diff --git a/eng/Versions.props b/eng/Versions.props
index 37fb9f5670bb1..1b6f493445fc6 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -147,7 +147,7 @@
     <UsingToolXUnit>false</UsingToolXUnit>
     <UseVSTestRunner>true</UseVSTestRunner>
     <!-- Prohibit the usage of .NET Standard 1.x dependencies. -->
-    <FlagNetStandard1XDependencies Condition="'$(DotNetBuildSourceOnly)' == 'true' and '$(DotNetBuildOrchestrator)' == 'true'">true</FlagNetStandard1XDependencies>
+    <FlagNetStandard1XDependencies Condition="'$(DotNetBuildSourceOnly)' == 'true' and '$(DotNetBuildFromVMR)' == 'true'">true</FlagNetStandard1XDependencies>
   </PropertyGroup>
   <PropertyGroup>
     <!--
diff --git a/src/Compilers/.editorconfig b/src/Compilers/.editorconfig
index 05f8a377cac7d..8882ce84e8ca5 100644
--- a/src/Compilers/.editorconfig
+++ b/src/Compilers/.editorconfig
@@ -12,9 +12,6 @@ dotnet_diagnostic.RS0100.severity = none
 # RS0102: Braces must not have blank lines between them
 dotnet_diagnostic.RS0102.severity = none
 
-# IDE0051: Unused member
-dotnet_diagnostic.IDE0051.severity = none
-
 # IDE0170: Prefer extended property pattern
 dotnet_diagnostic.IDE0170.severity = suggestion
 
diff --git a/src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs b/src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs
index d063ba7b9ceb4..3072ca7c03450 100644
--- a/src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs
+++ b/src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs
@@ -9,8 +9,10 @@
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 using System.Text;
+using System.Threading;
 using Microsoft.CodeAnalysis.Emit;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Text;
@@ -282,7 +284,22 @@ internal sealed override CommandLineArguments CommonParse(IEnumerable<string> ar
 
 #if DEBUG
                     case "attachdebugger":
-                        Debugger.Launch();
+                        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+                        {
+                            // Debugger.Launch() only works on Windows.
+                            _ = Debugger.Launch();
+                        }
+                        else
+                        {
+                            var timeout = TimeSpan.FromMinutes(2);
+                            Console.WriteLine($"Compiler started with process ID {Environment.ProcessId}");
+                            Console.WriteLine($"Waiting {timeout:g} for a debugger to attach");
+                            using var timeoutSource = new CancellationTokenSource(timeout);
+                            while (!Debugger.IsAttached && !timeoutSource.Token.IsCancellationRequested)
+                            {
+                                Thread.Sleep(100);
+                            }
+                        }
                         continue;
 #endif
                 }
diff --git a/src/Compilers/CSharp/Portable/Utilities/EnvironmentExtensions.cs b/src/Compilers/CSharp/Portable/Utilities/EnvironmentExtensions.cs
new file mode 100644
index 0000000000000..590bdc0ed79e9
--- /dev/null
+++ b/src/Compilers/CSharp/Portable/Utilities/EnvironmentExtensions.cs
@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace Microsoft.CodeAnalysis.CSharp;
+
+internal static class EnvironmentExtensions
+{
+    extension(Environment)
+    {
+        public static int ProcessId
+        {
+            get
+            {
+#if NET
+                return Environment.ProcessId;
+#else
+                return System.Diagnostics.Process.GetCurrentProcess().Id;
+#endif
+            }
+        }
+    }
+}
diff --git a/src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs b/src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs
index 2628ca1f35626..a4e8ec527fb5d 100644
--- a/src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs
+++ b/src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs
@@ -37623,6 +37623,84 @@ public void M() { }
         comp.VerifyDiagnostics();
     }
 
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/79309")]
+    public void FunctionType_InstanceReceiver_12()
+    {
+        // static non-extension method vs. extension property
+        var src = """
+var x = new C().M;
+
+public static class E
+{
+    extension(C c)
+    {
+        public int M => 42;
+    }
+}
+
+public class C
+{
+    public static int M() => throw null;
+}
+""";
+        var comp = CreateCompilation(src);
+        comp.VerifyEmitDiagnostics(
+            // (1,9): error CS8917: The delegate type could not be inferred.
+            // var x = new C().M;
+            Diagnostic(ErrorCode.ERR_CannotInferDelegateType, "new C().M").WithLocation(1, 9));
+
+        var tree = comp.SyntaxTrees.First();
+        var model = comp.GetSemanticModel(tree);
+        var localDeclaration = GetSyntax<VariableDeclarationSyntax>(tree, "var x = new C().M");
+        Assert.Equal("?", model.GetTypeInfo(localDeclaration.Type).Type.ToTestDisplayString());
+
+        // without non-extension method
+        src = """
+var x = new C().M;
+System.Console.Write(x);
+
+public static class E
+{
+    extension(C c)
+    {
+        public int M => 42;
+    }
+}
+
+public class C
+{
+}
+""";
+        comp = CreateCompilation(src);
+        CompileAndVerify(comp, expectedOutput: "42").VerifyDiagnostics();
+
+        tree = comp.SyntaxTrees.First();
+        model = comp.GetSemanticModel(tree);
+        localDeclaration = GetSyntax<VariableDeclarationSyntax>(tree, "var x = new C().M");
+        Assert.Equal("System.Int32", model.GetTypeInfo(localDeclaration.Type).Type.ToTestDisplayString());
+
+        // analogous non-extension scenario
+        src = """
+var x = new C().M;
+System.Console.Write(x);
+
+public class Base
+{
+    public int M => 42;
+}
+
+public class C : Base
+{
+    public static new int M() => throw null;
+}
+""";
+        comp = CreateCompilation(src);
+        comp.VerifyEmitDiagnostics(
+            // (1,9): error CS8917: The delegate type could not be inferred.
+            // var x = new C().M;
+            Diagnostic(ErrorCode.ERR_CannotInferDelegateType, "new C().M").WithLocation(1, 9));
+    }
+
     [Fact]
     public void FunctionType_ColorColorReceiver_01()
     {
diff --git a/src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCommandLineParser.vb b/src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCommandLineParser.vb
index 707f5b985cd23..a53023f771cd8 100644
--- a/src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCommandLineParser.vb
+++ b/src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCommandLineParser.vb
@@ -8,6 +8,7 @@ Imports System.IO
 Imports System.Runtime.InteropServices
 Imports System.Security.Cryptography
 Imports System.Text
+Imports System.Threading
 Imports Microsoft.CodeAnalysis.Collections
 Imports Microsoft.CodeAnalysis.Emit
 Imports Microsoft.CodeAnalysis.PooledObjects
@@ -446,7 +447,24 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
 #If DEBUG Then
                     Case "attachdebugger"
-                        Debugger.Launch()
+                        If RuntimeInformation.IsOSPlatform(OSPlatform.Windows) Then
+                            ' Debugger.Launch() only works on Windows
+                            Debugger.Launch()
+                        Else
+                            Dim timeout = TimeSpan.FromMinutes(2)
+#If NET Then
+                            Dim processId = Environment.ProcessId
+#Else
+                            Dim processId = System.Diagnostics.Process.GetCurrentProcess().Id
+#End If
+                            Console.WriteLine($"Compiler started with process ID {processId}")
+                            Console.WriteLine($"Waiting {timeout:g} for a debugger to attach")
+                            Using timeoutSource = New CancellationTokenSource(timeout)
+                                While Not Debugger.IsAttached AndAlso Not timeoutSource.Token.IsCancellationRequested
+                                    Thread.Sleep(100)
+                                End While
+                            End Using
+                        End If
                         Continue For
 #End If
                 End Select