[WIP] Emit type

src/Fable.Transforms/Dart/Dart.fs

@@ -36,6 +36,7 @@ type Type =
 
     | Generic of name: string
     | TypeReference of Ident * generics: Type list
+    | EmitType of value: string * generics: Type list
     | Function of argTypes: Type list * returnType: Type
 
 type Ident =

src/Fable.Transforms/Dart/DartPrinter.fs

@@ -59,6 +59,33 @@ module PrinterExtensions =
                 printer.Print(s)
                 printSeparator |> Option.iter (fun f -> f printer)
 
+        member printer.PrintEmitType(value: string, genArgs: Type list) =
+            let printSegment (printer: Printer) (value: string) segmentStart segmentEnd =
+                let segmentLength = segmentEnd - segmentStart
+                if segmentLength > 0 then
+                    let segment = value.Substring(segmentStart, segmentLength)
+                    printer.Print(segment)
+
+            let matches = Regex.Matches(value, @"\$\d+")
+            if matches.Count > 0 then
+                for i = 0 to matches.Count - 1 do
+                    let m = matches[i]
+                    let segmentStart =
+                        if i > 0 then matches[i-1].Index + matches[i-1].Length
+                        else 0
+
+                    printSegment printer value segmentStart m.Index
+
+                    let argIndex = int m.Value[1..]
+                    match List.tryItem argIndex genArgs with
+                    | Some t -> printer.PrintType(t)
+                    | None -> ()
+
+                let lastMatch = matches[matches.Count - 1]
+                printSegment printer value (lastMatch.Index + lastMatch.Length) value.Length
+            else
+                printSegment printer value 0 value.Length
+
         // TODO: Most of this code matches BabelPrinter.PrintEmitExpression, can we refactor it?
         member printer.PrintEmitExpression(value: string, args: Expression list) =
             let inline replace pattern (f: Match -> string) input =
@@ -233,6 +260,8 @@ module PrinterExtensions =
             | TypeReference(ref, gen) ->
                 printer.PrintIdent(ref)
                 printer.PrintList("<", ", ", ">", gen, printer.PrintType, skipIfEmpty=true)
+            | EmitType(macro, gen) ->
+                printer.PrintEmitType(macro, gen)
             | Function(argTypes, returnType) ->
                 printer.PrintType(returnType)
                 printer.Print(" ")

src/Fable.Transforms/Dart/Fable2Dart.fs

@@ -162,6 +162,14 @@ module Util =
         let tup = List.length genArgs |> getTupleTypeIdent com ctx
         TypeReference(tup, transformGenArgs com ctx genArgs)
 
+    let (|EmitAttribute|_|) (ent: Fable.Entity) =
+        ent.Attributes |> Seq.tryPick (fun att ->
+            if att.Entity.FullName.StartsWith(Atts.emit) then
+                match att.ConstructorArgs with
+                | [:? string as macro] -> Some macro
+                | _ -> None
+            else None)
+
     let transformDeclaredTypeIgnoreMeasure ignoreMeasure (com: IDartCompiler) ctx (entRef: Fable.EntityRef) genArgs =
         match entRef.FullName with
         | "System.Enum" -> Integer |> Some
@@ -175,10 +183,11 @@ module Util =
         // We use `dynamic` for now because there doesn't seem to be a type that catches all errors in Dart
         | Naming.EndsWith "Exception" _ -> Dynamic |> Some
         | _ ->
-            let ent = com.GetEntity(entRef)
-            if ignoreMeasure && ent.IsMeasure then
-                None
-            else
+            match com.GetEntity(entRef) with
+            | ent when ignoreMeasure && ent.IsMeasure -> None
+            | EmitAttribute(macro) ->
+                EmitType(macro, transformGenArgs com ctx genArgs) |> Some
+            | ent ->
                 let genArgs = transformGenArgs com ctx genArgs
                 TypeReference(getEntityIdent com ctx ent, genArgs) |> Some
 
@@ -2121,10 +2130,12 @@ module Util =
 
         | Fable.ClassDeclaration decl ->
             let entRef = decl.Entity
-            let ent = com.GetEntity(entRef)
-            if ent.IsInterface then
+            match com.GetEntity(entRef) with
+            // Ignore declaration for classes with Emit attribute
+            | EmitAttribute _ -> []
+            | ent when ent.IsInterface ->
                 transformInterfaceDeclaration com ctx decl ent
-            else
+            | ent ->
                 let instanceMethods =
                     decl.AttachedMembers |> List.choose (fun memb ->
                         match memb.Name with