[Nnyeah] Improve error messages for missing required arguments (#14949)

tools/nnyeah/nnyeah/Errors.Designer.cs

@@ -166,5 +166,17 @@ namespace Microsoft.MaciOS.Nnyeah {
                 return ResourceManager.GetString("E0013", resourceCulture);
             }
         }
+
+        internal static string E0014 {
+            get {
+                return ResourceManager.GetString("E0014", resourceCulture);
+            }
+        }
+
+        internal static string E0015 {
+            get {
+                return ResourceManager.GetString("E0015", resourceCulture);
+            }
+        }
     }
 }

tools/nnyeah/nnyeah/Errors.resx

@@ -84,5 +84,11 @@
 	<data name="E0013" xml:space="preserve">
 		<value>Error while attempting to map member {0} in old assembly. This member does not exist in the new assembly or has been renamed. Conversion can't continue. Your best option is to port the old assembly to .NET 6</value>
 	</data>
+	<data name="E0014" xml:space="preserve">
+		<value>File for conversion (--input) and output location (--output) are required options.</value>
+	</data>
+	<data name="E0015" xml:space="preserve">
+		<value>Support legacy and NET assemblies --xamarin-assembly and --microsoft-assembly are currently required options.</value>
+	</data>
 </root>
 

tools/nnyeah/nnyeah/Program.cs

@@ -34,10 +34,18 @@ namespace Microsoft.MaciOS.Nnyeah {
 				doHelp = true;
 			}
 
-			var badForMungingAssembly = infile is null || outfile is null;
-			var badForComparingAssemblies = xamarinAssembly is null || microsoftAssembly is null;
+			if (infile is null || outfile is null) {
+				Console.Error.WriteLine (Errors.E0014);
+				Environment.Exit (1);
+			}
 
-			if (doHelp || badForComparingAssemblies || badForMungingAssembly) {
+			// TODO - Long term this should default to files packaged within the tool but allow overrides
+			if (xamarinAssembly is null || microsoftAssembly is null) {
+				Console.Error.WriteLine (Errors.E0015);
+				Environment.Exit (1);
+			}
+
+			if (doHelp) {
 				PrintOptions (options, Console.Out);
 				Environment.Exit (0);
 			}