Change visit order for local function definite assignment (#14835)

This change visits the parameters before "replaying" reads+writes from
calls of local functions for the purposes of definite assignment. This
ordering is observable because a variable can be definitely assigned in
the argument to the call, and then used inside the call.

Fixes #14243

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

@@ -1761,12 +1761,16 @@ public override BoundNode VisitLocalDeclaration(BoundLocalDeclaration node)
 
         public override BoundNode VisitCall(BoundCall node)
         {
+            // Always visit the arguments first
+            var result = base.VisitCall(node);
+
             if (node.Method.MethodKind == MethodKind.LocalFunction)
             {
                 var localFunc = (LocalFunctionSymbol)node.Method.OriginalDefinition;
                 ReplayReadsAndWrites(localFunc, node.Syntax, writes: true);
             }
-            return base.VisitCall(node);
+
+            return result;
         }
 
         public override BoundNode VisitConversion(BoundConversion node)

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

@@ -7,6 +7,38 @@ namespace Microsoft.CodeAnalysis.CSharp.UnitTests
     [CompilerTrait(CompilerFeature.LocalFunctions)]
     public class LocalFunctions : FlowTestBase
     {
+        [Fact]
+        [WorkItem(14243, "https://github.com/dotnet/roslyn/issues/14243")]
+        public void AssignInsideCallToLocalFunc()
+        {
+            var comp = CreateCompilationWithMscorlib(@"
+class C
+{
+    public void M()
+    {
+        int x;
+        int Local(int p1) => x++;
+
+        Local(x = 0);
+
+        int z;
+        int Local2(int p1, int p2) => z++;
+        Local2(z = 0, z++);
+    }
+
+    public void M2()
+    {
+        int x;
+        int Local(int p1) => x++;
+        int Local2(int p1) => Local(p1);
+        int Local3(int p1) => x + Local2(p1);
+
+        Local3(x = 0);
+    }
+}");
+            comp.VerifyDiagnostics();
+        }
+
         [Fact]
         [WorkItem(14046, "https://github.com/dotnet/roslyn/issues/14046")]
         public void UnreachableAfterThrow()