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// 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 (
"errors"
"go/ast"
"go/types"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/ast/inspector"
"golang.org/x/tools/go/types/typeutil"
)
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{
(*ast.CallExpr)(nil),
}
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" {
return
}
if err := checkAsTarget(pass, call.Args[1]); err != nil {
pass.ReportRangef(call, "%v", err)
}
})
return nil, nil
}
var errorType = types.Universe.Lookup("error").Type()
// pointerToInterfaceOrError reports whether the type of e is a pointer to an interface or a type implementing error,
// or is the empty interface.
// checkAsTarget reports an error if the second argument to errors.As is invalid.
func checkAsTarget(pass *analysis.Pass, e ast.Expr) error {
t := pass.TypesInfo.Types[e].Type
if it, ok := t.Underlying().(*types.Interface); ok && it.NumMethods() == 0 {
// A target of interface{} is always allowed, since it often indicates
// a value forwarded from another source.
return nil
}
pt, ok := t.Underlying().(*types.Pointer)
if !ok {
return errors.New("second argument to errors.As must be a non-nil pointer to either a type that implements error, or to any interface type")
}
if pt.Elem() == errorType {
return errors.New("second argument to errors.As should not be *error")
}
_, ok = pt.Elem().Underlying().(*types.Interface)
if ok || types.Implements(pt.Elem(), errorType.Underlying().(*types.Interface)) {
return nil
}
return errors.New("second argument to errors.As must be a non-nil pointer to either a type that implements error, or to any interface type")
}
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