Use SHGetKnownFolderPath to get path to localappdata for current user

[stevenbrix]

On Windows, it's not guaranteed that USERPROFILE is equivalent to %SYSTEMDRIVE%\Users\%USERNAME%. So it's possible that UserDefaults tries to write to a non-existent location, in which case it will never work. When this happens, all writes silently no-op.

This PR uses the Shell API SHGetKnownFolderPath to get the location of %LOCALAPPDATA% instead of manually building the path.

See documentation for this API:

Fixes #4997

[ShikiSuen]

@stevenbrix You might want to remove the format changes introduced on your computer.
This minifies the modifications that only necessary changes are kept.

P.S.: This PR is really important and I don't know why it gets abandoned here for months.

[ShikiSuen]

@stevenbrix This PR is fallen behind the main branch too far.
The file to modified has been relocated to this folder:
/Sources/CoreFoundation/CFKnownLocations.c
And the part I guess you might want to modify is limited to this scope:

swift-corelibs-foundation/Sources/CoreFoundation/CFKnownLocations.c

Lines 97 to 123 in 0129358

	case _kCFKnownLocationUserCurrent:
	username = CFGetUserName();
	// fallthrough
	case _kCFKnownLocationUserByName: {
	DWORD size = 0;
	GetProfilesDirectoryW(NULL, &size);
	wchar_t* path = (wchar_t*)malloc(size * sizeof(wchar_t));
	GetProfilesDirectoryW(path, &size);
	CFStringRef pathRef = CFStringCreateWithCharacters(kCFAllocatorSystemDefault, path, size - 1);
	free(path);
	CFURLRef profilesDir = CFURLCreateWithFileSystemPath(kCFAllocatorSystemDefault, pathRef, kCFURLWindowsPathStyle, true);
	CFRelease(pathRef);
	CFURLRef usernameDir = CFURLCreateCopyAppendingPathComponent(kCFAllocatorSystemDefault, profilesDir, username, true);
	CFURLRef appdataDir = CFURLCreateCopyAppendingPathComponent(kCFAllocatorSystemDefault, usernameDir, CFSTR("AppData"), true);
	location = CFURLCreateCopyAppendingPathComponent(kCFAllocatorSystemDefault, appdataDir, CFSTR("Local"), true);
	CFRelease(usernameDir);
	CFRelease(appdataDir);
	CFRelease(profilesDir);
	if (user == _kCFKnownLocationUserCurrent) {
	CFRelease(username);
	}
	break;

[compnerd]

This seems incorrect. The path parameter is a wide C String not a CFStrimg. This should do the creation of the CFString and pass that.

[ShikiSuen]

@compnerd I emailed stevenbrix on Feb 18 trying to bring his attention towards your previous response here, but he has no response.

I am less familiar with the moral culture context in FOSS projects like this one. Is it appropriate for me (or anyone else) to replicate this PR and patch this? (with credits of stevenbrix in the commit message wherever necessary.)

[compnerd]

@compnerd I emailed stevenbrix on Feb 18 trying to bring his attention towards your previous response here, but he has no response.

I am less familiar with the moral culture context in FOSS projects like this one. Is it appropriate for me (or anyone else) to replicate this PR and patch this? (with credits of stevenbrix in the commit message wherever necessary.)

Yes, maintaining the authorship/credit is key. It would be very much acceptable for someone to pick up the patch and help push it along if the original author is unable to do so.

[ShikiSuen]

Yes, maintaining the authorship/credit is key. It would be very much acceptable for someone to pick up the patch and help push it along if the original author is unable to do so.

Solid copy. Thanks for your response.

While I may see whether I can have some time to handle this issue within the next week, anyone can go ahead doing this without having to wait for me. This issue directly affects the usability of Swift (especially UserDefaults) on Windows.

[stevenbrix]

Hi @ShikiSuen sorry for not responding. I'm not sure these changes are needed anymore now that the code has moved. I'll need to do more investigation here.

[ShikiSuen]

Hi @ShikiSuen sorry for not responding. I'm not sure these changes are needed anymore now that the code has moved. I'll need to do more investigation here.

Thanks for your response. Good to see you get back online.
I'll wait for your investigation results.

[parkera]

@swift-ci test

[ShikiSuen]

@compnerd Sorry for bothering you.
This PR is on halt for 2 weeks since the previous comment left above, hence my question.
Could you please take a look at stevenbrix's most-recent commit to see whether there's still any issue?

[compnerd]

This seems wrong. It is backwards no? LocalAppData would be for the current user, not a specified user. This seems like it would not return a location for the current user, and return the location for the current user when you specify a user name.