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basic_json, iterators, serializer: remove checks that invariants make dead

Browse Source 
Branch coverage of the test suite and of 24k mutated inputs showed
these conditions as never taken; each is implied by the code around it:

- copy_object_level(): `src_it != src_object.cend()`; dst was built from
  exactly src_object.size() unique keys and src_it advances at most once
  per member
- the general comparison operators (equal_general, less_general,
  three_way_general): the five same-type scalar cases, which the inline
  fast path of every operator handles before calling them (now an
  assert); and the NaN half of compares_unordered() in the mixed-type
  branch, reached only after all six number pairs returned, where only
  a discarded operand is unordered
- serializer, ensure_ascii: the reset of `bytes` under error_handler_t::keep
  and the surrogate-pair escape in the UTF8_ACCEPT case; every
  well-formed multi-byte character is escaped by write_u_escapes() before
  decode() sees it, so decode() only ever accepts DEL here, a single byte
  of which nothing was buffered (now asserts)
- iter_impl(pointer): the if/else chain assigned value-initialized
  iterators to the value-initialized m_it

No change in behaviour: a build that aborts on each removed side passes
the test suite, the fuzz corpora and 23.2M dumps of all 1-, 2- and
boundary 4-byte strings in both ensure_ascii modes.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-11-02 09:41:01 +01:00
1 parent f093573828
commit 2ac0851157
4 files changed
+36 -60
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include/nlohmann/detail/iterators/iter_impl.hpp
+2 -14
View File
@@ -107,20 +107,8 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
explicit iter_impl(pointer object) noexcept : m_object(object)
{
JSON_ASSERT(m_object != nullptr);
if (m_object->is_object())
{
m_it.object_iterator = typename object_t::iterator();
}
else if (m_object->is_array())
{
m_it.array_iterator = typename array_t::iterator();
}
else
{
// primitive (is_primitive(), including discarded)
m_it.primitive_iterator = primitive_iterator_t();
}
// m_it is value-initialized: its iterators are singular, and the
// primitive iterator is in its "uninitialized" state
}
/*!
include/nlohmann/detail/output/serializer.hpp
+5 -12
View File
@@ -1113,21 +1113,14 @@ class serializer
{
// the code point is at least 0x60 (smaller ones are handled
// above) and is not printable ASCII (which the scanner
// copies): it is DEL (0x7F) under EnsureAscii or a non-ASCII
// character
// copies). Under EnsureAscii it is DEL (0x7F): every
// well-formed multi-byte character is escaped by
// write_u_escapes() above, so decode() only ever accepts a
// single byte here, and nothing of it was buffered
if (EnsureAscii)
{
JSON_ASSERT(codepoint == 0x7F);
if (error_handler == error_handler_t::keep)
{
// this character was buffered as raw bytes below
// in case it turned out to be part of an
// ill-formed sequence (which is kept as is); now
// that it decoded to a well-formed code point,
// undo that and \u-escape it like any other
// character instead
bytes = bytes_after_last_accept;
}
JSON_ASSERT(bytes == bytes_after_last_accept);
write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
}
else
include/nlohmann/json.hpp
+11 -4
View File
@@ -1576,7 +1576,7 @@ public:
auto src_it = src_object.cbegin();
for (auto& element : *dst.m_data.m_value.object)
{
if (JSON_HEDLEY_LIKELY(src_it != src_object.cend() && copy_keys_equal(src_it->first, element.first)))
if (JSON_HEDLEY_LIKELY(copy_keys_equal(src_it->first, element.first)))
{
copy_shallow(src_it->second, element.second, worklist);
++src_it;
@@ -5404,8 +5404,15 @@ public:
return (*lhs.m_data.m_value.object) op (*rhs.m_data.m_value.object); \
} \
\
JSON_IMPLEMENT_SCALAR_CASES(op, null_result) \
\
/* same-type scalars never get here: the inline fast path of the operator handles them */ \
case value_t::null: \
case value_t::boolean: \
case value_t::number_integer: \
case value_t::number_unsigned: \
case value_t::number_float: \
JSON_ASSERT(false); /* NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) */ \
return (unordered_result); \
\
case value_t::string: \
return (*lhs.m_data.m_value.string) op (*rhs.m_data.m_value.string); \
\
@@ -5445,7 +5452,7 @@ public:
? (number_integer_t(-1) op number_integer_t(1)) \
: (static_cast<number_unsigned_t>(lhs.m_data.m_value.number_integer) op rhs.m_data.m_value.number_unsigned); \
} \
else if(compares_unordered(lhs, rhs))\
else if(lhs_type == value_t::discarded || rhs_type == value_t::discarded)\
{\
return (unordered_result);\
}\
single_include/nlohmann/json.hpp
Generated
+18 -30
View File
@@ -24063,20 +24063,8 @@ class iter_impl // NOLINT(cppcoreguidelines-special-member-functions,hicpp-speci
explicit iter_impl(pointer object) noexcept : m_object(object)
{
JSON_ASSERT(m_object != nullptr);
if (m_object->is_object())
{
m_it.object_iterator = typename object_t::iterator();
}
else if (m_object->is_array())
{
m_it.array_iterator = typename array_t::iterator();
}
else
{
// primitive (is_primitive(), including discarded)
m_it.primitive_iterator = primitive_iterator_t();
}
// m_it is value-initialized: its iterators are singular, and the
// primitive iterator is in its "uninitialized" state
}
/*!
@@ -36267,21 +36255,14 @@ class serializer
{
// the code point is at least 0x60 (smaller ones are handled
// above) and is not printable ASCII (which the scanner
// copies): it is DEL (0x7F) under EnsureAscii or a non-ASCII
// character
// copies). Under EnsureAscii it is DEL (0x7F): every
// well-formed multi-byte character is escaped by
// write_u_escapes() above, so decode() only ever accepts a
// single byte here, and nothing of it was buffered
if (EnsureAscii)
{
JSON_ASSERT(codepoint == 0x7F);
if (error_handler == error_handler_t::keep)
{
// this character was buffered as raw bytes below
// in case it turned out to be part of an
// ill-formed sequence (which is kept as is); now
// that it decoded to a well-formed code point,
// undo that and \u-escape it like any other
// character instead
bytes = bytes_after_last_accept;
}
JSON_ASSERT(bytes == bytes_after_last_accept);
write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
}
else
@@ -39305,7 +39286,7 @@ public:
auto src_it = src_object.cbegin();
for (auto& element : *dst.m_data.m_value.object)
{
if (JSON_HEDLEY_LIKELY(src_it != src_object.cend() && copy_keys_equal(src_it->first, element.first)))
if (JSON_HEDLEY_LIKELY(copy_keys_equal(src_it->first, element.first)))
{
copy_shallow(src_it->second, element.second, worklist);
++src_it;
@@ -43133,8 +43114,15 @@ public:
return (*lhs.m_data.m_value.object) op (*rhs.m_data.m_value.object); \
} \
\
JSON_IMPLEMENT_SCALAR_CASES(op, null_result) \
\
/* same-type scalars never get here: the inline fast path of the operator handles them */ \
case value_t::null: \
case value_t::boolean: \
case value_t::number_integer: \
case value_t::number_unsigned: \
case value_t::number_float: \
JSON_ASSERT(false); /* NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) */ \
return (unordered_result); \
\
case value_t::string: \
return (*lhs.m_data.m_value.string) op (*rhs.m_data.m_value.string); \
\
@@ -43174,7 +43162,7 @@ public:
? (number_integer_t(-1) op number_integer_t(1)) \
: (static_cast<number_unsigned_t>(lhs.m_data.m_value.number_integer) op rhs.m_data.m_value.number_unsigned); \
} \
else if(compares_unordered(lhs, rhs))\
else if(lhs_type == value_t::discarded || rhs_type == value_t::discarded)\
{\
return (unordered_result);\
}\