[dotnet] Use a different min OS version when building with NativeAOT.

This is because NativeAOT contains swift code, and we'd have to add code to
embed the Swift libraries in any apps that target early OS versions. We could
eventually implement this, but let's wait and see if there's a demand first.

Make.config

@@ -273,6 +273,12 @@ DOTNET_MIN_TVOS_SDK_VERSION=11.0
 DOTNET_MIN_MACCATALYST_SDK_VERSION=13.1
 DOTNET_MIN_MACOS_SDK_VERSION=10.15
 
+# Minimum OS versions when using NativeOAT - these are at least the general min versions above (but may be higher).
+DOTNET_MIN_NATIVEAOT_IOS_SDK_VERSION=12.2
+DOTNET_MIN_NATIVEAOT_TVOS_SDK_VERSION=12.2
+DOTNET_MIN_NATIVEAOT_MACCATALYST_SDK_VERSION=13.1
+DOTNET_MIN_NATIVEAOT_MACOS_SDK_VERSION=10.15
+
 # The min simulator version available in the Xcode we're using
 MIN_IOS_SIMULATOR_VERSION=13.7
 MIN_WATCHOS_SIMULATOR_VERSION=7.0

dotnet/generate-target-platforms.csharp

@@ -24,10 +24,16 @@ var doc = new XmlDocument ();
 doc.Load (plistPath);
 var nodes = doc.SelectNodes ($"/plist/dict/key[text()='KnownVersions']/following-sibling::dict[1]/key[text()='{platform}']/following-sibling::array[1]/string");
 
+var allLines = File.ReadAllLines ("../Make.config");
+
 var minSdkVersionName = $"DOTNET_MIN_{platform.ToUpper ()}_SDK_VERSION";
-var minSdkVersionString = File.ReadAllLines ("../Make.config").Single (v => v.StartsWith (minSdkVersionName + "=", StringComparison.Ordinal)).Substring (minSdkVersionName.Length + 1);
+var minSdkVersionString = allLines.Single (v => v.StartsWith (minSdkVersionName + "=", StringComparison.Ordinal)).Substring (minSdkVersionName.Length + 1);
 var minSdkVersion = Version.Parse (minSdkVersionString);
 
+var minNativeAotSdkVersionName = $"DOTNET_MIN_NATIVEAOT_{platform.ToUpper ()}_SDK_VERSION";
+var minNativeAotSdkVersionString = allLines.Single (v => v.StartsWith (minNativeAotSdkVersionName + "=", StringComparison.Ordinal)).Substring (minNativeAotSdkVersionName.Length + 1);
+var minNativeAotSdkVersion = Version.Parse (minNativeAotSdkVersionString);
+
 using (TextWriter writer = new StreamWriter (outputPath)) {
 	writer.WriteLine ($"<!-- This file contains a generated list of the {platform} platform versions that are supported for this SDK -->");
 	writer.WriteLine ($"<!-- Generation script: https://github.com/xamarin/xamarin-macios/blob/main/dotnet/generate-target-platforms.csharp -->");
@@ -36,17 +42,23 @@ using (TextWriter writer = new StreamWriter (outputPath)) {
 
 	foreach (XmlNode n in nodes) {
 		var version = n.InnerText;
-		if (Version.Parse (version) < minSdkVersion)
+		var parsedVersion = Version.Parse (version);
+		if (parsedVersion < minSdkVersion)
 			continue;
+		if (parsedVersion < minNativeAotSdkVersion) {
+			writer.WriteLine ($"\t\t<{platform}SdkSupportedTargetPlatformVersion Include=\"{n.InnerText}\" Condition=\"'$(PublishAot)' != 'true'\" />");
+		} else {
 			writer.WriteLine ($"\t\t<{platform}SdkSupportedTargetPlatformVersion Include=\"{n.InnerText}\" />");
 		}
+	}
 
 	writer.WriteLine ("\t</ItemGroup>");
 	writer.WriteLine ("\t<ItemGroup>");
 	writer.WriteLine ($"\t\t<SdkSupportedTargetPlatformVersion Condition=\"'$(TargetPlatformIdentifier)' == '{platform}'\" Include=\"@({platform}SdkSupportedTargetPlatformVersion)\" />");
 	writer.WriteLine ("\t</ItemGroup>");
 	writer.WriteLine ("\t<PropertyGroup>");
-	writer.WriteLine ($"\t\t<{platform}MinSupportedOSPlatformVersion>{minSdkVersionString}</{platform}MinSupportedOSPlatformVersion>");
+	writer.WriteLine ($"\t\t<{platform}MinSupportedOSPlatformVersion Condition=\"'$(PublishAot)' != 'true'\">{minSdkVersionString}</{platform}MinSupportedOSPlatformVersion>");
+	writer.WriteLine ($"\t\t<{platform}MinSupportedOSPlatformVersion Condition=\"'$(PublishAot)' == 'true'\">{minNativeAotSdkVersionString}</{platform}MinSupportedOSPlatformVersion>");
 	writer.WriteLine ("\t</PropertyGroup>");
 	writer.WriteLine ("</Project>");
 }