Guard the null value of a value-initialized iterator; drop the unneeded found flag

With the root's byte range, diagnostics() reaches get_byte_positions() also
with JSON_DIAGNOSTICS when there is no value, as for a value-initialized
iterator (invalid_iterator.212). get_byte_positions() now returns no range
for a null value, the same change as #6003, so either can be merged first.

In the view, a value that value_path() does not find leaves no tokens, so the
found flag added nothing to the tokens.empty() test.

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

docs/mkdocs/docs/api/basic_json/insert.md

@@ -65,17 +65,7 @@ the same index, which is now a different value.
 
 ## Exception safety
 
-1. Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
-2. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
-   value may be partially modified, but it stays a valid array.
-3. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
-   value may be partially modified, but it stays a valid array.
-4. Basic guarantee: if an exception is thrown while the elements are copied (for example, `std::bad_alloc`), the JSON
-   value may be partially modified, but it stays a valid array.
-5. Basic guarantee: if an exception is thrown while the members are copied (for example, `std::bad_alloc`), the JSON
-   value may be partially modified, but it stays a valid object.
-
-The exceptions listed below are thrown before the JSON value is changed.
+Strong exception safety: if an exception occurs, the original value stays intact.
 
 ## Exceptions
 

docs/mkdocs/docs/api/macros/json_diagnostic_positions.md

@@ -35,6 +35,9 @@ Note that enabling this macro increases the size of every JSON value by two `std
 overhead to parsing, copying JSON value objects, and the generation of error messages for exceptions. It also causes
 these values to be reported in those error messages.
 
+If [`JSON_DIAGNOSTICS`](json_diagnostics.md) is also set, the message contains the path and the byte range, such as
+`(/1) (bytes 4-8)`. An exception about the root value has no path and only the range, such as `(bytes 0-4)`.
+
 ## Default definition
 
 The default value is `0` (position diagnostics are switched off).

include/nlohmann/detail/exceptions.hpp

@@ -198,18 +198,19 @@ class exception : public std::exception
             // all other parent types (primitives) contribute no token
         }
 
-        if (tokens.empty())
+        // the root value has no path, but still has a byte range
+        std::string prefix;
+        if (!tokens.empty())
         {
-            return "";
+            const auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
+                                             [](const std::string & a, const std::string & b)
+            {
+                return concat(a, '/', detail::escape(b));
+            });
+            prefix = concat('(', str, ") ");
         }
 
-        auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
-                                   [](const std::string & a, const std::string & b)
-        {
-            return concat(a, '/', detail::escape(b));
-        });
-
-        return concat('(', str, ") ", get_byte_positions(leaf_element));
+        return concat(prefix, get_byte_positions(leaf_element));
 #else
         return get_byte_positions(leaf_element);
 #endif
@@ -222,7 +223,8 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        // a value-initialized iterator has no value (invalid_iterator.212)
+        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }

include/nlohmann/detail/view/errors.hpp

@@ -234,8 +234,7 @@ void value_range(const document_data& d, const node* n, std::size_t& start, std:
 
 /// the context basic_json puts in front of the message of an exception about
 /// a value: "(/path) " with JSON_DIAGNOSTICS (none for the root), then
-/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (with JSON_DIAGNOSTICS, only
-/// if there is a path)
+/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (also for the root)
 ///
 /// This and the throw helpers that take an error_site are templates, so that
 /// the path and range code is instantiated only where an exception can be
@@ -256,19 +255,19 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
-    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
-    if (!found || tokens.empty())
+    // a value that is not found leaves no tokens, like the root
+    static_cast<void>(edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens));
+    if (!tokens.empty())
     {
-        // context is still empty; returning it keeps the copy elided (-Wnrvo)
-        return context;
+        // the root value has no path, but still has a byte range
+        std::string path;
+        for (const std::string& token : tokens)
+        {
+            path.push_back('/');
+            path += detail::escape(token);
+        }
+        context = concat('(', path, ") ");
     }
-    std::string path;
-    for (const std::string& token : tokens)
-    {
-        path.push_back('/');
-        path += detail::escape(token);
-    }
-    context = concat('(', path, ") ");
 #endif
 #if JSON_DIAGNOSTIC_POSITIONS
     std::size_t start = 0;

include/nlohmann/json.hpp

@@ -4914,30 +4914,6 @@ public:
         return {it, res.second};
     }
 
-  private:
-    /// Sets the parents of a value when it goes out of scope, also when an
-    /// exception is thrown: a container insertion that throws may already
-    /// have added elements, whose parents must be set for the value to stay
-    /// valid (basic exception guarantee). Does nothing without JSON_DIAGNOSTICS.
-    class set_parents_on_exit
-    {
-      public:
-        explicit set_parents_on_exit(basic_json* v) noexcept : m_value(v) {}
-        set_parents_on_exit(const set_parents_on_exit&) = delete;
-        set_parents_on_exit& operator=(const set_parents_on_exit&) = delete;
-        set_parents_on_exit(set_parents_on_exit&&) = delete;
-        set_parents_on_exit& operator=(set_parents_on_exit&&) = delete;
-
-        ~set_parents_on_exit()
-        {
-            m_value->set_parents();
-        }
-
-      private:
-        basic_json* m_value;
-    };
-
-  public:
     /// Helper for insertion of an iterator
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
@@ -4947,7 +4923,6 @@ public:
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
 
-        const set_parents_on_exit parents(this);
         auto insert_pos = std::distance(m_data.m_value.array->begin(), pos.m_it.array_iterator);
         m_data.m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
         result.m_it.array_iterator = m_data.m_value.array->begin() + insert_pos;
@@ -4956,6 +4931,7 @@ public:
         // result.m_it.array_iterator = m_data.m_value.array->insert(pos.m_it.array_iterator, cnt, val);
         // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
 
+        set_parents();
         return result;
     }
 
@@ -4975,16 +4951,8 @@ public:
             throw_iterator_from_other_value(this);
         }
 
-        // vector::insert has no effects if copying a single element to the
-        // end throws; elsewhere, it may already have shifted the elements, so
-        // copy first and insert by move, which cannot throw but by allocating
-        if (pos.m_it.array_iterator == m_data.m_value.array->end())
-        {
-            return insert_iterator(pos, val);
-        }
-
-        basic_json tmp(val);
-        return insert_iterator(pos, std::move(tmp));
+        // insert to array and return iterator
+        return insert_iterator(pos, val);
     }
 
     /// @brief inserts element into array
@@ -5116,8 +5084,8 @@ public:
             detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterators first and last must point to objects", this);
         }
 
-        const set_parents_on_exit parents(this);
         m_data.m_value.object->insert(first.m_it.object_iterator, last.m_it.object_iterator);
+        set_parents();
     }
 
     /// @brief updates a JSON object from another object, overwriting existing keys

single_include/nlohmann/json.hpp

@@ -5695,18 +5695,19 @@ class exception : public std::exception
             // all other parent types (primitives) contribute no token
         }
 
-        if (tokens.empty())
+        // the root value has no path, but still has a byte range
+        std::string prefix;
+        if (!tokens.empty())
         {
-            return "";
+            const auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
+                                             [](const std::string & a, const std::string & b)
+            {
+                return concat(a, '/', detail::escape(b));
+            });
+            prefix = concat('(', str, ") ");
         }
 
-        auto str = std::accumulate(tokens.rbegin(), tokens.rend(), std::string{},
-                                   [](const std::string & a, const std::string & b)
-        {
-            return concat(a, '/', detail::escape(b));
-        });
-
-        return concat('(', str, ") ", get_byte_positions(leaf_element));
+        return concat(prefix, get_byte_positions(leaf_element));
 #else
         return get_byte_positions(leaf_element);
 #endif
@@ -5719,7 +5720,8 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        // a value-initialized iterator has no value (invalid_iterator.212)
+        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }
@@ -42706,30 +42708,6 @@ public:
         return {it, res.second};
     }
 
-  private:
-    /// Sets the parents of a value when it goes out of scope, also when an
-    /// exception is thrown: a container insertion that throws may already
-    /// have added elements, whose parents must be set for the value to stay
-    /// valid (basic exception guarantee). Does nothing without JSON_DIAGNOSTICS.
-    class set_parents_on_exit
-    {
-      public:
-        explicit set_parents_on_exit(basic_json* v) noexcept : m_value(v) {}
-        set_parents_on_exit(const set_parents_on_exit&) = delete;
-        set_parents_on_exit& operator=(const set_parents_on_exit&) = delete;
-        set_parents_on_exit(set_parents_on_exit&&) = delete;
-        set_parents_on_exit& operator=(set_parents_on_exit&&) = delete;
-
-        ~set_parents_on_exit()
-        {
-            m_value->set_parents();
-        }
-
-      private:
-        basic_json* m_value;
-    };
-
-  public:
     /// Helper for insertion of an iterator
     /// @note: This uses std::distance to support GCC 4.8,
     ///        see https://github.com/nlohmann/json/pull/1257
@@ -42739,7 +42717,6 @@ public:
         iterator result(this);
         JSON_ASSERT(m_data.m_value.array != nullptr);
 
-        const set_parents_on_exit parents(this);
         auto insert_pos = std::distance(m_data.m_value.array->begin(), pos.m_it.array_iterator);
         m_data.m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
         result.m_it.array_iterator = m_data.m_value.array->begin() + insert_pos;
@@ -42748,6 +42725,7 @@ public:
         // result.m_it.array_iterator = m_data.m_value.array->insert(pos.m_it.array_iterator, cnt, val);
         // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
 
+        set_parents();
         return result;
     }
 
@@ -42767,16 +42745,8 @@ public:
             throw_iterator_from_other_value(this);
         }
 
-        // vector::insert has no effects if copying a single element to the
-        // end throws; elsewhere, it may already have shifted the elements, so
-        // copy first and insert by move, which cannot throw but by allocating
-        if (pos.m_it.array_iterator == m_data.m_value.array->end())
-        {
-            return insert_iterator(pos, val);
-        }
-
-        basic_json tmp(val);
-        return insert_iterator(pos, std::move(tmp));
+        // insert to array and return iterator
+        return insert_iterator(pos, val);
     }
 
     /// @brief inserts element into array
@@ -42908,8 +42878,8 @@ public:
             detail::throw_literal<invalid_iterator>(detail::exception_id::iterator_from_other_value, "iterators first and last must point to objects", this);
         }
 
-        const set_parents_on_exit parents(this);
         m_data.m_value.object->insert(first.m_it.object_iterator, last.m_it.object_iterator);
+        set_parents();
     }
 
     /// @brief updates a JSON object from another object, overwriting existing keys

single_include/nlohmann/json_view.hpp

@@ -5076,8 +5076,7 @@ void value_range(const document_data& d, const node* n, std::size_t& start, std:
 
 /// the context basic_json puts in front of the message of an exception about
 /// a value: "(/path) " with JSON_DIAGNOSTICS (none for the root), then
-/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (with JSON_DIAGNOSTICS, only
-/// if there is a path)
+/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (also for the root)
 ///
 /// This and the throw helpers that take an error_site are templates, so that
 /// the path and range code is instantiated only where an exception can be
@@ -5098,19 +5097,19 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
-    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
-    if (!found || tokens.empty())
+    // a value that is not found leaves no tokens, like the root
+    static_cast<void>(edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens));
+    if (!tokens.empty())
     {
-        // context is still empty; returning it keeps the copy elided (-Wnrvo)
-        return context;
+        // the root value has no path, but still has a byte range
+        std::string path;
+        for (const std::string& token : tokens)
+        {
+            path.push_back('/');
+            path += detail::escape(token);
+        }
+        context = concat('(', path, ") ");
     }
-    std::string path;
-    for (const std::string& token : tokens)
-    {
-        path.push_back('/');
-        path += detail::escape(token);
-    }
-    context = concat('(', path, ") ");
 #endif
 #if JSON_DIAGNOSTIC_POSITIONS
     std::size_t start = 0;

tests/src/unit-allocator.cpp

@@ -12,7 +12,6 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <functional>
 #include <valarray>
 #if JSON_HAS_RANGES
     #include <ranges>
@@ -805,222 +804,3 @@ TEST_CASE("a failed allocation leaves the value unchanged")
 #endif
 }
 #endif
-
-// the no-exceptions CI job has no std::bad_alloc to catch; with iterator
-// debugging (MSVC STL debug builds) containers allocate inside noexcept
-// functions, so failing an allocation there terminates the program
-#if !defined(JSON_NOEXCEPTION) && !(defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
-namespace
-{
-// whether every child of j names j as its parent (always true without
-// JSON_DIAGNOSTICS, where no parents are stored)
-template<class BasicJsonType>
-bool children_name_their_parent(const BasicJsonType& j)
-{
-#if JSON_DIAGNOSTICS
-    if (j.is_array())
-    {
-        for (const auto& element : *j.m_data.m_value.array)
-        {
-            if (element.m_parent != &j)
-            {
-                return false;
-            }
-        }
-    }
-    else if (j.is_object())
-    {
-        for (const auto& element : *j.m_data.m_value.object)
-        {
-            if (element.second.m_parent != &j)
-            {
-                return false;
-            }
-        }
-    }
-#else
-    static_cast<void>(j);
-#endif
-    return true;
-}
-
-enum class guarantee
-{
-    basic, // the value stays valid and keeps its type
-    strong // the value is unchanged
-};
-
-// Runs op on a fresh value make() with the 0th, 1st, 2nd, ... allocation made
-// by the library failing in turn, until op completes. Every failed attempt
-// must have thrown std::bad_alloc and left the value valid, with all parent
-// pointers intact (copying a value asserts the invariant), and for the strong
-// guarantee exactly as it was.
-template<class BasicJsonType>
-void check_exception_guarantee(guarantee g,
-                               const std::function<BasicJsonType()>& make,
-                               const std::function<void(BasicJsonType&)>& op)
-{
-    fail_at_alloc_call = -1;
-
-    bool completed = false;
-    std::size_t failures = 0;
-    for (std::size_t n = 0; !completed; ++n)
-    {
-        CAPTURE(n)
-        REQUIRE(n < 1000);
-
-        BasicJsonType j = make();
-        const std::string before = j.dump();
-        const auto type_before = j.type();
-
-        alloc_call_count = 0;
-        fail_at_alloc_call = static_cast<long>(n);
-        try
-        {
-            op(j);
-            completed = true;
-        }
-        catch (const std::bad_alloc&)
-        {
-            ++failures;
-        }
-        fail_at_alloc_call = -1;
-
-        if (!completed)
-        {
-            CHECK((j.type() == type_before));
-            CHECK(children_name_their_parent(j));
-            const BasicJsonType copy(j); // NOLINT(performance-unnecessary-copy-initialization): the copy is the point, it allocates
-            CHECK(copy.dump() == j.dump());
-            if (g == guarantee::strong)
-            {
-                CHECK(j.dump() == before);
-            }
-        }
-    }
-
-    // the operation allocates, so at least one attempt must have failed
-    CHECK(failures > 0);
-}
-
-template<class BasicJsonType>
-void check_insert_exception_guarantees()
-{
-    using json_t = BasicJsonType;
-    using make_t = std::function<json_t()>;
-
-    // strings of this length do not fit into the small string buffer, so
-    // copying them allocates
-    const json_t val = std::string(64, 'x');
-    const json_t source = json_t::array({std::string(64, 'p'), std::string(64, 'q'), std::string(64, 'r')});
-
-    for (const bool spare_capacity :
-            {
-                false, true
-            })
-    {
-        CAPTURE(spare_capacity)
-
-        // [ "aaa...", "bbb...", "ccc..." ], with a spare slot if requested
-        const make_t make = [spare_capacity]()
-        {
-            json_t j = json_t::array({std::string(64, 'a'), std::string(64, 'b'), std::string(64, 'c')});
-            if (spare_capacity)
-            {
-                j.push_back(std::string(64, 'd'));
-                j.erase(3);
-            }
-            return json_t(std::move(j));
-        };
-
-        for (const bool at_end :
-                {
-                    false, true
-                })
-        {
-            CAPTURE(at_end)
-
-            SECTION("insert(pos, const basic_json&)")
-            {
-                check_exception_guarantee<json_t>(guarantee::strong, make, [&](json_t& j)
-                {
-                    j.insert(at_end ? j.end() : j.begin() + 1, val);
-                });
-            }
-
-            SECTION("insert(pos, basic_json&&)")
-            {
-                check_exception_guarantee<json_t>(guarantee::strong, make, [&](json_t& j)
-                {
-                    j.insert(at_end ? j.end() : j.begin() + 1, json_t(val));
-                });
-            }
-
-            SECTION("insert(pos, size_type, const basic_json&)")
-            {
-                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
-                {
-                    j.insert(at_end ? j.end() : j.begin() + 1, 3, val);
-                });
-            }
-
-            SECTION("insert(pos, const_iterator, const_iterator)")
-            {
-                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
-                {
-                    j.insert(at_end ? j.end() : j.begin() + 1, source.begin(), source.end());
-                });
-            }
-
-            SECTION("insert(pos, initializer_list_t)")
-            {
-                check_exception_guarantee<json_t>(guarantee::basic, make, [&](json_t& j)
-                {
-                    j.insert(at_end ? j.end() : j.begin() + 1, {val, val});
-                });
-            }
-        }
-    }
-
-    SECTION("insert(const_iterator, const_iterator) for objects")
-    {
-        const json_t members = {{"m", std::string(64, 'm')}, {"n", std::string(64, 'n')}, {"o", std::string(64, 'o')}};
-
-        SECTION("no member exists yet")
-        {
-            check_exception_guarantee<json_t>(guarantee::basic, []()
-            {
-                return json_t({{"a", 1}});
-            }, [&](json_t& j)
-            {
-                j.insert(members.begin(), members.end());
-            });
-        }
-
-        SECTION("some members exist already")
-        {
-            check_exception_guarantee<json_t>(guarantee::basic, []()
-            {
-                return json_t({{"a", 1}, {"n", std::string(64, 'x')}});
-            }, [&](json_t& j)
-            {
-                j.insert(members.begin(), members.end());
-            });
-        }
-    }
-}
-} // namespace
-
-TEST_CASE("insert() provides its documented exception guarantees (#5986)")
-{
-    SECTION("std::map-backed object_t")
-    {
-        check_insert_exception_guarantees<nlohmann::json::with_allocator_t<nth_alloc_fails_allocator>>();
-    }
-
-    SECTION("ordered_map-backed object_t")
-    {
-        check_insert_exception_guarantees<nlohmann::ordered_json::with_allocator_t<nth_alloc_fails_allocator>>();
-    }
-}
-#endif

tests/src/unit-diagnostic-positions.cpp

@@ -193,6 +193,28 @@ TEST_CASE("Better diagnostics with positions")
         check_conversion(300);
     }
 
+    SECTION("exception about the root value (#5987)")
+    {
+        // the root has no path, but still has a byte range
+        const json root = json::parse("true");
+        const json nested = json::parse("[1, true]");
+        const json constructed = true;
+#if JSON_DIAGNOSTICS
+        CHECK_THROWS_WITH_AS(root.get<std::string>(),
+                             "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean", json::type_error);
+        CHECK_THROWS_WITH_AS(nested[1].get<std::string>(),
+                             "[json.exception.type_error.302] (/1) (bytes 4-8) type must be string, but is boolean", json::type_error);
+#else
+        CHECK_THROWS_WITH_AS(root.get<std::string>(),
+                             "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean", json::type_error);
+        CHECK_THROWS_WITH_AS(nested[1].get<std::string>(),
+                             "[json.exception.type_error.302] (bytes 4-8) type must be string, but is boolean", json::type_error);
+#endif
+        // a value without positions gets no range and no stray whitespace
+        CHECK_THROWS_WITH_AS(constructed.get<std::string>(),
+                             "[json.exception.type_error.302] type must be string, but is boolean", json::type_error);
+    }
+
     SECTION("JSON patch add to primitive parent (#4292)")
     {
         // the JSON Patch "add" target /foo/bar/baz has a string parent
@@ -243,3 +265,14 @@ TEST_CASE("values read from a binary format have no positions")
         check_no_positions(j);
     }
 }
+
+TEST_CASE("comparing a value-initialized iterator throws invalid_iterator.212")
+{
+    // such an iterator has no value to take the byte positions from; the
+    // comparison used to dereference the null pointer instead of throwing
+    json j = {1, 2};
+    json::iterator it{};
+    CHECK_THROWS_WITH_AS(it == j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+    CHECK_THROWS_WITH_AS(it < j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+    CHECK_THROWS_WITH_AS(j.begin() == it, "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+}

tests/src/unit-json_view_builder.cpp

@@ -692,7 +692,7 @@ TEST_CASE("json_view builder: fraction digits")
             check_same(number);
             check_same("[" + number + "]");
             std::string pair;
-            pair.reserve((number.size() * 2) + 3);
+            pair.reserve(number.size() * 2 + 3);
             pair += '[';
             pair += number;
             pair += ',';

tests/src/unit-json_view_positions.cpp

@@ -300,6 +300,27 @@ TEST_CASE("json_view materialize() source positions")
             static_cast<void>(j.at("list").at(1).get<int>());
         }));
     }
+
+    SECTION("exception about the root value (#5987)")
+    {
+        const json_document root = json_document::parse("true");
+        const json_document nested = json_document::parse("[1, true]");
+        CHECK(json_view_test::exception_of_call([&]
+        {
+            static_cast<void>(root.root().get<std::string>());
+        }) == "[json.exception.type_error.302] (bytes 0-4) type must be string, but is boolean");
+#if JSON_DIAGNOSTICS
+        CHECK(json_view_test::exception_of_call([&]
+        {
+            static_cast<void>(nested.root()[1].get<std::string>());
+        }) == "[json.exception.type_error.302] (/1) (bytes 4-8) type must be string, but is boolean");
+#else
+        CHECK(json_view_test::exception_of_call([&]
+        {
+            static_cast<void>(nested.root()[1].get<std::string>());
+        }) == "[json.exception.type_error.302] (bytes 4-8) type must be string, but is boolean");
+#endif
+    }
 #endif
 
     SECTION("edited documents")
@@ -521,8 +542,7 @@ TEST_CASE("json_view exceptions name the path and the bytes of the value")
         std::string text = "7";
         for (int level = 0; level < 40; ++level)
         {
-            text.insert(0, R"([[1, [2]], )");
-            text += R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
+            text = R"([[1, [2]], )" + text + R"(, {"k": [3, {"l": [4]}]}, [5, [6, [7]]]])";
         }
         CAPTURE(text)
         const json j = json::parse(text);
@@ -551,12 +571,8 @@ TEST_CASE("json_view exceptions name the path and the bytes of the value")
         expected_zz += "(bytes 12-35) key 'zz' not found";
         CHECK(exception_of_call([&] { static_cast<void>(d.root().at(json::json_pointer("/people/0/zz"))); }) == expected_zz);
 
-        // the root has no path, and with JSON_DIAGNOSTICS then no bytes either (as basic_json)
-        std::string expected_missing = "[json.exception.out_of_range.403] ";
-#if !JSON_DIAGNOSTICS
-        expected_missing += "(bytes 0-79) ";
-#endif
-        expected_missing += "key 'missing' not found";
+        // the root has no path, but still its bytes (#5987)
+        const std::string expected_missing = "[json.exception.out_of_range.403] (bytes 0-79) key 'missing' not found";
         CHECK(exception_of_call([&] { static_cast<void>(d.root().at("missing")); }) == expected_missing);
     }