Merge branch 'develop' into ximinez/emptydirectoryinvariant

* XRPLF/develop:
  refactor: Modularize app/tx (6228)
  refactor: Decouple app/tx from `Application` and `Config` (6227)
  chore: Update clang-format to 21.1.8 (6352)
  refactor: Modularize `HashRouter`, `Conditions`, and `OrderBookDB` (6226)
  chore: Fix minor issues in comments (6346)
  refactor: Modularize the NetworkOPs interface (6225)
  chore: Fix `gcov` lib coverage build failure on macOS (6350)
  refactor: Modularize RelationalDB (6224)
  refactor: Modularize WalletDB and Manifest (6223)
  fix: Update invariant checks for Permissioned Domains (6134)
  refactor: Change main thread name to `xrpld-main` (6336)
  refactor: Fix spelling issues in tests (6199)
  test: Add file and line location to Env (6276)
  chore: Remove CODEOWNERS (6337)
  perf: Remove unnecessary caches (5439)
  chore: Restore unity builds (6328)
  refactor: Update secp256k1 to 0.7.1 (6331)
  fix: Increment sequence when accepting new manifests (6059)
  fix typo in LendingHelpers unit-test (6215)

include/xrpl/tx/InvariantCheck.h

@@ -687,6 +687,22 @@ public:
     finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&);
 };
 
+/**
+ * @brief Invariants: An account's directory should never be empty
+ *
+ */
+class NoEmptyDirectory
+{
+    bool bad_ = false;
+
+public:
+    void
+    visitEntry(bool, std::shared_ptr<SLE const> const&, std::shared_ptr<SLE const> const&);
+
+    bool
+    finalize(STTx const&, TER const, XRPAmount const, ReadView const&, beast::Journal const&);
+};
+
 // additional invariant checks can be declared above and then added to this
 // tuple
 using InvariantChecks = std::tuple<
@@ -713,7 +729,8 @@ using InvariantChecks = std::tuple<
     ValidPseudoAccounts,
     ValidLoanBroker,
     ValidLoan,
-    ValidVault>;
+    ValidVault,
+    NoEmptyDirectory>;
 
 /**
  * @brief get a tuple of all invariant checks

src/libxrpl/ledger/ApplyView.cpp

@@ -244,6 +244,7 @@ ApplyView::emptyDirDelete(Keylet const& directory)
 bool
 ApplyView::dirRemove(Keylet const& directory, std::uint64_t page, uint256 const& key, bool keepRoot)
 {
+    keepRoot = false;
     auto node = peek(keylet::page(directory, page));
 
     if (!node)

src/libxrpl/tx/InvariantCheck.cpp

@@ -1051,7 +1051,7 @@ ValidNewAccountRoot::finalize(
 
     JLOG(j.fatal()) << "Invariant failed: account root created illegally";
     return false;
-}  // namespace xrpl
+}
 
 //------------------------------------------------------------------------------
 
@@ -3480,4 +3480,42 @@ ValidVault::finalize(
     return true;
 }
 
+//------------------------------------------------------------------------------
+
+void
+NoEmptyDirectory::visitEntry(
+    bool isDelete,
+    std::shared_ptr<SLE const> const& before,
+    std::shared_ptr<SLE const> const& after)
+{
+    if (isDelete)
+        return;
+    if (before && before->getType() != ltDIR_NODE)
+        return;
+    if (after && after->getType() != ltDIR_NODE)
+        return;
+    if (!after->isFieldPresent(sfOwner))
+        // Not an account dir
+        return;
+
+    bad_ = after->at(sfIndexes).empty();
+}
+
+bool
+NoEmptyDirectory::finalize(
+    STTx const& tx,
+    TER const result,
+    XRPAmount const,
+    ReadView const& view,
+    beast::Journal const& j)
+{
+    if (bad_)
+    {
+        JLOG(j.fatal()) << "Invariant failed: empty owner directory.";
+        return false;
+    }
+
+    return true;
+}
+
 }  // namespace xrpl