json_view: no byte range in exceptions about a removed value

#5990 dropped the found flag from diagnostics(), reasoning that a value
value_path() does not find leaves no tokens, like the root. But the node
of a value that is no longer part of the document still holds the bytes
it had in the source, so with JSON_DIAGNOSTICS and
JSON_DIAGNOSTIC_POSITIONS its exceptions gained "(bytes 1-4)" for text
that is no longer there. The test #5997 added for exactly this case
(unit-json_view_positions.cpp, "views of values that are no longer part
of the document") has failed on develop since both were merged.

Restore the flag: a value that is not found gets no context, the root
keeps its byte range.

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

include/nlohmann/detail/view/builder.hpp

@@ -1168,20 +1168,20 @@ indent_done:
             if (negative)
             {
                 ++p;
-                if (NLOHMANN_VIEW_UNLIKELY(cur() < '0' || cur() > '9'))
-                {
-                    return fail(error_code::number_after_minus);
-                }
             }
             const unsigned char* const int_start = p;
             if (cur() == '0')
             {
                 ++p;
             }
+            else if (!negative || NLOHMANN_VIEW_LIKELY(cur() >= '1' && cur() <= '9'))
+            {
+                // (without a sign, the dispatch saw a digit)
+                p = skip_digits(p + 1, e);
+            }
             else
             {
-                // (a digit: the dispatch or the check after the sign saw it)
-                p = skip_digits(p + 1, e);
+                return fail(error_code::number_after_minus);
             }
             const auto int_digits = static_cast<std::size_t>(p - int_start);
             std::size_t frac_digits = 0;

include/nlohmann/detail/view/errors.hpp

@@ -230,7 +230,8 @@ 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 (also for the root)
+/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (also for the root); with
+/// JSON_DIAGNOSTICS, nothing for a value that is no longer part of the document
 ///
 /// 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
@@ -251,10 +252,12 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
+    // a value that is no longer part of the document has no path, and its
+    // node still holds the bytes it had in the source: no context at all
     const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
     if (!found)
     {
-        // a value that is not found has no path, and with it no bytes
+        // context is still empty; returning it keeps the copy elided (-Wnrvo)
         return context;
     }
     if (!tokens.empty())

single_include/nlohmann/json_view.hpp

@@ -2473,20 +2473,20 @@ indent_done:
             if (negative)
             {
                 ++p;
-                if (NLOHMANN_VIEW_UNLIKELY(cur() < '0' || cur() > '9'))
-                {
-                    return fail(error_code::number_after_minus);
-                }
             }
             const unsigned char* const int_start = p;
             if (cur() == '0')
             {
                 ++p;
             }
+            else if (!negative || NLOHMANN_VIEW_LIKELY(cur() >= '1' && cur() <= '9'))
+            {
+                // (without a sign, the dispatch saw a digit)
+                p = skip_digits(p + 1, e);
+            }
             else
             {
-                // (a digit: the dispatch or the check after the sign saw it)
-                p = skip_digits(p + 1, e);
+                return fail(error_code::number_after_minus);
             }
             const auto int_digits = static_cast<std::size_t>(p - int_start);
             std::size_t frac_digits = 0;
@@ -5059,7 +5059,8 @@ 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 (also for the root)
+/// "(bytes a-b) " with JSON_DIAGNOSTIC_POSITIONS (also for the root); with
+/// JSON_DIAGNOSTICS, nothing for a value that is no longer part of the document
 ///
 /// 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
@@ -5080,10 +5081,12 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
+    // a value that is no longer part of the document has no path, and its
+    // node still holds the bytes it had in the source: no context at all
     const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
     if (!found)
     {
-        // a value that is not found has no path, and with it no bytes
+        // context is still empty; returning it keeps the copy elided (-Wnrvo)
         return context;
     }
     if (!tokens.empty())

tests/src/unit-allocator.cpp

@@ -1038,14 +1038,6 @@ template<class T>
 struct sweep_allocator
 {
     using value_type = T;
-    // GCC 4.8's std::map takes these from the allocator instead of from
-    // std::allocator_traits
-    using pointer = T*;
-    using const_pointer = const T*;
-    using reference = T&;
-    using const_reference = const T&;
-    using size_type = std::size_t;
-    using difference_type = std::ptrdiff_t;
 
     sweep_allocator() = default;
     template<class U> sweep_allocator(const sweep_allocator<U>& /*unused*/) noexcept {}
@@ -1163,9 +1155,8 @@ TEST_CASE("parse() survives a failing allocation at every point (#5985)")
 
     // With iterator debugging (MSVC STL debug builds, also used by clang-cl),
     // containers allocate a debug proxy through the allocator inside their
-    // noexcept default and move constructors, so failing that allocation
-    // terminates the program instead of throwing std::bad_alloc. Nothing to
-    // check there.
+    // noexcept move constructors, so failing that allocation terminates the
+    // program instead of throwing std::bad_alloc. Nothing to check there.
 #if !(defined(_ITERATOR_DEBUG_LEVEL) && _ITERATOR_DEBUG_LEVEL > 0)
     SECTION("parser callback")
     {
@@ -1187,6 +1178,7 @@ TEST_CASE("parse() survives a failing allocation at every point (#5985)")
             return sweep_json::parse(text, drop_d);
         });
     }
+#endif
 
     SECTION("sax_parse into an existing value")
     {
@@ -1200,6 +1192,5 @@ TEST_CASE("parse() survives a failing allocation at every point (#5985)")
             return value;
         });
     }
-#endif
 }
 #endif

tests/src/unit-class_lexer.cpp

@@ -2222,10 +2222,9 @@ TEST_CASE("serialization of short strings")
     {
         CAPTURE(s)
         const json j = s;
-        const std::string quoted = "\"" + s + "\""; // NOLINT(performance-inefficient-string-concatenation)
-        CHECK(j.dump() == quoted);
-        CHECK(j.dump(-1, ' ', true) == quoted);
-        CHECK(json({{s, s}}).dump() == "{" + quoted + ":" + quoted + "}"); // NOLINT(performance-inefficient-string-concatenation)
+        CHECK(j.dump() == "\"" + s + "\"");
+        CHECK(j.dump(-1, ' ', true) == "\"" + s + "\"");
+        CHECK(json({{s, s}}).dump() == "{\"" + s + "\":\"" + s + "\"}");
     }
 
     // a character that needs an escape

tests/src/unit-json_view.cpp

@@ -111,7 +111,7 @@ struct failing_allocator
     template<typename U>
     explicit failing_allocator(const failing_allocator<U>& /*other*/) noexcept {}
 
-    [[noreturn]] T* allocate(std::size_t /*n*/) // NOLINT(readability-convert-member-functions-to-static)
+    T* allocate(std::size_t /*n*/) // NOLINT(readability-convert-member-functions-to-static)
     {
         throw std::bad_alloc();
     }

tests/src/unit-locale-cpp.cpp

@@ -505,8 +505,8 @@ struct locale_switching_token
 {
     using value_type = char;
 
-    locale_switching_token(std::string text_, std::string switch_to_)
-        : text(std::move(text_)), switch_to(std::move(switch_to_))
+    locale_switching_token(std::string text_, const char* switch_to_)
+        : text(std::move(text_)), switch_to(switch_to_)
     {}
 
     std::size_t size() const
@@ -523,13 +523,13 @@ struct locale_switching_token
     {
         if (!switched)
         {
-            switched = std::setlocale(LC_NUMERIC, switch_to.c_str()) != nullptr;
+            switched = std::setlocale(LC_NUMERIC, switch_to) != nullptr;
         }
         return &text[0];
     }
 
     std::string text;
-    std::string switch_to;
+    const char* switch_to;
     bool switched = false;
 };
 

tests/src/unit-msgpack-cpp17.cpp

@@ -122,8 +122,7 @@ TEST_CASE("JSON text with std::byte")
     SECTION("invalid text")
     {
         CHECK_FALSE(json::accept(to_bytes("[1,\n2,")));
-        json _;
-        CHECK_THROWS_WITH_AS(_ = json::parse(to_bytes("[1,\n2,")),
+        CHECK_THROWS_WITH_AS(json::parse(to_bytes("[1,\n2,")),
                              "[json.exception.parse_error.101] parse error at line 2, column 3: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal", json::parse_error&);
     }
 }