Update .NET SDKs to LTS versions

appveyor.bat

@@ -38,7 +38,7 @@ dotnet restore
 dotnet build -c %configuration% || goto error
 
 echo Testing C#
-dotnet test -c %configuration% -f netcoreapp2.1 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error
+dotnet test -c %configuration% -f netcoreapp3.1 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error
 dotnet test -c %configuration% -f net451 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error
 
 goto :EOF

conformance/Makefile.am

@@ -316,7 +316,7 @@ conformance-java-lite: javac_middleman_lite
 conformance-csharp: $(other_language_protoc_outputs)
 	@echo "Writing shortcut script conformance-csharp..."
 	@echo '#! /bin/sh' > conformance-csharp
-	@echo 'dotnet ../csharp/src/Google.Protobuf.Conformance/bin/Release/netcoreapp2.1/Google.Protobuf.Conformance.dll "$$@"' >> conformance-csharp
+	@echo 'dotnet ../csharp/src/Google.Protobuf.Conformance/bin/Release/netcoreapp3.1/Google.Protobuf.Conformance.dll "$$@"' >> conformance-csharp
 	@chmod +x conformance-csharp
 
 conformance-php:

csharp/buildall.sh

@@ -10,8 +10,8 @@ dotnet restore $SRC/Google.Protobuf.sln
 dotnet build -c $CONFIG $SRC/Google.Protobuf.sln
 
 echo Running tests.
-# Only test netcoreapp2.1, which uses the .NET Core runtime.
+# Only test netcoreapp3.1, which uses the .NET Core runtime.
 # If we want to test the .NET 4.5 version separately, we could
 # run Mono explicitly. However, we don't have any differences between
 # the .NET 4.5 and netstandard2.1 assemblies.
-dotnet test -c $CONFIG -f netcoreapp2.1 $SRC/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+dotnet test -c $CONFIG -f netcoreapp3.1 $SRC/Google.Protobuf.Test/Google.Protobuf.Test.csproj

csharp/compatibility_tests/v3.0.0/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFrameworks>net451;netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks>net451;netcoreapp3.1</TargetFrameworks>
     <AssemblyOriginatorKeyFile>../../keys/Google.Protobuf.snk</AssemblyOriginatorKeyFile>
     <SignAssembly>true</SignAssembly>
     <IsPackable>False</IsPackable>

csharp/compatibility_tests/v3.0.0/test.sh

@@ -22,7 +22,7 @@ function run_test() {
   dotnet restore src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
   dotnet build -c Release src/Google.Protobuf/Google.Protobuf.csproj
   dotnet build -c Release src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
-  dotnet run -c Release -f netcoreapp2.1 -p src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+  dotnet run -c Release -f netcoreapp3.1 -p src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
 }
 
 set -ex

csharp/install_dotnet_sdk.ps1

@@ -16,5 +16,5 @@ Invoke-WebRequest -Uri $InstallScriptUrl -OutFile $InstallScriptPath
 
 # The SDK versions to install should be kept in sync with versions
 # installed by kokoro/linux/dockerfile/test/csharp/Dockerfile
-&$InstallScriptPath -Version 2.1.802
-&$InstallScriptPath -Version 5.0.102
+&$InstallScriptPath -Version 3.1.415
+&$InstallScriptPath -Version 6.0.100

csharp/src/AddressBook/AddressBook.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <OutputType>Exe</OutputType>
     <StartupObject>Google.Protobuf.Examples.AddressBook.Program</StartupObject>
     <IsPackable>False</IsPackable>

csharp/src/Google.Protobuf.Benchmarks/Program.cs

@@ -36,7 +36,7 @@ namespace Google.Protobuf.Benchmarks
 {
     class Program
     {
-        // typical usage: dotnet run -c Release -f netcoreapp2.1
+        // typical usage: dotnet run -c Release -f netcoreapp3.1
         // (this can profile both .net core and .net framework; for some reason
         // if you start from "-f net461", it goes horribly wrong)
         public static void Main(string[] args)

csharp/src/Google.Protobuf.Conformance/Google.Protobuf.Conformance.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <OutputType>Exe</OutputType>
     <IsPackable>False</IsPackable>
   </PropertyGroup>

csharp/src/Google.Protobuf.JsonDump/Google.Protobuf.JsonDump.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <OutputType>Exe</OutputType>
     <IsPackable>False</IsPackable>
   </PropertyGroup>

csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs

@@ -840,7 +840,7 @@ namespace Google.Protobuf.Collections
             var list2 = new RepeatedField<double> { SampleNaNs.Regular, SampleNaNs.PayloadFlipped };
             var list3 = new RepeatedField<double> { SampleNaNs.Regular, SampleNaNs.SignallingFlipped };
 
-            // All SampleNaNs have the same hashcode under certain targets (e.g. netcoreapp2.1)
+            // All SampleNaNs have the same hashcode under certain targets (e.g. netcoreapp3.1)
             EqualityTester.AssertInequality(list1, list2, checkHashcode: false);
             EqualityTester.AssertEquality(list1, list3);
             Assert.True(list1.Contains(SampleNaNs.SignallingFlipped));

csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net451;netcoreapp2.1;net50</TargetFrameworks>
+    <TargetFrameworks>net451;netcoreapp3.1;net60</TargetFrameworks>
     <AssemblyOriginatorKeyFile>../../keys/Google.Protobuf.snk</AssemblyOriginatorKeyFile>
     <SignAssembly>true</SignAssembly>
     <IsPackable>False</IsPackable>

csharp/src/Google.Protobuf/Google.Protobuf.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <Description>C# runtime library for Protocol Buffers - Google's data interchange format.</Description>
@@ -43,7 +43,7 @@
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="System.Memory" Version="4.5.3"/>
-    <!-- Needed for netcoreapp2.1 to work correctly. .NET is not able to load the assembly without this -->
+    <!-- Needed for netcoreapp3.1 to work correctly. .NET is not able to load the assembly without this -->
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="4.5.2"/>
   </ItemGroup>
 

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "5.0.102",
+    "version": "6.0.100",
     "rollForward": "latestMinor"
   }
 }

kokoro/linux/aarch64/test_csharp_aarch64.sh

@@ -15,7 +15,7 @@ fi
 # First, build protobuf C# tests under x86_64 docker image
 # Tests are built "dotnet publish" because we want all the dependencies to the copied to the destination directory
 # (we want to avoid references to ~/.nuget that won't be available in the subsequent docker run)
-CSHARP_BUILD_COMMAND="dotnet publish -c Release -f net50 csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj"
+CSHARP_BUILD_COMMAND="dotnet publish -c Release -f net60 csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj"
 docker run $DOCKER_TTY_ARGS --rm --user "$(id -u):$(id -g)" -e "HOME=/home/fake-user" -e "DOTNET_CLI_TELEMETRY_OPTOUT=true" -e "DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true" -v "$(mktemp -d):/home/fake-user" -v "$(pwd)":/work -w /work mcr.microsoft.com/dotnet/sdk:5.0.202-buster-slim bash -c "$CSHARP_BUILD_COMMAND"
 
 # Use an actual aarch64 docker image to run protobuf C# tests with an emulator. "dotnet vstest" allows
@@ -25,5 +25,5 @@ docker run $DOCKER_TTY_ARGS --rm --user "$(id -u):$(id -g)" -e "HOME=/home/fake-
 #   running under current user's UID and GID. To be able to do that, we need to provide a home directory for the user
 #   otherwise the UID would be homeless under the docker container and pip install wouldn't work. For simplicity,
 #   we just run map the user's home to a throwaway temporary directory
-CSHARP_TEST_COMMAND="dotnet vstest csharp/src/Google.Protobuf.Test/bin/Release/net50/publish/Google.Protobuf.Test.dll"
+CSHARP_TEST_COMMAND="dotnet vstest csharp/src/Google.Protobuf.Test/bin/Release/net60/publish/Google.Protobuf.Test.dll"
 docker run $DOCKER_TTY_ARGS --rm --user "$(id -u):$(id -g)" -e "HOME=/home/fake-user" -e "DOTNET_CLI_TELEMETRY_OPTOUT=true" -e "DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true" -v "$(mktemp -d):/home/fake-user" -v "$(pwd)":/work -w /work mcr.microsoft.com/dotnet/sdk:5.0.202-buster-slim-arm64v8 bash -c "$CSHARP_TEST_COMMAND"

kokoro/linux/dockerfile/test/csharp/Dockerfile

@@ -32,8 +32,8 @@ RUN apt-get update && apt-get install -y libunwind8 libicu63 && apt-get clean
 # Install dotnet SDK via install script
 RUN wget -q https://dot.net/v1/dotnet-install.sh && \
     chmod u+x dotnet-install.sh && \
-    ./dotnet-install.sh --version 2.1.802 && \
-    ./dotnet-install.sh --version 5.0.102 && \
+    ./dotnet-install.sh --version 3.1.415 && \
+    ./dotnet-install.sh --version 6.0.100 && \
     ln -s /root/.dotnet/dotnet /usr/local/bin
 
 RUN wget -q www.nuget.org/NuGet.exe -O /usr/local/bin/nuget.exe