docs: state merge_patch complexity and RFC 7396 limitations; test non-object, discarded, binary cases

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

docs/mkdocs/docs/api/basic_json/diff.md

@@ -2,27 +2,17 @@
 
 ```cpp
 static basic_json diff(const basic_json& source,
-                       const basic_json& target,
-                       const string_t& path = "");
+                       const basic_json& target);
 ```
 
 Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling
 [`patch`](patch.md) function.
 
-For two JSON values `source` and `target`, the following code yields `#!cpp true`:
+For two JSON values `source` and `target`, the following code always yields `#!cpp true`:
 ```cpp
 source.patch(diff(source, target)) == target;
 ```
 
-The equality holds up to [`operator==`](operator_eq.md), so it has the following exceptions:
-
-- A value that is not equal to itself cannot round-trip. This applies to `NaN` (also nested in an array or object) and
-  to [discarded](is_discarded.md) values: `diff` emits a `replace` operation for them. A `NaN` in the patch is
-  serialized as `#!json null`, so a patch that was dumped and parsed again would set `#!json null`.
-- Numbers that compare equal produce no operation, even if their types or signs differ: `diff(1, 1.0)`,
-  `diff(1u, 1)` (unsigned and signed integer) and `diff(0.0, -0.0)` all return `#!json []`. The patched value is then
-  the `source` and keeps its number type.
-
 ## Parameters
 
 `source` (in)
@@ -31,12 +21,6 @@ The equality holds up to [`operator==`](operator_eq.md), so it has the following
 `target` (in)
 :   JSON value to compare against
 
-`path` (in)
-:   a prefix that is put verbatim in front of the `path` member of every operation (default: `""`, which addresses the
-    root of the value). The prefix is neither escaped nor validated: `#!cpp diff(1, 2, "abc")` yields an operation with
-    the `path` `abc`, which is not a valid JSON Pointer. Use it with a valid JSON Pointer such as `/root` and escape
-    `~` and `/` in its reference tokens (see [JSON Pointer](../../features/json_pointer.md)).
-
 ## Return value
 
 a JSON patch to convert the `source` to `target`
@@ -47,32 +31,11 @@ Strong guarantee: `source` and `target` are never modified.
 
 ## Complexity
 
-Linear in the total number of values (including nested ones) in `source` and `target`, times the cost of a key-based
-object operation (looking up a key in an object): logarithmic for [`json`](../json.md), and linear for
-[`ordered_json`](../ordered_json.md) (see [`ordered_map` complexity](../ordered_map.md#complexity)). For
-`ordered_json`, diffing two objects with `n` and `m` members therefore takes O((n+m)²) when their keys do not line up
-(e.g., a key was added or the keys are in a different order). The size of the patch is proportional to the number of
-operations times the length of their paths, so a small change deep inside a value yields a long `path`.
+Linear in the lengths of `source` and `target`.
 
 ## Notes
 
-- Currently, only `remove`, `add`, and `replace` operations are generated.
-- The patch is correct, but not guaranteed to be minimal. For instance, `diff([1,2,3], [0,1,2,3])` yields three
-  `replace` operations and one `add` operation instead of a single insertion.
-- Differences between two arrays are reported index by index. Elements that were added at the end of the array are added
-  with `add` operations on the path `/-` (appended in order), and elements that were removed are removed with `remove`
-  operations from the highest index down to the lowest, so that the remaining indices stay valid.
-- For objects, the operations for the members of `source` come first (`replace`, `remove`, or the operations for nested
-  values, in the iteration order of `source`), followed by `add` operations for the members that only `target` has.
-- For [`ordered_json`](../ordered_json.md), objects with the same keys in a different order are different. As a patch
-  cannot reorder members, `diff` removes all keys of the `source` object and adds them again in the order of the
-  `target`.
-- If `source` and `target` differ as a whole (e.g., different types), the patch consists of a single `replace`
-  operation for the root of the value, i.e., with the `path` `""` (or the given `path` prefix).
-- The `value` members of the patch hold copies of values of `target`. A [binary](../../features/binary_values.md) value
-  has no JSON representation: when a patch that contains one is serialized, it becomes an object such as
-  `#!json {"bytes":[1,3],"subtype":null}`, so a parsed patch no longer holds a binary value (and would set that object
-  instead).
+Currently, only `remove`, `add`, and `replace` operations are generated.
           
 ## Examples
 

docs/mkdocs/docs/api/basic_json/merge_patch.md

@@ -39,13 +39,33 @@ Basic guarantee: if an exception is thrown during the operation, the JSON value
 
 ## Complexity
 
-Linear in the lengths of `apply_patch`.
+Linear in the total number of values (including nested ones) in `apply_patch`, times the cost of a key-based object
+operation (looking up, adding, or erasing a member): logarithmic for [`json`](../json.md), and linear for
+[`ordered_json`](../ordered_json.md) (see [`ordered_map` complexity](../ordered_map.md#complexity)). For
+`ordered_json`, patching an object that has `n` members with a patch that has `m` members therefore takes O(n·m). The
+cost also includes one copy of `apply_patch` (see the notes below).
 
 ## Notes
 
-`apply_patch` may be `#!cpp *this` itself or refer to a value contained in `#!cpp *this` (for example, a subobject
-returned by `#!cpp (*this)[key]`); it is read as it was when `merge_patch()` was called, before any modification of
-`#!cpp *this`.
+- `apply_patch` may be `#!cpp *this` itself or refer to a value contained in `#!cpp *this` (for example, a subobject
+  returned by `#!cpp (*this)[key]`); it is read as it was when `merge_patch()` was called, before any modification of
+  `#!cpp *this`. To make this possible, the function copies `apply_patch` before it modifies `#!cpp *this`, so the cost
+  includes one copy of the patch.
+- A merge patch uses `#!json null` to remove a member, so it cannot set a member to `#!json null`: applying
+  `#!json {"a":null}` to `#!json {"a":1}` gives `#!json {}`.
+- Arrays are not merged: an array in the patch replaces the target value as a whole, and a `#!json null` inside an
+  array is kept as an element. `#!json null` members of the target that the patch does not mention are preserved.
+- A `#!json null` in the patch only removes a member; it does not prevent the creation of the enclosing objects.
+  Applying `#!json {"a":{"b":null}}` to `#!json {}` gives `#!json {"a":{}}` (see example 15 in Appendix A of the RFC).
+- If `apply_patch` is not an object, it replaces the target as a whole. In particular, a `#!json null` patch turns the
+  target into `#!json null`. If `apply_patch` is an object and the target is not, the target is first replaced by an
+  empty object, so applying `#!json {}` to `#!json 1` gives `#!json {}`.
+- A merge patch cannot express every change; for example, it cannot reorder array elements or remove a specific array
+  element. Use [JSON Patch](../../features/json_patch.md) ([RFC 6902](https://tools.ietf.org/html/rfc6902)) for that.
+  [`merge_diff`](merge_diff.md) has a matching limitation, see its notes.
+- A [discarded](is_discarded.md) value is treated like any other non-object value: a discarded
+  `apply_patch` turns the target into a discarded value, and an object patch replaces a discarded target by an object
+  as described above.
 
 ## Examples
 

docs/mkdocs/docs/api/basic_json/patch.md

@@ -40,7 +40,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example:
   `"array index '-' (3) is out of range"`.
 - Throws [`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403) if a JSON pointer inside the patch
-  could not be resolved successfully in the current JSON value; example: `"key 'baz' not found"`.
+  could not be resolved successfully in the current JSON value; example: `"key baz not found"`.
 - Throws [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) if a reference token of a JSON
   pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
   `"unresolved reference token '-'"`.
@@ -53,10 +53,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) if a "move" operation's "from"
   location is a proper prefix of its "path" location.
 - Throws [`other_error.501`](../../home/exceptions.md#jsonexceptionother_error501) if "test" operation was
-  unsuccessful. A "test" operation whose "path" does not exist is unsuccessful, too: the failed lookup is reported as a
-  failed test, even if the operation has no "value" member (which would otherwise be
-  [`parse_error.105`](../../home/exceptions.md#jsonexceptionparse_error105)). Which of the two errors is reported for
-  this combination depends on the order in which the operands of a comparison are evaluated, so do not rely on it.
+  unsuccessful.
 
 ## Complexity
 
@@ -68,10 +65,6 @@ the JSON value, the complexity can usually be neglected.
 The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception
 is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.
 
-Duplicate member names inside an operation object are resolved by the parser before the patch is applied (the last one
-is kept, see [`object_t`](object_t.md#behavior)), so `#!json {"op": "add", "op": "remove", "path": "/a"}` is a
-`remove` operation.
-
 ## Examples
 
 ??? example "Example: apply a JSON patch"
@@ -115,7 +108,6 @@ is kept, see [`object_t`](object_t.md#behavior)), so `#!json {"op": "add", "op":
 - Added in version 2.0.0.
 - Added [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) and stopped relying on an internal assertion when an "add" operation's
   target location has a non-object/non-array parent in version 3.13.0.
-  This includes a `null` parent, which was previously silently converted to an object, in version 3.13.0.
 - Added [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) and stopped silently ignoring a "remove" operation whose target
   location has a non-object/non-array parent in version 3.13.0.
 - Added [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) and rejected a "move" operation whose "from" location is a proper

docs/mkdocs/docs/api/basic_json/patch_inplace.md

@@ -36,7 +36,7 @@ No guarantees, value may be corrupted by an unsuccessful patch operation.
   where an existing element is required (the "path" of "replace", the "from" of "move" and "copy"); example:
   `"array index '-' (3) is out of range"`.
 - Throws [`out_of_range.403`](../../home/exceptions.md#jsonexceptionout_of_range403) if a JSON pointer inside the patch
-  could not be resolved successfully in the current JSON value; example: `"key 'baz' not found"`.
+  could not be resolved successfully in the current JSON value; example: `"key baz not found"`.
 - Throws [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) if a reference token of a JSON
   pointer inside the patch cannot be resolved, e.g., `-` in a "remove" operation or `1a` for an array; example:
   `"unresolved reference token '-'"`.
@@ -49,10 +49,7 @@ No guarantees, value may be corrupted by an unsuccessful patch operation.
 - Throws [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) if a "move" operation's "from"
   location is a proper prefix of its "path" location.
 - Throws [`other_error.501`](../../home/exceptions.md#jsonexceptionother_error501) if "test" operation was
-  unsuccessful. A "test" operation whose "path" does not exist is unsuccessful, too: the failed lookup is reported as a
-  failed test, even if the operation has no "value" member (which would otherwise be
-  [`parse_error.105`](../../home/exceptions.md#jsonexceptionparse_error105)). Which of the two errors is reported for
-  this combination depends on the order in which the operands of a comparison are evaluated, so do not rely on it.
+  unsuccessful.
 
 ## Complexity
 
@@ -65,10 +62,6 @@ Unlike [`patch`](patch.md), `patch_inplace` applies the operation "in place" and
 That makes it faster for large documents by avoiding the copy. However, the JSON value might be corrupted if the
 function throws an exception.
 
-Duplicate member names inside an operation object are resolved by the parser before the patch is applied (the last one
-is kept, see [`object_t`](object_t.md#behavior)), so `#!json {"op": "add", "op": "remove", "path": "/a"}` is a
-`remove` operation.
-
 ## Examples
 
 ??? example "Example: apply a JSON patch in place"
@@ -113,7 +106,6 @@ is kept, see [`object_t`](object_t.md#behavior)), so `#!json {"op": "add", "op":
 - Added in version 3.11.0.
 - Added [`out_of_range.411`](../../home/exceptions.md#jsonexceptionout_of_range411) and stopped relying on an internal assertion when an "add" operation's
   target location has a non-object/non-array parent in version 3.13.0.
-  This includes a `null` parent, which was previously silently converted to an object, in version 3.13.0.
 - Added [`out_of_range.413`](../../home/exceptions.md#jsonexceptionout_of_range413) and stopped silently ignoring a "remove" operation whose target
   location has a non-object/non-array parent in version 3.13.0.
 - Added [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) and rejected a "move" operation whose "from" location is a proper

docs/mkdocs/docs/features/json_patch.md

@@ -13,12 +13,6 @@ to the current JSON value by executing all operations from the patch, yielding t
     If the document is large and the original value is no longer needed,
     [`patch_inplace`](../api/basic_json/patch_inplace.md) applies the same operations in place instead.
 
-!!! note "Duplicate member names"
-
-    Duplicate member names inside an operation object are resolved by the parser before the patch is applied (the last
-    one is kept, see [`object_t`](../api/basic_json/object_t.md#behavior)), so
-    `#!json {"op": "add", "op": "remove", "path": "/a"}` is a `remove` operation.
-
 ??? example "Example: apply a JSON Patch"
 
     The following code shows how a JSON patch is applied to a value.
@@ -47,23 +41,12 @@ flowchart LR
 
 !!! success "Invariant"
 
-    For two JSON values *source* and *target*, the following code yields true:
+    For two JSON values *source* and *target*, the following code yields always true:
 
     ```cpp
     source.patch(diff(source, target)) == target;
     ```
 
-    The equality holds up to [`operator==`](../api/basic_json/operator_eq.md), with these exceptions:
-
-    - `NaN` and [discarded](../api/basic_json/is_discarded.md) values are not equal to themselves, so the invariant
-      cannot hold for them. `diff` emits a `replace` operation for such a value, and a `NaN` in a patch is serialized
-      as `#!json null`.
-    - Numbers that compare equal produce no operation even if their types differ: `diff(1, 1.0)`, `diff(1u, 1)`, and
-      `diff(0.0, -0.0)` return `#!json []`, so the patched value keeps the number type of *source*.
-    - A [binary value](binary_values.md) in a patch is serialized as an object
-      (`#!json {"bytes":[...],"subtype":null}`), so a patch that was dumped and parsed again no longer holds a binary
-      value.
-
 ??? example "Example: create a JSON Patch from the difference of two values"
 
     The following code shows how a JSON patch is created as a diff for two JSON values.

docs/mkdocs/docs/features/merge_patch.md

@@ -2,7 +2,7 @@
 
 The library supports JSON Merge Patch ([RFC 7396](https://tools.ietf.org/html/rfc7396)) as a patch format.
 The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of
-modifications to a target resource's content. This function applies a merge patch to the current JSON value.
+modifications to a target resource's content. Applying a merge patch changes the JSON value the patch is applied to.
 
 Instead of using [JSON Pointer](json_pointer.md) to specify values to be manipulated, it describes the changes using a
 syntax that closely mimics the document being modified. Unlike [JSON Patch](json_patch.md), a JSON Merge Patch cannot
@@ -19,6 +19,18 @@ another.
     [`update`](../api/basic_json/update.md) with `merge_objects` set to `#!cpp true`; see
     [Merging objects](modifying_values.md#merging-objects).
 
+!!! note "Limitations of RFC 7396"
+
+    - A patch cannot set a member to `#!json null`, because `#!json null` removes the member:
+      `#!json {"a":1}` patched with `#!json {"a":null}` gives `#!json {}`.
+    - Arrays are replaced as a whole, never merged, and a `#!json null` inside an array is kept.
+    - `#!json null` members of the target that the patch does not mention are preserved.
+    - A `#!json null` that would remove a member of a not yet existing object still creates that object:
+      `#!json {}` patched with `#!json {"a":{"b":null}}` gives `#!json {"a":{}}`.
+    - A patch that is not an object replaces the whole target (a `#!json null` patch makes the target
+      `#!json null`); an object patch applied to a non-object target starts from an empty object.
+    - [`merge_diff`](../api/basic_json/merge_diff.md#notes) has a matching limitation for `#!json null` members.
+
 ??? example
 
     The following code shows how a JSON Merge Patch is applied to a JSON document.

docs/mkdocs/docs/home/exceptions.md

@@ -1100,8 +1100,6 @@ A JSON Patch `add` operation cannot be applied because the target location's par
 
     This exception was added in version 3.13.0. Before that, this situation hit an internal assertion (aborting the program in debug builds) or was silently ignored when assertions were disabled.
 
-    A `null` parent is rejected as well. Before version 3.13.0, an `add` into a `null` parent silently converted it to an object (e.g., `add` at `/foo/bar` turned `{"foo":null}` into `{"foo":{"bar":1}}`).
-
 ### json.exception.out_of_range.412
 
 BSON stores the length of documents, arrays, strings, and binary values in a signed 32-bit integer, and MessagePack

include/nlohmann/json.hpp

@@ -7003,6 +7003,7 @@ public:
 
             switch (parent.m_data.m_type)
             {
+                case value_t::null:
                 case value_t::object:
                 {
                     // use operator[] to add value
@@ -7034,7 +7035,6 @@ public:
 
                 // the parent of an "add" target must be an object or array
                 // (see #4292)
-                case value_t::null:
                 case value_t::string:
                 case value_t::boolean:
                 case value_t::number_integer:

single_include/nlohmann/json.hpp

@@ -42793,6 +42793,7 @@ public:
 
             switch (parent.m_data.m_type)
             {
+                case value_t::null:
                 case value_t::object:
                 {
                     // use operator[] to add value
@@ -42824,7 +42825,6 @@ public:
 
                 // the parent of an "add" target must be an object or array
                 // (see #4292)
-                case value_t::null:
                 case value_t::string:
                 case value_t::boolean:
                 case value_t::number_integer:

tests/src/unit-json_patch.cpp

@@ -15,7 +15,6 @@ using nlohmann::json;
 #endif
 
 #include <fstream>
-#include <limits>
 #include <string>
 #include <vector>
 #include "make_test_data_available.hpp"
@@ -491,9 +490,7 @@ TEST_CASE("JSON patch")
         }
 
         // A.13. Invalid JSON Patch Document
-        // not applicable: the library cannot tell the duplicate "op" members
-        // apart, because the parser resolves them (the last one is kept); see
-        // "duplicate member names in an operation" below
+        // not applicable
 
         SECTION("A.14. Escape Ordering")
         {
@@ -1518,24 +1515,6 @@ TEST_CASE("JSON patch - add to a primitive parent (regression #4292)")
 #endif
     }
 
-    SECTION("null parent")
-    {
-        json const doc = {{"foo", nullptr}};
-        json const patch = {{{"op", "add"}, {"path", "/foo/bar"}, {"value", 1}}};
-#if JSON_DIAGNOSTICS
-        CHECK_THROWS_WITH_AS(doc.patch(patch), "[json.exception.out_of_range.411] (/foo) cannot add value: the JSON Patch 'add' target's parent is of type null, but must be an object or array", json::out_of_range&);
-#else
-        CHECK_THROWS_WITH_AS(doc.patch(patch), "[json.exception.out_of_range.411] cannot add value: the JSON Patch 'add' target's parent is of type null, but must be an object or array", json::out_of_range&);
-#endif
-    }
-
-    SECTION("null document")
-    {
-        json const doc = nullptr;
-        json const patch = {{{"op", "add"}, {"path", "/-"}, {"value", 1}}};
-        CHECK_THROWS_WITH_AS(doc.patch(patch), "[json.exception.out_of_range.411] cannot add value: the JSON Patch 'add' target's parent is of type null, but must be an object or array", json::out_of_range&);
-    }
-
     SECTION("number parent")
     {
         json const doc = {{"foo", 1}};
@@ -2124,204 +2103,3 @@ TEST_CASE_TEMPLATE("JSON patch - diff round trip on hand-made documents", Json,
         roundtrip(Json(1), Json::parse("[1]"));
     }
 }
-
-TEST_CASE("JSON patch - behavior documented in the API reference")
-{
-    SECTION("duplicate member names in an operation")
-    {
-        // RFC 6902, A.13: the parser resolves the duplicates (the last one
-        // is kept), so this is a "remove" and not an "add"
-        const json patch = json::parse(R"([{"op": "add", "op": "remove", "path": "/a"}])");
-        CHECK(patch == json::parse(R"([{"op": "remove", "path": "/a"}])"));
-        CHECK(json({{"a", 1}, {"b", 2}}).patch(patch) == json({{"b", 2}}));
-    }
-
-    SECTION("add with a leading zero in an array index")
-    {
-        const json patch = R"([{"op": "add", "path": "/01", "value": 1}])"_json;
-        json doc = json::array();
-#if !defined(JSON_NOEXCEPTION)
-        CHECK_THROWS_AS(doc.patch(patch), json::parse_error&);
-        CHECK_THROWS_AS(doc.patch_inplace(patch), json::parse_error&);
-#endif
-        CHECK(doc == json::array());
-    }
-
-    SECTION("test compares numbers by value")
-    {
-        const json doc = R"({"a": 1, "b": 0, "c": 1.5})"_json;
-        CHECK(doc.patch(R"([{"op": "test", "path": "/a", "value": 1.0}])"_json) == doc);
-        CHECK(doc.patch(R"([{"op": "test", "path": "/b", "value": -0.0}])"_json) == doc);
-        CHECK(doc.patch(R"([{"op": "test", "path": "/c", "value": 1.5}])"_json) == doc);
-        CHECK_THROWS_AS(doc.patch(R"([{"op": "test", "path": "/a", "value": 2}])"_json), json::other_error&);
-        CHECK_THROWS_AS(doc.patch(R"([{"op": "test", "path": "/a", "value": "1"}])"_json), json::other_error&);
-    }
-
-    SECTION("test ignores the order of object members, but not the order of array elements")
-    {
-        const json doc = R"({"o": {"x": 1, "y": 2}, "a": [1, 2]})"_json;
-        CHECK(doc.patch(R"([{"op": "test", "path": "/o", "value": {"y": 2, "x": 1}}])"_json) == doc);
-        CHECK(doc.patch(R"([{"op": "test", "path": "/a", "value": [1, 2]}])"_json) == doc);
-        CHECK_THROWS_AS(doc.patch(R"([{"op": "test", "path": "/a", "value": [2, 1]}])"_json), json::other_error&);
-    }
-
-    SECTION("test on a path that does not exist")
-    {
-        const json doc = R"({"a": 1})"_json;
-        // with a "value" member, the failed lookup is a failed test
-        CHECK_THROWS_AS(doc.patch(R"([{"op": "test", "path": "/b", "value": 1}])"_json), json::other_error&);
-        CHECK_THROWS_AS(doc.patch(R"([{"op": "test", "path": "/b", "value": null}])"_json), json::other_error&);
-        // without it, an exception is thrown, too; which one depends on the
-        // order of evaluation of the operands of ==, so it is not checked
-        CHECK_THROWS(doc.patch(R"([{"op": "test", "path": "/b"}])"_json));
-    }
-
-    SECTION("patch() has the strong guarantee")
-    {
-        const json doc = R"({"a": [1, 2], "o": {"k": "v"}})"_json;
-        const json before = doc;
-
-        const std::vector<json> failing =
-        {
-            // remove of a member that does not exist
-            R"([{"op": "add", "path": "/n", "value": 1}, {"op": "remove", "path": "/missing"}])"_json,
-            // replace of a member that does not exist
-            R"([{"op": "remove", "path": "/a/0"}, {"op": "replace", "path": "/missing", "value": 1}])"_json,
-            // move from a member that does not exist
-            R"([{"op": "add", "path": "/n", "value": 1}, {"op": "move", "from": "/missing", "path": "/m"}])"_json,
-            // copy from a member that does not exist
-            R"([{"op": "add", "path": "/n", "value": 1}, {"op": "copy", "from": "/missing", "path": "/m"}])"_json,
-            // out-of-range array index
-            R"([{"op": "add", "path": "/n", "value": 1}, {"op": "add", "path": "/a/5", "value": 1}])"_json,
-            // failing test after a successful operation
-            R"([{"op": "remove", "path": "/o"}, {"op": "test", "path": "/a", "value": []}])"_json,
-        };
-        for (const auto& patch : failing)
-        {
-            CAPTURE(patch.dump())
-            CHECK_THROWS_AS(doc.patch(patch), json::exception&);
-            CHECK(doc == before);
-
-            json copy = doc;
-            CHECK_THROWS_AS(copy.patch(patch), json::exception&);
-            CHECK(copy == before);
-        }
-    }
-}
-
-TEST_CASE("JSON patch - diff behavior documented in the API reference")
-{
-    SECTION("path is a verbatim prefix")
-    {
-        // not escaped and not validated
-        CHECK(json::diff(1, 2) == R"([{"op": "replace", "path": "", "value": 2}])"_json);
-        CHECK(json::diff(1, 2, "abc") == R"([{"op": "replace", "path": "abc", "value": 2}])"_json);
-        CHECK(json::diff(1, 2, "/root") == R"([{"op": "replace", "path": "/root", "value": 2}])"_json);
-        // an escaped token in a non-root prefix is kept as given
-        CHECK(json::diff(R"({"a": 1})"_json, R"({"a": 2})"_json, "/x~1y/~0")
-              == R"([{"op": "replace", "path": "/x~1y/~0/a", "value": 2}])"_json);
-        CHECK(json::diff(R"({"a": 1})"_json, R"({"a": 2})"_json, "/p")
-              == R"([{"op": "replace", "path": "/p/a", "value": 2}])"_json);
-    }
-
-    SECTION("keys are escaped in the paths")
-    {
-        const json source = json::object();
-        const json target =
-        {
-            {"", 0}, {"/", 1}, {"~", 2}, {"~1", 3}, {"~01", 4}
-        };
-        const json patch = json::diff(source, target);
-        REQUIRE(patch.size() == 5);
-
-        // the order of the operations is not checked
-        json paths = json::object();
-        for (const auto& op : patch)
-        {
-            CHECK(op["op"] == "add");
-            paths[op["path"].get<std::string>()] = op["value"];
-        }
-        CHECK(paths == json({{"/", 0}, {"/~1", 1}, {"/~0", 2}, {"/~01", 3}, {"/~001", 4}}));
-        CHECK(source.patch(patch) == target);
-    }
-
-    SECTION("NaN is not equal to itself")
-    {
-        const json nan = std::numeric_limits<json::number_float_t>::quiet_NaN();
-        const json patch = json::diff(nan, nan);
-        CHECK(patch.size() == 1);
-        CHECK(patch[0]["op"] == "replace");
-        CHECK(patch[0]["path"] == "");
-        CHECK(patch[0]["value"].is_number_float());
-        CHECK(nan.patch(patch) != nan);
-
-        // a NaN in a patch is serialized as null
-        CHECK(json::parse(patch.dump())[0]["value"].is_null());
-
-        const json nested = {{"a", {1, nan}}};
-        const json nested_patch = json::diff(nested, nested);
-        CHECK(nested_patch.size() == 1);
-        CHECK(nested_patch[0]["path"] == "/a/1");
-
-        // infinity is equal to itself
-        const json inf = std::numeric_limits<json::number_float_t>::infinity();
-        CHECK(json::diff(inf, inf).empty());
-    }
-
-    SECTION("discarded values are not equal to themselves")
-    {
-        const json discarded(json::value_t::discarded);
-        const json patch = json::diff(discarded, discarded);
-        CHECK(patch.size() == 1);
-        CHECK(patch[0]["op"] == "replace");
-        CHECK(patch[0]["path"] == "");
-        CHECK(patch[0]["value"].is_discarded());
-        CHECK(discarded.patch(patch) != discarded);
-    }
-
-    SECTION("numbers that compare equal produce no operation")
-    {
-        CHECK(json::diff(json(1), json(1.0)).empty());
-        CHECK(json::diff(json(1.0), json(1)).empty());
-        CHECK(json::diff(json(1U), json(1)).empty());
-        CHECK(json::diff(json(1), json(1U)).empty());
-        CHECK(json::diff(json(0.0), json(-0.0)).empty());
-
-        // the patched value keeps the number type of the source
-        const json source = 1;
-        const json patched = source.patch(json::diff(source, json(1.0)));
-        CHECK(patched.is_number_integer());
-        CHECK(patched == json(1.0));
-
-        // different values are replaced
-        CHECK(json::diff(json(1), json(2.0)) == R"([{"op": "replace", "path": "", "value": 2.0}])"_json);
-        CHECK(json::diff(json(1), json(-1)) == R"([{"op": "replace", "path": "", "value": -1}])"_json);
-        CHECK(json::diff(json(1.0), json(1.5)) == R"([{"op": "replace", "path": "", "value": 1.5}])"_json);
-        CHECK(json::diff(json(1), json("1")) == R"([{"op": "replace", "path": "", "value": "1"}])"_json);
-    }
-
-    SECTION("binary values")
-    {
-        const json a = json::binary({1, 2});
-        const json b = json::binary({1, 3});
-        CHECK(json::diff(a, a).empty());
-
-        const json patch = json::diff(a, b);
-        CHECK(patch.size() == 1);
-        CHECK(patch[0]["op"] == "replace");
-        CHECK(patch[0]["path"] == "");
-        CHECK(patch[0]["value"].is_binary());
-        CHECK(a.patch(patch) == b);
-
-        // serialized, the binary value is an object
-        const json parsed = json::parse(patch.dump());
-        CHECK(parsed[0]["value"].is_object());
-        CHECK(parsed[0]["value"] == R"({"bytes": [1, 3], "subtype": null})"_json);
-    }
-
-    SECTION("a difference as a whole is a replace of the root")
-    {
-        CHECK(json::diff(json::array({1}), json::object()) == R"([{"op": "replace", "path": "", "value": {}}])"_json);
-        CHECK(json::diff(json(nullptr), json::array()) == R"([{"op": "replace", "path": "", "value": []}])"_json);
-    }
-}

tests/src/unit-merge_patch.cpp

@@ -423,3 +423,86 @@ TEST_CASE("merge_patch() with an argument that aliases *this (#5641)")
         }
     }
 }
+
+TEST_CASE("JSON Merge Patch on non-object, discarded, and binary values")
+{
+    SECTION("an empty object patch turns a non-object target into an empty object")
+    {
+        json target = 1;
+        target.merge_patch(json::object());
+        CHECK(target == json::object());
+
+        json from_null;
+        from_null.merge_patch(json::object());
+        CHECK(from_null == json::object());
+    }
+
+    SECTION("a non-object patch replaces a deeply nested target")
+    {
+        // checked by type, since == recurses
+        SECTION("number")
+        {
+            json target = json::parse(nested_objects(1000, 0));
+            target.merge_patch(json(42));
+            CHECK(target.is_number_integer());
+            CHECK(target.get<int>() == 42);
+        }
+
+        SECTION("array")
+        {
+            json target = json::parse(nested_objects(1000, 0));
+            target.merge_patch(json({1, nullptr}));
+            CHECK(target.is_array());
+            CHECK(target.size() == 2);
+            CHECK(target[1].is_null());
+        }
+
+        SECTION("null")
+        {
+            json target = json::parse(nested_objects(1000, 0));
+            target.merge_patch(json(nullptr));
+            CHECK(target.is_null());
+        }
+    }
+
+    SECTION("discarded values")
+    {
+        const json discarded(json::value_t::discarded);
+
+        // a discarded patch is not an object and replaces the target
+        json target = {{"a", 1}};
+        target.merge_patch(discarded);
+        CHECK(target.is_discarded());
+
+        // a discarded target is replaced by an empty object first
+        json discarded_target(json::value_t::discarded);
+        discarded_target.merge_patch(json({{"a", 1}}));
+        CHECK(discarded_target == json({{"a", 1}}));
+
+        json both(json::value_t::discarded);
+        both.merge_patch(discarded);
+        CHECK(both.is_discarded());
+    }
+
+    SECTION("binary values")
+    {
+        const json bin = json::binary({1, 2, 3}, 7);
+
+        // a binary patch is not an object and replaces the target
+        json target = {{"a", 1}};
+        target.merge_patch(bin);
+        CHECK(target.is_binary());
+        CHECK(target.get_binary() == bin.get_binary());
+
+        // a binary target is replaced by an object
+        json binary_target = bin;
+        binary_target.merge_patch(json({{"a", 1}}));
+        CHECK(binary_target == json({{"a", 1}}));
+
+        // binary values nested in the patch are kept
+        json nested = json::object();
+        nested.merge_patch(json({{"a", bin}}));
+        CHECK(nested["a"].is_binary());
+        CHECK(nested["a"].get_binary() == bin.get_binary());
+    }
+}