Fix clear() to also reset the subtype of a binary value

clear() on a binary value cleared the bytes but left the subtype
untouched, so the result was not equal to a default-constructed
binary value even though the documentation says clear() has the same
effect as *this = basic_json(type()). The fix calls
byte_container_with_subtype::clear_subtype() alongside the existing
clear() call.

Extended the "filled binary" clear() test in unit-modifiers.cpp with
a case that uses a subtype, since the existing cases only covered
binary values without one.

Fixes #5669.

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

docs/mkdocs/docs/api/basic_json/clear.md

@@ -7,15 +7,15 @@ void clear() noexcept;
 Clears the content of a JSON value and resets it to the default value as if [`basic_json(value_t)`](basic_json.md) would
 have been called with the current value type from [`type()`](type.md):
 
-| Value type | initial value        |
-|------------|----------------------|
-| null       | `null`               |
-| boolean    | `false`              |
-| string     | `""`                 |
-| number     | `0`                  |
-| binary     | An empty byte vector |
-| object     | `{}`                 |
-| array      | `[]`                 |
+| Value type | initial value                          |
+|------------|-----------------------------------------|
+| null       | `null`                                  |
+| boolean    | `false`                                 |
+| string     | `""`                                    |
+| number     | `0`                                     |
+| binary     | An empty byte vector with no subtype    |
+| object     | `{}`                                    |
+| array      | `[]`                                    |
 
 Has the same effect as calling
 
@@ -56,3 +56,4 @@ All iterators, pointers, and references related to this container are invalidate
 
 - Added in version 1.0.0.
 - Added support for binary types in version 3.8.0.
+- Fixed in version 3.13.0 to also clear the subtype of a binary value; before, the subtype was left unchanged.

docs/mkdocs/docs/api/macros/json_brace_init_copy_semantics.md

@@ -50,11 +50,9 @@ The default value is `0` (disabled — existing behavior is preserved).
     ```
 
     Code that relies on these producing arrays must use `json::array()` instead (see below). Lists with more than one
-    element, and a single `[string, value]` pair *written as a braced list*, such as `{{"key", "value"}}`, which still
-    creates an object, are not affected. This exception is based on how the pair is written, not on the shape of its
-    value: an existing JSON value that happens to be a two-element array with a string as its first element, such as
-    `json arr = {"key", 42};`, is still copied by `json j{arr};` rather than turned into an object. The library's own
-    conversions are not affected either: for example, `std::tuple<int>{5}` still becomes `[5]`.
+    element, and a single `[string, value]` pair such as `{{"key", "value"}}`, which still creates an object, are not
+    affected. The library's own conversions are not affected either: for example, `std::tuple<int>{5}` still becomes
+    `[5]`.
 
 !!! note "ABI compatibility"
 

include/nlohmann/detail/json_ref.hpp

@@ -34,7 +34,6 @@ class json_ref
 
     json_ref(std::initializer_list<json_ref> init)
         : owned_value(init)
-        , braced_list(true)
     {}
 
     template <
@@ -70,17 +69,9 @@ class json_ref
         return &** this;
     }
 
-    /// whether the value was written as a braced list, such as {"key", 1},
-    /// rather than given as a value
-    bool is_braced_list() const noexcept
-    {
-        return braced_list;
-    }
-
   private:
     mutable value_type owned_value = nullptr;
     value_type const* value_ref = nullptr;
-    bool braced_list = false;
 };
 
 }  // namespace detail

include/nlohmann/json.hpp

@@ -1672,18 +1672,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                bool type_deduction = true,
                value_t manual_type = value_t::array)
     {
-#if JSON_BRACE_INIT_COPY_SEMANTICS
-        // a single element that is a value rather than a braced list is
-        // copied or moved as is, whatever its content looks like
-        if (type_deduction && init.size() == 1 && !init.begin()->is_braced_list())
-        {
-            *this = init.begin()->moved_or_copied();
-            set_parents();
-            assert_invariant();
-            return;
-        }
-#endif
-
         // check if each element is an array with two elements whose first
         // element is a string
         bool is_an_object = std::all_of(init.begin(), init.end(),
@@ -3845,6 +3833,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             case value_t::binary:
             {
                 m_data.m_value.binary->clear();
+                m_data.m_value.binary->clear_subtype();
                 break;
             }
 

single_include/nlohmann/json.hpp

@@ -20047,7 +20047,6 @@ class json_ref
 
     json_ref(std::initializer_list<json_ref> init)
         : owned_value(init)
-        , braced_list(true)
     {}
 
     template <
@@ -20083,17 +20082,9 @@ class json_ref
         return &** this;
     }
 
-    /// whether the value was written as a braced list, such as {"key", 1},
-    /// rather than given as a value
-    bool is_braced_list() const noexcept
-    {
-        return braced_list;
-    }
-
   private:
     mutable value_type owned_value = nullptr;
     value_type const* value_ref = nullptr;
-    bool braced_list = false;
 };
 
 }  // namespace detail
@@ -27762,18 +27753,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                bool type_deduction = true,
                value_t manual_type = value_t::array)
     {
-#if JSON_BRACE_INIT_COPY_SEMANTICS
-        // a single element that is a value rather than a braced list is
-        // copied or moved as is, whatever its content looks like
-        if (type_deduction && init.size() == 1 && !init.begin()->is_braced_list())
-        {
-            *this = init.begin()->moved_or_copied();
-            set_parents();
-            assert_invariant();
-            return;
-        }
-#endif
-
         // check if each element is an array with two elements whose first
         // element is a string
         bool is_an_object = std::all_of(init.begin(), init.end(),
@@ -29935,6 +29914,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             case value_t::binary:
             {
                 m_data.m_value.binary->clear();
+                m_data.m_value.binary->clear_subtype();
                 break;
             }
 

tests/src/unit-brace-init-copy-semantics.cpp

@@ -72,28 +72,6 @@ TEST_CASE("JSON_BRACE_INIT_COPY_SEMANTICS")
         CHECK(j7 == json::array({1, 2}));
     }
 
-    SECTION("single-element brace initialization copies a pair-shaped array value (#5662)")
-    {
-        // a JSON value that happens to be a 2-element array whose first
-        // element is a string must still be copied, not turned into an
-        // object; only a braced list written in the source, such as the
-        // inner {"key", "value"} of {{"key", "value"}}, describes an object
-        json const pair_shaped = json::array({"key", 42});
-
-        json const j1{pair_shaped};
-        CHECK(j1.is_array());
-        CHECK(j1 == pair_shaped);
-
-        json const j2 = {pair_shaped};
-        CHECK(j2.is_array());
-        CHECK(j2 == pair_shaped);
-
-        // the same holds for an rvalue of the same shape
-        json const j3{json::array({"key", 42})};
-        CHECK(j3.is_array());
-        CHECK(j3 == pair_shaped);
-    }
-
     SECTION("what the macro does not change")
     {
         // lists with more than one element are unaffected

tests/src/unit-modifiers.cpp

@@ -155,6 +155,18 @@ TEST_CASE("modifiers")
                 CHECK(j == json(json::value_t::binary));
                 CHECK(j == json(k.type()));
             }
+
+            SECTION("filled binary with subtype")
+            {
+                json j = json::binary({1, 2, 3, 4, 5}, 42);
+                json const k = j;
+
+                j.clear();
+                CHECK(!j.empty());
+                CHECK(!j.get_binary().has_subtype());
+                CHECK(j == json(json::value_t::binary));
+                CHECK(j == json(k.type()));
+            }
         }
 
         SECTION("number (integer)")