fix: treat a re-resolved anchor as a fresh session

Author: TaduJR

src/hooks/useShiftRangeSelection.ts

@@ -144,12 +144,12 @@ function seedRangeState<TItem>(params: Params<TItem>, isIncluded: (key: string)
 }
 
 /**
- * What a session with no history starts from. It adopts rows that read as selected without having been picked on their own,
- * since those came from a block selection like a group that a range is entitled to narrow. Empty unless `isItemProtected` is passed.
+ * A session with no continuity adopts rows that read as selected without having been picked on their own, since those came from a
+ * block selection a range may narrow. Inert unless `isItemProtected` is passed.
  */
-function startingPainted<TItem>(params: Params<TItem>, state: SessionState): ReadonlySet<string> {
+function startingPainted<TItem>(params: Params<TItem>, sameAnchor: boolean): ReadonlySet<string> {
     const keys = new Set<string>();
-    if (state.kind !== 'idle') {
+    if (sameAnchor) {
         return keys;
     }
     const isProtected = params.isItemProtected ?? params.isItemSelected;
@@ -197,7 +197,7 @@ function computeShiftRange<TItem>(params: Params<TItem>, state: SessionState, ta
     // The session survives only while the same anchor does; a re-resolved or cold anchor starts fresh.
     const sameAnchor = state.kind !== 'idle' && anchor === state.anchor;
     const continuing = state.kind === 'ranging' && sameAnchor;
-    const prevPainted: ReadonlySet<string> = continuing ? state.painted : startingPainted(params, state);
+    const prevPainted: ReadonlySet<string> = continuing ? state.painted : startingPainted(params, sameAnchor);
     const preSelected = protectedKeys(params, prevPainted);
 
     const anchorIdx = keyToIndex.get(anchor);

tests/unit/hooks/useShiftRangeSelection.test.ts

@@ -533,6 +533,22 @@ describe('useShiftRangeSelection', () => {
             expect(nthBatchKeys(onApplyRange, 1)).toEqual({toSelect: ['b', 'c'], toDeselect: ['d']});
         });
 
+        it('adopts the block when the remembered anchor is gone, since that session is over', () => {
+            const onApplyRange = makeApplyMock();
+            const {result, rerender} = renderHook(
+                ({items}: {items: Row[]}) => useShiftRangeSelection<Row>(makeParams({items, onApplyRange, isItemSelected: (row) => row.keyForList !== 'a', isItemProtected: () => false})),
+                {initialProps: {items: [...ROWS]}},
+            );
+            // Anchored on 'a', which the next render drops from the list
+            act(() => result.current.notifyAnchor(ROW_A));
+            rerender({items: ROWS.slice(1)});
+            act(() => {
+                result.current.applyShiftClick(ROW_C, true);
+            });
+            // The anchor re-resolved to the block's first row, and the rest of the block fell out of the range with it.
+            expect(nthBatchKeys(onApplyRange, 0)).toEqual({toSelect: ['b', 'c'], toDeselect: ['d', 'e']});
+        });
+
         it('leaves a block alone when the session already has an anchor, so an unrelated range cannot dissolve it', () => {
             const onApplyRange = makeApplyMock();
             const {result} = renderHook(() =>