fix: SyncedCollection

Author: EqualMa

packages/frender/src/elements/synced_collection.rs

@@ -0,0 +1,68 @@
+pub(super) enum MountState {
+    MountedAndUpToDate,
+    MountedAndUpToDateButPreviousWasSkipped,
+    Outdated,
+    OutdatedAndPreviousWasSkipped,
+    OutdatedAndMoved,
+    // UpdateToDateButMoved,
+}
+
+impl MountState {
+    // caller should mark the next one as previous_was_skipped
+    // There might be a UpdateToDateButMoved variant so this method is different from mark_as_outdated_and_moved
+    pub(crate) fn mark_as_moved(&mut self) {
+        *self = Self::OutdatedAndMoved
+    }
+
+    // caller should mark the next one as previous_was_skipped
+    pub(crate) fn mark_as_outdated_and_moved(&mut self) {
+        *self = Self::OutdatedAndMoved
+    }
+
+    pub(crate) fn mark_as_outdated(&mut self) {
+        *self = match self {
+            MountState::MountedAndUpToDate => Self::Outdated,
+            MountState::Outdated => Self::Outdated,
+            MountState::OutdatedAndMoved => MountState::OutdatedAndMoved,
+            MountState::MountedAndUpToDateButPreviousWasSkipped => {
+                MountState::OutdatedAndPreviousWasSkipped
+            }
+            MountState::OutdatedAndPreviousWasSkipped => MountState::OutdatedAndPreviousWasSkipped,
+        }
+    }
+
+    pub(crate) fn mark_previous_was_skipped(&mut self) {
+        match self {
+            MountState::MountedAndUpToDate => {
+                *self = MountState::MountedAndUpToDateButPreviousWasSkipped
+            }
+            MountState::Outdated => *self = MountState::OutdatedAndPreviousWasSkipped,
+            _ => {}
+        }
+    }
+
+    pub(crate) fn needs_reposition(&self) -> NeedsReposition {
+        match self {
+            MountState::MountedAndUpToDate => NeedsReposition::No {
+                previous_skipped: false,
+            },
+            MountState::MountedAndUpToDateButPreviousWasSkipped => NeedsReposition::No {
+                previous_skipped: true,
+            },
+            MountState::Outdated => NeedsReposition::No {
+                previous_skipped: false,
+            },
+            MountState::OutdatedAndPreviousWasSkipped => NeedsReposition::No {
+                previous_skipped: true,
+            },
+            MountState::OutdatedAndMoved => NeedsReposition::Yes,
+        }
+    }
+}
+
+pub(crate) enum NeedsReposition {
+    Yes,
+    No { previous_skipped: bool },
+}
+
+const _: () = assert!(std::mem::size_of::<NeedsReposition>() == 1);