Update CS0433 documentation to prioritize extern alias over csc compiler options (#47307)

* Initial plan

* Update CS0433 documentation to prioritize extern alias over csc compiler options

Co-authored-by: BillWagner <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BillWagner <[email protected]>

Author: Copilot

docs/csharp/language-reference/compiler-messages/cs0433.md

@@ -14,7 +14,7 @@ The type TypeName1 exists in both TypeName2 and TypeName3
 
  Two different assemblies referenced in your application contain the same namespace and type, which produces ambiguity.  
 
- To resolve this error, use the alias feature of the ([**References**](../compiler-options/inputs.md#references)) compiler option or do not reference one of your assemblies.  
+ To resolve this error, use the `extern alias` feature with project reference aliases or do not reference one of your assemblies. You can also use the alias feature of the ([**References**](../compiler-options/inputs.md#references)) compiler option when compiling directly with the C# compiler.  
 
 This error can also occur if:
 
@@ -27,7 +27,7 @@ This error can also occur if:
 
 ```csharp  
 // CS0433_1.cs in CS0433_1.csproj  
-// or compile with: /target:library  
+// compile with: dotnet build or /target:library  
 namespace TypeBindConflicts
 {  
    public class AggPubImpAggPubImp { }  
@@ -38,14 +38,14 @@ namespace TypeBindConflicts
 
 ```csharp  
 // CS0433_2.cs in CS0433_2.csproj  
-// or compile with: /target:library  
+// compile with: dotnet build or /target:library  
 namespace TypeBindConflicts
 {  
    public class AggPubImpAggPubImp { }  
 }  
 ```  
 
- So, when consuming these two libraries (`CS0433_1.dll` and `CS0433_2.dll`) in the project, using the `AggPubImpAddPubImp` type will be ambiguous and will lead to compiler error `CS0433`.
+ So, when consuming these two libraries (`CS0433_1.dll` and `CS0433_2.dll`) in the project, using the `AggPubImpAggPubImp` type will be ambiguous and will lead to compiler error `CS0433`.
 
 ```xml  
 <!-- CS0433_3.csproj -->
@@ -55,7 +55,7 @@ namespace TypeBindConflicts
 
 ```csharp  
 // CS0433_3.cs in CS0433_3.csproj  
-// or compile with: /reference:cs0433_1.dll /reference:cs0433_2.dll  
+// compile with: dotnet build or /reference:cs0433_1.dll /reference:cs0433_2.dll  
 using TypeBindConflicts;
 
 public class Test
@@ -67,7 +67,11 @@ public class Test
 }  
 ```  
 
- The following example shows how you can use the alias feature of the **/reference** compiler option or `<Aliases>` feature in `<ProjectReference>` to resolve this CS0433 error.  
+ The following example shows how you can use the `extern alias` feature with project references to resolve this CS0433 error. This is the recommended approach for modern .NET projects.
+
+### Step 1: Add an alias to one of the project references
+
+First, modify your project file to add an alias to one of the conflicting project references:  
 
 ```xml  
 <!-- CS0433_4.csproj -->  
@@ -76,21 +80,25 @@ public class Test
 </ProjectReference>
 <ProjectReference Include="..\CS0433_2\CS0433_2.csproj" />  
 ```  
+
+### Step 2: Use the extern alias in your code
+
+Then, use the `extern alias` directive and qualified type names to distinguish between the two types:  
 
 ```csharp  
 // CS0433_4.cs in CS0433_4.csproj  
-// compile with: /reference:cs0433_1.dll /reference:CustomTypes=cs0433_2.dll  
+// compile with: dotnet build or /reference:cs0433_1.dll /reference:CustomTypes=cs0433_2.dll  
 extern alias CustomTypes;  
 using TypeBindConflicts;  
 
 public class Test
 {  
    public static void Main()
    {  
-      // AggPubImpAggPubImp taken from CS0433_1.dll 
+      // AggPubImpAggPubImp taken from CS0433_2.dll (no alias, default global namespace)
       AggPubImpAggPubImp n6 = new AggPubImpAggPubImp();
 
-      // AggPubImpAggPubImp taken from CS0433_2.dll
+      // AggPubImpAggPubImp taken from CS0433_1.dll (via CustomTypes alias)
       CustomTypes.TypeBindConflicts.AggPubImpAggPubImp n7 =
           new CustomTypes.TypeBindConflicts.AggPubImpAggPubImp();
    }