Add `#if !NETCORE` around extension methods that are included with .NET Core 3

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -515,10 +515,10 @@ namespace ICSharpCode.Decompiler.IL
 			var blockBuilder = new BlockBuilder(body, variableByExceptionHandler);
 			blockBuilder.CreateBlocks(mainContainer, instructionBuilder, isBranchTarget, cancellationToken);
 			var function = new ILFunction(this.method, body.GetCodeSize(), this.genericContext, mainContainer, kind);
-			CollectionExtensions.AddRange(function.Variables, parameterVariables);
+			function.Variables.AddRange(parameterVariables);
-			CollectionExtensions.AddRange(function.Variables, localVariables);
+			function.Variables.AddRange(localVariables);
-			CollectionExtensions.AddRange(function.Variables, stackVariables);
+			function.Variables.AddRange(stackVariables);
-			CollectionExtensions.AddRange(function.Variables, variableByExceptionHandler.Values);
+			function.Variables.AddRange(variableByExceptionHandler.Values);
 			function.AddRef(); // mark the root node
 			var removedBlocks = new List<Block>();
 			foreach (var c in function.Descendants.OfType<BlockContainer>()) {

ICSharpCode.Decompiler/IL/Instructions/DynamicInstructions.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Linq.Expressions;
 using ICSharpCode.Decompiler.IL.Patterns;
 using ICSharpCode.Decompiler.TypeSystem;

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -138,7 +138,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				};
 				block.Instructions.Insert(i++, new StLoc(uninlinedArgs[j], arg));
 			}
-			CollectionExtensions.AddRange(v.Function.Variables, uninlinedArgs);
+			v.Function.Variables.AddRange(uninlinedArgs);
 			// perform copy propagation:
 			foreach (var expr in v.LoadInstructions.ToArray()) {
 				var clone = copiedExpr.Clone();

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -12,10 +12,12 @@ namespace ICSharpCode.Decompiler.Util
 			value = pair.Value;
 		}
 
+#if !NETCORE
 		public static IEnumerable<(A, B)> Zip<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
 		{
 			return input1.Zip(input2, (a, b) => (a, b));
 		}
+#endif
 
 		public static IEnumerable<(A, B)> ZipLongest<A, B>(this IEnumerable<A> input1, IEnumerable<B> input2)
 		{
@@ -51,10 +53,12 @@ namespace ICSharpCode.Decompiler.Util
 			}
 		}
 
+#if !NETCORE
 		public static HashSet<T> ToHashSet<T>(this IEnumerable<T> input)
 		{
 			return new HashSet<T>(input);
 		}
+#endif
 
 		public static IEnumerable<T> SkipLast<T>(this IReadOnlyCollection<T> input, int count)
 		{