[Blazor] TypeDescriptor is not working

[stsrki]

Describe the bug

I'm trying to use TypeDescriptor for conversion between value types but it is not working in Blazor project. As soon as I try to use it it will break and raise an exception. In the example bellow the second Console.WriteLine is never called.

To Reproduce

class ValueConverter<TValue>
{
    public TValue Convert( object value )
    {
        try
        {
            Console.WriteLine( "before" );
            TypeConverter conv = TypeDescriptor.GetConverter( typeof( TValue ) );
            Console.WriteLine( "after" );

            return (TValue)conv.ConvertFrom( value );
        }
        catch
        {
            Console.WriteLine( $"error: {value}" );
            Console.WriteLine( exc.ToString() );
            return default;
        }
    }
}

Exception Stack Trace

WASM: System.MissingMethodException: Constructor on type 'System.ComponentModel.Int32Converter' not found.
components.webassembly.js:1 WASM: at System.RuntimeType.CreateInstanceImpl (System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes, System.Threading.StackCrawlMark& stackMark) <0x1de9a28 + 0x00348> in :0
components.webassembly.js:1 WASM: at System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture, System.Object[] activationAttributes) <0x1ddf940 + 0x000de> in :0
components.webassembly.js:1 WASM: at System.Activator.CreateInstance (System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Object[] args, System.Globalization.CultureInfo culture) <0x22e6cd0 + 0x0002a> in :0
components.webassembly.js:1 WASM: at System.SecurityUtils.SecureCreateInstance (System.Type type, System.Object[] args, System.Boolean allowNonPublic) <0x22e6bf0 + 0x0009c> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.SecurityUtils.SecureCreateInstance (System.Type type) <0x22e6b18 + 0x0000c> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.ReflectTypeDescriptionProvider.CreateInstance (System.Type objectType, System.Type callingType) <0x22e1b90 + 0x0003c> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.ReflectTypeDescriptionProvider.SearchIntrinsicTable (System.Collections.Hashtable table, System.Type callingType) <0x22e1608 + 0x002f0> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.ReflectTypeDescriptionProvider+ReflectedTypeData.GetConverter (System.Object instance) <0x22c3400 + 0x00188> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.ReflectTypeDescriptionProvider.GetConverter (System.Type type, System.Object instance) <0x22c2cc8 + 0x00022> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.TypeDescriptor+TypeDescriptionNode+DefaultTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetConverter () <0x22c2a00 + 0x00042> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at System.ComponentModel.TypeDescriptor.GetConverter (System.Type type) <0x22c7e18 + 0x00014> in <485de8e868c44158864a67df7e8a64c8>:0
components.webassembly.js:1 WASM: at Blazorise.JSRunner+<>c__DisplayClass10_0`1[TValue].b__0 (System.String value) [0x0000d] in D:\Projects\Other\Blazorise\Source\Blazorise\JSRunner.cs:96

[rynowak]

I think it's definitely the case that the linker is trimming this out. The specific type Int32Converter is getting trimmed by the linker because it's not used directly by any code.

One workaround you could use it to set <BlazorLinkOnBuild>false</BlazorLinkOnBuild> in the project file. This will turn off linking, which will increase the size of the app. A more desirable thing would be to change the settings to include the type converters.

@javiercn any ideas?

[miroslavp]

I declared static variables like this to prevent IL stripping:

    private static readonly Int32Converter i32c = new Int32Converter();
    private static readonly Int64Converter i64c = new Int64Converter();
    private static readonly StringConverter sc = new StringConverter();
    private static readonly NullableConverter nc = new NullableConverter(typeof(bool?));
    private static readonly BooleanConverter bc = new BooleanConverter();

@rynowak @javiercn
Any better solution for this?

A more desirable thing would be to change the settings to include the type converters.

Where can I find those settings?

[javiercn]

@SteveSandersonMS Can users still add a custom descriptor file to tweak the linking process?

[SteveSandersonMS]

Yes, but weirdly the docs for that feature seem to have been deleted. I found an old copy in Git history here: https://github.com/aspnet/Blazor.Docs/blob/7ced0029b97b3b8afdda4e2a235bd6cecebfc2fd/docs/host-and-deploy/configure-linker.md

@danroth27 Do you know why that was removed? Also on https://blazor.net/, the "docs" link in the header goes to a 404, and there's still the "experimental" tag in the top right.

[danroth27]

weirdly the docs for that feature seem to have been deleted. @danroth27 Do you know why that was removed?

The IL linker doc is here: https://docs.microsoft.com/aspnet/core/host-and-deploy/blazor/configure-linker

Also on https://blazor.net/, the "docs" link in the header goes to a 404

I'm not seeing this. When I click on Docs I get redirected to https://docs.microsoft.com/aspnet/core/blazor/

there's still the "experimental" tag in the top right.

That's expected for now