json_view: exceptions name the path and the bytes of the value

With JSON_DIAGNOSTICS and JSON_DIAGNOSTIC_POSITIONS, the exceptions of views
now carry the same context as those of basic_json: "(/path) " and
"(bytes a-b) " in front of the message, in basic_json's format (with
JSON_DIAGNOSTICS, no context for the root). Before, views threw without any
context, and since get<T>() reads the view directly, conversions had lost
even the relative path they used to get through materialize().

The throw helpers of detail/view/errors.hpp take an error_site (document
and node; empty without the two macros). Only on the error path, the path is
found by descending from the root (pruned by subtree extent before the first
edit, a full walk through edited sequences after), and the bytes as
materialize() sets them (position_source; a container's end by following the
chain of last elements and scanning to the closing brackets). from_json() for
views and the strict enum macro put the same context in front through
exception_prefix(). Iterators keep their container only under the two
macros, for key(). Without the macros, the accessors compile to the same
code as before.

Tests compare every value's exceptions with those of the parsed or
materialized basic_json value, including edited documents; the checks that
were disabled under the two macros run again.

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

include/nlohmann/detail/view/edit.hpp

@@ -157,7 +157,7 @@ class editor
         node* const o = own(object);
         if (o->kind != node_kind::object && o->kind != node_kind::null)
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", object.type_name());
+            throw_type_error(site_of(object), exception_id::subscript_wrong_type, "cannot use operator[] with a string argument with ", object.type_name());
         }
         check_utf8(key.data(), key.size());
         const encoded e = encode(std::forward<V>(value));
@@ -208,9 +208,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::subscript_wrong_type, "cannot use operator[] with a numeric argument with ", array.type_name());
         }
-        check_index(idx, a->len);
+        check_index(a, idx, a->len);
         const encoded e = encode(std::forward<V>(value));
         node* const slot = const_cast<node*>(nav::value(element_at<true>(m_doc, a, idx))); // NOLINT(cppcoreguidelines-pro-type-const-cast)
         assign(slot, e, a, true);
@@ -225,7 +225,7 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array && a->kind != node_kind::null)
         {
-            throw_type_error(exception_id::push_back_wrong_type, "cannot use push_back() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::push_back_wrong_type, "cannot use push_back() with ", array.type_name());
         }
         const encoded e = encode(std::forward<V>(value));
         if (a->kind == node_kind::null)
@@ -249,9 +249,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::insert_wrong_type, "cannot use insert() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::insert_wrong_type, "cannot use insert() with ", array.type_name());
         }
-        check_index(idx, a->len + 1);
+        check_index(a, idx, a->len + 1);
         const encoded e = encode(std::forward<V>(value));
         node* const slot = new_slot(e);
         node* const h = block_of(m_doc, a, 1);
@@ -269,7 +269,7 @@ class editor
         node* const o = own(object);
         if (o->kind != node_kind::object)
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", object.type_name());
+            throw_type_error(site_of(object), exception_id::erase_wrong_type, "cannot use erase() with ", object.type_name());
         }
         for (const node* k = nav::first(m_doc, o), *end = nav::end(m_doc, o); k != end; k = document_data::after(k + 1))
         {
@@ -287,9 +287,9 @@ class editor
         node* const a = own(array);
         if (a->kind != node_kind::array)
         {
-            throw_type_error(exception_id::erase_wrong_type, "cannot use erase() with ", array.type_name());
+            throw_type_error(site_of(array), exception_id::erase_wrong_type, "cannot use erase() with ", array.type_name());
         }
-        check_index(idx, a->len);
+        check_index(a, idx, a->len);
         node* const h = block_of(m_doc, a, 0);
         std::memmove(h + 1 + idx, h + 2 + idx, (h->next - 2 - idx) * sizeof(node));
         --h->next;
@@ -316,11 +316,11 @@ class editor
         return const_cast<node*>(v.m_node); // NOLINT(cppcoreguidelines-pro-type-const-cast): the nodes belong to this document
     }
 
-    static void check_index(std::size_t idx, std::size_t limit)
+    void check_index(const node* array, std::size_t idx, std::size_t limit) const
     {
         if (idx >= limit)
         {
-            throw_array_index_out_of_range(idx);
+            throw_array_index_out_of_range(error_site(&m_doc, array), idx);
         }
     }