if err != nil {
		return TypeAndValue{}, err
	}

	info := &Info{
		Types: make(map[ast.Expr]TypeAndValue),
	}
	err = CheckExpr(fset, pkg, pos, node, info)
	return info.Types[node], err
}

// CheckExpr type checks the expression expr as if it had appeared at position
// pos of package pkg. [Type] information about the expression is recorded in

	if err != nil {
		t.Fatal(err)
	}

	checkExpr := func(pos token.Pos, str string) (Object, error) {
		expr, err := parser.ParseExprFrom(fset, "eval", str, 0)
		if err != nil {
			return nil, err
		}

		info := &Info{
			Uses:       make(map[*ast.Ident]Object),
			Selections: make(map[*ast.SelectorExpr]*Selection),
		}
		if err := CheckExpr(fset, pkg, pos, expr, info); err != nil {

// If there are no files, the result is nil.
// The position must be valid.
func (check *Checker) fileFor(pos token.Pos) *ast.File {
	assert(pos.IsValid())
	// Eval and CheckExpr tests may not have any source files.
	if len(check.files) == 0 {
		return nil
	}
	for _, file := range check.files {
		if file.FileStart <= pos && pos < file.FileEnd {
			return file
		}
	}