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Fix element path for map/unordered_map JSON_DIAGNOSTICS errors (#5681)

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When converting a JSON array to std::map or std::unordered_map with a
non-string key, each element must itself be a [key, value] array. If an
element is not an array, from_json() threw type_error 302 with the outer
array's value (&j) as the exception context, so with JSON_DIAGNOSTICS
enabled the message pointed at the whole array instead of the offending
element (e.g. "(/outer/m)" instead of "(/outer/m/2)"), even though the
message text already described the element's type.

Both from_json() overloads now pass the element (&p) as the context, so
the reported JSON Pointer matches the type named in the message, the
same way std::vector<std::vector<T>> and similar conversions already do.

Fixes #5668.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 20:06:55 +02:00
committed by GitHub
parent fc4c9c3446
commit 678fd3017b
3 changed files with 29 additions and 4 deletions
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4
include/nlohmann/detail/conversions/from_json.hpp
View File

@@ -568,7 +568,7 @@ inline void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allo
{
if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &j));
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &p));
}
m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
}
@@ -588,7 +588,7 @@ inline void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Has
{
if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &j));
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &p));
}
m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
}

4
single_include/nlohmann/json.hpp
View File

@@ -6065,7 +6065,7 @@ inline void from_json(const BasicJsonType& j, std::map<Key, Value, Compare, Allo
{
if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &j));
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &p));
}
m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
}
@@ -6085,7 +6085,7 @@ inline void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Has
{
if (JSON_HEDLEY_UNLIKELY(!p.is_array()))
{
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &j));
JSON_THROW(type_error::create(302, concat("type must be array, but is ", p.type_name()), &p));
}
m.emplace(p.at(0).template get<Key>(), p.at(1).template get<Value>());
}

25
tests/src/unit-diagnostics.cpp
View File

@@ -17,6 +17,9 @@
#include <nlohmann/json.hpp>
using nlohmann::json;
#include <map>
#include <unordered_map>
TEST_CASE("Better diagnostics")
{
SECTION("empty JSON Pointer")
@@ -331,6 +334,28 @@ TEST_CASE("Regression tests for extended diagnostics")
}
}
SECTION("Regression test for issue #5668 - wrong path for std::map/unordered_map with non-string keys")
{
// a map with non-string keys is read from an array of [key, value] arrays;
// element 2 of "m" is not an array, so the path must point at "m/2", not "m"
json j;
j["outer"]["m"] = json::array({json::array({1, 2}), json::array({3, 4}), 5});
SECTION("std::map")
{
CHECK_THROWS_WITH_AS((j["outer"]["m"].get<std::map<int, int>>()),
"[json.exception.type_error.302] (/outer/m/2) type must be array, "
"but is number", json::type_error);
}
SECTION("std::unordered_map")
{
CHECK_THROWS_WITH_AS((j["outer"]["m"].get<std::unordered_map<int, int>>()),
"[json.exception.type_error.302] (/outer/m/2) type must be array, "
"but is number", json::type_error);
}
}
SECTION("Regression test - swap(array_t&)/swap(object_t&) must update JSON_DIAGNOSTICS parent pointers")
{
// swap(array_t&)