go/types: initial steps towards customizing method signatures

Needs more work and tests.

Change-Id: Ic54e5798c374254d55b46cb582d7cf87efe125d1

src/go/types/object.go

@@ -319,7 +319,7 @@ type Func struct {
 // NewFunc returns a new function with the given signature, representing
 // the function's type.
 func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
-	// don't store a nil signature
+	// don't store a (typed) nil signature
 	var typ Type
 	if sig != nil {
 		typ = sig

src/go/types/subst.go

@@ -90,7 +90,9 @@ func (s *subster) typ(typ Type) (res Type) {
 		return s.tuple(t)
 
 	case *Signature:
-		recv := s.var_(t.recv) // not strictly needed (receivers cannot be parametrized)
+		// TODO(gri) rethink the recv situation with respect to methods on parameterized types
+		//recv := s.var_(t.recv) // not strictly needed (receivers cannot be parameterized) (?)
+		recv := t.recv
 		params := s.tuple(t.params)
 		results := s.tuple(t.results)
 		if recv != t.recv || params != t.params || results != t.results {
@@ -123,19 +125,26 @@ func (s *subster) typ(typ Type) (res Type) {
 		if underlying != t.underlying {
 			// create a new named type - for now use printed type in name
 			// TODO(gri) consider type map to map types to indices (on the other hand, a type string seems just as good)
-			if len(t.methods) > 0 {
-				panic("cannot handle instantiation of types with methods yet")
-			}
 			// TODO(gri) review name creation and factor out
 			name := TypeString(t, nil) + "<" + typeListString(s.targs) + ">"
 			//s.check.dump("NAME = %s", name)
 			tname, found := s.check.typMap[name]
 			if !found {
+				// instantiate custom methods as necessary
+				var methods []*Func
+				for _, m := range t.methods {
+					//sig := s.typ(m.typ).(*Signature)
+					sig := s.check.subst(m.typ, m.tparams, s.targs).(*Signature)
+					m1 := NewFunc(m.pos, m.pkg, m.name, sig)
+					//s.check.dump("%s: method %s => %s", name, m, m1)
+					methods = append(methods, m1)
+				}
 				// TODO(gri) what is the correct position to use here?
 				tname = NewTypeName(t.obj.pos, s.check.pkg, name, nil)
 				//s.check.dump("name = %s", name)
-				NewNamed(tname, underlying, nil) // TODO(gri) provide correct method list
+				NewNamed(tname, underlying, methods)
 				s.check.typMap[name] = tname
+				// TODO(gri) update the method receivers?
 			}
 			return tname.typ
 		}

src/go/types/testdata/tmp.go2

@@ -12,5 +12,3 @@ func (l List(E)) First() E {
         }
         return l[0]
 }
-
-// var _ string = List(string){"foo"}.First()

src/go/types/testdata/typeinst2.go2

@@ -46,4 +46,7 @@ var (
 	_ [](List(int)) = f(List(int){})
         _ List(List(int)) = [](List(int)){}
         _ = [](List(int)){}
-)
+)
+
+// Parameterized types with methods
+

src/go/types/type.go

@@ -201,7 +201,8 @@ type Signature struct {
 	// We then unpack the *Signature and use the scope for the literal body.
 	scope *Scope // function scope, present for package-local signatures
 	recv  *Var   // nil if not a method
-	// TODO(gri) do we need to keep tparams in the signature?
+	// TODO(gri) do we need to keep tparams in the Signature, rather than the Func object?
+	// (how are they different from type parameters which we keep with the TypeName?)
 	tparams  []*TypeName // type parameters from left to right; or nil
 	params   *Tuple      // (incoming) parameters from left to right; or nil
 	results  *Tuple      // (outgoing) results from left to right; or nil