+      return IDWALK_RET_NOP;
+    }
+
+    /* The Action ID of the destination scene has already been added (created actually) in the copy

@@ -187,0 +223,4 @@
+      };
+      id_dst = copy_buffer.id_add(
+          id_src,
+          {blendfile::PartialWriteContext::IDAddOperations::CLEAR_DEPENDENCIES},