Fix fuzzer driver step lists to match the checks the code performs

The header comment of six of the seven binary-format fuzzer drivers
listed an invariant the code does not check: CBOR, MessagePack, BSON
and BON8 said "assert(j1 == j2)", but the code checks byte stability,
assert(to_X(j2) == vec). UBJSON and BJData still described the old
"assert(j1 == j2/j3/j4)" byte-exact check from before PR #5494 replaced
it with a use_size/use_type-aware round trip (UBJSON) and a
value-stability check (BJData); BJData's added paragraph already
explained the new check, but the step list above it did not.

Also remove a dead branch in fuzzer-parse_bson.cpp: from_bson() is
called with allow_exceptions = true, so it throws instead of returning
a discarded value, and the "if (j1.is_discarded()) return 0;" guard
could never trigger. Drop the unused <iostream> include from all seven
drivers and <sstream> from all but fuzzer-parse_bon8.cpp, which is the
only one that uses std::istringstream.

Overlaps #5601, which edits all seven drivers in the same hunks.

Closes #5714 item 4.

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

tests/src/fuzzer-parse_bjdata.cpp

@@ -11,15 +11,15 @@ This file implements a parser test suitable for fuzz testing. Given a byte
 array data, it performs the following steps:
 
 - j1 = from_bjdata(data)
-- vec = to_bjdata(j1)
-- j2 = from_bjdata(vec)
-- assert(j1 == j2)
-- vec2 = to_bjdata(j1, use_size = true, use_type = false)
-- j3 = from_bjdata(vec2)
-- assert(j1 == j3)
-- vec3 = to_bjdata(j1, use_size = true, use_type = true)
-- j4 = from_bjdata(vec3)
-- assert(j1 == j4)
+- vec2 = to_bjdata(j1, use_size = false, use_type = false)
+- vec3 = to_bjdata(j1, use_size = true, use_type = false)
+- vec4 = to_bjdata(j1, use_size = true, use_type = true)
+- j2 = from_bjdata(vec2)
+- j3 = from_bjdata(vec3)
+- j4 = from_bjdata(vec4)
+- assert(from_bjdata(to_bjdata(j2, use_size = false, use_type = false)) is value-stable with j2)
+- assert(from_bjdata(to_bjdata(j3, use_size = true, use_type = false)) is value-stable with j3)
+- assert(from_bjdata(to_bjdata(j4, use_size = true, use_type = true)) is value-stable with j4)
 
 Re-serializing j2/j3/j4 with the same use_size/use_type settings is checked
 for value-stability rather than byte-exact stability: from_bjdata(to_bjdata(j2))
@@ -50,8 +50,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_bon8.cpp

@@ -13,7 +13,7 @@ array data, it performs the following steps:
 - j1 = from_bon8(data)
 - vec = to_bon8(j1)
 - j2 = from_bon8(vec)
-- assert(j1 == j2)
+- assert(to_bon8(j2) == vec)
 
 It also checks that reading the data from a stream, which reads strings byte by
 byte, gives the same value or error as reading it from contiguous memory, which
@@ -24,7 +24,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 

tests/src/fuzzer-parse_bson.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_bson(data)
 - vec = to_bson(j1)
 - j2 = from_bson(vec)
-- assert(j1 == j2)
+- assert(to_bson(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away
@@ -40,11 +38,6 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
         std::vector<uint8_t> const vec1(data, data + size);
         json const j1 = json::from_bson(vec1);
 
-        if (j1.is_discarded())
-        {
-            return 0;
-        }
-
         try
         {
             // step 2: round trip

tests/src/fuzzer-parse_cbor.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_cbor(data)
 - vec = to_cbor(j1)
 - j2 = from_cbor(vec)
-- assert(j1 == j2)
+- assert(to_cbor(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_json.cpp

@@ -21,8 +21,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_msgpack.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_msgpack(data)
 - vec = to_msgpack(j1)
 - j2 = from_msgpack(vec)
-- assert(j1 == j2)
+- assert(to_msgpack(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_ubjson.cpp

@@ -11,15 +11,15 @@ This file implements a parser test suitable for fuzz testing. Given a byte
 array data, it performs the following steps:
 
 - j1 = from_ubjson(data)
-- vec = to_ubjson(j1)
-- j2 = from_ubjson(vec)
-- assert(j1 == j2)
-- vec2 = to_ubjson(j1, use_size = true, use_type = false)
-- j3 = from_ubjson(vec2)
-- assert(j1 == j3)
-- vec3 = to_ubjson(j1, use_size = true, use_type = true)
-- j4 = from_ubjson(vec3)
-- assert(j1 == j4)
+- vec2 = to_ubjson(j1, use_size = false, use_type = false)
+- vec3 = to_ubjson(j1, use_size = true, use_type = false)
+- vec4 = to_ubjson(j1, use_size = true, use_type = true)
+- j2 = from_ubjson(vec2)
+- j3 = from_ubjson(vec3)
+- j4 = from_ubjson(vec4)
+- assert(to_ubjson(j2, use_size = false, use_type = false) == vec2)
+- assert(to_ubjson(j3, use_size = true, use_type = false) == vec3)
+- assert(to_ubjson(j4, use_size = true, use_type = true) == vec4)
 
 The unit tests run the same checks on a fixed corpus (see the "UBJSON round-trip
 invariants" test case), so keep both in sync.
@@ -29,8 +29,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away