Build bgen and the product assemblies using/referencing netcore3.1.

Make.config

@@ -374,6 +374,9 @@ endif
 
 DOTNET_VERSION=3.1.100
 DOTNET_URL=https://download.visualstudio.microsoft.com/download/pr/787e81f1-f0da-4e3b-a989-8a199132ed8c/61a8dba81fbf2b3d533562d7b96443ec/dotnet-sdk-3.1.100-osx-x64.pkg
+DOTNET_BCL_REF_URL=https://www.nuget.org/api/v2/package/Microsoft.NETCore.App.Ref/3.1.0
+DOTNET_BCL_REF_NAME=microsoft.netcore.app.ref.3.1.0.nupkg
+DOTNET_BCL_DIR:=$(abspath $(TOP)/builds/downloads/$(basename $(DOTNET_BCL_REF_NAME)))/ref/netcoreapp3.1
 
 .SUFFIXES:
 MAKEFLAGS += --no-builtin-rules

builds/Makefile

@@ -15,14 +15,20 @@ download-mono: downloads/$(basename $(MONO_IOS_FILENAME)) downloads/$(basename $
 
 downloads/$(basename $(MONO_IOS_FILENAME)): MONO_URL=$(MONO_IOS_URL)
 downloads/$(basename $(MONO_MAC_FILENAME)): MONO_URL=$(MONO_MAC_URL)
+downloads/$(DOTNET_BCL_REF_NAME): MONO_URL=$(DOTNET_BCL_REF_URL)
 
 include $(TOP)/mk/colors.mk
 
+DOWNLOADS = \
+	downloads/$(MONO_IOS_FILENAME) \
+	downloads/$(MONO_MAC_FILENAME) \
+	downloads/$(DOTNET_BCL_REF_NAME) \
+
 # This target downloads the mono archives, there's one for Xamarin.iOS and one for Xamarin.Mac.
 # If doing many clean builds, it's possible to copy the downloaded zip file to ~/Library/Caches/xamarin-macios
 # to avoid having to download it every time. The zip files have to be copied manually, otherwise
 # we'd end up filling up a lot of hard drives around the world.
-downloads/$(MONO_IOS_FILENAME) downloads/$(MONO_MAC_FILENAME):
+$(DOWNLOADS):
 	$(Q) mkdir -p downloads
 	$(Q) echo "Downloading $(MONO_URL)..."
 	$(Q) if test -f ~/Library/Caches/xamarin-macios/$(notdir $@); then \
@@ -49,9 +55,25 @@ downloads/%: downloads/%.7z
 	$(Q) mv [email protected] $@
 	$(Q) echo "Unzipped $*."
 
+downloads/%: downloads/%.nupkg
+	$(Q) echo "Unzipping $*..."
+	$(Q) rm -Rf [email protected]
+	$(Q) unzip -d [email protected] $<
+	$(Q) find [email protected] -exec touch {} +
+	$(Q) mv [email protected] $@
+	$(Q) echo "Unzipped $*."
+
 .stamp-download-mono: download-mono $(TOP)/Make.config $(TOP)/mk/mono.mk
 	$(Q) touch $@
 
+DOTNET_DOWNLOADS = \
+	downloads/$(basename $(DOTNET_BCL_REF_NAME)) \
+
+dotnet: $(DOTNET_DOWNLOADS)
+ifdef ENABLE_DOTNET
+all-local:: $(DOTNET_DOWNLOADS)
+endif
+
 clean-local::
 	$(Q) rm -Rf downloads .stamp-download-mono
 

mk/quiet.mk

@@ -31,6 +31,9 @@ Q_XBUILD=$(if $(V),,@echo "XBUILD  $(@F)";)
 Q_TT=   $(if $(V),,@echo "TT       $(@F)";)
 Q_BUILD=$(if $(V),,@echo "BUILD    $(@F)";)
 
+Q_DOTNET_BUILD=$(if $(V),,@echo "CSC      [dotnet] $(@F)";)
+Q_DOTNET_GEN  =$(if $(V),,@echo "GEN      [dotnet] $(@F)";)
+
 Q_PROF_MCS =  $(if $(V),,@echo "MCS      [$(1)] $(@F)";)
 Q_PROF_CSC =  $(if $(V),,@echo "CSC      [$(1)] $(@F)";)
 Q_PROF_GEN  = $(if $(V),,@echo "GEN      [$(1)] $(@F)";)

src/CFNetwork/Content.cs

@@ -46,7 +46,7 @@ internal Content (WebResponseStream stream)
 			this.responseStream = stream;
 		}
 
-#if MONOMAC && XAMCORE_2_0
+#if (MONOMAC && XAMCORE_2_0) && !DOTNET
 		internal
 #endif
 		protected override bool TryComputeLength (out long length)

src/CFNetwork/MessageHandler.cs

@@ -78,7 +78,7 @@ public WorkerThread WorkerThread {
 		CFHTTPAuthentication auth;
 
 		#region implemented abstract members of HttpMessageHandler
-#if MONOMAC && XAMCORE_2_0
+#if (MONOMAC && XAMCORE_2_0) && !DOTNET
 		internal
 #endif
 		protected override async Task<HttpResponseMessage> SendAsync (HttpRequestMessage request,

src/Compression/Compression.cs

@@ -300,11 +300,19 @@ private static void ThrowCannotWriteToDeflateStreamException()
 			throw new InvalidOperationException ("Writing to the compression stream is not supported.");
 		}
 
+#if !DOTNET_TODO
+		// DOTNET_TODO: TaskToApm is internal API in mscorlib, so we can't use it.
+		// Although I'm not sure if we even need to override these methods,
+		// the base class implementation works (but synchronously),
+		// and the documentation recommends using ReadAsync instead.
+		// If we decide to implement this, we could just copy the TaskToApm implementation:
+		// https://github.com/microsoft/referencesource/blob/a7bd3242bd7732dec4aebb21fbc0f6de61c2545e/mscorlib/system/threading/Tasks/TaskToApm.cs
 		public override IAsyncResult BeginRead (byte[] buffer, int offset, int count, AsyncCallback asyncCallback, object asyncState) =>
 			TaskToApm.Begin(ReadAsync (buffer, offset, count, CancellationToken.None), asyncCallback, asyncState);
 
 		public override int EndRead (IAsyncResult asyncResult) =>
 			TaskToApm.End<int> (asyncResult);
+#endif // !DOTNET_TODO
 
 		public override Task<int> ReadAsync (byte[] array, int offset, int count, CancellationToken cancellationToken)
 		{
@@ -547,10 +555,13 @@ protected override void Dispose (bool disposing)
 			}
 		}
 
+#if !DOTNET_TODO
+		// DOTNET_TODO: See comment about TaskToApm elsewhere in this file.
 		public override IAsyncResult BeginWrite (byte[] array, int offset, int count, AsyncCallback asyncCallback, object asyncState) =>
 			TaskToApm.Begin(WriteAsync (array, offset, count, CancellationToken.None), asyncCallback, asyncState);
 
 		public override void EndWrite (IAsyncResult asyncResult) => TaskToApm.End (asyncResult);
+#endif // !DOTNET_TODO
 
 		public override Task WriteAsync (byte[] array, int offset, int count, CancellationToken cancellationToken)
 		{

src/Foundation/NSUrlSessionHandler.cs

@@ -473,7 +473,7 @@ async Task<NSUrlRequest> CreateRequest (HttpRequestMessage request)
 			return nsrequest;
 		}
 
-#if SYSTEM_NET_HTTP || MONOMAC
+#if (SYSTEM_NET_HTTP || MONOMAC) && !DOTNET
 		internal
 #endif
 		protected override async Task<HttpResponseMessage> SendAsync (HttpRequestMessage request, CancellationToken cancellationToken)
@@ -935,7 +935,10 @@ protected override Task SerializeToStreamAsync (Stream stream, TransportContext
 				return content.CopyToAsync (stream, bufferSize, cancellationToken);
 			}
 
-			protected internal override bool TryComputeLength (out long length)
+#if !DOTNET
+			internal
+#endif
+			protected override bool TryComputeLength (out long length)
 			{
 				if (!content.CanSeek) {
 					length = 0;