Fix NLOHMANN_JSON_SERIALIZE_ENUM_STRICT's from_json message

from_json built its out_of_range.410 message with "..." + j.dump(). If the
unmatched value is (or contains) a string with invalid UTF-8, that dump()
itself throws type_error.316, so the caller got type_error.316 instead of
the documented out_of_range.410; such strings can reach get<Enum>()
unvalidated, e.g. from from_cbor()/from_msgpack(). With a custom string_t,
j.dump() returns that type, and "const char*" + string_t does not compile
unless the type happens to provide operator+, so the macro failed to
compile for such types.

Build the message with detail::concat(), which appends any type exposing
data()/size() and always yields a std::string, and dump with
error_handler_t::replace so building the message itself cannot throw.

Added regression tests: an invalid-UTF-8 case in the existing strict-enum
test in unit-conversions.cpp, and a strict-enum use with alt_string (the
custom string_t from unit-alt-string.cpp) to cover the compile failure.

Fixes #5667.

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

docs/mkdocs/docs/api/basic_json/parse.md

@@ -88,12 +88,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 ## Exceptions
 
 - Throws [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or
-  empty input like a null `FILE*` or `char*` pointer, or an `std::istream` without a stream buffer
-  (`#!cpp i.rdbuf() == nullptr`, for instance `#!cpp std::istream(nullptr)`).
-- If reading from an `std::istream` reaches the end of the input and `eofbit` is part of the stream's
-  [`exceptions()`](https://en.cppreference.com/w/cpp/io/basic_ios/exceptions) mask, the `std::ios_base::failure`
-  thrown by the stream itself propagates instead of a `parse_error`, the same as it would for the standard library's
-  own extraction operators.
+  empty input like a null `FILE*` or `char*` pointer.
 
 ## Complexity
 
@@ -259,8 +254,6 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
 - `JSON_STRICT_NUL_HANDLING` added in version 3.13.0 to optionally reject a NUL byte in the input instead of treating
   it as end of input; planned to become the default in version 4.0.0.
-- Extended empty-input detection to also cover an `std::istream` without a stream buffer, and fixed a crash
-  (`std::terminate`) when parsing from an `std::istream` with `eofbit` in its exception mask, in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/operator_gtgt.md

@@ -20,12 +20,7 @@ the stream `i`
 
 ## Exceptions
 
-- Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or if
-  `i` has no stream buffer (`#!cpp i.rdbuf() == nullptr`, for instance `#!cpp std::istream(nullptr)`).
-- If reading from `i` reaches the end of the input and `eofbit` is part of `i`'s
-  [`exceptions()`](https://en.cppreference.com/w/cpp/io/basic_ios/exceptions) mask, the `std::ios_base::failure`
-  thrown by `i` itself propagates instead of a `parse_error`, the same as it would for the standard library's own
-  extraction operators.
+- Throws [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token.
 
 ## Complexity
 
@@ -123,5 +118,3 @@ being read.
   it as end of input; planned to become the default in version 4.0.0.
 - `JSON_PRECISE_STREAM_POSITION` added in version 3.13.0 to optionally leave the character that terminates a number in
   the stream; planned to become the default in version 4.0.0.
-- Fixed a null pointer dereference for an `std::istream` without a stream buffer (now throws `parse_error.101`), and a
-  crash (`std::terminate`) when `i` has `eofbit` in its exception mask, in version 3.13.0.

include/nlohmann/detail/input/input_adapters.hpp

@@ -106,13 +106,7 @@ class input_stream_adapter
             // was given back with release_lookahead()
             commit_lookahead();
 #endif
-            // only call clear() if there is something to clear: it throws
-            // std::ios_base::failure if the stream has exceptions() enabled
-            // for a state bit that remains set, and a destructor must not throw
-            if ((is->rdstate() & ~std::ios::eofbit) != 0)
-            {
-                is->clear(is->rdstate() & std::ios::eofbit);
-            }
+            is->clear(is->rdstate() & std::ios::eofbit);
         }
     }
 
@@ -817,16 +811,12 @@ inline file_input_adapter input_adapter(std::FILE* file)
 
 inline input_stream_adapter input_adapter(std::istream& stream)
 {
-    if (stream.rdbuf() == nullptr)
-    {
-        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
-    }
     return input_stream_adapter(stream);
 }
 
 inline input_stream_adapter input_adapter(std::istream&& stream)
 {
-    return input_adapter(stream);
+    return input_stream_adapter(stream);
 }
 #endif  // JSON_NO_IO
 

include/nlohmann/detail/macro_scope.hpp

@@ -336,7 +336,7 @@ void templated_json_throw(ExceptionType exception)
             return ej_pair.second == j;                                                         \
         });                                                                                     \
         if (it != std::end(m)) e = it->first;                                                   \
-        else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
+        else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", j.dump(-1, ' ', false, nlohmann::detail::error_handler_t::replace)), &j)); \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They

single_include/nlohmann/json.hpp

@@ -2747,7 +2747,7 @@ void templated_json_throw(ExceptionType exception)
             return ej_pair.second == j;                                                         \
         });                                                                                     \
         if (it != std::end(m)) e = it->first;                                                   \
-        else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410,"enum value out of range for " #ENUM_TYPE ": " + j.dump(), &j)); \
+        else templated_json_throw<nlohmann::detail::out_of_range>(nlohmann::detail::out_of_range::create(410, nlohmann::detail::concat("enum value out of range for " #ENUM_TYPE ": ", j.dump(-1, ' ', false, nlohmann::detail::error_handler_t::replace)), &j)); \
     }
 
 // Ugly macros to avoid uglier copy-paste when specializing basic_json. They
@@ -7650,13 +7650,7 @@ class input_stream_adapter
             // was given back with release_lookahead()
             commit_lookahead();
 #endif
-            // only call clear() if there is something to clear: it throws
-            // std::ios_base::failure if the stream has exceptions() enabled
-            // for a state bit that remains set, and a destructor must not throw
-            if ((is->rdstate() & ~std::ios::eofbit) != 0)
-            {
-                is->clear(is->rdstate() & std::ios::eofbit);
-            }
+            is->clear(is->rdstate() & std::ios::eofbit);
         }
     }
 
@@ -8361,16 +8355,12 @@ inline file_input_adapter input_adapter(std::FILE* file)
 
 inline input_stream_adapter input_adapter(std::istream& stream)
 {
-    if (stream.rdbuf() == nullptr)
-    {
-        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
-    }
     return input_stream_adapter(stream);
 }
 
 inline input_stream_adapter input_adapter(std::istream&& stream)
 {
-    return input_adapter(stream);
+    return input_stream_adapter(stream);
 }
 #endif  // JSON_NO_IO
 

tests/src/unit-alt-string.cpp

@@ -174,6 +174,15 @@ bool operator<(const char* op1, const alt_string& op2) noexcept
     return op1 < op2.str_impl;
 }
 
+enum class alt_color { red, green };
+
+// NOLINTNEXTLINE(misc-use-internal-linkage,misc-const-correctness,cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays) - false positive
+NLOHMANN_JSON_SERIALIZE_ENUM_STRICT(alt_color,
+{
+    {alt_color::red, "red"},
+    {alt_color::green, "green"},
+})
+
 TEST_CASE("alternative string type")
 {
     SECTION("binary formats")
@@ -374,4 +383,19 @@ TEST_CASE("alternative string type")
         const auto j2 = j.flatten();
         CHECK(j2.dump() == R"({"/foo/0":"bar","/foo/1":"baz"})");
     }
+
+    SECTION("strict enum")
+    {
+        // regression test for #5667: NLOHMANN_JSON_SERIALIZE_ENUM_STRICT's from_json
+        // built its exception message with "..." + j.dump(), which does not compile
+        // when j.dump() returns a custom string_t (here alt_string) instead of
+        // std::string
+        alt_json doc;
+        doc = "red";
+        CHECK(doc.get<alt_color>() == alt_color::red);
+
+        alt_json _;
+        doc = "blue";
+        CHECK_THROWS_WITH_AS(_ = doc.get<alt_color>(), "[json.exception.out_of_range.410] enum value out of range for alt_color: \"blue\"", alt_json::out_of_range&);
+    }
 }

tests/src/unit-conversions.cpp

@@ -1740,6 +1740,12 @@ TEST_CASE("Strict JSON to enum mapping")
 
         // conversion of unmapped enum -> exception thrown
         CHECK_THROWS_WITH_AS(json(strict_cards::andere), "[json.exception.out_of_range.410] enum value out of range for strict_cards", json::out_of_range&);
+
+        // invalid UTF-8 -> out_of_range.410, not the type_error.316 thrown while building the
+        // message (regression test for #5667); such strings can reach get<Enum>() unvalidated,
+        // e.g. from from_cbor()/from_msgpack() (#5529)
+        const json j_invalid_utf8 = "\xFF";
+        CHECK_THROWS_WITH_AS(_ = j_invalid_utf8.get<strict_cards>(), "[json.exception.out_of_range.410] enum value out of range for strict_cards: \"\xEF\xBF\xBD\"", json::out_of_range&);
     }
 
     SECTION("traditional enum")

tests/src/unit-deserialization.cpp

@@ -388,37 +388,6 @@ TEST_CASE("deserialization")
             }));
         }
 
-        SECTION("stream with eofbit in its exception mask (issue #5646)")
-        {
-            // reaching EOF while parsing a value that fills the whole input
-            // (e.g., a number, or any value under strict parsing) makes
-            // get_character() call std::istream::clear() to record eofbit;
-            // with eofbit in the exception mask, that clear() itself throws
-            // std::ios_base::failure - it must propagate to the caller instead
-            // of ~input_stream_adapter() throwing a second exception while the
-            // first is still unwinding, which would call std::terminate
-            json _;
-
-            std::istringstream is1("1");
-            is1.exceptions(std::ios::eofbit);
-            CHECK_THROWS_AS(_ = json::parse(is1), std::ios_base::failure&);
-
-            // the same holds for the common std::ifstream::exceptions(failbit |
-            // badbit | eofbit) pattern, because only eofbit ends up set
-            std::istringstream is2("1");
-            is2.exceptions(std::ios::failbit | std::ios::badbit | std::ios::eofbit);
-            CHECK_THROWS_AS(_ = json::parse(is2), std::ios_base::failure&);
-        }
-
-        SECTION("stream without a streambuf (issue #5646)")
-        {
-            // std::istream(nullptr) has badbit set and rdbuf() == nullptr;
-            // get_character() must not dereference that null streambuf
-            std::istream is(nullptr);
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::parse(is), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
-        }
-
         SECTION("string")
         {
             json::string_t const s = R"(["foo",1,2,3,false,{"one":1})";

tests/src/unit-precise-stream-position.cpp

@@ -234,33 +234,4 @@ TEST_CASE("JSON_PRECISE_STREAM_POSITION")
         CHECK(j == json(1));
         CHECK(remaining(is) == "true");
     }
-
-    SECTION("stream with eofbit in its exception mask (issue #5646)")
-    {
-        // with JSON_PRECISE_STREAM_POSITION, get_character() peeks via
-        // sb->sgetc() rather than consuming via sb->sbumpc(), but it still
-        // calls std::istream::clear() to record eofbit once the streambuf is
-        // exhausted; with eofbit in the exception mask, that clear() itself
-        // throws std::ios_base::failure, which must propagate to the caller
-        // instead of ~input_stream_adapter() throwing a second exception
-        // while the first is still unwinding (which would call std::terminate)
-        json _;
-
-        std::istringstream is1("1");
-        is1.exceptions(std::ios::eofbit);
-        CHECK_THROWS_AS(_ = json::parse(is1), std::ios_base::failure&);
-
-        std::istringstream is2("1");
-        is2.exceptions(std::ios::failbit | std::ios::badbit | std::ios::eofbit);
-        CHECK_THROWS_AS(_ = json::parse(is2), std::ios_base::failure&);
-    }
-
-    SECTION("stream without a streambuf (issue #5646)")
-    {
-        // std::istream(nullptr) has badbit set and rdbuf() == nullptr;
-        // get_character() must not dereference that null streambuf
-        std::istream is(nullptr);
-        json _;
-        CHECK_THROWS_WITH_AS(_ = json::parse(is), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
-    }
 }