Share one nesting depth limit between all bounded descents

Copying and comparing stopped their descent at
basic_json::nesting_depth_limit(), while serializing, hashing and
merging used detail::recursion_depth_limit(). Both were 128, but
nothing kept them equal. The thread-local count now tests against
detail::recursion_depth_limit() as well, and a static_assert keeps
the limit small enough for the byte that holds the count.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/features/types/template_parameters.md

@@ -389,7 +389,6 @@ using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
 | Functionality                                                                                                                     | Additional requirement                                                                                                                                                                       |
 |-----------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | [`diff`](../../api/basic_json/diff.md), [`items`](../../api/basic_json/items.md), [`std::hash`](../../api/basic_json/std_hash.md) | conversion of a `#!cpp std::size_t` to `StringType`: either assignability from the result of `#!cpp std::to_string`, or an ADL overload `#!cpp void int_to_string(StringType&, std::size_t)` |
-| [`operator/(std::size_t)`](../../api/json_pointer/operator_slash.md)                                                              | the same conversion of a `#!cpp std::size_t` to `StringType` as `diff`, `items`, and `std::hash` above                                                                                       |
 | [`std::hash<basic_json>`](../../api/basic_json/std_hash.md)                                                                       | additionally a specialization of `#!cpp std::hash<StringType>`                                                                                                                               |
 | [`to_bson`](../../api/basic_json/to_bson.md)                                                                                      | `find(value_type)` and `npos`                                                                                                                                                                |
 | [`parse`](../../api/basic_json/parse.md) from a `string_t`                                                                        | the input adapters must accept it; otherwise pass a character range                                                                                                                          |

include/nlohmann/detail/json_pointer.hpp

@@ -26,7 +26,6 @@
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/string_escape.hpp>
-#include <nlohmann/detail/string_utils.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
@@ -117,7 +116,7 @@ class json_pointer
     /// @sa https://json.nlohmann.me/api/json_pointer/operator_slasheq/
     json_pointer& operator/=(std::size_t array_idx)
     {
-        return *this /= detail::to_string<string_t>(array_idx);
+        return *this /= std::to_string(array_idx);
     }
 
     /// @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
@@ -747,7 +746,7 @@ class json_pointer
                         // "-" always fails the range check
                         return false;
                     }
-                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !('0' <= reference_token[0] && reference_token[0] <= '9')))
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
                     {
                         // invalid char
                         return false;
@@ -775,7 +774,7 @@ class json_pointer
                     // not throw (see #5395), so such a reference token is treated as "not found"
                     errno = 0; // strtoull() does not reset errno on success
                     char* p_end = nullptr; // NOLINT(misc-const-correctness)
-                    const unsigned long long magnitude = std::strtoull(reference_token.data(), &p_end, 10); // NOLINT(runtime/int)
+                    const unsigned long long magnitude = std::strtoull(reference_token.c_str(), &p_end, 10); // NOLINT(runtime/int)
                     if (JSON_HEDLEY_UNLIKELY(errno == ERANGE // the value exceeds ULLONG_MAX
                                              || magnitude >= static_cast<unsigned long long>((std::numeric_limits<typename BasicJsonType::size_type>::max)()))) // NOLINT(runtime/int)
                     {

include/nlohmann/detail/recursion_depth_limit.hpp

@@ -19,11 +19,17 @@ namespace detail
 /*!
 @brief the number of nesting levels an operation recurses into
 
-Operations that walk a value (serializing, hashing, merging, ...) recurse once
+Operations that walk a value (copying, comparing, serializing, hashing, merging,
+...) recurse once
 per nesting level, which is fastest, but a value nested deeply enough would
 exhaust the call stack. So they recurse only this many levels deep and finish
 whatever lies below with an explicit stack. All of them share this limit.
 
+Most of them pass the depth down as an argument. The copy constructor and the
+comparison operators cannot, as their signatures are fixed, so they count it
+in basic_json::nesting_depth() instead, a byte per thread; the limit must
+therefore stay below 255.
+
 @sa https://github.com/nlohmann/json/issues/5387
 */
 constexpr std::size_t recursion_depth_limit() noexcept

include/nlohmann/json.hpp

@@ -898,12 +898,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     }
 
 #ifndef JSON_NO_THREAD_LOCAL
-    /// the number of levels an operation descends into before it finishes the
-    /// value below it without the call stack
-    static constexpr std::uint8_t nesting_depth_limit()
-    {
-        return 128;
-    }
+    // nesting_depth() is a byte and may exceed the limit by one level
+    static_assert(detail::recursion_depth_limit() < 255, "the nesting depth count must fit in a byte");
 
     /*!
     @brief how many levels the operation going on in this thread has descended into
@@ -945,7 +941,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         static_cast<void>(may_descend);
         return true;
 #else
-        return !may_descend || nesting_depth() >= nesting_depth_limit();
+        return !may_descend || nesting_depth() >= detail::recursion_depth_limit();
 #endif
     }
 
@@ -969,7 +965,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #ifdef JSON_NO_THREAD_LOCAL
             : m_okay(false)
 #else
-            : m_okay(nesting_depth() < nesting_depth_limit())
+            : m_okay(nesting_depth() < detail::recursion_depth_limit())
 #endif
         {
 #ifndef JSON_NO_THREAD_LOCAL
@@ -1173,7 +1169,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     The values whose copy has not been created yet are kept on an explicit
     worklist rather than on the call stack. This is only reached for values
-    nested deeper than @ref nesting_depth_limit levels, which is why it copies
+    nested deeper than @ref detail::recursion_depth_limit levels, which is why it copies
     every container by hand instead of letting the container do it: the fast
     ways of doing so would descend into the elements and defeat the purpose.
     */
@@ -1239,7 +1235,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     Copying a container copies its elements, so a value nested deeply enough
     used to exhaust the call stack. The descent is bounded here: the first
-    @ref nesting_depth_limit levels are copied by the containers themselves, just
+    @ref detail::recursion_depth_limit levels are copied by the containers themselves, just
     as they always were, and anything below that is copied without the call
     stack by @ref copy_iteratively. Copying a value can therefore no longer
     exhaust the stack, however deeply it is nested, just like destroying one
@@ -1377,7 +1373,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief compare @a lhs and @a rhs without descending into them
 
-    Reached once a comparison has descended @ref nesting_depth_limit levels, so
+    Reached once a comparison has descended @ref detail::recursion_depth_limit levels, so
     that comparing values cannot exhaust the call stack however deeply they are
     nested. The two values are walked in lockstep on an explicit stack and
     compared lexicographically, element by element in the order the containers

single_include/nlohmann/json.hpp

@@ -7281,11 +7281,17 @@ namespace detail
 /*!
 @brief the number of nesting levels an operation recurses into
 
-Operations that walk a value (serializing, hashing, merging, ...) recurse once
+Operations that walk a value (copying, comparing, serializing, hashing, merging,
+...) recurse once
 per nesting level, which is fastest, but a value nested deeply enough would
 exhaust the call stack. So they recurse only this many levels deep and finish
 whatever lies below with an explicit stack. All of them share this limit.
 
+Most of them pass the depth down as an argument. The copy constructor and the
+comparison operators cannot, as their signatures are fixed, so they count it
+in basic_json::nesting_depth() instead, a byte per thread; the limit must
+therefore stay below 255.
+
 @sa https://github.com/nlohmann/json/issues/5387
 */
 constexpr std::size_t recursion_depth_limit() noexcept
@@ -18867,8 +18873,6 @@ NLOHMANN_JSON_NAMESPACE_END
 
 // #include <nlohmann/detail/string_escape.hpp>
 
-// #include <nlohmann/detail/string_utils.hpp>
-
 // #include <nlohmann/detail/value_t.hpp>
 
 
@@ -18960,7 +18964,7 @@ class json_pointer
     /// @sa https://json.nlohmann.me/api/json_pointer/operator_slasheq/
     json_pointer& operator/=(std::size_t array_idx)
     {
-        return *this /= detail::to_string<string_t>(array_idx);
+        return *this /= std::to_string(array_idx);
     }
 
     /// @brief create a new JSON pointer by appending the right JSON pointer at the end of the left JSON pointer
@@ -19590,7 +19594,7 @@ class json_pointer
                         // "-" always fails the range check
                         return false;
                     }
-                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !('0' <= reference_token[0] && reference_token[0] <= '9')))
+                    if (JSON_HEDLEY_UNLIKELY(reference_token.size() == 1 && !("0" <= reference_token && reference_token <= "9")))
                     {
                         // invalid char
                         return false;
@@ -19618,7 +19622,7 @@ class json_pointer
                     // not throw (see #5395), so such a reference token is treated as "not found"
                     errno = 0; // strtoull() does not reset errno on success
                     char* p_end = nullptr; // NOLINT(misc-const-correctness)
-                    const unsigned long long magnitude = std::strtoull(reference_token.data(), &p_end, 10); // NOLINT(runtime/int)
+                    const unsigned long long magnitude = std::strtoull(reference_token.c_str(), &p_end, 10); // NOLINT(runtime/int)
                     if (JSON_HEDLEY_UNLIKELY(errno == ERANGE // the value exceeds ULLONG_MAX
                                              || magnitude >= static_cast<unsigned long long>((std::numeric_limits<typename BasicJsonType::size_type>::max)()))) // NOLINT(runtime/int)
                     {
@@ -26981,12 +26985,8 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     }
 
 #ifndef JSON_NO_THREAD_LOCAL
-    /// the number of levels an operation descends into before it finishes the
-    /// value below it without the call stack
-    static constexpr std::uint8_t nesting_depth_limit()
-    {
-        return 128;
-    }
+    // nesting_depth() is a byte and may exceed the limit by one level
+    static_assert(detail::recursion_depth_limit() < 255, "the nesting depth count must fit in a byte");
 
     /*!
     @brief how many levels the operation going on in this thread has descended into
@@ -27028,7 +27028,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         static_cast<void>(may_descend);
         return true;
 #else
-        return !may_descend || nesting_depth() >= nesting_depth_limit();
+        return !may_descend || nesting_depth() >= detail::recursion_depth_limit();
 #endif
     }
 
@@ -27052,7 +27052,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 #ifdef JSON_NO_THREAD_LOCAL
             : m_okay(false)
 #else
-            : m_okay(nesting_depth() < nesting_depth_limit())
+            : m_okay(nesting_depth() < detail::recursion_depth_limit())
 #endif
         {
 #ifndef JSON_NO_THREAD_LOCAL
@@ -27256,7 +27256,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     The values whose copy has not been created yet are kept on an explicit
     worklist rather than on the call stack. This is only reached for values
-    nested deeper than @ref nesting_depth_limit levels, which is why it copies
+    nested deeper than @ref detail::recursion_depth_limit levels, which is why it copies
     every container by hand instead of letting the container do it: the fast
     ways of doing so would descend into the elements and defeat the purpose.
     */
@@ -27322,7 +27322,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     Copying a container copies its elements, so a value nested deeply enough
     used to exhaust the call stack. The descent is bounded here: the first
-    @ref nesting_depth_limit levels are copied by the containers themselves, just
+    @ref detail::recursion_depth_limit levels are copied by the containers themselves, just
     as they always were, and anything below that is copied without the call
     stack by @ref copy_iteratively. Copying a value can therefore no longer
     exhaust the stack, however deeply it is nested, just like destroying one
@@ -27460,7 +27460,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /*!
     @brief compare @a lhs and @a rhs without descending into them
 
-    Reached once a comparison has descended @ref nesting_depth_limit levels, so
+    Reached once a comparison has descended @ref detail::recursion_depth_limit levels, so
     that comparing values cannot exhaust the call stack however deeply they are
     nested. The two values are walked in lockstep on an explicit stack and
     compared lexicographically, element by element in the order the containers

tests/src/unit-alt-string.cpp

@@ -343,41 +343,6 @@ TEST_CASE("alternative string type")
         CHECK(j2.flatten().unflatten() == j2);
     }
 
-    SECTION("contains(json_pointer)")
-    {
-        // contains(json_pointer) must compile and work with a string_t that has
-        // no c_str() and no comparison with const char* (see #5666)
-        auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
-
-        // present: object key and array indices
-        CHECK(j.contains(alt_json::json_pointer("/foo")));
-        CHECK(j.contains(alt_json::json_pointer("/foo/0")));
-        CHECK(j.contains(alt_json::json_pointer("/foo/1")));
-
-        // missing: absent object key and out-of-range array index
-        CHECK_FALSE(j.contains(alt_json::json_pointer("/bar")));
-        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/2")));
-
-        // "-" always fails the range check
-        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/-")));
-
-        // an array index must not have a leading zero
-        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/01")));
-
-        // a reference token that is not a number
-        CHECK_FALSE(j.contains(alt_json::json_pointer("/foo/bar")));
-    }
-
-    SECTION("operator/(std::size_t)")
-    {
-        // json_pointer::operator/=(std::size_t) must compile without string_t
-        // being constructible from std::string (see #5666)
-        auto j = alt_json::parse(R"({"foo": ["bar", "baz"]})");
-
-        CHECK(j.at(alt_json::json_pointer("/foo") / std::size_t(0)) == j["foo"][0]);
-        CHECK(j.at(alt_json::json_pointer("/foo") / std::size_t(1)) == j["foo"][1]);
-    }
-
     SECTION("patch")
     {
         alt_json const patch1 = alt_json::parse(R"([{ "op": "add", "path": "/a/b", "value": [ "foo", "bar" ] }])");