Add tests for ExtensionEncodingV1 and ExtensionEncodingV2.

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -133,7 +133,7 @@ namespace ICSharpCode.Decompiler.Tests.Helpers
 
 			await vswhereToolset.Fetch().ConfigureAwait(false);
 			await RefAssembliesToolset.Fetch("5.0.0", sourcePath: "ref/net5.0").ConfigureAwait(false);
-			await RefAssembliesToolset.Fetch("10.0.0-preview.4.25258.110", sourcePath: "ref/net10.0").ConfigureAwait(false);
+			await RefAssembliesToolset.Fetch("10.0.0-rc.2.25502.107", sourcePath: "ref/net10.0").ConfigureAwait(false);
 
 
 #if DEBUG

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -96,6 +96,8 @@
     <None Include="TestCases\Disassembler\Pretty\InterfaceImplAttributes.il" />
     <None Include="TestCases\Disassembler\Pretty\SortMembers.expected.il" />
     <None Include="TestCases\Disassembler\Pretty\SortMembers.il" />
+    <None Include="TestCases\ILPretty\ExtensionEncodingV2.il" />
+    <None Include="testcases\ilpretty\ExtensionEncodingV1.il" />
     <None Include="TestCases\ILPretty\GuessAccessors.cs" />
     <None Include="TestCases\ILPretty\GuessAccessors.il" />
     <None Include="TestCases\ILPretty\Issue2260SwitchString.il" />
@@ -145,6 +147,8 @@
     <Compile Include="ProjectDecompiler\TargetFrameworkTests.cs" />
     <Compile Include="ProjectDecompiler\WholeProjectDecompilerTests.cs" />
     <Compile Include="TestAssemblyResolver.cs" />
+    <Compile Include="TestCases\ILPretty\ExtensionEncodingV2.cs" />
+    <Compile Include="TestCases\ILPretty\ExtensionEncodingV1.cs" />
     <Compile Include="TestCases\ILPretty\Issue3344CkFinite.cs" />
     <Compile Include="TestCases\ILPretty\Issue3421.cs" />
     <Compile Include="TestCases\ILPretty\Issue3465.cs" />

ICSharpCode.Decompiler.Tests/ILPrettyTestRunner.cs

@@ -323,6 +323,22 @@ namespace ICSharpCode.Decompiler.Tests
 			await Run();
 		}
 
+		[Test]
+		public async Task ExtensionEncodingV1()
+		{
+			// uses Microsoft.Net.Compilers.Toolset 5.0.0-2.25380.108
+			// see ExtensionEncodingV1.il for details
+			await Run();
+		}
+
+		[Test]
+		public async Task ExtensionEncodingV2()
+		{
+			// uses Microsoft.Net.Compilers.Toolset 5.0.0-2.25451.107
+			// see ExtensionEncodingV2.il for details
+			await Run();
+		}
+
 		async Task Run([CallerMemberName] string testName = null, DecompilerSettings settings = null,
 			AssemblerOptions assemblerOptions = AssemblerOptions.Library)
 		{

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/ExtensionEncodingV1.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.ILPretty
+{
+	internal static class ExtensionPropertiesV1
+	{
+		extension<T>(ICollection<T> collection) where T : notnull
+		{
+			public bool IsEmpty => collection.Count == 0;
+
+			public int Test {
+				get {
+					return 42;
+				}
+				set {
+				}
+			}
+
+			public void AddIfNotNull(T item)
+			{
+				if (item != null)
+				{
+					collection.Add(item);
+				}
+			}
+
+			public T2 Cast<T2>(int index) where T2 : T
+			{
+				return (T2)(object)collection.ElementAt(index);
+			}
+
+			public static void StaticExtension()
+			{
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/ExtensionEncodingV1.il

@@ -0,0 +1,253 @@
+// To extend use:
+// see https://lab.razor.fyi/#fVHNbhMxEFYRqrBP0CcYbpsDVlioVDU_UrSNUBCqImVPnHC8k8TgtRd7tiSqcuMh-gbceQBeihdA66bJNlK5WDPzfTPffGP-65TzqXdLL0uhwtndaR20XcJsEwjLHm9nInPGoCLtbBAf0KLX6j-MSVnWJOcGjzhXWi6tC6RVeBoRmStwZKXZBH1M-6Tt96NSvvIoC22XT9VFLsO30OPcyhJDJRXCJJutpK8aIXGFypWVNuhFjoFCfDMZMIipR6INv-VMW0JvpYFAkrQCZWQIMF4T2qCdnXpXoSeNgbNbzhg-AP18mEwOl-nnQ1D7rAM_VugRcrgE68jWxnAW-1lVz41WMHfOwCSMy4o2MGj3iszVlmAwgG6Ptzq0JWgMQBzDlvgQMY9Uewvv017Mt_ENezzm2_aoG6cLGBXFZHHt6Lo2JslBE5adhnPfpBeQNCV4PYBm_QjtMNZadlQUkddpaT_SylPIZKB-ng6TxoK2Ba7390nhEvKD6s5JkqedxM2_oqJOS2tssERLI0ruh0TJR2K7P4z-ZjHef2RyMNcsueVsy7f87NW56Irum1Sk5-8uuuJt9-LjM20-sxd3P__-_rN4-fzLyfrkHw
+// created using https://dev.azure.com/dnceng/public/_artifacts/feed/dotnet-tools/NuGet/Microsoft.Net.Compilers.Toolset/overview/5.0.0-2.25380.108
+
+.class private auto ansi abstract sealed beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV1
+    extends [System.Runtime]System.Object
+{
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableContextAttribute::.ctor(uint8) = (
+        01 00 01 00 00
+    )
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8) = (
+        01 00 00 00 00
+    )
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = (
+        01 00 00 00
+    )
+    // Nested Types
+    .class nested public auto ansi sealed specialname beforefieldinit '<>E__0`1'<T>
+        extends [System.Runtime]System.Object
+    {
+        // Methods
+        .method private hidebysig specialname static 
+            void '<Extension>$' (
+                class [System.Runtime]System.Collections.Generic.ICollection`1<!T> collection
+            ) cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
+                01 00 00 00
+            )
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 1 (0x1)
+            .maxstack 8
+
+            IL_0000: ret
+        } // end of method '<>E__0`1'::'<Extension>$'
+
+        .method public hidebysig specialname 
+            instance bool get_IsEmpty () cil managed 
+        {
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::get_IsEmpty
+
+        .method public hidebysig specialname 
+            instance int32 get_Test () cil managed 
+        {
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::get_Test
+
+        .method public hidebysig specialname 
+            instance void set_Test (
+                int32 'value'
+            ) cil managed 
+        {
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::set_Test
+
+        .method public hidebysig 
+            instance void AddIfNotNull (
+                !T item
+            ) cil managed 
+        {
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::AddIfNotNull
+
+        .method public hidebysig 
+            instance !!T2 Cast<(!T) T2> (
+                int32 index
+            ) cil managed 
+        {
+            .param type T2
+                .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8) = (
+                    01 00 00 00 00
+                )
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::Cast
+
+        .method public hidebysig static 
+            void StaticExtension () cil managed 
+        {
+            // Method begins at RVA 0x209f
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<>E__0`1'::StaticExtension
+
+        // Properties
+        .property instance bool IsEmpty()
+        {
+            .get instance bool ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV1/'<>E__0`1'::get_IsEmpty()
+        }
+        .property instance int32 Test()
+        {
+            .get instance int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV1/'<>E__0`1'::get_Test()
+            .set instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV1/'<>E__0`1'::set_Test(int32)
+        }
+
+    } // end of class <>E__0`1
+
+
+    // Methods
+    .method public hidebysig static 
+        bool get_IsEmpty<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection
+        ) cil managed 
+    {
+        // Method begins at RVA 0x2050
+        // Header size: 1
+        // Code size: 10 (0xa)
+        .maxstack 8
+
+        IL_0000: ldarg.0
+        IL_0001: callvirt instance int32 class [System.Runtime]System.Collections.Generic.ICollection`1<!!T>::get_Count()
+        IL_0006: ldc.i4.0
+        IL_0007: ceq
+        IL_0009: ret
+    } // end of method ExtensionProperties::get_IsEmpty
+
+    .method public hidebysig static 
+        int32 get_Test<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection
+        ) cil managed 
+    {
+        // Method begins at RVA 0x205b
+        // Header size: 1
+        // Code size: 4 (0x4)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ldc.i4.s 42
+        IL_0003: ret
+    } // end of method ExtensionProperties::get_Test
+
+    .method public hidebysig static 
+        void set_Test<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            int32 'value'
+        ) cil managed 
+    {
+        // Method begins at RVA 0x2060
+        // Header size: 1
+        // Code size: 2 (0x2)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ret
+    } // end of method ExtensionProperties::set_Test
+
+    .method public hidebysig static 
+        void AddIfNotNull<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            !!T item
+        ) cil managed 
+    {
+        .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = (
+            01 00 00 00
+        )
+        // Method begins at RVA 0x2064
+        // Header size: 12
+        // Code size: 25 (0x19)
+        .maxstack 2
+        .locals init (
+            [0] bool
+        )
+
+        IL_0000: nop
+        IL_0001: ldarg.1
+        IL_0002: box !!T
+        IL_0007: ldnull
+        IL_0008: cgt.un
+        IL_000a: stloc.0
+        IL_000b: ldloc.0
+        IL_000c: brfalse.s IL_0018
+
+        IL_000e: nop
+        IL_000f: ldarg.0
+        IL_0010: ldarg.1
+        IL_0011: callvirt instance void class [System.Runtime]System.Collections.Generic.ICollection`1<!!T>::Add(!0)
+        IL_0016: nop
+        IL_0017: nop
+
+        IL_0018: ret
+    } // end of method ExtensionProperties::AddIfNotNull
+
+    .method public hidebysig static 
+        !!T2 Cast<T, (!!T) T2> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            int32 index
+        ) cil managed 
+    {
+        .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = (
+            01 00 00 00
+        )
+        // Method begins at RVA 0x2089
+        // Header size: 1
+        // Code size: 19 (0x13)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ldarg.0
+        IL_0002: ldarg.1
+        IL_0003: call !!0 [System.Linq]System.Linq.Enumerable::ElementAt<!!T>(class [System.Runtime]System.Collections.Generic.IEnumerable`1<!!0>, int32)
+        IL_0008: box !!T
+        IL_000d: unbox.any !!T2
+        IL_0012: ret
+    } // end of method ExtensionProperties::Cast
+
+    .method public hidebysig static 
+        void StaticExtension<T> () cil managed 
+    {
+        // Method begins at RVA 0x2060
+        // Header size: 1
+        // Code size: 2 (0x2)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ret
+    } // end of method ExtensionProperties::StaticExtension
+
+} // end of class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV1

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/ExtensionEncodingV2.cs

@@ -0,0 +1,33 @@
+using System.Collections.Generic;
+using System.Linq;
+namespace ICSharpCode.Decompiler.Tests.TestCases.ILPretty
+{
+	internal static class ExtensionPropertiesV2
+	{
+		extension<T>(ICollection<T> collection) where T : notnull
+		{
+			public bool IsEmpty => collection.Count == 0;
+			public int Test {
+				get {
+					return 42;
+				}
+				set {
+				}
+			}
+			public void AddIfNotNull(T item)
+			{
+				if (item != null)
+				{
+					collection.Add(item);
+				}
+			}
+			public T2 Cast<T2>(int index) where T2 : T
+			{
+				return (T2)(object)collection.ElementAt(index);
+			}
+			public static void StaticExtension()
+			{
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/ILPretty/ExtensionEncodingV2.il

@@ -0,0 +1,328 @@
+// To extend use:
+// see https://lab.razor.fyi/#fVHBbtNAEFUQArwn6BcMPdkSrFyrFVKbVIrcgIKqKKKrHkBIbOyps3S9a3bHtFEViQvfwy9w4Qf4D66ckd00dSOVy2pn3nvz5u2y748ZmzpbOFnyzG_9fVR7ZQo4WXjC8oB1K55arTEjZY3nb9CgU9l_GOOyrEnONG5wjpQsjPWkMn8_wlOb49BIvfBqk3aszJeNlpg7lLkyxX19LqQ_3xz0rjakSuSn6LyyppWzD9J7LGd6sQ9CugLptZMlXlh3Hm7zyUik1uGwql6sRIOdmMfb0UfGjCzRVzJDGKcnc-mqJgI_wsyWldLouEBPvj1T6dHz8fHUIdGCXbFAGUJnpAZPklQGmZbew-iS0DQuU2crdKTQnyYsuGJBgDdQXxyG49t374tDyNZVBBdzdAgC9sFYMrXWLGj1QVXPtMpgZq2GsR-VFS1g0NXy1NaGYDCA-IB1FMoQNCGgHRMUeHMLHFLtDOwmB229bE-_xtt62R311aochnk-PptYmtRahwIUYRk1nGuROoOwacHzATTrt9AKCzrLDvO85UUd7zteIoFUeuqL5DBsIiiT4-X6fRLYB3HrukoSiiQK7ewzZhR1vEYaSzQ0pPB6SGt5x2z1i22-k_a-_srwNlyz5JIFS7ZkW8_2eMzjlwlP9nb3dvhO_OrtA6XfB09-__n14-fZ04efevPeZe9br_cP
+// created using https://dev.azure.com/dnceng/public/_artifacts/feed/dotnet-tools/NuGet/Microsoft.Net.Compilers.Toolset/overview/5.0.0-2.25451.107
+
+.assembly TestProject
+{
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = {
+    }
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = {
+        int32(8)
+    }
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = {
+        property bool WrapNonExceptionThrows = bool(true)
+    }
+    .custom instance void [System.Runtime]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [System.Runtime]System.Diagnostics.DebuggableAttribute/DebuggingModes) = {
+        int32(263)
+    }
+    .custom instance void [System.Runtime]System.Runtime.Versioning.TargetFrameworkAttribute::.ctor(string) = {
+        string('.NETCoreApp,Version=10.0')
+    }
+    .permissionset reqmin = {
+        [System.Runtime]System.Security.Permissions.SecurityPermissionAttribute = {
+            property bool SkipVerification = bool(true)
+        }
+    }
+    .hash algorithm 0x00008004 // SHA1
+    .ver 0:0:0:0
+}
+
+.class private auto ansi '<Module>'
+{
+} // end of class <Module>
+
+.class private auto ansi abstract sealed beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV2
+    extends [System.Runtime]System.Object
+{
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableContextAttribute::.ctor(uint8) = {
+        uint8(1)
+    }
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8) = {
+        uint8(0)
+    }
+    .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = {
+    }
+    // Nested Types
+    .class nested public auto ansi sealed specialname '<G>$847CB318C385471B1F4E7BD0A197DBCA'<$T0>
+        extends [System.Runtime]System.Object
+    {
+        .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = {
+        }
+        // Nested Types
+        .class nested public auto ansi abstract sealed specialname '<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B'<T>
+            extends [System.Runtime]System.Object
+        {
+            // Methods
+            .method public hidebysig specialname static 
+                void '<Extension>$' (
+                    class [System.Runtime]System.Collections.Generic.ICollection`1<!T> collection
+                ) cil managed 
+            {
+                .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = {
+                }
+                // Method begins at RVA 0x20a0
+                // Header size: 1
+                // Code size: 1 (0x1)
+                .maxstack 8
+
+                IL_0000: ret
+            } // end of method '<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B'::'<Extension>$'
+
+        } // end of class <M>$6A79ECC07A7731C57E8EB4E3D9C8B38B
+
+
+        // Methods
+        .method public hidebysig specialname 
+            instance bool get_IsEmpty () cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::get_IsEmpty
+
+        .method public hidebysig specialname 
+            instance int32 get_Test () cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::get_Test
+
+        .method public hidebysig specialname 
+            instance void set_Test (
+                int32 'value'
+            ) cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::set_Test
+
+        .method public hidebysig 
+            instance void AddIfNotNull (
+                !$T0 item
+            ) cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::AddIfNotNull
+
+        .method public hidebysig 
+            instance !!T2 Cast<(!$T0) T2> (
+                int32 index
+            ) cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            .param type T2
+                .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(uint8) = {
+                    uint8(0)
+                }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::Cast
+
+        .method public hidebysig static 
+            void StaticExtension () cil managed 
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            // Method begins at RVA 0x209d
+            // Header size: 1
+            // Code size: 2 (0x2)
+            .maxstack 8
+
+            IL_0000: ldnull
+            IL_0001: throw
+        } // end of method '<G>$847CB318C385471B1F4E7BD0A197DBCA'::StaticExtension
+
+        // Properties
+        .property instance bool IsEmpty()
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            .get instance bool ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV2/'<G>$847CB318C385471B1F4E7BD0A197DBCA'::get_IsEmpty()
+        }
+        .property instance int32 Test()
+        {
+            .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionMarkerAttribute::.ctor(string) = {
+                string('<M>$6A79ECC07A7731C57E8EB4E3D9C8B38B')
+            }
+            .get instance int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV2/'<G>$847CB318C385471B1F4E7BD0A197DBCA'::get_Test()
+            .set instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV2/'<G>$847CB318C385471B1F4E7BD0A197DBCA'::set_Test(int32)
+        }
+
+    } // end of class <G>$847CB318C385471B1F4E7BD0A197DBCA
+
+
+    // Methods
+    .method public hidebysig static 
+        bool get_IsEmpty<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection
+        ) cil managed 
+    {
+        // Method begins at RVA 0x2050
+        // Header size: 1
+        // Code size: 10 (0xa)
+        .maxstack 8
+
+        IL_0000: ldarg.0
+        IL_0001: callvirt instance int32 class [System.Runtime]System.Collections.Generic.ICollection`1<!!T>::get_Count()
+        IL_0006: ldc.i4.0
+        IL_0007: ceq
+        IL_0009: ret
+    } // end of method ExtensionPropertiesV2::get_IsEmpty
+
+    .method public hidebysig static 
+        int32 get_Test<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection
+        ) cil managed 
+    {
+        // Method begins at RVA 0x205b
+        // Header size: 1
+        // Code size: 4 (0x4)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ldc.i4.s 42
+        IL_0003: ret
+    } // end of method ExtensionPropertiesV2::get_Test
+
+    .method public hidebysig static 
+        void set_Test<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            int32 'value'
+        ) cil managed 
+    {
+        // Method begins at RVA 0x2060
+        // Header size: 1
+        // Code size: 2 (0x2)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ret
+    } // end of method ExtensionPropertiesV2::set_Test
+
+    .method public hidebysig static 
+        void AddIfNotNull<T> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            !!T item
+        ) cil managed 
+    {
+        .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = {
+        }
+        // Method begins at RVA 0x2064
+        // Header size: 12
+        // Code size: 25 (0x19)
+        .maxstack 2
+        .locals init (
+            [0] bool
+        )
+
+        IL_0000: nop
+        IL_0001: ldarg.1
+        IL_0002: box !!T
+        IL_0007: ldnull
+        IL_0008: cgt.un
+        IL_000a: stloc.0
+        IL_000b: ldloc.0
+        IL_000c: brfalse.s IL_0018
+
+        IL_000e: nop
+        IL_000f: ldarg.0
+        IL_0010: ldarg.1
+        IL_0011: callvirt instance void class [System.Runtime]System.Collections.Generic.ICollection`1<!!T>::Add(!0)
+        IL_0016: nop
+        IL_0017: nop
+
+        IL_0018: ret
+    } // end of method ExtensionPropertiesV2::AddIfNotNull
+
+    .method public hidebysig static 
+        !!T2 Cast<T, (!!T) T2> (
+            class [System.Runtime]System.Collections.Generic.ICollection`1<!!T> collection,
+            int32 index
+        ) cil managed 
+    {
+        .custom instance void [System.Runtime]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = {
+        }
+        // Method begins at RVA 0x2089
+        // Header size: 1
+        // Code size: 19 (0x13)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ldarg.0
+        IL_0002: ldarg.1
+        IL_0003: call !!0 [System.Linq]System.Linq.Enumerable::ElementAt<!!T>(class [System.Runtime]System.Collections.Generic.IEnumerable`1<!!0>, int32)
+        IL_0008: box !!T
+        IL_000d: unbox.any !!T2
+        IL_0012: ret
+    } // end of method ExtensionPropertiesV2::Cast
+
+    .method public hidebysig static 
+        void StaticExtension<T> () cil managed 
+    {
+        // Method begins at RVA 0x2060
+        // Header size: 1
+        // Code size: 2 (0x2)
+        .maxstack 8
+
+        IL_0000: nop
+        IL_0001: ret
+    } // end of method ExtensionPropertiesV2::StaticExtension
+
+} // end of class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.ExtensionPropertiesV2
+
+// references
+.assembly extern System.Runtime
+{
+    .publickeytoken = (
+        b0 3f 5f 7f 11 d5 0a 3a
+    )
+    .ver 10:0:0:0
+}
+.assembly extern System.Linq
+{
+    .publickeytoken = (
+        b0 3f 5f 7f 11 d5 0a 3a
+    )
+    .ver 10:0:0:0
+}

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1367,13 +1367,16 @@ namespace ICSharpCode.Decompiler.CSharp
 					foreach (var group in typeDef.ExtensionInfo?.GetGroups() ?? [])
 					{
 						var ext = new ExtensionDeclaration();
-						ext.TypeParameters.AddRange(group.Key.DeclaringTypeDefinition.TypeParameters.Select(tp => typeSystemAstBuilder.ConvertTypeParameter(tp)));
+						ITypeParameter[] typeParameters = group.Key.TypeParameters;
-						ext.ReceiverParameters.Add(typeSystemAstBuilder.ConvertParameter(group.Key.Parameters.Single()));
+						var subst = new TypeParameterSubstitution(typeParameters, null);
-						ext.Constraints.AddRange(group.Key.DeclaringTypeDefinition.TypeParameters.Select(c => typeSystemAstBuilder.ConvertTypeParameterConstraint(c)));
+						ext.TypeParameters.AddRange(typeParameters.Select(tp => typeSystemAstBuilder.ConvertTypeParameter(tp)));
+						var marker = group.Key.Marker.Specialize(subst);
+						ext.ReceiverParameters.Add(typeSystemAstBuilder.ConvertParameter(marker.Parameters.Single()));
+						ext.Constraints.AddRange(typeParameters.Select(c => typeSystemAstBuilder.ConvertTypeParameterConstraint(c)));
 
 						foreach (var member in group)
 						{
-							IMember extMember = member.ExtensionMember;
+							IMember extMember = member.ExtensionMember.Specialize(subst);
 							if (member.ExtensionMember.IsAccessor)
 							{
 								extMember = member.ExtensionMember.AccessorOwner;
@@ -1508,9 +1511,15 @@ namespace ICSharpCode.Decompiler.CSharp
 					return;
 				}
 
-				if (settings.ExtensionMembers && extensionInfo != null && entity is IMethod m && extensionInfo.InfoOfImplementationMember(m).HasValue)
+				if (settings.ExtensionMembers && extensionInfo != null)
 				{
-					return;
+					switch (entity)
+					{
+						case ITypeDefinition td when extensionInfo.IsExtensionGroupingType(td):
+							return;
+						case IMethod m when extensionInfo.InfoOfImplementationMember(m).HasValue:
+							return;
+					}
 				}
 
 				EntityDeclaration entityDecl;
@@ -1584,9 +1593,21 @@ namespace ICSharpCode.Decompiler.CSharp
 			switch (extMember)
 			{
 				case IProperty p:
-					return DoDecompile(p, decompileRun, decompilationContext.WithCurrentMember(p), info);
+					var prop = DoDecompile(p, decompileRun, decompilationContext.WithCurrentMember(p), info);
+					RemoveAttribute(prop, KnownAttribute.ExtensionMarker);
+					if (p.Getter != null)
+					{
+						RemoveAttribute(prop.GetChildByRole(PropertyDeclaration.GetterRole), KnownAttribute.ExtensionMarker);
+					}
+					if (p.Setter != null)
+					{
+						RemoveAttribute(prop.GetChildByRole(PropertyDeclaration.SetterRole), KnownAttribute.ExtensionMarker);
+					}
+					return prop;
 				case IMethod m:
-					return DoDecompile(m, decompileRun, decompilationContext.WithCurrentMember(m), info);
+					var meth = DoDecompile(m, decompileRun, decompilationContext.WithCurrentMember(m), info);
+					RemoveAttribute(meth, KnownAttribute.ExtensionMarker);
+					return meth;
 			}
 
 			throw new NotSupportedException($"Extension member {extMember} is not supported for decompilation.");
@@ -1762,7 +1783,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				{
 					if (!method.IsStatic)
 						parameterOffset = 1; // implementation method has an additional receiver parameter
-					method = extensionInfo.InfoOfExtensionMember(method).Value.ImplementationMethod;
+					method = extensionInfo.InfoOfExtensionMember((IMethod)method.MemberDefinition).Value.ImplementationMethod;
 				}
 
 				var methodDef = metadata.GetMethodDefinition((MethodDefinitionHandle)method.MetadataToken);

ICSharpCode.Decompiler/TypeSystem/ExtensionInfo.cs

@@ -20,9 +20,12 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection.Metadata;
 
+using ICSharpCode.Decompiler.TypeSystem.Implementation;
+
 namespace ICSharpCode.Decompiler.TypeSystem
 {
 	public class ExtensionInfo
@@ -59,6 +62,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				IMethod? marker = null;
 				bool hasMultipleMarkers = false;
 				List<IMethod> extensionMethods = [];
+				ITypeParameter[] extensionGroupTypeParameters = extGroup.TypeParameters.ToArray();
 
 				// For easier access to accessors we use SRM
 				foreach (var h in td.GetMethods())
@@ -82,7 +86,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				if (marker == null || hasMultipleMarkers)
 					return false;
 
-				CollectImplementationMethods(extGroup, marker, extensionMethods);
+				CollectImplementationMethods(extGroup, marker, extensionMethods, extensionGroupTypeParameters);
 				return true;
 			}
 
@@ -102,6 +106,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 				TypeDefinition td = metadata.GetTypeDefinition((TypeDefinitionHandle)extGroup.MetadataToken);
 				List<IMethod> extensionMethods = [];
+				ITypeParameter[] extensionGroupTypeParameters = new ITypeParameter[extGroup.TypeParameterCount];
 
 				// For easier access to accessors we use SRM
 				foreach (var h in td.GetMethods())
@@ -121,12 +126,16 @@ namespace ICSharpCode.Decompiler.TypeSystem
 					extensionMethods.Add(method);
 				}
 
-				CollectImplementationMethods(extGroup, marker, extensionMethods);
+				CollectImplementationMethods(extGroup, marker, extensionMethods, extensionGroupTypeParameters);
 				return true;
 			}
 
-			void CollectImplementationMethods(ITypeDefinition extGroup, IMethod marker, List<IMethod> extensionMethods)
+			void CollectImplementationMethods(ITypeDefinition extGroup, IMethod marker, List<IMethod> extensionMethods, ITypeParameter[] extensionGroupTypeParameters)
 			{
+				List<(IMethod extension, IMethod implementation)> implementations = [];
+
+				string[] typeParameterNames = new string[extGroup.TypeParameterCount];
+
 				foreach (var extension in extensionMethods)
 				{
 					int expectedTypeParameterCount = extension.TypeParameters.Count + extGroup.TypeParameterCount;
@@ -165,15 +174,62 @@ namespace ICSharpCode.Decompiler.TypeSystem
 						);
 					}
 
+					IMethod? foundImpl = null;
+
 					foreach (var impl in extensionContainer.Methods)
 					{
 						if (!IsMatchingImplementation(impl))
 							continue;
-						var emi = new ExtensionMemberInfo(marker, extension, impl);
+						Debug.Assert(foundImpl == null, "Multiple matching implementations found");
-						extensionMemberMap[extension] = emi;
+						foundImpl = impl;
-						implementationMemberMap[impl] = emi;
+					}
+
+					Debug.Assert(foundImpl != null, "No matching implementation found");
+
+					implementations.Add((extension, foundImpl));
+				}
+
+				foreach (var (extension, implementation) in implementations)
+				{
+					for (int i = 0; i < extensionGroupTypeParameters.Length; i++)
+					{
+						if (typeParameterNames[i] == null)
+						{
+							typeParameterNames[i] = implementation.TypeParameters[i].Name;
+						}
+						else if (typeParameterNames[i] != implementation.TypeParameters[i].Name)
+						{
+							// TODO: Handle name conflicts properly
+							typeParameterNames[i] = $"T{i + 1}";
+						}
 					}
 				}
+
+				for (int i = 0; i < extensionGroupTypeParameters.Length; i++)
+				{
+					var originalTypeParameter = extGroup.TypeParameters[i];
+					if (extensionGroupTypeParameters[i] == null)
+					{
+						extensionGroupTypeParameters[i] = new DefaultTypeParameter(
+							extGroup, i, typeParameterNames[i],
+							VarianceModifier.Invariant,
+							attributes: originalTypeParameter.GetAttributes().ToArray(),
+							originalTypeParameter.HasValueTypeConstraint,
+							originalTypeParameter.HasReferenceTypeConstraint,
+							originalTypeParameter.HasDefaultConstructorConstraint,
+							originalTypeParameter.TypeConstraints.Select(c => c.Type).ToArray(),
+							originalTypeParameter.NullabilityConstraint
+						);
+					}
+				}
+
+				foreach (var (extension, implementation) in implementations)
+				{
+					var info = new ExtensionMemberInfo(marker, extension, implementation, extensionGroupTypeParameters);
+					this.extensionMemberMap[extension] = info;
+					this.implementationMemberMap[implementation] = info;
+				}
+
 			}
 		}
 
@@ -187,13 +243,18 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			return this.implementationMemberMap.TryGetValue(method, out var value) ? value : null;
 		}
 
-		public IEnumerable<IGrouping<IMethod, ExtensionMemberInfo>> GetGroups()
+		public IEnumerable<IGrouping<(IMethod Marker, ITypeParameter[] TypeParameters), ExtensionMemberInfo>> GetGroups()
+		{
+			return this.extensionMemberMap.Values.GroupBy(x => (x.ExtensionMarkerMethod, x.ExtensionGroupingTypeParameters));
+		}
+
+		public bool IsExtensionGroupingType(ITypeDefinition type)
 		{
-			return this.extensionMemberMap.Values.GroupBy(x => x.ExtensionMarkerMethod);
+			return this.extensionMemberMap.Values.Any(x => x.ExtensionGroupingType.Equals(type));
 		}
 	}
 
-	public readonly struct ExtensionMemberInfo(IMethod marker, IMethod extension, IMethod implementation)
+	public readonly struct ExtensionMemberInfo(IMethod marker, IMethod extension, IMethod implementation, ITypeParameter[] extensionGroupingTypeParameters)
 	{
 		/// <summary>
 		/// Metadata-only method called '&lt;Extension&gt;$'. Has the C# signature for the extension declaration.
@@ -223,6 +284,11 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// </summary>
 		public ITypeDefinition ExtensionGroupingType => ExtensionMember.DeclaringTypeDefinition!;
 
+		/// <summary>
+		/// This is the array of type parameters for the extension declaration.
+		/// </summary>
+		public ITypeParameter[] ExtensionGroupingTypeParameters => extensionGroupingTypeParameters;
+
 		/// <summary>
 		/// This class holds the type parameters for the extension declaration with full fidelity of C# constraints.
 		/// </summary>