go/types: move method collection out of type declaration processing

Simplifies Checker.typeDecl. Also, methods can only be added to
top-level types; no need to try to collect them for local types.

Change-Id: I05b926df7ffa70c32c1dd5faed3c68617be8f270

src/go/types/decl.go

@@ -200,6 +200,7 @@ func (check *Checker) objDecl(obj Object, def *Named) {
 	case *TypeName:
 		// invalid recursive types are detected via path
 		check.typeDecl(obj, d.tdecl, def)
+		check.collectMethods(obj) // methods can only be added to top-level types
 	case *Func:
 		// functions may be recursive - no need to track dependencies
 		check.funcDecl(obj, d)
@@ -580,6 +581,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 
 		if tdecl.TParams != nil {
 			check.openScope(tdecl, "type parameters")
+			defer check.closeScope()
 			named.tparams = check.collectTypeParams(tdecl.TParams)
 		}
 
@@ -600,16 +602,8 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 		// Determine the (final, unnamed) underlying type by resolving
 		// any forward chain.
 		named.underlying = check.underlying(named)
-
-		// this must happen before addMethodDecls - cannot use defer
-		// TODO(gri) consider refactoring this
-		if tdecl.TParams != nil {
-			check.closeScope()
-		}
-
 	}
 
-	check.addMethodDecls(obj)
 }
 
 func (check *Checker) collectTypeParams(list *ast.FieldList) (tparams []*TypeName) {
@@ -780,7 +774,7 @@ func (check *Checker) declareTypeParams(tparams []*TypeName, names []*ast.Ident)
 	return tparams
 }
 
-func (check *Checker) addMethodDecls(obj *TypeName) {
+func (check *Checker) collectMethods(obj *TypeName) {
 	// get associated methods
 	// (Checker.collectObjects only collects methods with non-blank names;
 	// Checker.resolveBaseTypeName ensures that obj is not an alias name

src/go/types/resolver.go

@@ -626,7 +626,7 @@ func (check *Checker) packageObjects() {
 	// add new methods to already type-checked types (from a prior Checker.Files call)
 	for _, obj := range objList {
 		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
-			check.addMethodDecls(obj)
+			check.collectMethods(obj)
 		}
 	}
 

src/go/types/subst.go

@@ -187,7 +187,7 @@ func (subst *subster) typ(typ Type) Type {
 		// TODO(gri) BUG: If we instantiate this signature but it has no value params, we don't get a copy!
 		//           We need to look at the actual type parameters of the signature as well.
 		// 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 := subst.var_(t.recv) // TODO(gri) this causes a stack overflow - explain
 		recv := t.recv
 		params := subst.tuple(t.params)
 		results := subst.tuple(t.results)