fix: type constraint should not be generated when the type is a "return type"

src/Glutinum.Converter/Printer.fs

@@ -163,68 +163,74 @@ let private printAttributes
         printer.NewLine
     )
 
-let rec private tryTransformTypeParametersToText
+let rec printTypeParametersDeclaration
+    (printer: Printer)
     (typeParameters: FSharpTypeParameter list)
     =
-    let printer = new Printer()
+    let innterPrinter = new Printer()
 
     if not typeParameters.IsEmpty then
-        printer.WriteInline("<")
+        innterPrinter.WriteInline("<")
 
         typeParameters
         |> List.iteri (fun index typeParameter ->
             if index <> 0 then
-                printer.WriteInline(", ")
+                innterPrinter.WriteInline(", ")
 
-            printer.WriteInline($"'{typeParameter.Name}")
+            innterPrinter.WriteInline($"'{typeParameter.Name}")
         )
 
+        // Print the constraints only if we are in the initial declaration.
+        // We want to avoid situations like the following:
+        // static member User<'T when 'T :> A> () : User<'T when 'T :> A> = nativeOnly
+        // Which should be:
+        // static member User<'T when 'T :> A> () : User<'T> = nativeOnly
         typeParameters
         |> List.filter _.Constraint.IsSome
         |> List.iteri (fun index typeParameter ->
             match typeParameter.Constraint with
             | Some constraint_ ->
                 if index = 0 then
-                    printer.WriteInline(" when ")
+                    innterPrinter.WriteInline(" when ")
                 else
-                    printer.WriteInline(" and ")
+                    innterPrinter.WriteInline(" and ")
 
-                printer.WriteInline($"'{typeParameter.Name}")
-                printer.WriteInline(" :> ")
-                printer.WriteInline(printType constraint_)
+                innterPrinter.WriteInline($"'{typeParameter.Name}")
+                innterPrinter.WriteInline(" :> ")
+                innterPrinter.WriteInline(printType constraint_)
             | None -> ()
         )
 
-        printer.WriteInline(">")
-
-        printer.ToStringWithoutTrailNewLine() |> Some
+        innterPrinter.WriteInline(">")
 
-    else
-        None
+        innterPrinter.ToStringWithoutTrailNewLine() |> printer.WriteInline
 
-and printTypeParameters
-    (printer: Printer)
+and printTypeNameWithTypeParameters
+    (name: string)
     (typeParameters: FSharpTypeParameter list)
     =
-    match tryTransformTypeParametersToText typeParameters with
-    | Some typeParameters -> printer.WriteInline(typeParameters)
-    | None -> ()
+    let printer = new Printer()
 
-and printType (fsharpType: FSharpType) =
-    let printTypeNameWithTypeParemeters
-        (name: string)
-        (typeParameters: FSharpTypeParameter list)
-        =
-        match tryTransformTypeParametersToText typeParameters with
-        | Some typeParameters -> $"{name}{typeParameters}"
-        | None -> name
+    if not typeParameters.IsEmpty then
+        printer.WriteInline("<")
 
+        typeParameters
+        |> List.iteri (fun index typeParameter ->
+            if index <> 0 then
+                printer.WriteInline(", ")
+
+            printer.WriteInline($"'{typeParameter.Name}")
+        )
+
+        printer.WriteInline(">")
+
+    $"{name}{printer.ToStringWithoutTrailNewLine()}"
+
+and printType (fsharpType: FSharpType) =
     match fsharpType with
     | FSharpType.Object -> "obj"
     | FSharpType.Mapped info ->
-        match tryTransformTypeParametersToText info.TypeParameters with
-        | Some typeParameters -> $"{info.Name}{typeParameters}"
-        | None -> info.Name
+        printTypeNameWithTypeParameters info.Name info.TypeParameters
 
     | FSharpType.SingleErasedCaseUnion info -> info.Name
 
@@ -247,7 +253,7 @@ and printType (fsharpType: FSharpType) =
         $"{info.Name}<{cases}>{option}"
 
     | FSharpType.ThisType thisTypeInfo ->
-        printTypeNameWithTypeParemeters
+        printTypeNameWithTypeParameters
             thisTypeInfo.Name
             thisTypeInfo.TypeParameters
 
@@ -309,14 +315,14 @@ and printType (fsharpType: FSharpType) =
         match apiInfo with
         | FSharpJSApi.ReadonlyArray typ -> $"ReadonlyArray<{printType typ}>"
     | FSharpType.Interface interfaceInfo ->
-        printTypeNameWithTypeParemeters
+        printTypeNameWithTypeParameters
             interfaceInfo.Name
             interfaceInfo.TypeParameters
     | FSharpType.Class classInfo -> classInfo.Name
     | FSharpType.TypeAlias aliasInfo ->
-        printTypeNameWithTypeParemeters aliasInfo.Name aliasInfo.TypeParameters
+        printTypeNameWithTypeParameters aliasInfo.Name aliasInfo.TypeParameters
     | FSharpType.Delegate delegateInfo ->
-        printTypeNameWithTypeParemeters
+        printTypeNameWithTypeParameters
             delegateInfo.Name
             delegateInfo.TypeParameters
     | FSharpType.Module _
@@ -503,7 +509,7 @@ let private printInterface (printer: Printer) (interfaceInfo: FSharpInterface) =
     printAttributes printer interfaceInfo.Attributes
 
     printer.Write($"type {interfaceInfo.Name}")
-    printTypeParameters printer interfaceInfo.TypeParameters
+    printTypeParametersDeclaration printer interfaceInfo.TypeParameters
     printer.WriteInline(" =")
     printer.NewLine
 
@@ -532,7 +538,7 @@ let private printInterface (printer: Printer) (interfaceInfo: FSharpInterface) =
 
             printer.WriteInline($"member {methodInfo.Name}")
 
-            printTypeParameters printer methodInfo.TypeParameters
+            printTypeParametersDeclaration printer methodInfo.TypeParameters
 
             if methodInfo.IsStatic then
                 printer.WriteInline(" ")
@@ -704,7 +710,9 @@ import {{ %s{interfaceInfo.OriginalName} }} from \"{Naming.MODULE_PLACEHOLDER}\"
 
             printer.Write($"static member inline {staticMemberInfo.Name} ")
 
-            printTypeParameters printer staticMemberInfo.TypeParameters
+            printTypeParametersDeclaration
+                printer
+                staticMemberInfo.TypeParameters
 
             if staticMemberInfo.Parameters.IsEmpty then
                 printer.WriteInline("() : ")
@@ -811,7 +819,7 @@ let private printClass (printer: Printer) (classInfo: FSharpClass) =
     printAttributes printer classInfo.Attributes
 
     printer.Write($"type {classInfo.Name}")
-    printTypeParameters printer classInfo.TypeParameters
+    printTypeParametersDeclaration printer classInfo.TypeParameters
     printer.NewLine
     printer.Indent
     printPrimaryConstructor printer classInfo.PrimaryConstructor
@@ -897,7 +905,7 @@ let private printTypeAlias (printer: Printer) (aliasInfo: FSharpTypeAlias) =
     printAttributes printer aliasInfo.Attributes
 
     printer.Write($"type {aliasInfo.Name}")
-    printTypeParameters printer aliasInfo.TypeParameters
+    printTypeParametersDeclaration printer aliasInfo.TypeParameters
     printer.WriteInline(" =")
 
     printer.NewLine
@@ -908,7 +916,7 @@ let private printTypeAlias (printer: Printer) (aliasInfo: FSharpTypeAlias) =
 
 let private printDelegate (printer: Printer) (delegateInfo: FSharpDelegate) =
     printer.Write($"type {delegateInfo.Name}")
-    printTypeParameters printer delegateInfo.TypeParameters
+    printTypeParametersDeclaration printer delegateInfo.TypeParameters
     printer.WriteInline(" =")
 
     printer.NewLine
@@ -992,7 +1000,11 @@ let rec private print (printer: Printer) (fsharpTypes: FSharpType list) =
                 (FSharpAttribute.Erase :: erasedCaseUnionInfo.Attributes)
 
             printer.Write($"type {erasedCaseUnionInfo.Name}")
-            printTypeParameters printer [ erasedCaseUnionInfo.TypeParameter ]
+
+            printTypeParametersDeclaration
+                printer
+                [ erasedCaseUnionInfo.TypeParameter ]
+
             printer.WriteInline(" =")
 
             printer.NewLine

tests/specs/references/class/generics/oneWithConstraint.d.ts

@@ -0,0 +1,3 @@
+class A {}
+
+class User<T extends A = A> {}

tests/specs/references/class/generics/oneWithConstraint.fsx

@@ -0,0 +1,28 @@
+module rec Glutinum
+
+open Fable.Core
+open Fable.Core.JsInterop
+open System
+
+[<AbstractClass>]
+[<Erase>]
+type Exports =
+    [<Import("A", "REPLACE_ME_WITH_MODULE_NAME"); EmitConstructor>]
+    static member A () : A = nativeOnly
+    [<Import("User", "REPLACE_ME_WITH_MODULE_NAME"); EmitConstructor>]
+    static member User<'T when 'T :> A> () : User<'T> = nativeOnly
+
+[<AllowNullLiteral>]
+[<Interface>]
+type A =
+    interface end
+
+[<AllowNullLiteral>]
+[<Interface>]
+type User<'T when 'T :> A> =
+    interface end
+
+(***)
+#r "nuget: Fable.Core"
+#r "nuget: Glutinum.Types"
+(***)