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

* XRPLF/develop: (81 commits)
  ci: Only publish docs in public repos (6687)
  chore: Enable remaining clang-tidy `performance` checks (6648)
  refactor: Address PR comments after the modularisation PRs (6389)
  chore: Fix clang-tidy header filter (6686)
  ci: [DEPENDABOT] bump actions/deploy-pages from 4.0.5 to 5.0.0 (6684)
  ci: [DEPENDABOT] bump codecov/codecov-action from 5.5.3 to 6.0.0 (6685)
  fix: Guard Coro::resume() against completed coroutines (6608)
  refactor: Split LoanInvariant into LoanBrokerInvariant and LoanInvariant (6674)
  ci: Don't publish docs on release branches (6673)
  refactor: Make function naming in ServiceRegistry consistent (6390)
  chore: Shorten job names to stay within Linux 15-char thread limit (6669)
  fix: Improve loan invariant message (6668)
  ci: Upload artifacts only in public repositories (6670)
  ci: Add conflicting-pr workflow (6656)
  chore: Add more AI tools to .gitignore (6658)
  chore: Show warning message if user may need to connect to VPN (6619)
  feat: Add placeholder amendment for assorted bug fixes (6652)
  chore: Update sqlite3->3.51.0, protobuf->6.33.5, openssl->3.6.1, grpc->1.78.1 (6653)
  refactor: Modularise ledger (6536)
  chore: Use unpatched version of soci (6649)
  ...

include/xrpl/protocol/detail/features.macro

@@ -16,6 +16,7 @@
 // Add new amendments to the top of this list.
 // Keep it sorted in reverse chronological order.
 
+XRPL_FEATURE(DefragDirectories,          Supported::no,  VoteBehavior::DefaultNo)
 XRPL_FIX   (Security3_1_3,               Supported::no, VoteBehavior::DefaultNo)
 XRPL_FIX   (PermissionedDomainInvariant, Supported::yes, VoteBehavior::DefaultNo)
 XRPL_FIX    (ExpiredNFTokenOfferRemoval, Supported::yes, VoteBehavior::DefaultNo)

src/libxrpl/ledger/ApplyView.cpp

@@ -10,6 +10,14 @@ namespace xrpl {
 
 namespace directory {
 
+struct Gap
+{
+    uint64_t const page;
+    SLE::pointer node;
+    uint64_t const nextPage;
+    SLE::pointer next;
+};
+
 std::uint64_t
 createRoot(
     ApplyView& view,
@@ -111,7 +119,9 @@ insertPage(
     if (page == 0)
         return std::nullopt;
     if (!view.rules().enabled(fixDirectoryLimit) && page >= dirNodeMaxPages)  // Old pages limit
+    {
         return std::nullopt;
+    }
 
     // We are about to create a new node; we'll link it to
     // the chain first:
@@ -133,12 +143,8 @@ insertPage(
     // it's the default.
     if (page != 1)
         node->setFieldU64(sfIndexPrevious, page - 1);
-    XRPL_ASSERT_PARTS(!nextPage, "xrpl::directory::insertPage", "nextPage has default value");
-    /* Reserved for future use when directory pages may be inserted in
-     * between two other pages instead of only at the end of the chain.
     if (nextPage)
         node->setFieldU64(sfIndexNext, nextPage);
-    */
     describe(node);
     view.insert(node);
 
@@ -154,7 +160,7 @@ ApplyView::dirAdd(
     uint256 const& key,
     std::function<void(std::shared_ptr<SLE> const&)> const& describe)
 {
-    auto root = peek(directory);
+    auto const root = peek(directory);
 
     if (!root)
     {
@@ -164,6 +170,43 @@ ApplyView::dirAdd(
 
     auto [page, node, indexes] = directory::findPreviousPage(*this, directory, root);
 
+    if (rules().enabled(featureDefragDirectories))
+    {
+        // If there are more nodes than just the root, and there's no space in
+        // the last one, walk backwards to find one with space, or to find one
+        // missing.
+        std::optional<directory::Gap> gapPages;
+        while (page && indexes.size() >= dirNodeMaxEntries)
+        {
+            // Find a page with space, or a gap in pages.
+            auto [prevPage, prevNode, prevIndexes] =
+                directory::findPreviousPage(*this, directory, node);
+            if (!gapPages && prevPage != page - 1)
+                gapPages.emplace(prevPage, prevNode, page, node);
+            page = prevPage;
+            node = prevNode;
+            indexes = prevIndexes;
+        }
+        // We looped through all the pages back to the root.
+        if (!page)
+        {
+            // If we found a gap, use it.
+            if (gapPages)
+            {
+                return directory::insertPage(
+                    *this,
+                    gapPages->page,
+                    gapPages->node,
+                    gapPages->nextPage,
+                    gapPages->next,
+                    key,
+                    directory,
+                    describe);
+            }
+            std::tie(page, node, indexes) = directory::findPreviousPage(*this, directory, root);
+        }
+    }
+
     // If there's space, we use it:
     if (indexes.size() < dirNodeMaxEntries)
     {

src/libxrpl/protocol/BuildInfo.cpp

@@ -23,7 +23,7 @@ namespace {
 //  and follow the format described at http://semver.org/
 //------------------------------------------------------------------------------
 // clang-format off
-char const* const versionString = "3.2.0-b2"
+char const* const versionString = "3.2.0-b0"
     // clang-format on
     ;