Merge pull request #32 from gzuidhof/fix-interface-types

Fix "empty" interfaces

examples/interface/index.ts

@@ -0,0 +1,9 @@
+// Code generated by tygo. DO NOT EDIT.
+
+//////////
+// source: interface.go
+
+/**
+ * Plain interfaces should output the unknown type, which is `any` by default but can also be configured as `unknown`).
+ */
+export type InterfaceOnly = any;

examples/interface/interface.go

@@ -0,0 +1,6 @@
+package interfaceoutput
+
+// Plain interfaces should output the unknown type, which is `any` by default but can also be configured as `unknown`).
+type InterfaceOnly interface {
+	InterfaceMethod() string
+}

tygo.yaml

@@ -34,3 +34,6 @@ packages:
   - path: "github.com/gzuidhof/tygo/examples/yaml"
     output_path: "./examples/yaml/index.ts"
     flavor: "yaml"
+  - path: "github.com/gzuidhof/tygo/examples/interface"
+
+

tygo/write.go

@@ -148,15 +148,23 @@ func (g *PackageGenerator) writeTypeParamsFields(s *strings.Builder, fields []*a
 }
 
 func (g *PackageGenerator) writeInterfaceFields(s *strings.Builder, fields []*ast.Field, depth int) {
+	// Usually interfaces in Golang don't have fields, but generic (union) interfaces we can map to Typescript.
+
 	if len(fields) == 0 { // Type without any fields (probably only has methods)
 		s.WriteString(g.conf.FallbackType)
 		return
 	}
-	s.WriteByte('\n')
+
+	didContainNonFuncFields := false
 	for _, f := range fields {
 		if _, isFunc := f.Type.(*ast.FuncType); isFunc {
 			continue
 		}
+		if !didContainNonFuncFields {
+			s.WriteByte('\n') // We need to write a newline so comments of generic components render nicely.
+			didContainNonFuncFields = true
+		}
+
 		if g.PreserveTypeComments() {
 			g.writeCommentGroupIfNotNil(s, f.Doc, depth+1)
 		}
@@ -168,6 +176,10 @@ func (g *PackageGenerator) writeInterfaceFields(s *strings.Builder, fields []*as
 			s.WriteString(f.Comment.Text())
 		}
 	}
+
+	if !didContainNonFuncFields {
+		s.WriteString(g.conf.FallbackType)
+	}
 }
 
 func (g *PackageGenerator) writeStructFields(s *strings.Builder, fields []*ast.Field, depth int) {