Merge remote-tracking branch 'origin/develop' into claude/fix-issue-3989-db7e45

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

tests/src/fuzzer-parse_json.cpp

@@ -10,7 +10,9 @@
 This file implements a parser test suitable for fuzz testing. Given a byte
 array data, it performs the following steps:
 
+- j0 = parse(data, allow_exceptions = false)
 - j1 = parse(data)
+- assert(j0 is discarded if parsing j1 fails, and j0 == j1 otherwise)
 - s1 = serialize(j1)
 - j2 = parse(s1)
 - s2 = serialize(j2)
@@ -36,20 +38,52 @@ drivers.
 
 using json = nlohmann::json;
 
+// compares dumps rather than values, because NaN != NaN; keep writes strings
+// byte for byte, so ill-formed UTF-8 that a binary reader accepts cannot throw
+static bool same_value(const json& lhs, const json& rhs)
+{
+    return lhs.dump(-1, ' ', false, json::error_handler_t::keep) == rhs.dump(-1, ' ', false, json::error_handler_t::keep);
+}
+
 // see http://llvm.org/docs/LibFuzzer.html
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
 {
-    // step 0: recover from all errors, reading from memory and from a stream
+    // recover from all errors, reading from memory and from a stream
     {
         const auto checker = check_recovering_parse(data, size, json::input_format_t::json);
         assert(checker.events <= (4 * size) + 4);
         assert((checker.errors == 0) == json::accept(data, data + size));
     }
 
+    // step 0: parse input without exceptions; a parse error must then be
+    // reported as a discarded value, never thrown
+    json j_noexcept;
+    bool noexcept_threw = false;
+    try
+    {
+        j_noexcept = json::parse(data, data + size, nullptr, false);
+    }
+    catch (const json::parse_error&)
+    {
+        assert(false);
+    }
+    catch (const json::exception&)
+    {
+        // type and out-of-range errors are not parse errors and still throw
+        noexcept_threw = true;
+    }
+    // whether step 1 succeeded; if not, the catch blocks below check that
+    // step 0 failed, too
+    bool parsed = false;
+
     try
     {
         // step 1: parse input
         json const j1 = json::parse(data, data + size);
+        parsed = true;
+
+        // without exceptions, the same input must give the same value
+        assert(!noexcept_threw && !j_noexcept.is_discarded() && same_value(j_noexcept, j1));
 
         try
         {
@@ -76,10 +110,12 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
     catch (const json::parse_error&)
     {
         // parse errors are ok, because input may be random bytes
+        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
     }
     catch (const json::out_of_range&)
     {
         // out of range errors may happen if provided sizes are excessive
+        assert(parsed || noexcept_threw || j_noexcept.is_discarded());
     }
 
     // return 0 - non-zero return values are reserved for future use