Merge remote-tracking branch 'XRPLF/develop' into ximinez/emptydirectoryinvariant

* XRPLF/develop: (21 commits)
  fix: Re-store nodes missing from both backends during online_delete rotation (7763)
  fix: Add amendment sponsor for AccountRootsDeletedClean (7801)
  fix: Update base_uint and test changes released in 3.1.3 (7570)
  fix: Handle rounding just above kMaxRep more accurately (7389)
  fix: Document and assert "after" is never null in invariants (7354)
  ci: Run full matrix only on `Ready to merge` or `Full CI build` labeled PRs (7689)
  fix: Strengthen Clawback invariant checks for MPT balances (7285)
  test: Add unit tests for IP address related functions (7744)
  ci: Add Rust to Nix docker image (7571)
  docs: Add more information about pre-commit hooks and how to set them up (7802)
  test: Add JSON array size tests (7592)
  chore: Enable most readability checks (7772)
  ci: Do not run conflict checker when label is applied (7774)
  chore: Run clang_tidy_check with `pass_filenames: false` from pre-commit (7800)
  feat: Add delegate filter param for account_tx RPC (6126)
  refactor: Move `jss.h` `include` out of `Indexes.h` (7799)
  test: Add tests for check doxygen style (7795)
  style: Add pre-commit hook to check doxygen style (7794)
  style: Unify style for all Doxygen comments (7776)
  fix: Improve Number addition/subtraction rounding (7369)
  ...

include/xrpl/tx/invariants/InvariantCheck.h

@@ -394,6 +394,22 @@ 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&);
+};
+
 /**
  * Verify that MPT/XRP STAmounts are canonical in any ledger entries left after the
  * transaction applies.
@@ -463,7 +479,9 @@ using InvariantChecks = std::tuple<
     ValidMPTTransfer,
     ObjectHasPseudoAccount,
     SponsorshipOwnerCountsMatch,
-    SponsorshipAccountCountMatchesField>;
+    SponsorshipAccountCountMatchesField,
+    ObjectHasPseudoAccount,
+    NoEmptyDirectory>;
 
 /**
  * @brief get a tuple of all invariant checks

src/libxrpl/ledger/ApplyView.cpp

@@ -255,6 +255,7 @@ 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/invariants/InvariantCheck.cpp

@@ -1206,6 +1206,46 @@ NoModifiedUnmodifiableFields::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;
+}
+
+//------------------------------------------------------------------------------
+
 void
 ValidAmounts::visitEntry(
     bool isDelete,