To tell if an assembly is compiled in debug or release mode in c#

I have seen quite a few articles or tips talking about how to find out if an assembly is in debug mode or not (in the assembly), like this: (C#) Determining whether the current build mode is Debug or Release[^]

But there are scenarios that we need to tell an assembly is compiled as debug or release configuration (out of the assembly).

Because it is a small function, I try to put intact reference so that I do not include namespace:

public static bool IsInDebugMode(string FileName)
{
    return IsInDebugMode(FileName, false);
}

public static bool IsInDebugMode(string FileName, bool IsAssemlbyName)
{
    System.Reflection.Assembly assembly;
    if (IsAssemlbyName)
        assembly = System.Reflection.Assembly.Load(FileName);
    else
        assembly = System.Reflection.Assembly.LoadFile(FileName);
    return IsInDebugMode(assembly);
}

public static bool IsInDebugMode(System.Reflection.Assembly Assembly)
{
    var attributes = Assembly.GetCustomAttributes(typeof(System.Diagnostics.DebuggableAttribute), false);
    if (attributes.Length > 0)
    {
        var debuggable = attributes[0] as System.Diagnostics.DebuggableAttribute;
        if (debuggable != null)
            return (debuggable.DebuggingFlags & System.Diagnostics.DebuggableAttribute.DebuggingModes.Default) == System.Diagnostics.DebuggableAttribute.DebuggingModes.Default;
        else
            return false;
    }
    else
        return false;
}

The function is universal, works for library/gui/cui(console) assemblies, does not require developer to put customized property or functions to indicate.

You may wonder how I got this solution. I believe that the compiler must store some information in the assembly so that it can tell the debugging is supported or not.

First I run the IL DASM, open a debug as well as release version of a hello world application side by side, and compare the manifest, I found some differences like:

--debug version

// --- The following custom attribute is added automatically, do not uncomment -------
// .custom instance void [mscorlib]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 )

--release version

// --- The following custom attribute is added automatically, do not uncomment -------
// .custom instance void [mscorlib]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 02 00 00 00 00 00 )

Immediately, I figured out that we can use reflection to get the System.Diagnostics.DebuggableAttribute custom attribute.

After some testing for GUI/CUI/Library applications, I believe that System.Diagnostics.DebuggableAttribute.DebuggingModes.Default is the one to distinguish between debug and release.

Details of the DebuggableAttribute value:

1. debug mode:
   
   1. standard (Output = full), (01 00 07 01) = 263, Default | DisableOptimizations | IgnoreSymbolStoreSequencePoints | EnableEditAndContinue
      
   2. Project Settings -> Optimize code, (01 00 03 00) = 3, Default | IgnoreSymbolStoreSequencePoints
      
   3. Project Settings -> Advanced -> Output -> none, no custom attribute available (oops...)
      
   4. Project Settings -> Advanced -> Output -> pdb-only, no custom attribute available (oops...)
      
   
   
2. release mode:
   
   1. standard (Output = pdb-only, Optimize Code), (01 00 02 00) = 2, IgnoreSymbolStoreSequencePoints
      
   2. Project Settings -> Advanced -> Output -> none, no custom attribute available (oops...)
      
   3. Project Settings -> Advanced -> Output -> full, (01 00 03 00) = 3, Default | IgnoreSymbolStoreSequencePoints
      
   
   

To sum up, as long as the user does not play with the "Output" method, we should be fairly sure if the application is being built in debug or release mode.