build: Drop support for .NET Core 2.x

Remove build targets for .NET Core 2.0 and 2.1 and target .NET Core 3.1 instead.
Since the library still targets .NET Standard 2.0, too, it continues to be usable from .NET Core 2.x, however, there might be build errors because some extension methods exist in both this library as well as in the .NET Core 2 base class library.

BREAKING CHANGE:  .NET Core 2.0 and  .NET Core 2.1 are no longer supported. Projects targeting these projects might encounter conflicts between extensions methods provided by this library and extension methods provided by the .NET Core Base Class Library.
Pull-Request: #90

azure-pipelines.yml

@@ -91,13 +91,13 @@ jobs:
   - task: CmdLine@2
     displayName: Restore NuGet packages
     inputs:
-      script: dotnet restore $(solutionPath)
+      script: dotnet restore $(solutionPath) /warnaserror
   - task: DotNetCoreCLI@2
     displayName: Build
     inputs:
       command: build
       projects: $(solutionPath)
-      arguments: '--configuration $(configuration) --no-restore /m:1'  
+      arguments: '--configuration $(configuration) --no-restore /warnaserror /m:1'  
   - task: DotNetCoreCLI@2
     displayName: Test
     inputs:
@@ -111,7 +111,7 @@ jobs:
     inputs:
       command: pack
       projects: $(solutionPath)
-      arguments: '--configuration $(configuration) --output $(Build.ArtifactStagingDirectory) --no-build'  
+      arguments: '--configuration $(configuration) --output $(Build.ArtifactStagingDirectory) --no-build /warnaserror'  
   - task: PublishBuildArtifacts@1
     displayName: 'Publish Artifacts: $(artifactsName_Binaries)'
     inputs:

src/Utilities.ReferenceAssemblies/Grynwald.Utilities.ReferenceAssemblies.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp2.0;netcoreapp2.1;net472</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp3.1;net472</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <NoWarn>1591;$(NoWarn)</NoWarn>
   </PropertyGroup>

src/Utilities/Collections/DictionaryExtensions.cs

@@ -36,9 +36,9 @@ public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TVal
         }
 
         // GetValueOrDefault was added in .NET Core 2.0.
-        // Exclude the method from the reference assembly for .NET Core 2.0,
-        // so a project targeting netcoreapp2.0, uses the built-in method
-#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0 || NETCOREAPP2_1 || NETSTANDARD2_1))
+        // Exclude the method from the reference assembly for .NET Core 2.0 or later,
+        // so a project targeting netcoreapp2.0 or later, uses the built-in method
+#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER))
 
         /// <summary>
         /// Tries to get the element with the specified key.
@@ -56,7 +56,7 @@ public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TVal
         /// <typeparam name="TValue">The type of values in the dictionary.</typeparam>
         /// <param name="dictionary">The dictionary to retrieve the value from.</param>
         /// <param name="key">The key to locate in the dictionary.</param>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key) => dictionary.GetValueOrDefault(key, default);
 

src/Utilities/Collections/EnumerableExtensions.cs

@@ -48,8 +48,8 @@ public static IEnumerable<T> Concat<T>(this IEnumerable<T> enumerable, T newItem
 
         // ToHashSet exists in .NET Core 2.0, .NET Standard 2.1 and .NET Framework 4.7.2
         // Exclude the method from the reference assembly for these target frameworks
-        // so a project targeting netcoreapp2.0, uses the built-in method
-#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0 || NETCOREAPP2_1 || NET472 || NETSTANDARD2_1))
+        // so a project targeting these frameworks, uses the built-in method
+#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0_OR_GREATER|| NET472_OR_GREATER || NETSTANDARD2_1_OR_GREATER))
 
         /// <summary>
         /// Creates a new <see cref="HashSet{T}"/> with elements copied from the enumerable
@@ -67,7 +67,7 @@ public static IEnumerable<T> Concat<T>(this IEnumerable<T> enumerable, T newItem
         /// <typeparam name="T">The type of elements in the enumerable.</typeparam>
         /// <param name="enumerable">The collection of items to copy to the set.</param>
         [HiddenFromReferenceAssembly("net472")]
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static HashSet<T> ToHashSet<T>(this IEnumerable<T> enumerable) => new HashSet<T>(enumerable);
 
@@ -88,7 +88,7 @@ public static IEnumerable<T> Concat<T>(this IEnumerable<T> enumerable, T newItem
         /// <param name="enumerable">The collection of items to copy to the set.</param>
         /// <param name="comparer">The comparer to use for creating the set.</param>
         [HiddenFromReferenceAssembly("net472")]
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static HashSet<T> ToHashSet<T>(this IEnumerable<T> enumerable, IEqualityComparer<T> comparer) =>
             new HashSet<T>(enumerable, comparer);

src/Utilities/StringExtensions.cs

@@ -31,7 +31,7 @@ public static Stream ToStream(this string s)
 
         // Hide Methods from projects targeting .NET Core 2.0 or later / .NET Standard 2.1 or later
         // because for that target, String.StartsWith(char) and String.EndsWith(char) are built-in
-#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0 || NETCOREAPP2_1 || NETSTANDARD2_1))
+#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0_OR_GREATER|| NETSTANDARD2_1_OR_GREATER))
         /// <summary>
         /// Determines if the string starts with the specified character.
         /// </summary>
@@ -46,7 +46,7 @@ public static Stream ToStream(this string s)
         /// <param name="str">The string which's first character to check.</param>
         /// <param name="c">The character to compare to the string's first character.</param>
         /// <returns>Returns true if the string has at least one character and the first character matches <paramref name="c"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static bool StartsWith(this string str, char c)
         {
@@ -70,7 +70,7 @@ public static bool StartsWith(this string str, char c)
         /// <param name="str">The string which's last character to check.</param>
         /// <param name="c">The character to compare to the string's last character.</param>
         /// <returns>Returns true if the string has at least one character and the last character matches <paramref name="c"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static bool EndsWith(this string str, char c)
         {

src/Utilities/Text/StringBuilderExtensions.cs

@@ -12,7 +12,7 @@ public static class StringBuilderExtensions
 
         // Hide AppendJoin() methods from projects targeting .NET Core 2.0 or later / .NET Standard 2.1 or later
         // because AppendJoin() is available as built-in functionality.
-#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0 || NETCOREAPP2_1 || NETSTANDARD2_1))
+#if !(REFERENCE_ASSEMBLY && (NETCOREAPP2_0_OR_GREATER|| NETSTANDARD2_1_OR_GREATER))
 
         /// <summary>
         /// Appends the members of a collection, separated by the specified separator.
@@ -31,7 +31,7 @@ public static class StringBuilderExtensions
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin<T>(this StringBuilder stringBuilder, string separator, IEnumerable<T> values)
         {
@@ -55,7 +55,7 @@ public static StringBuilder AppendJoin<T>(this StringBuilder stringBuilder, stri
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin(this StringBuilder stringBuilder, string separator, params string[] values)
         {
@@ -79,7 +79,7 @@ public static StringBuilder AppendJoin(this StringBuilder stringBuilder, string
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin(this StringBuilder stringBuilder, string separator, params object[] values)
         {
@@ -103,7 +103,7 @@ public static StringBuilder AppendJoin(this StringBuilder stringBuilder, string
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin(this StringBuilder stringBuilder, char separator, params object[] values)
         {
@@ -127,7 +127,7 @@ public static StringBuilder AppendJoin(this StringBuilder stringBuilder, char se
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin(this StringBuilder stringBuilder, char separator, params string[] values)
         {
@@ -151,7 +151,7 @@ public static StringBuilder AppendJoin(this StringBuilder stringBuilder, char se
         /// <param name="separator">The separator to insert between the values.</param>
         /// <param name="values">The values to concatenate.</param>
         /// <returns>Returns the specified <see cref="StringBuilder"/>.</returns>
-        [HiddenFromReferenceAssembly("netcoreapp2.0")]
+        [HiddenFromReferenceAssembly("netcoreapp3.1")]
         [HiddenFromReferenceAssembly("netstandard2.1")]
         public static StringBuilder AppendJoin<T>(this StringBuilder stringBuilder, char separator, IEnumerable<T> values)
         {