Shell_NotifyIcon APIs marked as arch-specific due to upstream no-op packing instructions

[citelao]

I'm not sure, but I believe the Shell_NotifyIcon* APIs are marked as architecture-specific, but they are not.

I do not think there are any layout changes to Shell_NotifyIcon* and the NotifyIconData* struct between 32-bit & 64-bit. Not sure how to verify this, though.

https://learn.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shell_notifyicona
https://learn.microsoft.com/en-us/windows/win32/api/shellapi/ns-shellapi-notifyicondataa
https://learn.microsoft.com/en-us/windows/win32/api/shellapi/ns-shellapi-notifyicondataw
https://microsoft.github.io/windows-docs-rs/doc/windows/Win32/UI/Shell/struct.NOTIFYICONDATAW.html

A random online copy of the definition: https://github.com/TDahlmann/canpp/blob/7f6873c64cccc4c85e18351676fe2b5605d6f84a/canl/dm/include/WIN32/SHELLAPI.H#L378

[riverar]

Took a quick look, here's a diff:

+[StructLayout(LayoutKind.Sequential, Pack = 1)]
 [Unicode]
 [StructSizeField("cbSize")]
 [Documentation("https://learn.microsoft.com/windows/win32/api/shellapi/ns-shellapi-notifyicondataw")]
-[SupportedArchitecture(Windows.Win32.Foundation.Metadata.Architecture.X64 | Windows.Win32.Foundation.Metadata.Architecture.Arm64)]
+[SupportedArchitecture(Windows.Win32.Foundation.Metadata.Architecture.X86)]
 public struct NOTIFYICONDATAW
 {
-	[StructLayout(LayoutKind.Explicit)]
+	[StructLayout(LayoutKind.Explicit, Pack = 1)]
 	public struct _Anonymous_e__Union
 	{
 		[FieldOffset(0)]
 		public uint uTimeout;

There's a packing difference across architectures. shellapi.h has this near the top:

#if !defined(_WIN64)
#include <pshpack1.h>
#endif

...

[riverar]

Closing this issue as there doesn't appear to be any work needed, but feel free to keep the discussion going!

Quick tip: In Visual Studio, you can hover over a C++ struct type and quickly retrieve size, alignment, and memory layout information.

[citelao]

Thanks for investigating! We were investigating yesterday and noticed that packing difference as well, but we noticed that prior art (e.g. TerraFx's impl) does not distinguish between 32- and 64-bit, with no obvious ill effect.

win32metadata is indeed parsing the struct & pack commands correctly, but we couldn't figure out (by inspection) what would change in the material layout of the structs. Everything seemed pointer-aligned.

FYI @jevansaks

[jevansaks]

@riverar the question is whether the NOTIFYICONDATAW layout is architecture independent from the WinMD perspective. The 64-bit and 32-bit versions obviously have different memory layouts because they contain pointers so we can't compare that way. The question is whether this struct will have the same layout with Pack=1 as the default struct layout on x86.

[riverar]

I see what you're saying now. Effectively the Pack=1 here is a no-op and when ignored, turns this into a arch-neutral struct definition.

I'm not sure metadata has facilities to override this but will re-open for tracking. Ideally this would be a change made to the SDK itself.