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Use the shared recursion limit in update() and merge_patch()

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merge_depth_limit() is gone in favor of detail::recursion_depth_limit().
The two identical function-local frame structs become one member struct,
merge_frame, with a constructor, so both loops emplace_back() their
frames. merge_patch_iteratively() copies the frame it works on out of the
stack and changes it only through stack.back().

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-24 09:38:20 +02:00
parent 2f628be156
commit 0ebe0a0132
5 changed files with 61 additions and 71 deletions
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include/nlohmann/json.hpp
+29 -34
View File
@@ -3615,30 +3615,35 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
update_members(first, last, merge_objects, 0);
}
JSON_PRIVATE_UNLESS_TESTED:
/// the number of nested objects @ref update and @ref merge_patch descend
/// into before handing over to their iterative versions
static constexpr std::size_t merge_depth_limit() noexcept
{
return 128;
}
private:
/// @brief an object @ref update_members_iteratively or @ref
/// merge_patch_iteratively is merging into, and the members still to merge
struct merge_frame
{
merge_frame(basic_json* target_, const_iterator position_, const_iterator last_) noexcept
: target(target_), position(std::move(position_)), last(std::move(last_))
{}
basic_json* target;
const_iterator position;
const_iterator last;
};
/*!
@brief the members loop of @ref update, for this object and range
Merging a nested object calls this function again, once per nesting
level, so a value nested deeply enough used to exhaust the call stack and
terminate the process. The descent is bounded here: once @ref
merge_depth_limit levels have been entered, @ref update_members_iteratively
merges what is left without the call stack.
detail::recursion_depth_limit levels have been entered, @ref
update_members_iteratively merges what is left without the call stack.
@param[in] depth nesting level of this object, counted from the object
@ref update was called on
*/
void update_members(const const_iterator& first, const const_iterator& last, const bool merge_objects, const std::size_t depth)
{
if (JSON_HEDLEY_UNLIKELY(depth >= merge_depth_limit()))
if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
{
update_members_iteratively(first, last);
return;
@@ -3675,17 +3680,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
objects whose merge was interrupted by a nested one on an explicit stack
instead of descending into them. A nested object is still merged
completely before the next member, in the same order as the recursive
version. Only reached for values nested deeper than @ref merge_depth_limit.
version. Only reached for values nested deeper than @ref
detail::recursion_depth_limit.
*/
void update_members_iteratively(const_iterator first, const_iterator last)
{
struct update_frame
{
basic_json* target;
const_iterator position;
const_iterator last;
};
std::vector<update_frame> stack;
std::vector<merge_frame> stack;
basic_json* target = this;
while (true)
@@ -3715,7 +3715,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
{
const basic_json& source = first.value();
++first;
stack.push_back({target, first, last});
stack.emplace_back(target, first, last);
target = &it2->second;
first = source.cbegin();
last = source.cend();
@@ -5636,14 +5636,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
Applying a nested object calls this function again, once per nesting
level, so a patch nested deeply enough used to exhaust the call stack and
terminate the process. The descent is bounded here: once @ref
merge_depth_limit levels have been entered, @ref merge_patch_iteratively
applies what is left without the call stack.
detail::recursion_depth_limit levels have been entered, @ref
merge_patch_iteratively applies what is left without the call stack.
*/
void apply_merge_patch(const basic_json& apply_patch, const std::size_t depth)
{
if (apply_patch.is_object())
{
if (JSON_HEDLEY_UNLIKELY(depth >= merge_depth_limit()))
if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
{
merge_patch_iteratively(apply_patch);
return;
@@ -5678,16 +5678,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
explicit stack instead of descending into them. A nested object is still
patched completely before the next member, in the same order as the
recursive version. Only reached for patches nested deeper than @ref
merge_depth_limit.
detail::recursion_depth_limit.
*/
void merge_patch_iteratively(const basic_json& apply_patch)
{
struct merge_frame
{
basic_json* target;
const_iterator position;
const_iterator last;
};
std::vector<merge_frame> stack;
// patch `target` with `patch`, or start patching it member by member
@@ -5699,7 +5693,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
{
target = basic_json::object();
}
stack.push_back({&target, patch.cbegin(), patch.cend()});
stack.emplace_back(&target, patch.cbegin(), patch.cend());
}
else
{
@@ -5710,7 +5704,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
apply(*this, apply_patch);
while (!stack.empty())
{
merge_frame& frame = stack.back();
// a copy, as applying a member below can reallocate the stack;
// the frame itself is only changed through stack.back()
const merge_frame frame = stack.back();
if (frame.position == frame.last)
{
stack.pop_back();
@@ -5718,14 +5714,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
const const_iterator member = frame.position;
++frame.position;
++stack.back().position;
if (member.value().is_null())
{
frame.target->erase(member.key());
}
else
{
// may push, which invalidates `frame`
apply(frame.target->operator[](member.key()), member.value());
}
}
single_include/nlohmann/json.hpp
+29 -34
View File
@@ -27974,30 +27974,35 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
update_members(first, last, merge_objects, 0);
}
JSON_PRIVATE_UNLESS_TESTED:
/// the number of nested objects @ref update and @ref merge_patch descend
/// into before handing over to their iterative versions
static constexpr std::size_t merge_depth_limit() noexcept
{
return 128;
}
private:
/// @brief an object @ref update_members_iteratively or @ref
/// merge_patch_iteratively is merging into, and the members still to merge
struct merge_frame
{
merge_frame(basic_json* target_, const_iterator position_, const_iterator last_) noexcept
: target(target_), position(std::move(position_)), last(std::move(last_))
{}
basic_json* target;
const_iterator position;
const_iterator last;
};
/*!
@brief the members loop of @ref update, for this object and range
Merging a nested object calls this function again, once per nesting
level, so a value nested deeply enough used to exhaust the call stack and
terminate the process. The descent is bounded here: once @ref
merge_depth_limit levels have been entered, @ref update_members_iteratively
merges what is left without the call stack.
detail::recursion_depth_limit levels have been entered, @ref
update_members_iteratively merges what is left without the call stack.
@param[in] depth nesting level of this object, counted from the object
@ref update was called on
*/
void update_members(const const_iterator& first, const const_iterator& last, const bool merge_objects, const std::size_t depth)
{
if (JSON_HEDLEY_UNLIKELY(depth >= merge_depth_limit()))
if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
{
update_members_iteratively(first, last);
return;
@@ -28034,17 +28039,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
objects whose merge was interrupted by a nested one on an explicit stack
instead of descending into them. A nested object is still merged
completely before the next member, in the same order as the recursive
version. Only reached for values nested deeper than @ref merge_depth_limit.
version. Only reached for values nested deeper than @ref
detail::recursion_depth_limit.
*/
void update_members_iteratively(const_iterator first, const_iterator last)
{
struct update_frame
{
basic_json* target;
const_iterator position;
const_iterator last;
};
std::vector<update_frame> stack;
std::vector<merge_frame> stack;
basic_json* target = this;
while (true)
@@ -28074,7 +28074,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
{
const basic_json& source = first.value();
++first;
stack.push_back({target, first, last});
stack.emplace_back(target, first, last);
target = &it2->second;
first = source.cbegin();
last = source.cend();
@@ -29995,14 +29995,14 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
Applying a nested object calls this function again, once per nesting
level, so a patch nested deeply enough used to exhaust the call stack and
terminate the process. The descent is bounded here: once @ref
merge_depth_limit levels have been entered, @ref merge_patch_iteratively
applies what is left without the call stack.
detail::recursion_depth_limit levels have been entered, @ref
merge_patch_iteratively applies what is left without the call stack.
*/
void apply_merge_patch(const basic_json& apply_patch, const std::size_t depth)
{
if (apply_patch.is_object())
{
if (JSON_HEDLEY_UNLIKELY(depth >= merge_depth_limit()))
if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
{
merge_patch_iteratively(apply_patch);
return;
@@ -30037,16 +30037,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
explicit stack instead of descending into them. A nested object is still
patched completely before the next member, in the same order as the
recursive version. Only reached for patches nested deeper than @ref
merge_depth_limit.
detail::recursion_depth_limit.
*/
void merge_patch_iteratively(const basic_json& apply_patch)
{
struct merge_frame
{
basic_json* target;
const_iterator position;
const_iterator last;
};
std::vector<merge_frame> stack;
// patch `target` with `patch`, or start patching it member by member
@@ -30058,7 +30052,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
{
target = basic_json::object();
}
stack.push_back({&target, patch.cbegin(), patch.cend()});
stack.emplace_back(&target, patch.cbegin(), patch.cend());
}
else
{
@@ -30069,7 +30063,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
apply(*this, apply_patch);
while (!stack.empty())
{
merge_frame& frame = stack.back();
// a copy, as applying a member below can reallocate the stack;
// the frame itself is only changed through stack.back()
const merge_frame frame = stack.back();
if (frame.position == frame.last)
{
stack.pop_back();
@@ -30077,14 +30073,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
const const_iterator member = frame.position;
++frame.position;
++stack.back().position;
if (member.value().is_null())
{
frame.target->erase(member.key());
}
else
{
// may push, which invalidates `frame`
apply(frame.target->operator[](member.key()), member.value());
}
}
tests/src/unit-diagnostics.cpp
+1 -1
View File
@@ -308,7 +308,7 @@ TEST_CASE("Regression tests for extended diagnostics")
TEST_CASE("Better diagnostics past the descent bound of update() and merge_patch()")
{
// Both merge objects nested more than basic_json::merge_depth_limit()
// Both merge objects nested more than detail::recursion_depth_limit()
// (128) levels deep without recursing; the values they add or replace
// there must still know their parents.
const std::size_t depth = 200;
tests/src/unit-merge_patch.cpp
+1 -1
View File
@@ -302,7 +302,7 @@ TEST_CASE("JSON Merge Patch on deeply nested values")
SECTION("patching past the descent bound gives the same result")
{
// every depth on either side of where the iterative version takes
// over (basic_json::merge_depth_limit(), 128)
// over (detail::recursion_depth_limit(), 128)
for (std::size_t depth = 0; depth <= 300; ++depth)
{
CAPTURE(depth);
tests/src/unit-modifiers.cpp
+1 -1
View File
@@ -1041,7 +1041,7 @@ TEST_CASE("update() on deeply nested values")
SECTION("merging past the descent bound gives the same result")
{
// every depth on either side of where the iterative version takes
// over (basic_json::merge_depth_limit(), 128)
// over (detail::recursion_depth_limit(), 128)
for (std::size_t depth = 0; depth <= 300; ++depth)
{
CAPTURE(depth);