Kernel: Convert try_make_ref_counted to use ErrorOr

This allows more ergonomic memory allocation failure related error
checking using the TRY macro.

AK/RefPtr.h

@@ -336,16 +336,16 @@ inline RefPtr<T> adopt_ref_if_nonnull(T* object)
 }
 
 template<typename T, class... Args>
-requires(IsConstructible<T, Args...>) inline RefPtr<T> try_make_ref_counted(Args&&... args)
+requires(IsConstructible<T, Args...>) inline ErrorOr<NonnullRefPtr<T>> try_make_ref_counted(Args&&... args)
 {
-    return adopt_ref_if_nonnull(new (nothrow) T(forward<Args>(args)...));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) T(forward<Args>(args)...));
 }
 
 // FIXME: Remove once P0960R3 is available in Clang.
 template<typename T, class... Args>
-inline RefPtr<T> try_make_ref_counted(Args&&... args)
+inline ErrorOr<NonnullRefPtr<T>> try_make_ref_counted(Args&&... args)
 {
-    return adopt_ref_if_nonnull(new (nothrow) T { forward<Args>(args)... });
+    return adopt_nonnull_ref_or_enomem(new (nothrow) T { forward<Args>(args)... });
 }
 
 template<typename T>

Documentation/SmartPointers.md

@@ -98,13 +98,14 @@ NonnullRefPtr<Bar> another_owner = our_object;
 ```
 
 
-The `try_make_ref_counted<T>()` function constructs an object wrapped in `RefPtr<T>` which may be null if the allocation does not succeed. This allows the calling code to handle allocation failure as it wishes. All arguments passed to it are forwarded to `T`'s constructor.
+The `try_make_ref_counted<T>()` function constructs an object wrapped in `ErrorOr<NonnullRefPtr<T>>` which may be an error if the allocation does not succeed. This allows the calling code to handle allocation failure as it wishes. All arguments passed to it are forwarded to `T`'s constructor.
 
 ```cpp
-RefPtr<Bar> our_object = try_make_ref_counted<Bar>();
-if (!our_object) {
+auto our_object_or_error = try_make_ref_counted<Bar>();
+if (our_object_or_error.is_error()) {
     // handle allocation failure...
 }
+NonnullRefPtr<Bar> our_object = our_object_or_error.release_value();
 RefPtr<Bar> another_owner = our_object;
 ```
 

Kernel/Library/ThreadSafeRefPtr.h

@@ -486,16 +486,16 @@ inline RefPtr<T> adopt_ref_if_nonnull(T* object)
 }
 
 template<typename T, class... Args>
-requires(IsConstructible<T, Args...>) inline RefPtr<T> try_make_ref_counted(Args&&... args)
+requires(IsConstructible<T, Args...>) inline ErrorOr<NonnullRefPtr<T>> try_make_ref_counted(Args&&... args)
 {
-    return adopt_ref_if_nonnull(new (nothrow) T(forward<Args>(args)...));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) T(forward<Args>(args)...));
 }
 
 // FIXME: Remove once P0960R3 is available in Clang.
 template<typename T, class... Args>
-inline RefPtr<T> try_make_ref_counted(Args&&... args)
+inline ErrorOr<NonnullRefPtr<T>> try_make_ref_counted(Args&&... args)
 {
-    return adopt_ref_if_nonnull(new (nothrow) T { forward<Args>(args)... });
+    return adopt_nonnull_ref_or_enomem(new (nothrow) T { forward<Args>(args)... });
 }
 
 template<typename T>

Kernel/Thread.cpp

@@ -45,12 +45,10 @@ ErrorOr<NonnullRefPtr<Thread>> Thread::try_create(NonnullRefPtr<Process> process
     auto kernel_stack_region = TRY(MM.allocate_kernel_region(default_kernel_stack_size, {}, Memory::Region::Access::ReadWrite, AllocationStrategy::AllocateNow));
     kernel_stack_region->set_stack(true);
 
-    auto block_timer = try_make_ref_counted<Timer>();
-    if (!block_timer)
-        return ENOMEM;
+    auto block_timer = TRY(try_make_ref_counted<Timer>());
 
     auto name = TRY(KString::try_create(process->name()));
-    return adopt_nonnull_ref_or_enomem(new (nothrow) Thread(move(process), move(kernel_stack_region), block_timer.release_nonnull(), move(name)));
+    return adopt_nonnull_ref_or_enomem(new (nothrow) Thread(move(process), move(kernel_stack_region), move(block_timer), move(name)));
 }
 
 Thread::Thread(NonnullRefPtr<Process> process, NonnullOwnPtr<Memory::Region> kernel_stack_region, NonnullRefPtr<Timer> block_timer, NonnullOwnPtr<KString> name)