Everywhere: Switch from (void) to [[maybe_unused]] (#4473)

Problem:
- `(void)` simply casts the expression to void. This is understood to
  indicate that it is ignored, but this is really a compiler trick to
  get the compiler to not generate a warning.

Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.

Note:
- Functions taking a `(void)` argument list have also been changed to
  `()` because this is not needed and shows up in the same grep
  command.

Author: ldm5180

AK/Random.h

@@ -43,16 +43,13 @@
 
 namespace AK {
 
-inline void fill_with_random(void* buffer, size_t length)
+inline void fill_with_random([[maybe_unused]] void* buffer, [[maybe_unused]] size_t length)
 {
 #if defined(__serenity__)
     arc4random_buf(buffer, length);
 #elif defined(OSS_FUZZ)
-    (void)buffer;
-    (void)length;
 #elif defined(__unix__) or defined(__APPLE__)
-    int rc = getentropy(buffer, length);
-    (void)rc;
+    [[maybe_unused]] int rc = getentropy(buffer, length);
 #endif
 }
 

AK/SharedBuffer.cpp

@@ -89,16 +89,14 @@ RefPtr<SharedBuffer> SharedBuffer::create_with_size(int size)
     return adopt(*new SharedBuffer(shbuf_id, size, data));
 }
 
-bool SharedBuffer::share_with(pid_t peer)
+bool SharedBuffer::share_with([[maybe_unused]] pid_t peer)
 {
 #    if defined(__serenity__)
     int ret = shbuf_allow_pid(shbuf_id(), peer);
     if (ret < 0) {
         perror("shbuf_allow_pid");
         return false;
     }
-#    else
-    (void)peer;
 #    endif
     return true;
 }

AK/Singleton.h

@@ -114,7 +114,7 @@ class Singleton {
 
     void ensure_instance()
     {
-        (void)ptr();
+        ptr();
     }
 
 private:

AK/StdLibExtras.h

@@ -26,8 +26,6 @@
 
 #pragma once
 
-#define UNUSED_PARAM(x) (void)x
-
 constexpr unsigned round_up_to_power_of_two(unsigned value, unsigned power_of_two)
 {
     return ((value - 1) & ~(power_of_two - 1)) + power_of_two;

AK/Tests/TestByteBuffer.cpp

@@ -65,7 +65,7 @@ TEST_CASE(negative_operator_lt)
 {
     ByteBuffer a = ByteBuffer::copy("Hello, world", 10);
     ByteBuffer b = ByteBuffer::copy("Hello, friend", 10);
-    (void)(a < b);
+    [[maybe_unused]] auto res = a < b;
     // error: error: use of deleted function ‘bool AK::ByteBuffer::operator<(const AK::ByteBuffer&) const’
 }
 #endif /* COMPILE_NEGATIVE_TESTS */

AK/Tests/TestDistinctNumeric.cpp

@@ -264,35 +264,35 @@ TEST_CASE(negative_incr)
 TEST_CASE(negative_cmp)
 {
     BareNumeric a = 12;
-    (void)(a < a);
+    [[maybe_unused]] auto res = (a < a);
     // error: static assertion failed: 'a<b' is only available for DistinctNumeric types with 'Cmp'.
 }
 
 TEST_CASE(negative_bool)
 {
     BareNumeric a = 12;
-    (void)!a;
+    [[maybe_unused]] auto res = !a;
     // error: static assertion failed: '!a', 'a&&b', 'a||b' and similar operators are only available for DistinctNumeric types with 'Bool'.
 }
 
 TEST_CASE(negative_flags)
 {
     BareNumeric a = 12;
-    (void)(a & a);
+    [[maybe_unused]] auto res = (a & a);
     // error: static assertion failed: 'a&b' is only available for DistinctNumeric types with 'Flags'.
 }
 
 TEST_CASE(negative_shift)
 {
     BareNumeric a = 12;
-    (void)(a << a);
+    [[maybe_unused]] auto res = (a << a);
     // error: static assertion failed: 'a<<b' is only available for DistinctNumeric types with 'Shift'.
 }
 
 TEST_CASE(negative_arith)
 {
     BareNumeric a = 12;
-    (void)(a + a);
+    [[maybe_unused]] auto res = (a + a);
     // error: static assertion failed: 'a+b' is only available for DistinctNumeric types with 'Arith'.
 }
 
@@ -302,13 +302,13 @@ TEST_CASE(negative_incompatible)
     ArithNumeric b = 345;
     // And this is the entire point of `DistinctNumeric`:
     // Theoretically, the operation *could* be supported, but we declared those int types incompatible.
-    (void)(a + b);
+    [[maybe_unused]] auto res = (a + b);
     // error: no match for ‘operator+’ (operand types are ‘GeneralNumeric’ {aka ‘AK::DistinctNumeric<int, true, true, true, true, true, true, 64, 64>’} and ‘ArithNumeric’ {aka ‘AK::DistinctNumeric<int, false, false, false, false, false, true, 64, 63>’})
-    //    313 |     (void)(a + b);
-    //        |            ~ ^ ~
-    //        |            |   |
-    //        |            |   DistinctNumeric<[...],false,false,false,false,false,[...],[...],63>
-    //        |            DistinctNumeric<[...],true,true,true,true,true,[...],[...],64>
+    //    313 |     [[maybe_unused]] auto res = (a + b);
+    //        |                                  ~ ^ ~
+    //        |                                  |   |
+    //        |                                  |   DistinctNumeric<[...],false,false,false,false,false,[...],[...],63>
+    //        |                                  DistinctNumeric<[...],true,true,true,true,true,[...],[...],64>
 }
 #endif /* COMPILE_NEGATIVE_TESTS */
 

AK/Tests/TestJSON.cpp

@@ -61,9 +61,7 @@ TEST_CASE(load_form)
     widgets.for_each([&](const JsonValue& widget_value) {
         auto& widget_object = widget_value.as_object();
         auto widget_class = widget_object.get("class").as_string();
-        widget_object.for_each_member([&](auto& property_name, const JsonValue& property_value) {
-            (void)property_name;
-            (void)property_value;
+        widget_object.for_each_member([&]([[maybe_unused]] auto& property_name, [[maybe_unused]] const JsonValue& property_value) {
             //dbgprintf("Set property %s.%s to '%s'\n", widget_class.characters(), property_name.characters(), property_value.serialized().characters());
         });
     });

AK/Tests/TestSourceGenerator.cpp

@@ -44,9 +44,9 @@ TEST_CASE(generate_c_code)
     SourceGenerator generator { builder };
     generator.set("name", "foo");
 
-    generator.append("const char* @name@ (void) { return \"@name@\"; }");
+    generator.append("const char* @name@ () { return \"@name@\"; }");
 
-    EXPECT_EQ(generator.as_string_view(), "const char* foo (void) { return \"foo\"; }");
+    EXPECT_EQ(generator.as_string_view(), "const char* foo () { return \"foo\"; }");
 }
 
 TEST_CASE(scoped)

AK/Utf8View.cpp

@@ -138,8 +138,7 @@ bool Utf8View::validate(size_t& valid_bytes) const
 size_t Utf8View::calculate_length() const
 {
     size_t length = 0;
-    for (auto code_point : *this) {
-        (void)code_point;
+    for ([[maybe_unused]] auto code_point : *this) {
         ++length;
     }
     return length;
@@ -170,7 +169,6 @@ Utf8CodepointIterator& Utf8CodepointIterator::operator++()
     bool first_byte_makes_sense = decode_first_byte(*m_ptr, code_point_length_in_bytes, value);
 
     ASSERT(first_byte_makes_sense);
-    (void)value;
 
     ASSERT(code_point_length_in_bytes <= m_length);
     m_ptr += code_point_length_in_bytes;

Applications/Browser/DownloadWidget.cpp

@@ -156,11 +156,8 @@ void DownloadWidget::did_progress(Optional<u32> total_size, u32 downloaded_size)
     }
 }
 
-void DownloadWidget::did_finish(bool success, ReadonlyBytes payload, RefPtr<SharedBuffer> payload_storage, const HashMap<String, String, CaseInsensitiveStringTraits>& response_headers)
+void DownloadWidget::did_finish(bool success, [[maybe_unused]] ReadonlyBytes payload, [[maybe_unused]] RefPtr<SharedBuffer> payload_storage, [[maybe_unused]] const HashMap<String, String, CaseInsensitiveStringTraits>& response_headers)
 {
-    (void)payload;
-    (void)payload_storage;
-    (void)response_headers;
     dbg() << "did_finish, success=" << success;
 
     m_close_button->set_enabled(true);