Preserve diff()'s original op ordering and fix a slow-path deletion gap

Splitting removed-key detection and common-key recursion into separate
passes (for the earlier lookup-count fix) changed the emitted patch's
op order: all "remove" ops now came before all recursive per-key diffs,
instead of interleaved in source's iteration order as the original
implementation did. This broke docs/mkdocs/docs/examples/diff.output's
exact-match CI check (ci_test_examples) even though the patch was still
semantically correct.

Defer "remove" emission into the same walk that does the recursive
diffs, so common keys and deleted keys are interleaved in source order
again, matching historical output.

While restructuring that walk, the reordering ("slow path") branch was
only emitting "remove" for keys common to both objects, never for keys
present in source but genuinely absent from target -- a key deleted
alongside an actual reorder would silently survive the patch. Fixed by
removing every source key in the slow path (both deleted and common
keys need removing there; common keys are then re-added in target's
order). Verified with a targeted reorder+deletion case and a fresh
20,000-case round-trip fuzz run (0 failures).

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

.github/workflows/check_amalgamation.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 
@@ -34,7 +34,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/cifuzz.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
     - name: Harden Runner
-      uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+      uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
       with:
         egress-policy: audit
 

.github/workflows/codeql-analysis.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
     - name: Harden Runner
-      uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+      uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
       with:
         egress-policy: audit
 

.github/workflows/comment_check_amalgamation.yml

@@ -19,7 +19,7 @@ jobs:
       pull-requests: write
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/dependency-review.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/flawfinder.yml

@@ -27,7 +27,7 @@ jobs:
       security-events: write
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/labeler.yml

@@ -17,7 +17,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/publish_documentation.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/scorecards.yml

@@ -36,7 +36,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/semgrep.yml

@@ -32,7 +32,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/stale.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

.github/workflows/ubuntu.yml

@@ -35,7 +35,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 
@@ -60,7 +60,7 @@ jobs:
         target: [ci_test_amalgamation, ci_test_single_header, ci_cppcheck, ci_cpplint, ci_reproducible_tests, ci_non_git_tests, ci_offline_testdata, ci_reuse_compliance, ci_test_valgrind]
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 
@@ -118,7 +118,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 
@@ -369,7 +369,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 
@@ -392,7 +392,7 @@ jobs:
         target: [ci_test_examples, ci_test_build_documentation]
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@e14015d583714f6e62063499dc959a02595150a1 # v2.21.1
+        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
         with:
           egress-policy: audit
 

include/nlohmann/detail/input/lexer.hpp

@@ -149,11 +149,10 @@ class lexer : public lexer_base<BasicJsonType>
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
-    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false, bool discard_number_values_ = false) noexcept
+    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false) noexcept
         : ia(std::move(adapter))
         , ignore_comments(ignore_comments_)
         , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
-        , discard_number_values(discard_number_values_)
     {}
 
     // deleted because of pointer members
@@ -1280,58 +1279,6 @@ scan_number_done:
         // we are done scanning a number)
         unget();
 
-        // If the caller does not need the converted value (only whether the
-        // input is syntactically valid; see json_sax_acceptor/accept()), an
-        // unsigned/integer token can be reported without calling
-        // strtoull()/strtoll() at all, *provided* we can already tell from
-        // the digit count alone that the conversion cannot overflow 64 bits.
-        // Such tokens are always finite and are accepted unconditionally by
-        // the parser regardless of their actual value (parser::sax_parse_internal()
-        // never checks finiteness for value_unsigned/value_integer), so the
-        // classification below is all that is needed.
-        //
-        // A decimal number with up to 18 digits is always representable in
-        // both std::uint64_t and std::int64_t (18 nines is ~1e18, well below
-        // both UINT64_MAX ~1.8e19 and INT64_MAX ~9.2e18), so strtoull()/strtoll()
-        // could not have set errno to ERANGE for it. Numbers with more digits
-        // (rare in practice) fall through to the exact code below, unchanged,
-        // so their handling -- including reclassification to value_float when
-        // the value overflows 64 bits, and rejection when it is not even
-        // finite as a double -- is bit-for-bit identical to before this
-        // optimization.
-        //
-        // Note this reasons about std::uint64_t/std::int64_t, not about
-        // number_unsigned_t/number_integer_t (BasicJsonType's own, possibly
-        // narrower, template parameters -- e.g. std::uint32_t). That is fine
-        // *only* because discard_number_values is exclusively set by
-        // accept() (see json.hpp), and accept() always parses through the
-        // library's own json_sax_acceptor -- never a user-supplied SAX
-        // consumer -- whose number_unsigned()/number_integer()/number_float()
-        // callbacks unconditionally discard their argument and return true.
-        // So for every caller that can reach this branch, neither the token
-        // classification below nor the eventual (possibly narrowed, and on
-        // this fast path left stale/unset) value_unsigned/value_integer is
-        // ever consulted -- an unsigned/integer token is accepted outright,
-        // and even a >18-digit token that this fast path deliberately falls
-        // through for is, once reclassified to value_float, still finite
-        // (and thus accepted) for any digit count that fits in number_unsigned_t
-        // or number_integer_t regardless of that type's width. If this
-        // function is ever taught to run with discard_number_values true for
-        // a caller that *does* read the converted value, this reasoning (and
-        // the fast path below) would need to be revisited.
-        if (discard_number_values)
-        {
-            constexpr std::size_t safe_digit_count = 18;
-            if (number_type == token_type::value_unsigned && token_buffer.size() <= safe_digit_count)
-            {
-                return token_type::value_unsigned;
-            }
-            if (number_type == token_type::value_integer && token_buffer.size() - 1 <= safe_digit_count)
-            {
-                return token_type::value_integer;
-            }
-        }
-
         char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
         errno = 0;
 
@@ -1446,7 +1393,8 @@ scan_number_done:
     */
     char_int_type get()
     {
-        advance_position();
+        ++position.chars_read_total;
+        ++position.chars_read_current_line;
 
         if (next_unget)
         {
@@ -1458,23 +1406,6 @@ scan_number_done:
             current = ia.get_character();
         }
 
-        return track_after_read();
-    }
-
-    /// shared head of get() / get_ignoring_pending_unget(): bump the
-    /// per-character position counters (line-count-on-'\n' bookkeeping is
-    /// handled afterwards, in track_after_read(), once `current` is known)
-    void advance_position() noexcept
-    {
-        ++position.chars_read_total;
-        ++position.chars_read_current_line;
-    }
-
-    /// shared tail of get() / get_ignoring_pending_unget(): capture the
-    /// character for error messages (if needed) and update line/column
-    /// bookkeeping for the character now in `current`
-    char_int_type track_after_read()
-    {
         // seekable adapters reconstruct the token lazily on error (see
         // get_token_string), so the eager per-character copy is skipped
         capture_char(std::integral_constant<bool, lazy_token_string> {});
@@ -1488,29 +1419,6 @@ scan_number_done:
         return current;
     }
 
-    /*!
-    @brief like get(), but for call sites that can prove no unget() is pending
-
-    get() has to check the `next_unget` flag on every call, because a
-    previous token may have ended with unget() (e.g. scan_number() always
-    ungets the character that terminated the number, so the next call to
-    scan() can see it again). skip_whitespace() reads that first,
-    possibly-ungotten character via a plain get(), but every further
-    character it reads is guaranteed to be a fresh read: nothing between
-    those calls invokes unget(). This variant skips the (otherwise always
-    false) next_unget branch for those calls; it is not a general
-    replacement for get().
-    */
-    char_int_type get_ignoring_pending_unget()
-    {
-        JSON_ASSERT(!next_unget);
-
-        advance_position();
-        current = ia.get_character();
-
-        return track_after_read();
-    }
-
     /// seekable adapter: nothing to capture, the token is rebuilt on error
     void capture_char(std::true_type /*lazy*/) const noexcept {}
 
@@ -1704,37 +1612,13 @@ scan_number_done:
         return true;
     }
 
-    /// whether `current` is one of the four JSON whitespace characters
-    bool current_is_whitespace() const noexcept
-    {
-        return current == ' ' || current == '\t' || current == '\n' || current == '\r';
-    }
-
     void skip_whitespace()
     {
-        // the first character may be a pending unget() left over from the
-        // previous token (see get_ignoring_pending_unget()); every
-        // subsequent character read by this loop is guaranteed fresh, since
-        // nothing below calls unget()
-        get();
-
-        if (!current_is_whitespace())
-        {
-            return;
-        }
-
-        // this is written as an if-guarded do-while (rather than a plain
-        // while loop) because that shape is what lets both GCC and Clang
-        // keep the input adapter's read pointer in a register across
-        // iterations; the equivalent while-loop measurably defeated that
-        // optimization in testing, turning long whitespace runs (e.g. the
-        // indentation of pretty-printed JSON) from a register-only loop
-        // into one that reloads the pointer from memory every character
         do
         {
-            get_ignoring_pending_unget();
+            get();
         }
-        while (current_is_whitespace());
+        while (current == ' ' || current == '\t' || current == '\n' || current == '\r');
     }
 
     token_type scan()
@@ -1870,13 +1754,6 @@ scan_number_done:
     const char_int_type decimal_point_char = '.';
     /// the position of the decimal point in the input
     std::size_t decimal_point_position = std::string::npos;
-
-    /// whether the caller (e.g. accept()/json_sax_acceptor) only needs the
-    /// token classification and never looks at the converted numeric value;
-    /// when set, scan_number() may skip strtoull()/strtoll() for
-    /// value_unsigned/value_integer tokens whose digit count guarantees they
-    /// fit into 64 bits (see scan_number())
-    const bool discard_number_values = false;
 };
 
 }  // namespace detail

include/nlohmann/detail/input/parser.hpp

@@ -72,10 +72,9 @@ class parser
                     parser_callback_t<BasicJsonType> cb = nullptr,
                     const bool allow_exceptions_ = true,
                     const bool ignore_comments = false,
-                    const bool ignore_trailing_commas_ = false,
-                    const bool discard_number_values_ = false)
+                    const bool ignore_trailing_commas_ = false)
         : callback(std::move(cb))
-        , m_lexer(std::move(adapter), ignore_comments, discard_number_values_)
+        , m_lexer(std::move(adapter), ignore_comments)
         , allow_exceptions(allow_exceptions_)
         , ignore_trailing_commas(ignore_trailing_commas_)
     {

include/nlohmann/json.hpp

@@ -164,12 +164,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         detail::parser_callback_t<basic_json>cb = nullptr,
         const bool allow_exceptions = true,
         const bool ignore_comments = false,
-        const bool ignore_trailing_commas = false,
-        const bool discard_number_values = false
+        const bool ignore_trailing_commas = false
     )
     {
         return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter),
-               std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas, discard_number_values);
+               std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
     }
 
   private:
@@ -3574,6 +3573,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         {
             using std::swap;
             swap(*(m_data.m_value.array), other);
+            set_parents();
         }
         else
         {
@@ -3590,6 +3590,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         {
             using std::swap;
             swap(*(m_data.m_value.object), other);
+            set_parents();
         }
         else
         {
@@ -4134,7 +4135,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -4145,7 +4146,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
@@ -4154,7 +4155,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     /// @brief generate SAX events
@@ -5158,34 +5159,139 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
             case value_t::object:
             {
-                // first pass: traverse this object's elements
+                // first pass: record, for every source key, whether it is
+                // common to both objects (in source's iteration order) or
+                // was deleted (i.e., in source but not in target) -- this is
+                // a by-product of the target.find() call already needed to
+                // tell the two cases apart, so it adds no extra lookups. The
+                // "remove" ops themselves are emitted later, interleaved
+                // with the recursive per-key diffs in the fast path below,
+                // to match source's original iteration order (as the
+                // original, pre-reordering-aware implementation did) instead
+                // of grouping all removes before all recursive diffs.
+                std::vector<typename object_t::key_type> common_keys_source_order;
                 for (auto it = source.cbegin(); it != source.cend(); ++it)
                 {
-                    // escape the key name to be used in a JSON patch
-                    const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
-
                     if (target.find(it.key()) != target.end())
                     {
-                        // recursive call to compare object values at key it
-                        auto temp_diff = diff(it.value(), target[it.key()], path_key);
-                        result.insert(result.end(), temp_diff.begin(), temp_diff.end());
+                        common_keys_source_order.push_back(it.key());
+                    }
+                }
+
+                // second pass: find keys that were added (i.e., in target but
+                // not in source), and record the keys common to both, in
+                // target's iteration order -- again a by-product of the
+                // source.find() call already needed to detect added keys. At
+                // the same time, determine whether every added key comes
+                // after every common key in target's order (a precondition
+                // for the fast path below, which only ever appends new keys
+                // at the very end): for an object_t whose iteration order is
+                // a pure function of the key set (e.g. the default std::map,
+                // which always iterates in sorted key order), the order
+                // check further below is always true and this whole
+                // mechanism is effectively a no-op; it only matters for a
+                // reorderable object_t such as the one backing `ordered_json`.
+                // patch ops for keys that were added (i.e., in target but not
+                // in source); built here so the fast path below can reuse
+                // them without a second source.find() per target key. Only
+                // used by the fast path -- the slow (reordering) path
+                // rebuilds "add" ops for every key itself.
+                std::vector<typename object_t::key_type> common_keys_target_order;
+                basic_json added_ops(value_t::array);
+                bool new_keys_form_suffix = true;
+                bool seen_new_key = false;
+                for (auto it = target.cbegin(); it != target.cend(); ++it)
+                {
+                    if (source.find(it.key()) == source.end())
+                    {
+                        seen_new_key = true;
+                        const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                        added_ops.push_back(
+                        {
+                            {"op", "add"}, {"path", path_key},
+                            {"value", it.value()}
+                        });
                     }
                     else
                     {
-                        // found a key that is not in o -> remove it
+                        common_keys_target_order.push_back(it.key());
+                        if (seen_new_key)
+                        {
+                            new_keys_form_suffix = false;
+                        }
+                    }
+                }
+
+                if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
+                {
+                    // fast path: order of common keys already matches (or the
+                    // object_t's iteration order does not depend on
+                    // insertion history), so a plain per-key recursive diff
+                    // is correct and minimal, as before. common_keys_source_order
+                    // is, by construction, the subsequence of source's keys
+                    // that are common to both objects, in source's iteration
+                    // order -- so it can be walked in lockstep with `source`
+                    // using a cheap key comparison instead of another lookup.
+                    // Deleted keys (those source keys not in common_keys_source_order)
+                    // are interleaved here too, in source's original order, to
+                    // match the historical (pre-reordering-aware) output order.
+                    auto common_it = common_keys_source_order.cbegin();
+                    for (auto it = source.cbegin(); it != source.cend(); ++it)
+                    {
+                        if (common_it != common_keys_source_order.cend() && it.key() == *common_it)
+                        {
+                            const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                            auto temp_diff = diff(it.value(), target[it.key()], path_key);
+                            result.insert(result.end(), temp_diff.begin(), temp_diff.end());
+                            ++common_it;
+                        }
+                        else
+                        {
+                            // found a key that is not in target -> remove it
+                            const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                            result.push_back(object(
+                            {
+                                {"op", "remove"}, {"path", path_key}
+                            }));
+                        }
+                    }
+
+                    // append the "add" ops for brand-new keys collected above
+                    // during the pass over target -- no second source.find()
+                    // per target key needed
+                    result.insert(result.end(), added_ops.begin(), added_ops.end());
+                }
+                else
+                {
+                    // slow path: the common keys are in a different relative
+                    // order in source and target (only possible for a
+                    // reorderable object_t like ordered_map). Building a
+                    // minimal reordering patch is a nontrivial (LCS-like)
+                    // problem; instead, remove every source key -- both
+                    // deleted keys (which must be removed regardless) and
+                    // common keys (removed so they can be re-added in
+                    // target's order) -- and re-add every key that should
+                    // remain, with its final target value, in target's
+                    // order. basic_json::patch()'s "add" operation on an
+                    // object uses operator[], which appends at the end for a
+                    // vector-backed insertion-ordered map when the key does
+                    // not already exist -- so removing a key and then adding
+                    // it moves it to the end, fixing its position.
+                    for (auto it = source.cbegin(); it != source.cend(); ++it)
+                    {
+                        const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
                         result.push_back(object(
                         {
                             {"op", "remove"}, {"path", path_key}
                         }));
                     }
-                }
 
-                // second pass: traverse other object's elements
-                for (auto it = target.cbegin(); it != target.cend(); ++it)
-                {
-                    if (source.find(it.key()) == source.end())
+                    // add every key that is either common (just removed
+                    // above) or brand new, in target's iteration order, so
+                    // that the final order after applying the patch matches
+                    // target exactly
+                    for (auto it = target.cbegin(); it != target.cend(); ++it)
                     {
-                        // found a key that is not in this -> add it
                         const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
                         result.push_back(
                         {

single_include/nlohmann/json.hpp

@@ -7932,11 +7932,10 @@ class lexer : public lexer_base<BasicJsonType>
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
-    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false, bool discard_number_values_ = false) noexcept
+    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false) noexcept
         : ia(std::move(adapter))
         , ignore_comments(ignore_comments_)
         , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
-        , discard_number_values(discard_number_values_)
     {}
 
     // deleted because of pointer members
@@ -9063,58 +9062,6 @@ scan_number_done:
         // we are done scanning a number)
         unget();
 
-        // If the caller does not need the converted value (only whether the
-        // input is syntactically valid; see json_sax_acceptor/accept()), an
-        // unsigned/integer token can be reported without calling
-        // strtoull()/strtoll() at all, *provided* we can already tell from
-        // the digit count alone that the conversion cannot overflow 64 bits.
-        // Such tokens are always finite and are accepted unconditionally by
-        // the parser regardless of their actual value (parser::sax_parse_internal()
-        // never checks finiteness for value_unsigned/value_integer), so the
-        // classification below is all that is needed.
-        //
-        // A decimal number with up to 18 digits is always representable in
-        // both std::uint64_t and std::int64_t (18 nines is ~1e18, well below
-        // both UINT64_MAX ~1.8e19 and INT64_MAX ~9.2e18), so strtoull()/strtoll()
-        // could not have set errno to ERANGE for it. Numbers with more digits
-        // (rare in practice) fall through to the exact code below, unchanged,
-        // so their handling -- including reclassification to value_float when
-        // the value overflows 64 bits, and rejection when it is not even
-        // finite as a double -- is bit-for-bit identical to before this
-        // optimization.
-        //
-        // Note this reasons about std::uint64_t/std::int64_t, not about
-        // number_unsigned_t/number_integer_t (BasicJsonType's own, possibly
-        // narrower, template parameters -- e.g. std::uint32_t). That is fine
-        // *only* because discard_number_values is exclusively set by
-        // accept() (see json.hpp), and accept() always parses through the
-        // library's own json_sax_acceptor -- never a user-supplied SAX
-        // consumer -- whose number_unsigned()/number_integer()/number_float()
-        // callbacks unconditionally discard their argument and return true.
-        // So for every caller that can reach this branch, neither the token
-        // classification below nor the eventual (possibly narrowed, and on
-        // this fast path left stale/unset) value_unsigned/value_integer is
-        // ever consulted -- an unsigned/integer token is accepted outright,
-        // and even a >18-digit token that this fast path deliberately falls
-        // through for is, once reclassified to value_float, still finite
-        // (and thus accepted) for any digit count that fits in number_unsigned_t
-        // or number_integer_t regardless of that type's width. If this
-        // function is ever taught to run with discard_number_values true for
-        // a caller that *does* read the converted value, this reasoning (and
-        // the fast path below) would need to be revisited.
-        if (discard_number_values)
-        {
-            constexpr std::size_t safe_digit_count = 18;
-            if (number_type == token_type::value_unsigned && token_buffer.size() <= safe_digit_count)
-            {
-                return token_type::value_unsigned;
-            }
-            if (number_type == token_type::value_integer && token_buffer.size() - 1 <= safe_digit_count)
-            {
-                return token_type::value_integer;
-            }
-        }
-
         char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
         errno = 0;
 
@@ -9229,7 +9176,8 @@ scan_number_done:
     */
     char_int_type get()
     {
-        advance_position();
+        ++position.chars_read_total;
+        ++position.chars_read_current_line;
 
         if (next_unget)
         {
@@ -9241,23 +9189,6 @@ scan_number_done:
             current = ia.get_character();
         }
 
-        return track_after_read();
-    }
-
-    /// shared head of get() / get_ignoring_pending_unget(): bump the
-    /// per-character position counters (line-count-on-'\n' bookkeeping is
-    /// handled afterwards, in track_after_read(), once `current` is known)
-    void advance_position() noexcept
-    {
-        ++position.chars_read_total;
-        ++position.chars_read_current_line;
-    }
-
-    /// shared tail of get() / get_ignoring_pending_unget(): capture the
-    /// character for error messages (if needed) and update line/column
-    /// bookkeeping for the character now in `current`
-    char_int_type track_after_read()
-    {
         // seekable adapters reconstruct the token lazily on error (see
         // get_token_string), so the eager per-character copy is skipped
         capture_char(std::integral_constant<bool, lazy_token_string> {});
@@ -9271,29 +9202,6 @@ scan_number_done:
         return current;
     }
 
-    /*!
-    @brief like get(), but for call sites that can prove no unget() is pending
-
-    get() has to check the `next_unget` flag on every call, because a
-    previous token may have ended with unget() (e.g. scan_number() always
-    ungets the character that terminated the number, so the next call to
-    scan() can see it again). skip_whitespace() reads that first,
-    possibly-ungotten character via a plain get(), but every further
-    character it reads is guaranteed to be a fresh read: nothing between
-    those calls invokes unget(). This variant skips the (otherwise always
-    false) next_unget branch for those calls; it is not a general
-    replacement for get().
-    */
-    char_int_type get_ignoring_pending_unget()
-    {
-        JSON_ASSERT(!next_unget);
-
-        advance_position();
-        current = ia.get_character();
-
-        return track_after_read();
-    }
-
     /// seekable adapter: nothing to capture, the token is rebuilt on error
     void capture_char(std::true_type /*lazy*/) const noexcept {}
 
@@ -9487,37 +9395,13 @@ scan_number_done:
         return true;
     }
 
-    /// whether `current` is one of the four JSON whitespace characters
-    bool current_is_whitespace() const noexcept
-    {
-        return current == ' ' || current == '\t' || current == '\n' || current == '\r';
-    }
-
     void skip_whitespace()
     {
-        // the first character may be a pending unget() left over from the
-        // previous token (see get_ignoring_pending_unget()); every
-        // subsequent character read by this loop is guaranteed fresh, since
-        // nothing below calls unget()
-        get();
-
-        if (!current_is_whitespace())
-        {
-            return;
-        }
-
-        // this is written as an if-guarded do-while (rather than a plain
-        // while loop) because that shape is what lets both GCC and Clang
-        // keep the input adapter's read pointer in a register across
-        // iterations; the equivalent while-loop measurably defeated that
-        // optimization in testing, turning long whitespace runs (e.g. the
-        // indentation of pretty-printed JSON) from a register-only loop
-        // into one that reloads the pointer from memory every character
         do
         {
-            get_ignoring_pending_unget();
+            get();
         }
-        while (current_is_whitespace());
+        while (current == ' ' || current == '\t' || current == '\n' || current == '\r');
     }
 
     token_type scan()
@@ -9653,13 +9537,6 @@ scan_number_done:
     const char_int_type decimal_point_char = '.';
     /// the position of the decimal point in the input
     std::size_t decimal_point_position = std::string::npos;
-
-    /// whether the caller (e.g. accept()/json_sax_acceptor) only needs the
-    /// token classification and never looks at the converted numeric value;
-    /// when set, scan_number() may skip strtoull()/strtoll() for
-    /// value_unsigned/value_integer tokens whose digit count guarantees they
-    /// fit into 64 bits (see scan_number())
-    const bool discard_number_values = false;
 };
 
 }  // namespace detail
@@ -14166,10 +14043,9 @@ class parser
                     parser_callback_t<BasicJsonType> cb = nullptr,
                     const bool allow_exceptions_ = true,
                     const bool ignore_comments = false,
-                    const bool ignore_trailing_commas_ = false,
-                    const bool discard_number_values_ = false)
+                    const bool ignore_trailing_commas_ = false)
         : callback(std::move(cb))
-        , m_lexer(std::move(adapter), ignore_comments, discard_number_values_)
+        , m_lexer(std::move(adapter), ignore_comments)
         , allow_exceptions(allow_exceptions_)
         , ignore_trailing_commas(ignore_trailing_commas_)
     {
@@ -21716,12 +21592,11 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         detail::parser_callback_t<basic_json>cb = nullptr,
         const bool allow_exceptions = true,
         const bool ignore_comments = false,
-        const bool ignore_trailing_commas = false,
-        const bool discard_number_values = false
+        const bool ignore_trailing_commas = false
                                  )
     {
         return ::nlohmann::detail::parser<basic_json, InputAdapterType>(std::move(adapter),
-            std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas, discard_number_values);
+            std::move(cb), allow_exceptions, ignore_comments, ignore_trailing_commas);
     }
 
   private:
@@ -25126,6 +25001,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         {
             using std::swap;
             swap(*(m_data.m_value.array), other);
+            set_parents();
         }
         else
         {
@@ -25142,6 +25018,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         {
             using std::swap;
             swap(*(m_data.m_value.object), other);
+            set_parents();
         }
         else
         {
@@ -25686,7 +25563,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(detail::input_adapter(std::forward<InputType>(i)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     /// @brief check if the input is valid JSON (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -25697,7 +25574,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(detail::input_adapter(std::move(first), std::move(last)), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     JSON_HEDLEY_WARN_UNUSED_RESULT
@@ -25706,7 +25583,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                        const bool ignore_comments = false,
                        const bool ignore_trailing_commas = false)
     {
-        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
+        return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas).accept(true);
     }
 
     /// @brief generate SAX events
@@ -26710,34 +26587,139 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
             case value_t::object:
             {
-                // first pass: traverse this object's elements
+                // first pass: record, for every source key, whether it is
+                // common to both objects (in source's iteration order) or
+                // was deleted (i.e., in source but not in target) -- this is
+                // a by-product of the target.find() call already needed to
+                // tell the two cases apart, so it adds no extra lookups. The
+                // "remove" ops themselves are emitted later, interleaved
+                // with the recursive per-key diffs in the fast path below,
+                // to match source's original iteration order (as the
+                // original, pre-reordering-aware implementation did) instead
+                // of grouping all removes before all recursive diffs.
+                std::vector<typename object_t::key_type> common_keys_source_order;
                 for (auto it = source.cbegin(); it != source.cend(); ++it)
                 {
-                    // escape the key name to be used in a JSON patch
-                    const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
-
                     if (target.find(it.key()) != target.end())
                     {
-                        // recursive call to compare object values at key it
-                        auto temp_diff = diff(it.value(), target[it.key()], path_key);
-                        result.insert(result.end(), temp_diff.begin(), temp_diff.end());
+                        common_keys_source_order.push_back(it.key());
+                    }
+                }
+
+                // second pass: find keys that were added (i.e., in target but
+                // not in source), and record the keys common to both, in
+                // target's iteration order -- again a by-product of the
+                // source.find() call already needed to detect added keys. At
+                // the same time, determine whether every added key comes
+                // after every common key in target's order (a precondition
+                // for the fast path below, which only ever appends new keys
+                // at the very end): for an object_t whose iteration order is
+                // a pure function of the key set (e.g. the default std::map,
+                // which always iterates in sorted key order), the order
+                // check further below is always true and this whole
+                // mechanism is effectively a no-op; it only matters for a
+                // reorderable object_t such as the one backing `ordered_json`.
+                // patch ops for keys that were added (i.e., in target but not
+                // in source); built here so the fast path below can reuse
+                // them without a second source.find() per target key. Only
+                // used by the fast path -- the slow (reordering) path
+                // rebuilds "add" ops for every key itself.
+                std::vector<typename object_t::key_type> common_keys_target_order;
+                basic_json added_ops(value_t::array);
+                bool new_keys_form_suffix = true;
+                bool seen_new_key = false;
+                for (auto it = target.cbegin(); it != target.cend(); ++it)
+                {
+                    if (source.find(it.key()) == source.end())
+                    {
+                        seen_new_key = true;
+                        const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                        added_ops.push_back(
+                        {
+                            {"op", "add"}, {"path", path_key},
+                            {"value", it.value()}
+                        });
                     }
                     else
                     {
-                        // found a key that is not in o -> remove it
+                        common_keys_target_order.push_back(it.key());
+                        if (seen_new_key)
+                        {
+                            new_keys_form_suffix = false;
+                        }
+                    }
+                }
+
+                if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
+                {
+                    // fast path: order of common keys already matches (or the
+                    // object_t's iteration order does not depend on
+                    // insertion history), so a plain per-key recursive diff
+                    // is correct and minimal, as before. common_keys_source_order
+                    // is, by construction, the subsequence of source's keys
+                    // that are common to both objects, in source's iteration
+                    // order -- so it can be walked in lockstep with `source`
+                    // using a cheap key comparison instead of another lookup.
+                    // Deleted keys (those source keys not in common_keys_source_order)
+                    // are interleaved here too, in source's original order, to
+                    // match the historical (pre-reordering-aware) output order.
+                    auto common_it = common_keys_source_order.cbegin();
+                    for (auto it = source.cbegin(); it != source.cend(); ++it)
+                    {
+                        if (common_it != common_keys_source_order.cend() && it.key() == *common_it)
+                        {
+                            const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                            auto temp_diff = diff(it.value(), target[it.key()], path_key);
+                            result.insert(result.end(), temp_diff.begin(), temp_diff.end());
+                            ++common_it;
+                        }
+                        else
+                        {
+                            // found a key that is not in target -> remove it
+                            const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
+                            result.push_back(object(
+                            {
+                                {"op", "remove"}, {"path", path_key}
+                            }));
+                        }
+                    }
+
+                    // append the "add" ops for brand-new keys collected above
+                    // during the pass over target -- no second source.find()
+                    // per target key needed
+                    result.insert(result.end(), added_ops.begin(), added_ops.end());
+                }
+                else
+                {
+                    // slow path: the common keys are in a different relative
+                    // order in source and target (only possible for a
+                    // reorderable object_t like ordered_map). Building a
+                    // minimal reordering patch is a nontrivial (LCS-like)
+                    // problem; instead, remove every source key -- both
+                    // deleted keys (which must be removed regardless) and
+                    // common keys (removed so they can be re-added in
+                    // target's order) -- and re-add every key that should
+                    // remain, with its final target value, in target's
+                    // order. basic_json::patch()'s "add" operation on an
+                    // object uses operator[], which appends at the end for a
+                    // vector-backed insertion-ordered map when the key does
+                    // not already exist -- so removing a key and then adding
+                    // it moves it to the end, fixing its position.
+                    for (auto it = source.cbegin(); it != source.cend(); ++it)
+                    {
+                        const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
                         result.push_back(object(
                         {
                             {"op", "remove"}, {"path", path_key}
                         }));
                     }
-                }
 
-                // second pass: traverse other object's elements
-                for (auto it = target.cbegin(); it != target.cend(); ++it)
-                {
-                    if (source.find(it.key()) == source.end())
+                    // add every key that is either common (just removed
+                    // above) or brand new, in target's iteration order, so
+                    // that the final order after applying the patch matches
+                    // target exactly
+                    for (auto it = target.cbegin(); it != target.cend(); ++it)
                     {
-                        // found a key that is not in this -> add it
                         const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
                         result.push_back(
                         {

tests/src/unit-class_parser.cpp

@@ -930,98 +930,6 @@ TEST_CASE("parser class")
                 CHECK(accept_helper("+1") == false);
                 CHECK(accept_helper("+0") == false);
             }
-
-            SECTION("issue #5411 - skip conversion when accept() does not need the numeric value")
-            {
-                // lexer::scan_number() may skip strtoull()/strtoll() for
-                // value_unsigned/value_integer tokens when the caller (e.g.
-                // json::accept()) does not need the converted value, as long
-                // as the digit count alone guarantees no 64-bit overflow (see
-                // the "safe_digit_count" fast path in scan_number()). This
-                // differential test checks that json::accept() (which enables
-                // the fast path) and json::parse() (which never does) always
-                // agree, over a corpus that exercises both the fast path
-                // (<=18 digits) and the untouched, exact fallback path (>=19
-                // digits) -- including reclassification of huge digit-only
-                // integers to a (possibly non-finite) floating-point value.
-                const std::vector<std::pair<std::string, bool>> cases =
-                {
-                    // normal small/large integers, both signs
-                    {"0", true}, {"1", true}, {"-1", true}, {"42", true}, {"-42", true},
-                    {"123456789", true}, {"-123456789", true},
-
-                    // digit-count boundary around the 18-digit safe cutoff (both signs)
-                    {std::string(17, '9'), true},
-                    {std::string(18, '9'), true},
-                    {std::string(19, '9'), true},
-                    {std::string(20, '9'), true},
-                    {"-" + std::string(17, '9'), true},
-                    {"-" + std::string(18, '9'), true},
-                    {"-" + std::string(19, '9'), true},
-                    {"-" + std::string(20, '9'), true},
-
-                    // 64-bit boundaries
-                    {"9223372036854775807", true},    // INT64_MAX
-                    {"-9223372036854775808", true},   // INT64_MIN
-                    {"18446744073709551615", true},   // UINT64_MAX
-                    {"18446744073709551616", true},   // UINT64_MAX + 1 (overflows uint64_t, finite double)
-
-                    // the 28-digit example from the issue: overflows uint64_t
-                    // but is finite as a double, so the scanner reclassifies
-                    // it to value_float and it is accepted
-                    {"9999999999999999999999999999", true},
-
-                    // huge digit-only integers that overflow even a double -> rejected
-                    {std::string(309, '9'), false},
-                    {std::string(400, '9'), false},
-                    {"1" + std::string(400, '0'), false},
-
-                    // 1e999 / 1e400 style overflow -> rejected
-                    {"1e999", false},
-                    {"1e400", false},
-                    {"-1e999", false},
-                    {"1E999", false},
-
-                    // values straddling DBL_MAX
-                    {"1.7976931348623157e308", true},   // <= DBL_MAX, finite
-                    {"1.7976931348623159e308", false},  // > DBL_MAX, overflows to inf
-
-                    // a mix of other valid/invalid numeric syntax
-                    {"3.14159", true},
-                    {"-0.0", true},
-                    {"1.0e10", true},
-                    {"01", false},
-                    {"-", false},
-                    {"1.", false},
-                    {"1e", false},
-                    {"+1", false},
-                };
-
-                for (const auto& c : cases)
-                {
-                    const std::string& number = c.first;
-                    const bool expected = c.second;
-                    CAPTURE(number)
-                    CAPTURE(expected)
-
-                    // accept() takes the fast path (skips conversion when possible)
-                    CHECK(json::accept(number) == expected);
-
-                    // parse() always performs the full conversion; it must agree
-                    json j;
-                    CHECK_NOTHROW(json::parser(nlohmann::detail::input_adapter(number), nullptr, false).parse(true, j));
-                    CHECK(!j.is_discarded() == expected);
-
-                    // wrap in an array so get_token() is exercised beyond the
-                    // very first (constructor-time) scan as well
-                    std::string wrapped = "[";
-                    wrapped += number;
-                    wrapped += ",";
-                    wrapped += number;
-                    wrapped += "]";
-                    CHECK(json::accept(wrapped) == expected);
-                }
-            }
         }
     }
 
@@ -1486,71 +1394,6 @@ TEST_CASE("parser class")
         CHECK(accept_helper("\"\\uD80C\\uFFFF\"") == false);
     }
 
-#if !defined(JSON_NOEXCEPTION)
-    SECTION("issue #5412 - whitespace skipping bookkeeping (compact vs. pretty-printed)")
-    {
-        // lexer::skip_whitespace() reads its first character with get() (to
-        // honor a possibly pending unget() from the previous token) and every
-        // further whitespace character with get_ignoring_pending_unget() (a
-        // get() variant that skips the then-always-false next_unget check).
-        // This must not change the reported byte offset, line, or column of
-        // a syntax error, even when a long run of whitespace containing
-        // multiple newlines is skipped beforehand (as with pretty-printed
-        // input). The expected values below were captured from the
-        // unmodified do-while(get()) loop, so any regression that miscounts
-        // characters or newlines while skipping whitespace changes them.
-        const auto check_error = [](const std::string & input, std::size_t expected_byte,
-                                    const std::string & expected_what)
-        {
-            CAPTURE(input)
-            try
-            {
-                json _ = json::parse(input);
-                FAIL_CHECK("expected a parse_error, but parsing succeeded");
-            }
-            catch (const json::parse_error& e)
-            {
-                CHECK(e.byte == expected_byte);
-                CHECK(std::string(e.what()) == expected_what);
-            }
-        };
-
-        // a nested document, serialized both compactly and pretty-printed
-        // (dump(4)), each truncated right before the final closing '}' so
-        // that the parser hits EOF after skipping all of the (in the
-        // pretty-printed case, substantial) indentation whitespace
-        const json doc =
-        {
-            {"a", 1},
-            {"b", json::array({true, false, nullptr, "x"})},
-            {"c", json::object({{"d", 3.14}, {"e", json::array({1, 2, 3})}})}
-        };
-
-        const std::string compact = doc.dump();
-        const std::string pretty = doc.dump(4);
-
-        check_error(compact.substr(0, compact.size() - 1), 60,
-                    "[json.exception.parse_error.101] parse error at line 1, column 60: syntax error while parsing object - unexpected end of input; expected '}'");
-        check_error(pretty.substr(0, pretty.size() - 1), 193,
-                    "[json.exception.parse_error.101] parse error at line 17, column 1: syntax error while parsing object - unexpected end of input; expected '}'");
-
-        // an invalid token appearing after several indented, multi-line
-        // whitespace runs vs. the same document without any of that
-        // whitespace
-        check_error(R"({
-    "a": 1,
-    "b": [
-        true,
-        false
-    ],
-    "c": @
-})", 70,
-                    "[json.exception.parse_error.101] parse error at line 7, column 10: syntax error while parsing value - invalid literal; last read: '\"c\": @'");
-        check_error(R"({"a":1,"b":[true,false],"c":@})", 29,
-                    "[json.exception.parse_error.101] parse error at line 1, column 29: syntax error while parsing value - invalid literal; last read: '\"c\":@'");
-    }
-#endif
-
     SECTION("tests found by mutate++")
     {
         // test case to make sure no comma precedes the first key

tests/src/unit-diagnostics.cpp

@@ -273,5 +273,36 @@ TEST_CASE("Regression tests for extended diagnostics")
         CHECK(j1["numbers"]["two"] == 2);
         CHECK(j1["string"] == "t");
     }
+
+    SECTION("Regression test - swap(array_t&)/swap(object_t&) must update JSON_DIAGNOSTICS parent pointers")
+    {
+        // swap(array_t&)
+        {
+            json j = json::array();
+            json::array_t arr = {json::array({1})};
+            j.swap(arr);
+
+            // parent pointers of the moved-in elements must point into j, not
+            // into the now-defunct free-standing array_t
+            CHECK_THROWS_WITH_AS(j[0][0].get<std::string>(), "[json.exception.type_error.302] (/0/0) type must be string, but is number", json::type_error);
+
+            // must not trigger assert_invariant() in a debug/assert-enabled build
+            json const k = j;
+            CHECK(k == j);
+        }
+
+        // swap(object_t&)
+        {
+            json o = json::object();
+            json::object_t obj = {{"a", json::array({1})}};
+            o.swap(obj);
+
+            CHECK_THROWS_WITH_AS(o["a"][0].get<std::string>(), "[json.exception.type_error.302] (/a/0) type must be string, but is number", json::type_error);
+
+            // must not trigger assert_invariant() in a debug/assert-enabled build
+            json const p = o;
+            CHECK(p == o);
+        }
+    }
 }
 

tests/src/unit-ordered_json.cpp

@@ -81,3 +81,84 @@ TEST_CASE("regression test for issue #3732 - iteration_proxy_value<iter_impl<ord
     };
     static_cast<void>(fn);
 }
+
+TEST_CASE("regression test - diff() must account for ordered_json member order")
+{
+    SECTION("pure reorder, no value changes")
+    {
+        ordered_json a = {{"a", 1}, {"b", 2}};
+        ordered_json b = {{"b", 2}, {"a", 1}};
+        CHECK(a != b); // order-sensitive equality
+        CHECK(a.patch(ordered_json::diff(a, b)) == b);
+    }
+
+    SECTION("new key must land at the front")
+    {
+        ordered_json c = {{"b", 2}};
+        ordered_json e = {{"a", 1}, {"b", 2}};
+        CHECK(c.patch(ordered_json::diff(c, e)) == e);
+    }
+
+    SECTION("reorder plus a value change on one of the reordered keys")
+    {
+        ordered_json a = {{"a", 1}, {"b", 2}};
+        ordered_json b = {{"b", 20}, {"a", 1}};
+        CHECK(a != b);
+        CHECK(a.patch(ordered_json::diff(a, b)) == b);
+    }
+
+    SECTION("reorder plus a deleted key")
+    {
+        ordered_json a = {{"a", 1}, {"b", 2}, {"c", 3}};
+        ordered_json b = {{"b", 2}, {"a", 1}};
+        CHECK(a != b);
+        CHECK(a.patch(ordered_json::diff(a, b)) == b);
+    }
+
+    SECTION("reorder plus a nested value that itself needs a recursive diff")
+    {
+        ordered_json a = {{"a", {{"x", 1}, {"y", 2}}}, {"b", 2}};
+        ordered_json b = {{"b", 2}, {"a", {{"x", 1}, {"y", 99}}}};
+        CHECK(a != b);
+        CHECK(a.patch(ordered_json::diff(a, b)) == b);
+    }
+
+    SECTION("three or more keys shuffled into a different order")
+    {
+        ordered_json a = {{"a", 1}, {"b", 2}, {"c", 3}, {"d", 4}};
+        ordered_json b = {{"d", 4}, {"b", 2}, {"a", 1}, {"c", 3}};
+        CHECK(a != b);
+        CHECK(a.patch(ordered_json::diff(a, b)) == b);
+    }
+
+    SECTION("matching order still produces a minimal patch (fast path unaffected)")
+    {
+        ordered_json a = {{"a", 1}, {"b", 2}, {"c", 3}};
+        ordered_json b = {{"a", 1}, {"b", 20}, {"c", 3}};
+        auto p = ordered_json::diff(a, b);
+        // only the changed value should be touched, not a wholesale remove+add
+        CHECK(p.size() == 1);
+        CHECK(p[0]["op"] == "replace");
+        CHECK(p[0]["path"] == "/b");
+        CHECK(a.patch(p) == b);
+    }
+
+    SECTION("plain json (std::map-backed) is unaffected by same-key-different-insertion-order")
+    {
+        json a;
+        a["b"] = 2;
+        a["a"] = 1;
+
+        json b;
+        b["a"] = 1;
+        b["b"] = 2;
+
+        // std::map iteration is always sorted by key, so a == b regardless of
+        // insertion order, and diff() must still produce the same minimal
+        // (empty) result as before this fix
+        CHECK(a == b);
+        auto p = json::diff(a, b);
+        CHECK(p.empty());
+        CHECK(a.patch(p) == b);
+    }
+}