Fix regression

Author: jcouv

src/Compilers/CSharp/Portable/FlowAnalysis/AbstractFlowPass.cs

@@ -1517,7 +1517,7 @@ public override BoundNode VisitDelegateCreationExpression(BoundDelegateCreationE
                 {
                     VisitLocalFunctionUse(localFunc, node.Syntax, isCall: false);
                 }
-                else if (node.MethodOpt is not null && methodGroup.ReceiverOpt is not null)
+                else if (node.MethodOpt is { } method && methodGroup.ReceiverOpt is { } receiver && !ignoreReceiver(receiver, method))
                 {
                     EnterRegionIfNeeded(methodGroup);
                     VisitRvalue(methodGroup.ReceiverOpt);
@@ -1530,6 +1530,12 @@ public override BoundNode VisitDelegateCreationExpression(BoundDelegateCreationE
             }
 
             return null;
+
+            static bool ignoreReceiver(BoundExpression receiver, MethodSymbol method)
+            {
+                // ignore the implicit `this` receiver on a static method
+                return method.IsStatic && receiver is { Kind: BoundKind.ThisReference, WasCompilerGenerated: true };
+            }
         }
 
         public override BoundNode VisitTypeExpression(BoundTypeExpression node)

src/Compilers/CSharp/Test/Semantic/FlowAnalysis/RegionAnalysisTests.cs

@@ -9309,5 +9309,54 @@ static class Extension
                 Diagnostic(ErrorCode.ERR_UseDefViolation, "i").WithArguments("i").WithLocation(4, 42)
                 );
         }
+
+        [Fact, WorkItem(59738, "https://github.com/dotnet/roslyn/issues/59738")]
+        public void DefiniteAssignmentShouldSkipImplicitThisInStaticMethodConversion()
+        {
+            var comp = CreateCompilation(@"
+using System;
+public struct C
+{
+    private object field;
+    public C(Action a)
+    {
+        // implicit `this` receiver should be ignored in definite assignment
+        a = new(M);
+        field = 1;
+    }
+
+    public C(Action a, int ignored)
+    {
+        // implicit `this` receiver should be ignored in definite assignment
+        a = new Action(M);
+        field = 1;
+    }
+
+    public void Method1(Action a)
+    {
+        // explicit `this` disallowed
+        a = new Action(this.M);
+    }
+
+    public void Method2(Action a, C c)
+    {
+        // instance receiver disallowed
+        a = new Action(c.M);
+    }
+
+    private static void M()
+    {
+    }
+}
+");
+            comp.VerifyDiagnostics(
+                // (23,24): error CS0176: Member 'C.M()' cannot be accessed with an instance reference; qualify it with a type name instead
+                //         a = new Action(this.M);
+                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M").WithArguments("C.M()").WithLocation(23, 24),
+                // (29,24): error CS0176: Member 'C.M()' cannot be accessed with an instance reference; qualify it with a type name instead
+                //         a = new Action(c.M);
+                Diagnostic(ErrorCode.ERR_ObjectProhibited, "c.M").WithArguments("C.M()").WithLocation(29, 24)
+                );
+        }
     }
 }