fix(liveslots): collection.clear(pattern) vs getSize (#10008)

The `.clear()` method, on (strong) collections, will delete all entries. But it can also be called with `keyPatt` and/or `valuePatt` argument, and only the matching entries will be deleted.

Previously, the `|entryCount` metadata field was unconditionally set to zero for any call to `.clear()`, even those with patterns which caused some entries to be retained. This caused a subsequent `collection.getSize()` to return the wrong value, yielding zero even if the collection still had entries.

This commit fixes the logic to decrement the `|entryCount` field by the number of entries actually deleted. As an optimization, it is still set directly to zero if `clear()` is not limited by patterns.

fixes #10007

packages/swingset-liveslots/src/collectionManager.js

@@ -616,16 +616,21 @@ export function makeCollectionManager(
 
     function clearInternal(isDeleting, keyPatt, valuePatt) {
       let doMoreGC = false;
-      if (isDeleting || (matchAny(keyPatt) && matchAny(valuePatt))) {
+      if (isDeleting) {
         doMoreGC = clearInternalFull();
+        // |entryCount will be deleted along with metadata keys
+      } else if (matchAny(keyPatt) && matchAny(valuePatt)) {
+        doMoreGC = clearInternalFull();
+        if (!hasWeakKeys) {
+          syscall.vatstoreSet(prefix('|entryCount'), '0');
+        }
       } else {
+        let numDeleted = 0;
         for (const k of keys(keyPatt, valuePatt)) {
+          numDeleted += 1;
           doMoreGC = deleteInternal(k) || doMoreGC;
         }
-      }
-      if (!hasWeakKeys && !isDeleting) {
-        // TODO: broken, see #10007
-        syscall.vatstoreSet(prefix('|entryCount'), '0');
+        updateEntryCount(-numDeleted);
       }
       return doMoreGC;
     }

packages/swingset-liveslots/test/collections.test.js

@@ -503,8 +503,7 @@ test('map clear', t => {
   t.is(testStore.getSize(), 0);
 });
 
-// see #10007
-test.failing('map clear with pattern', t => {
+test('map clear with pattern', t => {
   const testStore = makeScalarBigMapStore('cmap', { keyShape: M.any() });
   testStore.init('a', 'ax');
   testStore.init('b', 'bx');
@@ -529,8 +528,7 @@ test('set clear', t => {
   t.is(testStore.getSize(), 0);
 });
 
-// see #10007
-test.failing('set clear with pattern', t => {
+test('set clear with pattern', t => {
   const testStore = makeScalarBigSetStore('cset', { keyShape: M.any() });
   testStore.add('a');
   testStore.add('b');