8 files changed, 159 insertions(+), 14 deletions(-)

M cmd/goast/main.go
M pkg/codegen/mangle.go
M pkg/codegen/position.go
M pkg/codegen/testdata/fn_assign_call_interface.snow
A pkg/codegen/testdata/fn_assign_call_interface.snow.err
A pkg/codegen/testdata/fn_assign_call_interface.snow.want
M pkg/codegen/translate.go
M pkg/codegen/treebuild.go

@@ 10,9 10,11 @@ func main() {
 	src := `
 package main
 
+type I interface {
+	foo(int) int
+}
+
 func main() { 
-	s := map[string]bool{"a": true}
-	_ = s
 }
 `
 

@@ 125,6 125,13 @@ func (r *nameResolver) NameForStructType(st *semantic.StructType, resolve map[*s
 	return r.NameForGenericDeclAndTypes(st.Decl, st.Inst, resolve)
 }
 
+func (r *nameResolver) NameForInterfaceType(it *semantic.InterfaceType, resolve map[*semantic.GenericType]semantic.Type) string {
+	if !it.Decl.IsGeneric() {
+		return r.NameForDecl(it.Decl)
+	}
+	return r.NameForGenericDeclAndTypes(it.Decl, it.Inst, resolve)
+}
+
 func (r *nameResolver) NameForGenericInst(gi *semantic.GenericInst, resolve map[*semantic.GenericType]semantic.Type) string {
 	gd := gi.GenericDecl.Ref.(semantic.GenericDecl)
 	_, insts := gd.GenInsts()


@@ 200,7 207,9 @@ type fmtBuilder struct {
 func (b *fmtBuilder) withPrefixFor(decl semantic.Decl) {
 	switch decl := decl.(type) {
 	case *semantic.Fn:
-		if decl.Scope().IsTopLevel() || decl.MethodOf != nil {
+		if decl.Scope().IsTopLevel() || decl.MethodOf != nil || decl.AbstractMethodOf != nil {
+			// TODO: this will be an issue with pub/exported methods eventually: the mangling of
+			// an interface method might not match the one of an otherwise matching struct method.
 			b.withExport(false)
 		}
 	case *semantic.Var:


@@ 212,12 221,13 @@ func (b *fmtBuilder) withPrefixFor(decl semantic.Decl) {
 		if !decl.Scope().IsTopLevel() {
 			b.withScope(decl.Scope())
 		}
-
 	case *semantic.Interface:
 		b.withExport(false)
 		if !decl.Scope().IsTopLevel() {
 			b.withScope(decl.Scope())
 		}
+	default:
+		panic(fmt.Sprintf("invalid declaration type for mangler prefix: %T", decl))
 	}
 }
 

@@ 130,6 130,8 @@ func (p *positioner) Visit(n goast.Node) goast.Visitor {
 		return nil
 	case *goast.IfStmt:
 		n.If = p.getIncByLen("if ")
+	case *goast.InterfaceType:
+		n.Interface = p.getIncByLen("interface ")
 	}
 	return p
 }

@@ 8,14 8,23 @@ struct S {
   fn foo() {
     println(s)
   }
+
+  struct S2 {
+    fn foo() {
+      println("s2")
+    }
+  }
 }
 
 @extern(import: "fmt", symbol: "Println")
 fn println(s: string)
 
 fn main() {
-  let iface: I = S(s: "hello!")
+  var iface: I = S(s: "hello!")
+  iface.foo()
+  iface = S.S2()
   iface.foo()
 }
 
 #=hello!
+#=s2

@@ 0,0 1,58 @@
+package main
+
+import "fmt"
+
+type _اS struct {
+	_اs string
+}
+
+func (
+	self _اS,
+) _اfoo() {
+	_اprintln(self._اs)
+}
+
+type _ا6اS2 struct {
+}
+
+func (
+	self _ا6اS2,
+) _اfoo() {
+	_اprintln("s2")
+}
+
+func _ا6اS2اnew(
+	s _ا6اS2,
+	m map[string]bool,
+) _ا6اS2 {
+	var r _ا6اS2
+	return r
+}
+
+func _اSاnew(
+	s _اS,
+	m map[string]bool,
+) _اS {
+	var r _اS
+	if m["s"] {
+		r._اs = s._اs
+	}
+	return r
+}
+
+func _اprintln(
+	s string,
+) {
+	fmt.Println(s)
+}
+
+func main() {
+	var iface _اI = _اSاnew(_اS{_اs: "hello!"}, map[string]bool{"s": true})
+	iface._اfoo()
+	iface = _ا6اS2اnew(_ا6اS2{}, map[string]bool{})
+	iface._اfoo()
+}
+
+type _اI interface {
+	_اfoo()
+}

@@ 124,6 124,9 @@ func (t *translator) Visit(n semantic.Node) semantic.Visitor {
 			for _, fn := range n.Fns {
 				semantic.Walk(t, fn)
 			}
+			for _, iface := range n.Interfaces {
+				semantic.Walk(t, iface)
+			}
 		})
 
 		// ************** DECLARATIONS *****************


@@ 418,21 421,22 @@ func (t *translator) createFn(nm string, fn *semantic.Fn) {
 
 	var body *goast.BlockStmt
 	t.withContainer(cont, func() {
-		if fn.Body == nil {
-			body = createExternalFnBody(ft, t.fnImports[fn])
-		} else {
+		if fn.Body != nil {
 			semantic.Walk(t, fn.Body)
+		} else if fn.AbstractMethodOf == nil {
+			// this is an external function
+			body = createExternalFnBody(ft, t.fnImports[fn])
 		}
 	})
 
 	// the function declaration is a top-level func statement if it is top-level
 	// in snow or is a struct method.
+	fd := &goast.FuncDecl{
+		Name: &goast.Ident{Name: nm},
+		Type: ft,
+		Body: body,
+	}
 	if fn.Scope().IsTopLevel() || fn.MethodOf != nil {
-		fd := &goast.FuncDecl{
-			Name: &goast.Ident{Name: nm},
-			Type: ft,
-			Body: body,
-		}
 		if str := fn.MethodOf; str != nil {
 			t.convertFuncToMethod(fd, str, fn.IsRef)
 		}


@@ 444,6 448,14 @@ func (t *translator) createFn(nm string, fn *semantic.Fn) {
 			t.topLevel.PushBack(cont)
 		}
 		return
+
+	}
+	if fn.AbstractMethodOf != nil {
+		// if it is an interface method, create the function declaration inside the
+		// interface's container. It cannot be a generic itself (only the interface can).
+		cont.nodes = []goast.Node{fd}
+		t.parentContainer.PushBack(cont)
+		return
 	}
 
 	cont.nodes = createFuncLit(nm, ft, body)


@@ 509,13 521,16 @@ func (t *translator) createStruct(nm string, strTyp *semantic.StructType) {
 	// generate struct initializer function
 	strInit := t.createStructInit(nm, strTyp, propInit)
 
-	// generate methods and nested structs
+	// generate methods and nested structs and interfaces
 	for _, meth := range strTyp.Decl.Fns {
 		semantic.Walk(t, meth)
 	}
 	for _, str := range strTyp.Decl.Structs {
 		semantic.Walk(t, str)
 	}
+	for _, iface := range strTyp.Decl.Interfaces {
+		semantic.Walk(t, iface)
+	}
 
 	if mark := t.genDeclMarks[strTyp.Decl]; mark != nil {
 		mark.list.InsertBefore(strInit, mark.elem)


@@ 524,6 539,40 @@ func (t *translator) createStruct(nm string, strTyp *semantic.StructType) {
 	}
 }
 
+func (t *translator) createInterface(nm string, ifaceTyp *semantic.InterfaceType) {
+	// all interface declarations are attached to the top-level scope of the file.
+	fields := &goast.FieldList{List: make([]*goast.Field, len(ifaceTyp.Decl.Methods))}
+
+	// create the container but don't set its Go node yet, it will be created
+	// only after looping over the methods.
+	cont := &container{snode: ifaceTyp.Decl, children: list.New()}
+
+	t.withContainer(cont, func() {
+		for i, m := range ifaceTyp.Decl.Methods {
+			semantic.Walk(t, m)
+			node := t.parentContainer.Back().Value
+			fnDecl := node.(*container).nodes[0].(*goast.FuncDecl)
+			fields.List[i] = &goast.Field{
+				Names: []*goast.Ident{fnDecl.Name},
+				Type:  fnDecl.Type,
+			}
+		}
+	})
+
+	decl := &goast.GenDecl{
+		Tok: gotoken.TYPE,
+		Specs: []goast.Spec{
+			&goast.TypeSpec{Name: &goast.Ident{Name: nm}, Type: &goast.InterfaceType{Methods: fields}},
+		},
+	}
+	cont.nodes = []goast.Node{decl}
+	if mark := t.genDeclMarks[ifaceTyp.Decl]; mark != nil {
+		mark.list.InsertBefore(cont, mark.elem)
+	} else {
+		t.topLevel.PushBack(cont)
+	}
+}
+
 func (t *translator) addFileImports(f *semantic.File, gof *goast.File) {
 	imports := t.fileImports[f]
 	set := make(map[string]bool, len(imports))


@@ 590,6 639,10 @@ func (t *translator) goTypeExprFor(T semantic.Type) goast.Expr {
 		name := t.resolver.NameForStructType(T, t.curGenInst)
 		return &goast.Ident{Name: name}
 
+	case *semantic.InterfaceType:
+		name := t.resolver.NameForInterfaceType(T, t.curGenInst)
+		return &goast.Ident{Name: name}
+
 	default:
 		panic(fmt.Sprintf("invalid type: %T", T))
 	}


@@ 605,6 658,12 @@ func (t *translator) reconcileExprWith(LT, RT semantic.Type, expr goast.Expr) go
 func (t *translator) convertExprFromTo(expr goast.Expr, fromT, toT semantic.Type) goast.Expr {
 	var convertCallExpr goast.Expr
 
+	// if toT is an interface, no explicit conversion needed, Go will be able to assign fromT
+	// to it (as the rules for assignability are the same).
+	if semantic.AsInterfaceType(toT) != nil {
+		return expr
+	}
+
 	fromTupT, ok1 := fromT.(*semantic.TupleType)
 	toTupT, ok2 := toT.(*semantic.TupleType)
 	if ok1 && ok2 {


@@ 829,6 888,8 @@ func (t *translator) renderGenInst(gi *semantic.GenericInst, name string) {
 		t.createFn(name, decl)
 	case *semantic.Struct:
 		t.createStruct(name, semantic.AsStructType(gi.Type()))
+	case *semantic.Interface:
+		t.createInterface(name, semantic.AsInterfaceType(gi.Type()))
 	default:
 		panic(fmt.Sprintf("invalid generic type to render: %T", decl))
 	}

@@ 99,6 99,9 @@ func (tb *treebuilder) Visit(n semantic.Node) semantic.Visitor {
 	case *semantic.Struct:
 		// a struct container has a single Go node, the struct decl, and it is fully
 		// formed, no need to append children, so nothing to do.
+	case *semantic.Interface:
+		// an interface container has a single Go node, the interface decl, and it is fully
+		// formed, no need to append children, so nothing to do.
 
 	case *semantic.Block:
 		cont := tb.curContainer