The generator fail on maps where the value is a message

[vbfox]

To Reproduce
Steps to reproduce the behavior:

1. Run the tool on this proto file :

   syntax = "proto3";
   
   message SomeMessage {
       int64 id = 1;
   }
   
   message SomeMessageWithMap {
       map<string, SomeMessage> some_map = 1;
   }

2. See the Unable to cast object of type 'Downcast' to type 'InferredUpcast'. error.

Additional context

Tested on master

[7sharp9]

@kevmal This looks familiar to that one you fixed in Enum a while back, can you remember what was causing it? A cast from object or something like that?

[7sharp9]

Think Ive found it...

[kevmal]

Seems like two issues here. First problem is that typeof<obj>.IsAssignableFrom(--provided type--) always returns false resulting in a downcast here:

falanx/Falanx.Machinery/QuotationToAst.fs

Lines 143 to 152 in eb83880

	| Coerce(e, t) ->
	//dependencies.Append t
	let synExpr = exprToAst e
	let synType = sysTypeToSynType range t knownNamespaces ommitEnclosingType
	let synCoerce =
	// Need to manually check for interface. <interface>.IsAssignableFrom(<provided_type :> interface>) does not properly return true
	if (t.IsInterface && (Array.contains t (e.Type.GetInterfaces()))) || t.IsAssignableFrom e.Type then
	SynExpr.Upcast(synExpr, synType, range)
	else
	SynExpr.Downcast(synExpr, synType, range)

Second issue is with the referenced version of fantomas, this fails

Fantomas.CodeFormatter.FormatDocument("bleh.fsx", "let a = 1 :> obj",Fantomas.FormatConfig.FormatConfig.Default)

with System.InvalidCastException: Unable to cast object of type 'Upcast' to type 'Downcast'..

Luckily it seems like testing with fantomas master this may be fixed.

[7sharp9]

I dropped all the box operations and coercions to obj and it seems to work, not got to upgrading Fantomas yet...

[7sharp9]

So we also need to fix | Coerce(e, t) with special consideration for ProvidedTypes.

[7sharp9]

@kevmal So on a ProvidedType instance maybe Utils.isAssignableFrom could work

[kevmal]

Seems like Utils.isAssignableFrom just reduces to the same call.

        let isAssignableFrom (ty: Type) (otherTy: Type) =
            eqTypes ty otherTy || (match otherTy.BaseType with null -> false | bt -> ty.IsAssignableFrom(bt))

[7sharp9]

Fixed by #73