Permit throwaway parameters (#10209)

* Permit throwaway parameters

* Switch to _

* Fix NRE

* Real NRE fix

* Create real string

* Refactor and make work again

* With TESTS!

src/Build.UnitTests/Evaluation/Expander_Tests.cs

@@ -1294,6 +1294,39 @@ public void StaticMethodErrorMessageHaveMethodName1()
 
             Assert.True(false);
         }
+
+        [Fact]
+        public void StaticMethodWithThrowawayParameterSupported()
+        {
+            MockLogger logger = Helpers.BuildProjectWithNewOMExpectSuccess(@"
+<Project>
+  <PropertyGroup>
+    <MyProperty>Value is $([System.Int32]::TryParse(""3"", _))</MyProperty>
+  </PropertyGroup>
+  <Target Name='Build'>
+    <Message Text='$(MyProperty)' />
+  </Target>
+</Project>");
+
+            logger.FullLog.ShouldContain("Value is True");
+        }
+
+        [Fact]
+        public void StaticMethodWithThrowawayParameterSupported2()
+        {
+            MockLogger logger = Helpers.BuildProjectWithNewOMExpectSuccess(@"
+<Project>
+  <PropertyGroup>
+    <MyProperty>Value is $([System.Int32]::TryParse(""notANumber"", _))</MyProperty>
+  </PropertyGroup>
+  <Target Name='Build'>
+    <Message Text='$(MyProperty)' />
+  </Target>
+</Project>");
+
+            logger.FullLog.ShouldContain("Value is False");
+        }
+
         /// <summary>
         /// Creates a set of complicated item metadata and properties, and items to exercise
         /// the Expander class.  The data here contains escaped characters, metadata that

src/Build/Evaluation/Expander.cs

@@ -3593,8 +3593,17 @@ internal object Execute(object objectInstance, IPropertyProvider<T> properties,
                             // otherwise there is the potential of running a function twice!
                             try
                             {
-                                // First use InvokeMember using the standard binder - this will match and coerce as needed
-                                functionResult = _receiverType.InvokeMember(_methodMethodName, _bindingFlags, Type.DefaultBinder, objectInstance, args, CultureInfo.InvariantCulture);
+                                // If there are any out parameters, try to figure out their type and create defaults for them as appropriate before calling the method.
+                                if (args.Any(a => "_".Equals(a)))
+                                {
+                                    IEnumerable<MethodInfo> methods = _receiverType.GetMethods(_bindingFlags).Where(m => m.Name.Equals(_methodMethodName) && m.GetParameters().Length == args.Length);
+                                    functionResult = GetMethodResult(objectInstance, methods, args, 0);
+                                }
+                                else
+                                {
+                                    // If there are no out parameters, use InvokeMember using the standard binder - this will match and coerce as needed
+                                    functionResult = _receiverType.InvokeMember(_methodMethodName, _bindingFlags, Type.DefaultBinder, objectInstance, args, CultureInfo.InvariantCulture);
+                                }
                             }
                             // If we're invoking a method, then there are deeper attempts that can be made to invoke the method.
                             // If not, we were asked to get a property or field but found that we cannot locate it. No further argument coercion is possible, so throw.
@@ -3669,6 +3678,48 @@ internal object Execute(object objectInstance, IPropertyProvider<T> properties,
                 }
             }
 
+            private object GetMethodResult(object objectInstance, IEnumerable<MethodInfo> methods, object[] args, int index)
+            {
+                for (int i = index; i < args.Length; i++)
+                {
+                    if (args[i].Equals("_"))
+                    {
+                        object toReturn = null;
+                        foreach (MethodInfo method in methods)
+                        {
+                            Type t = method.GetParameters()[i].ParameterType;
+                            args[i] = t.IsValueType ? Activator.CreateInstance(t) : null;
+                            object currentReturnValue = GetMethodResult(objectInstance, methods, args, i + 1);
+                            if (currentReturnValue is not null)
+                            {
+                                if (toReturn is null)
+                                {
+                                    toReturn = currentReturnValue;
+                                }
+                                else if (!toReturn.Equals(currentReturnValue))
+                                {
+                                    // There were multiple methods that seemed viable and gave different results. We can't differentiate between them so throw.
+                                    ErrorUtilities.ThrowArgument("CouldNotDifferentiateBetweenCompatibleMethods", _methodMethodName, args.Length);
+                                    return null;
+                                }
+                            }
+                        }
+
+                        return toReturn;
+                    }
+                }
+
+                try
+                {
+                    return _receiverType.InvokeMember(_methodMethodName, _bindingFlags, Type.DefaultBinder, objectInstance, args, CultureInfo.InvariantCulture);
+                }
+                catch (Exception)
+                {
+                    // This isn't a viable option, but perhaps another set of parameters will work.
+                    return null;
+                }
+            }
+
             /// <summary>
             /// Shortcut to avoid calling into binding if we recognize some most common functions.
             /// Binding is expensive and throws first-chance MissingMethodExceptions, which is

src/Build/Resources/Strings.resx

@@ -604,6 +604,9 @@
       LOCALIZATION: "{0}" is the expression that was bad. "{1}" is a message from an FX exception that describes why the expression is bad.
     </comment>
   </data>
+  <data name="CouldNotDifferentiateBetweenCompatibleMethods">
+    <value>Found multiple overloads for method "{0}" with {1} parameter(s). That is currently not supported.</value>
+  </data>
   <data name="InvalidFunctionPropertyExpression" xml:space="preserve">
     <value>MSB4184: The expression "{0}" cannot be evaluated. {1}</value>
     <comment>{StrBegin="MSB4184: "}