Fix Ix.NET build break on Ubuntu 24 (#2209)

* Remove netcoreapp3.1 from tests. It looks like this runtime no longer works on the hosted agents. (This means we currently have no way to test netcoreapp2.1.)
* Fix tests that suddenly no longer compile. I think this may be due to the compiler fixing what was technically a bug
* Put build agent back to Windows. The Ubuntu-24 agents dropped support for mono and MSBuild.

Ix.NET/Source/Ix.NET.sln

@@ -5,7 +5,7 @@ VisualStudioVersion = 17.2.32131.331
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{87534290-A7A6-47A4-9A3A-D0D21A9AD1D4}"
 	ProjectSection(SolutionItems) = preProject
-		NetCore31TestReadme.txt = NetCore31TestReadme.txt
+		NetStandard21TestReadme.txt = NetStandard21TestReadme.txt
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B733D97A-F1ED-4FC3-BF8E-9AC47A89DE96}"

Ix.NET/Source/NetCore31TestReadme.txt

@@ -1,7 +0,0 @@
-The tests all include a .NET Core 3.1 target, even though that has long since been out of support.
-
-The reason for this is that Ix.NET 6.0 offers a .NET Standard 2.1 target, and currently, the only way we have of testing this is through .NET Core 3.1.
-
-Although current versions of .NET (but not .NET Framework) support .NET Standard 2.1, they are all going to prefer the net6.0 target. We do test on currently supported versions of .NET, but we also want to test the .NET Standard 2.1 target.
-
-It might be possible to test via Mono instead, or possibly even Unity, but this would likely involve additional CI/CD work, so for now we're sticking with the .NET Core 3.1 target framework. It's unsupported, but it's better than doing no testing at all.

Ix.NET/Source/NetStandard21TestReadme.txt

@@ -0,0 +1,5 @@
+Ix.NET 6.0 offers a .NET Standard 2.1 target, but currently, we have no way of testing this.
+
+We used to test this target by running tests in .NET Core 3.1. Unfortunately, the test runners now crash when running tests in .NET Core 3.1. .NET Core 3.1 has long since been out of support, so there's not much we can do about this. (It now reports the absence of ssllib on the hosted build agents.)
+
+Although current versions of .NET (but not .NET Framework) support .NET Standard 2.1, they are all going to prefer the net6.0 target. It might be possible to test via Mono instead, or possibly even Unity, but this would likely involve additional CI/CD work. But for now this target is untested. If we can't find a way to test netstandard2.1, that suggests there's no scenario in which it is useful now, so we may remove it in a future release.

Ix.NET/Source/System.Interactive.Async.Providers.Tests/System.Interactive.Async.Providers.Tests.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <!-- See NetCore31TestReadme.txt for why we still use netcoreapp3.1 -->
-    <TargetFrameworks>net48;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0;net6.0</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0618</NoWarn>
   </PropertyGroup>
 

Ix.NET/Source/System.Interactive.Async.Tests/System.Interactive.Async.Tests.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <!-- See NetCore31TestReadme.txt for why we still use netcoreapp3.1 -->
-    <TargetFrameworks>net48;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0;net6.0</TargetFrameworks>
 
     <!--
       CA1510: Use ArgumentNullException.ThrowIfNull - not available on .NET 4.8

Ix.NET/Source/System.Interactive.Async.Tests/System/Linq/Operators/Distinct.cs

@@ -41,8 +41,9 @@ namespace Tests
         {
             var xs = new[] { 1, 2, 1, 3, 5, 2, 1, 4 }.ToAsyncEnumerable().Distinct(k => k);
 
-            var res = new[] { 1, 2, 3, 5, 4 };
-            Assert.True(res.SequenceEqual(await xs.ToArrayAsync()));
+            var expected = new[] { 1, 2, 3, 5, 4 };
+            var actual = await xs.ToArrayAsync();
+            Assert.True(expected.SequenceEqual(actual));
         }
 
         [Fact]

Ix.NET/Source/System.Interactive.Tests/System.Interactive.Tests.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <!-- See NetCore31TestReadme.txt for why we still use netcoreapp3.1 -->
-    <TargetFrameworks>net48;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0;net6.0</TargetFrameworks>
 
     <!--
       CA1822: Make member static. Not necessary for test code.

Ix.NET/Source/System.Linq.Async.Queryable.Tests/System.Linq.Async.Queryable.Tests.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <!-- See NetCore31TestReadme.txt for why we still use netcoreapp3.1 -->
-    <TargetFrameworks>net48;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0;net6.0</TargetFrameworks>
     <NoWarn>$(NoWarn);CS0618</NoWarn>
   </PropertyGroup>
 

Ix.NET/Source/System.Linq.Async.Tests/System.Linq.Async.Tests.csproj

@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <!-- See NetCore31TestReadme.txt for why we still use netcoreapp3.1 -->
-    <TargetFrameworks>net48;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0;net6.0</TargetFrameworks>
 
     <!--
     CA1510: Use ArgumentNullException.ThrowIfNull - not available on .NET 4.8

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/Concat.cs

@@ -104,8 +104,9 @@ namespace Tests
 
             var c = xs.Concat(ys).Concat(zs);
 
-            var res = new[] { 1, 2, 3, 4, 5, 6, 7, 8 };
-            Assert.True(res.SequenceEqual(await c.ToArrayAsync()));
+            var expected = new[] { 1, 2, 3, 4, 5, 6, 7, 8 };
+            var actual = await c.ToArrayAsync();
+            Assert.True(expected.SequenceEqual(actual));
         }
 
         [Fact]

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/DefaultIfEmpty.cs

@@ -136,9 +136,10 @@ namespace Tests
         {
             var xs = AsyncEnumerable.Empty<int>().DefaultIfEmpty(42);
 
-            var res = new[] { 42 };
+            var expected = new[] { 42 };
+            var actual = await xs.ToArrayAsync();
 
-            Assert.True(res.SequenceEqual(await xs.ToArrayAsync()));
+            Assert.True(expected.SequenceEqual(actual));
         }
 
         [Fact]
@@ -156,9 +157,10 @@ namespace Tests
         {
             var xs = new[] { 1, 2, 3, 4 }.ToAsyncEnumerable().DefaultIfEmpty();
 
-            var res = new[] { 1, 2, 3, 4 };
+            var expected = new[] { 1, 2, 3, 4 };
 
-            Assert.True(res.SequenceEqual(await xs.ToArrayAsync()));
+            var actual = await xs.ToArrayAsync();
+            Assert.True(expected.SequenceEqual(actual));
         }
 
         [Fact]

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/Distinct.cs

@@ -52,8 +52,9 @@ namespace Tests
         {
             var xs = new[] { 1, 2, 1, 3, 5, 2, 1, 4 }.ToAsyncEnumerable().Distinct();
 
-            var res = new[] { 1, 2, 3, 5, 4 };
-            Assert.True(res.SequenceEqual(await xs.ToArrayAsync()));
+            var expected = new[] { 1, 2, 3, 5, 4 };
+            var actual = await xs.ToArrayAsync();
+            Assert.True(expected.SequenceEqual(actual));
         }
 
         [Fact]

Ix.NET/Source/System.Linq.Async.Tests/System/Linq/Operators/OrderBy.Generated.cs

@@ -7498,8 +7498,10 @@ namespace Tests
         private async Task AssertSorted<T>(IAsyncEnumerable<T> asyncRes, IEnumerable<T> syncRes)
         {
             Assert.True(await syncRes.ToAsyncEnumerable().SequenceEqualAsync(asyncRes));
-            Assert.True(syncRes.ToList().SequenceEqual(await asyncRes.ToListAsync()));
-            Assert.True(syncRes.ToArray().SequenceEqual(await asyncRes.ToArrayAsync()));
+            var toListResult = await asyncRes.ToListAsync();
+            Assert.True(syncRes.ToList().SequenceEqual(toListResult));
+            var toArrayResult = await asyncRes.ToArrayAsync();
+            Assert.True(syncRes.ToArray().SequenceEqual(toArrayResult));
 
             int syncCount = syncRes.Count();
             int asyncCount = await asyncRes.CountAsync();

azure-pipelines.ix.yml

@@ -29,7 +29,7 @@ stages:
   jobs:
   - job: Build
     pool:
-      vmImage: ubuntu-latest
+      vmImage: windows-latest
     steps:
     - task: UseDotNet@2
       displayName: Use .NET Core 8.x SDK
@@ -42,12 +42,6 @@ stages:
         version: '6.x'
         packageType: runtime
 
-    - task: UseDotNet@2
-      displayName: .NET Core 3.1 runtime
-      inputs:
-        version: '3.1.x'
-        packageType: runtime
-
     - task: DotNetCoreCLI@2
       inputs:
         command: custom
@@ -55,7 +49,7 @@ stages:
         arguments: install --tool-path . nbgv
       displayName: Install NBGV tool
 
-    - script: ./nbgv cloud -p Ix.NET/Source
+    - script: nbgv cloud -a -p Ix.NET/Source
       displayName: Set Version
 
     - task: DotNetCoreCLI@2
@@ -97,7 +91,7 @@ stages:
         arguments: -c $(BuildConfiguration) --settings Ix.NET/Source/CodeCoverage.runsettings --collect:"XPlat Code Coverage" -- RunConfiguration.DisableAppDomain=true
       displayName: Run Tests
 
-    - script: ./reportgenerator -reports:$(Agent.TempDirectory)/**/coverage.cobertura.xml -targetdir:$(Build.SourcesDirectory)/Ix.NET/Source/coverlet/reports -reporttypes:"Cobertura"
+    - script: reportgenerator -reports:$(Agent.TempDirectory)/**/coverage.cobertura.xml -targetdir:$(Build.SourcesDirectory)/Ix.NET/Source/coverlet/reports -reporttypes:"Cobertura"
       displayName: Create reports
 
     - task: PublishCodeCoverageResults@1