fix: Tree::relocate() triggers assertions with zero-length strings

... when they string are placed at the beginning or end of the arena

.github/workflows-in/benchmarks.ys

@@ -23,7 +23,7 @@ jobs:
         - {std: 17, comp: clang18, os: ubuntu-24.04, cmkflags: -DCMAKE_CXX_COMPILER=clang++-18 -DCMAKE_C_COMPILER=clang-18}
         #- {std: 17, comp: vs2019 , os: windows-2019, cmkflags: -G 'Visual Studio 16 2019' -A x64}
         - {std: 17, comp: vs2022 , os: windows-2022, cmkflags: -G 'Visual Studio 17 2022' -A x64}
-        - {std: 17, comp: xcode15, os: macos-13, xcver: 15, cmkflags: -G Xcode -DCMAKE_OSX_ARCHITECTURES=x86_64}
+        - {std: 17, comp: xcode15, os: macos-15-intel, xcver: 16, cmkflags: -G Xcode -DCMAKE_OSX_ARCHITECTURES=x86_64}
     env:: -{'BM' 'ON'} + load('share/env.yaml')
     steps:
     - :: checkout-action

.github/workflows/benchmarks.yml

@@ -108,8 +108,8 @@ jobs:
           cmkflags: -G 'Visual Studio 17 2022' -A x64
         - std: 17
           comp: xcode15
-          os: macos-13
-          xcver: 15
+          os: macos-15-intel
+          xcver: 16
           cmkflags: -G Xcode -DCMAKE_OSX_ARCHITECTURES=x86_64
     env:
       BM: 'ON'

changelog/current.md

@@ -1,5 +1,6 @@
 ### Changes
 
+- [PR#565](https://github.com/biojppm/rapidyaml/pull/565) (fixes [#564](https://github.com/biojppm/rapidyaml/issues/564)) - `Tree` arena: allow relocation of zero-length strings when placed at the end (relax assertions triggered in `Tree::_relocated()`)
 - [PR#561](https://github.com/biojppm/rapidyaml/pull/561) (fixes [#559](https://github.com/biojppm/rapidyaml/issues/559)) - Byte Order Mark: account for BOM when determining block indentation
 - [PR#563](https://github.com/biojppm/rapidyaml/pull/563) (fixes [#562](https://github.com/biojppm/rapidyaml/issues/562)) - Fix bug in `NodeRef::cend()`
 - [PR#547](https://github.com/biojppm/rapidyaml/pull/547) - Fix parsing of implicit first documents with empty sequences, caused by a problem in `Tree::set_root_as_stream()`:

src/c4/yml/tree.hpp

@@ -1009,12 +1009,12 @@ private:
 
     substr _relocated(csubstr s, substr next_arena) const
     {
-        _RYML_CB_ASSERT(m_callbacks, m_arena.is_super(s));
-        _RYML_CB_ASSERT(m_callbacks, m_arena.sub(0, m_arena_pos).is_super(s));
+        _RYML_CB_ASSERT(m_callbacks, m_arena.is_super(s) || s.len == 0);
+        _RYML_CB_ASSERT(m_callbacks, m_arena.sub(0, m_arena_pos).is_super(s) || s.len == 0);
         auto pos = (s.str - m_arena.str); // this is larger than 0 based on the assertions above
         substr r(next_arena.str + pos, s.len);
         _RYML_CB_ASSERT(m_callbacks, r.str - next_arena.str == pos);
-        _RYML_CB_ASSERT(m_callbacks, next_arena.sub(0, m_arena_pos).is_super(r));
+        _RYML_CB_ASSERT(m_callbacks, next_arena.sub(0, m_arena_pos).is_super(r) || r.len == 0);
         return r;
     }
 

test/test_tree.cpp

@@ -10,6 +10,7 @@
 #include "./test_lib/callbacks_tester.hpp"
 
 #include <gtest/gtest.h>
+#include <unordered_map>
 
 #if defined(_MSC_VER)
 #   pragma warning(push)
@@ -938,6 +939,46 @@ TEST(Tree, reserve_arena_issue288)
     EXPECT_EQ(t.arena().last(pluses.size()), to_csubstr(pluses));
 }
 
+// https://github.com/biojppm/rapidyaml/issues/564
+namespace issue564 {
+struct AdjacentSizedBlocks {
+    std::vector<char> mem;
+    char* start;
+    char* next;
+};
+using AvailableBlocks = std::unordered_map<size_t, AdjacentSizedBlocks>;
+static void free(void* , size_t size, void* user_data) {
+    (*static_cast<AvailableBlocks *>(user_data))[size].next -= size;
+}
+static void* alloc(size_t len, void* /*hint*/, void* user_data) {
+    auto& blocks = (*static_cast<AvailableBlocks*>(user_data))[len];
+    if (blocks.start == nullptr) {
+        blocks.mem.resize(10 * len);
+        blocks.start = blocks.next = blocks.mem.data();
+    }
+    void *ret = blocks.next;
+    blocks.next += len;
+    return ret;
+}
+} // namespace issue564
+TEST(Tree, issue564_relocate_arena_0)
+{
+    issue564::AvailableBlocks blocks_by_size;
+    Callbacks cb(&blocks_by_size, issue564::alloc, issue564::free, nullptr);
+    Tree dest(cb);
+    Tree source(cb);
+    parse_in_arena("[]", &dest);
+    parse_in_arena("[]", &source);
+    // Shallow copy `source` as a child of `dest`
+    NodeRef child = dest.rootref().append_child();
+    dest.duplicate_contents(&source, source.root_id(), child.id());
+    // trigger a relocation in dest
+    std::string loong(10000, ' ');
+    ExpectError::check_success([&]{
+        dest.to_arena(to_csubstr(loong));  // error
+    });
+}
+
 TEST(Tree, clear)
 {
     Tree t(16, 64);