Review use of `CA1838` warning - Avoid 'StringBuilder' parameters for P/Invokes

[RussKie]

To update the underlying SDK/toolsets to 5.0-RC1 we had to suppress A1838 // Avoid 'StringBuilder' parameters for P/Invokes in 9dfaaa1.

https://github.com/dotnet/winforms/search?q=CA1838

The suppression needs to be reviewed, and corrected.

[AraHaan]

Speaking of updating warnings why is hDrop here an IntPtr and not HandleRef or SafeHandle?

winforms/src/System.Windows.Forms.Primitives/src/Interop/Shell32/Interop.DragQueryFileW.cs

Lines 13 to 16 in 2178e7a

	[DllImport(Libraries.Shell32, ExactSpelling = true, EntryPoint = "DragQueryFileW", CharSet = CharSet.Unicode)]
	#pragma warning disable CA1838 // Avoid 'StringBuilder' parameters for P/Invokes
	private static extern uint DragQueryFileWInternal(IntPtr hDrop, uint iFile, StringBuilder? lpszFile, uint cch);
	#pragma warning restore CA1838 // Avoid 'StringBuilder' parameters for P/Invokes

[weltkante]

I don't think thats a handle? doc says its a HDROP and I don't think thats something CloseHandle can operate on. In other words there would be nothing to keep alive and no ownership to manage, I believe.

[AraHaan]

lpszFile

Type: LPTSTR

The address of a buffer that receives the file name of a dropped file when the function returns. This file name is a null-terminated string. If this parameter is NULL, DragQueryFile returns the required size, in characters, of this buffer.

Ah I thought everwhere that StringBuilder was used was for buffers... I got to change the code a bit more before I open a pr.

[weltkante]

Ah I thought everwhere that StringBuilder was used was for buffers... I got to change the code a bit more before I open a pr.

Yes, your quote is about a buffer. Buffers are often optional, no contradiction here. What exactly did you have in mind?

[weltkante]

Looking at your PR you may be misunderstanding what "buffer" means. A buffer is a mutable memory area where the called function can write into. Specifically you can not use C# string because it is immutable and not supposed to be modified. Using a C# string has the semantics of a readonly LPCTSTR (node the 'C' for const) but not the semantics of a buffer.

[AraHaan]

Looking at your PR you may be misunderstanding what "buffer" means. A buffer is a mutable memory area where the called function can write into. Specifically you can not use C# string because it is immutable and not supposed to be modified. Using a C# string has the semantics of a readonly LPCTSTR (node the 'C' for const) but not the semantics of a buffer.

RIP so Span<char> or char* might be the only way. I think using Span<char> could be better then for it.

[RussKie]

In the interop signatures we generally use char*, and there are different way to get to it depending on a situation.