Fix the build of develop: tests from #5997 and #5991

- unit-msgpack-cpp17: assign the result of json::parse in
  CHECK_THROWS_WITH_AS (GCC -Werror=unused-result)
- unit-json_view: failing_allocator::allocate is [[noreturn]]
  (clang -Wmissing-noreturn)
- unit-class_lexer: build the quoted string once
  (clang-tidy performance-inefficient-string-concatenation)
- unit-allocator: sweep_allocator provides pointer, reference and size
  typedefs, which GCC 4.8's std::map takes from the allocator
- unit-allocator: skip the "sax_parse into an existing value" sweep with
  iterator debugging, like the parser callback sweep: MSVC's std::vector
  default constructor is noexcept but allocates its debug proxy through
  the allocator, so a failing allocation in create<array_t>() terminates

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

tests/src/unit-allocator.cpp

@@ -1038,6 +1038,14 @@ 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 {}
@@ -1155,8 +1163,9 @@ 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 move constructors, so failing that allocation terminates the
-    // program instead of throwing std::bad_alloc. Nothing to check there.
+    // noexcept default and 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")
     {
@@ -1178,7 +1187,6 @@ 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")
     {
@@ -1192,5 +1200,6 @@ TEST_CASE("parse() survives a failing allocation at every point (#5985)")
             return value;
         });
     }
+#endif
 }
 #endif

tests/src/unit-class_lexer.cpp

@@ -2222,9 +2222,10 @@ TEST_CASE("serialization of short strings")
     {
         CAPTURE(s)
         const json j = s;
-        CHECK(j.dump() == "\"" + s + "\"");
-        CHECK(j.dump(-1, ' ', true) == "\"" + s + "\"");
-        CHECK(json({{s, s}}).dump() == "{\"" + s + "\":\"" + 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)
     }
 
     // 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 {}
 
-    T* allocate(std::size_t /*n*/) // NOLINT(readability-convert-member-functions-to-static)
+    [[noreturn]] T* allocate(std::size_t /*n*/) // NOLINT(readability-convert-member-functions-to-static)
     {
         throw std::bad_alloc();
     }

tests/src/unit-msgpack-cpp17.cpp

@@ -122,7 +122,8 @@ TEST_CASE("JSON text with std::byte")
     SECTION("invalid text")
     {
         CHECK_FALSE(json::accept(to_bytes("[1,\n2,")));
-        CHECK_THROWS_WITH_AS(json::parse(to_bytes("[1,\n2,")),
+        json _;
+        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&);
     }
 }