Undo reported "nothing left to undo" after a successful undo (#72)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

web/src/lib/history.ts

@@ -224,20 +224,23 @@ export interface UndoOutcome {
  */
 export function describeUndo(target: UndoTarget, result: RevertResult): UndoOutcome {
   const skipped = result.conflicts.map(describeConflict).join('; ')
+  // A NULL change set is the server's signal that nothing needed doing. An empty
+  // `counts` is not the same thing and must not be read as one — that conflation
+  // made a successful undo report "nothing left to undo", which is the worst
+  // possible thing to tell someone about an action that just worked.
+  const didSomething = result.changeSet != null
   const applied = result.changeSet ? totalChanges(result.changeSet) : 0
   if (result.conflicts.length === 0) {
-    // The server answers 200 with a null change set when every revision was
-    // already a no-op — reachable by undoing a creation whose object is gone.
-    // Claiming "Undone." there would be reporting work that didn't happen.
-    if (applied === 0) return { tone: 'ok', message: 'Nothing left to undo — this was already reversed.' }
+    // Reachable by undoing a creation whose object is already gone.
+    if (!didSomething) return { tone: 'ok', message: 'Nothing left to undo — this was already reversed.' }
     return { tone: 'ok', message: 'Undone.' }
   }
-  if (applied === 0) {
+  if (!didSomething) {
     return { tone: 'error', message: `Nothing was undone — ${skipped}.` }
   }
   // Only claim a denominator when we have one. "2 of 3" from a caller that
   // never knew the total would be a number invented to fill a sentence.
   const total = totalChanges(target)
-  const scale = total > 0 ? `${applied} of ${total} changes undone` : 'Partly undone'
+  const scale = total > 0 && applied > 0 ? `${applied} of ${total} changes undone` : 'Partly undone'
   return { tone: 'partial', message: `${scale} — ${skipped}.` }
 }