Always append the "dll" extension for native libraries loads on Windows

[AaronRobinsonMSFT]

Fixes #66608

Due to case-sensitive file systems on Windows the runtime will now always append the ".dll" extension unless the name contains a trailing "." or a known loadable extension. This is an attempt to mitigate the default Windows behavior that appends a ".DLL" which is rarely the casing used for Windows shared libraries.

Documentation PR to follow.

/cc @dotnet/interop-contrib

[AaronRobinsonMSFT]

My cursory look in Mono indicates they do not suffer from this issue. @lambdageek can you confirm my understanding of the following code:

runtime/src/mono/mono/metadata/native-library.c

Lines 492 to 510 in ba5a582

	static MonoDl *
	netcore_probe_for_module_variations (const char *mdirname, const char *file_name, int raw_flags)
	{
	void *iter = NULL;
	char *full_name = NULL;
	MonoDl *module = NULL;
	while (module == NULL && (full_name = mono_dl_build_path (mdirname, file_name, &iter))) {
	char *error_msg = NULL;
	module = mono_dl_open_full (full_name, MONO_DL_LAZY, raw_flags, &error_msg);
	if (!module) {
	mono_trace (G_LOG_LEVEL_DEBUG, MONO_TRACE_DLLIMPORT, "DllImport error loading library '%s': '%s'.", full_name, error_msg);
	g_free (error_msg);
	}
	g_free (full_name);
	}
	return module;
	}

[jkotas]

Does https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/LibraryNameVariation.Windows.cs need fixing to be in sync?

[AaronRobinsonMSFT]

Does https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/LibraryNameVariation.Windows.cs need fixing to be in sync?

Yes. I don't think how this was done makes a lot of sense. Having this code duplication logic is a recipe for failure. Thanks for pointing it out.

[jkoritzinsky]

Based on commit history, the duplicate implementation in managed is used by NativeAOT.

[jkotas]

Based on commit history, the duplicate implementation in managed is used by NativeAOT.

And AssemblyDependencyResolver.

[lambdageek]

My cursory look in Mono indicates they do not suffer from this issue. @lambdageek can you confirm my understanding of the following code:

Mono will probe for several different variations on the name - first as given, then with the mono_dl_get_so_suffixes suffixes (".dll" on Windows - lowercase), and also with a prefix mono_dl_get_so_prefix () ("" on Windows)- until it finds a name that works.

So I agree - I don't think Mono is affected.