blob: b80271afb9515c0a111b6fe17b2825aeba2a6b37 [file] [log] [blame]
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The errorsas package defines an Analyzer that checks that the second argument to
// errors.As is a pointer to a type implementing error.
package errorsas
import (
const Doc = `report passing non-pointer or non-error values to errors.As
The errorsas analysis reports calls to errors.As where the type
of the second argument is not a pointer to a type implementing error.`
var Analyzer = &analysis.Analyzer{
Name: "errorsas",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
func run(pass *analysis.Pass) (interface{}, error) {
switch pass.Pkg.Path() {
case "errors", "errors_test":
// These packages know how to use their own APIs.
// Sometimes they are testing what happens to incorrect programs.
return nil, nil
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
inspect.Preorder(nodeFilter, func(n ast.Node) {
call := n.(*ast.CallExpr)
fn := typeutil.StaticCallee(pass.TypesInfo, call)
if fn == nil {
return // not a static call
if len(call.Args) < 2 {
return // not enough arguments, e.g. called with return values of another function
if fn.FullName() == "errors.As" && !pointerToInterfaceOrError(pass, call.Args[1]) {
pass.ReportRangef(call, "second argument to errors.As must be a pointer to an interface or a type implementing error")
return nil, nil
var errorType = types.Universe.Lookup("error").Type().Underlying().(*types.Interface)
// pointerToInterfaceOrError reports whether the type of e is a pointer to an interface or a type implementing error,
// or is the empty interface.
func pointerToInterfaceOrError(pass *analysis.Pass, e ast.Expr) bool {
t := pass.TypesInfo.Types[e].Type
if it, ok := t.Underlying().(*types.Interface); ok && it.NumMethods() == 0 {
return true
pt, ok := t.Underlying().(*types.Pointer)
if !ok {
return false
_, ok = pt.Elem().Underlying().(*types.Interface)
return ok || types.Implements(pt.Elem(), errorType)