Improve location of ERR_ParamUnassigned error for local functions.

Fixes #12467.

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

@@ -111,16 +111,26 @@ public override BoundNode VisitLocalFunctionStatement(BoundLocalFunctionStatemen
             RestorePending(oldPending2); // process any forward branches within the lambda body
             ImmutableArray<PendingBranch> pendingReturns = RemoveReturns();
             RestorePending(oldPending);
-            LeaveParameters(localFunc.Symbol.Parameters, localFunc.Syntax, null);
+
+            Location location = null;
+
+            if (!localFunc.Symbol.Locations.IsDefaultOrEmpty)
+            {
+                location = localFunc.Symbol.Locations[0];
+            }
+
+            LeaveParameters(localFunc.Symbol.Parameters, localFunc.Syntax, location);
 
             LocalState stateAtReturn = this.State;
             foreach (PendingBranch pending in pendingReturns)
             {
                 this.State = pending.State;
-                if (pending.Branch.Kind == BoundKind.ReturnStatement)
+                BoundNode branch = pending.Branch;
+                if (branch.Kind == BoundKind.ReturnStatement)
                 {
                     // ensure out parameters are definitely assigned at each return
-                    LeaveParameters(localFunc.Symbol.Parameters, pending.Branch.Syntax, null);
+                    LeaveParameters(localFunc.Symbol.Parameters, branch.Syntax, 
+                                    branch.WasCompilerGenerated ? location : null);
                     IntersectWith(ref stateAtReturn, ref this.State);
                 }
                 else

src/Compilers/CSharp/Test/Semantic/Semantics/LocalFunctionTests.cs

@@ -1606,5 +1606,139 @@ async Task<async> Test(Task<async> t)
                     expectedOutput: "async");
             }
         }
+
+        [Fact]
+        [WorkItem(12467, "https://github.com/dotnet/roslyn/issues/12467")]
+        public void ParamUnassigned_01()
+        {
+            var src = @"
+class C
+{
+    public void M1()
+    {
+        void TakeOutParam1(out int x)
+        {
+        }
+
+        int y;
+        TakeOutParam1(out y);
+    }
+
+        void TakeOutParam2(out int x)
+        {
+        }
+}";
+            VerifyDiagnostics(src,
+                // (6,14): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //         void TakeOutParam1(out int x)
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "TakeOutParam1").WithArguments("x").WithLocation(6, 14),
+                // (14,14): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //         void TakeOutParam2(out int x)
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "TakeOutParam2").WithArguments("x").WithLocation(14, 14)
+                );
+        }
+
+        [Fact]
+        [WorkItem(12467, "https://github.com/dotnet/roslyn/issues/12467")]
+        public void ParamUnassigned_02()
+        {
+            var src = @"
+class C
+{
+    public void M1()
+    {
+        void TakeOutParam1(out int x)
+        {
+            return; // 1 
+        }
+
+        int y;
+        TakeOutParam1(out y);
+    }
+
+        void TakeOutParam2(out int x)
+        {
+            return; // 2 
+        }
+}";
+            VerifyDiagnostics(src,
+                // (8,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //             return; // 1 
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "return;").WithArguments("x").WithLocation(8, 13),
+                // (17,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //             return; // 2 
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "return;").WithArguments("x").WithLocation(17, 13)
+                );
+        }
+
+        [Fact]
+        [WorkItem(12467, "https://github.com/dotnet/roslyn/issues/12467")]
+        public void ParamUnassigned_03()
+        {
+            var src = @"
+class C
+{
+    public void M1()
+    {
+        int TakeOutParam1(out int x)
+        {
+        }
+
+        int y;
+        TakeOutParam1(out y);
+    }
+
+        int TakeOutParam2(out int x)
+        {
+        }
+}";
+            VerifyDiagnostics(src,
+                // (6,13): error CS0161: 'TakeOutParam1(out int)': not all code paths return a value
+                //         int TakeOutParam1(out int x)
+                Diagnostic(ErrorCode.ERR_ReturnExpected, "TakeOutParam1").WithArguments("TakeOutParam1(out int)").WithLocation(6, 13),
+                // (6,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //         int TakeOutParam1(out int x)
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "TakeOutParam1").WithArguments("x").WithLocation(6, 13),
+                // (14,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //         int TakeOutParam2(out int x)
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "TakeOutParam2").WithArguments("x").WithLocation(14, 13),
+                // (14,13): error CS0161: 'C.TakeOutParam2(out int)': not all code paths return a value
+                //         int TakeOutParam2(out int x)
+                Diagnostic(ErrorCode.ERR_ReturnExpected, "TakeOutParam2").WithArguments("C.TakeOutParam2(out int)").WithLocation(14, 13)
+                );
+        }
+
+        [Fact]
+        [WorkItem(12467, "https://github.com/dotnet/roslyn/issues/12467")]
+        public void ParamUnassigned_04()
+        {
+            var src = @"
+class C
+{
+    public void M1()
+    {
+        int TakeOutParam1(out int x)
+        {
+            return 1;
+        }
+
+        int y;
+        TakeOutParam1(out y);
+    }
+
+        int TakeOutParam2(out int x)
+        {
+            return 2;
+        }
+}";
+            VerifyDiagnostics(src,
+                // (8,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //             return 1;
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "return 1;").WithArguments("x").WithLocation(8, 13),
+                // (17,13): error CS0177: The out parameter 'x' must be assigned to before control leaves the current method
+                //             return 2;
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "return 2;").WithArguments("x").WithLocation(17, 13)
+                );
+        }
     }
 }

src/Compilers/CSharp/Test/Semantic/Semantics/OutVarTests.cs

@@ -17751,9 +17751,9 @@ public static void Main()
                 // (8,23): error CS0103: The name 'x3' does not exist in the current context
                 //         int c[out var x3] = null; // fatal syntax error - 'out' is skipped
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "x3").WithArguments("x3").WithLocation(8, 23),
-                // (7,9): error CS0177: The out parameter 'x2' must be assigned to before control leaves the current method
+                // (7,13): error CS0177: The out parameter 'x2' must be assigned to before control leaves the current method
                 //         int b(out var x2) = null; // parsed as a local function with syntax error
-                Diagnostic(ErrorCode.ERR_ParamUnassigned, "int b(out var x2) ").WithArguments("x2").WithLocation(7, 9),
+                Diagnostic(ErrorCode.ERR_ParamUnassigned, "b").WithArguments("x2").WithLocation(7, 13),
                 // (6,25): warning CS0219: The variable 'a' is assigned but its value is never used
                 //         int[out var x1] a = null; // fatal syntax error - 'out' is skipped
                 Diagnostic(ErrorCode.WRN_UnreferencedVarAssg, "a").WithArguments("a").WithLocation(6, 25),