| 1 | // Copyright 2018 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // The errorsas package defines an Analyzer that checks that the second argument to |
| 6 | // errors.As is a pointer to a type implementing error. |
| 7 | package errorsas |
| 8 | |
| 9 | import ( |
| 10 | "errors" |
| 11 | "go/ast" |
| 12 | "go/types" |
| 13 | |
| 14 | "golang.org/x/tools/go/analysis" |
| 15 | "golang.org/x/tools/go/analysis/passes/inspect" |
| 16 | "golang.org/x/tools/go/ast/inspector" |
| 17 | "golang.org/x/tools/go/types/typeutil" |
| 18 | ) |
| 19 | |
| 20 | const Doc = `report passing non-pointer or non-error values to errors.As |
| 21 | |
| 22 | The errorsas analysis reports calls to errors.As where the type |
| 23 | of the second argument is not a pointer to a type implementing error.` |
| 24 | |
| 25 | var Analyzer = &analysis.Analyzer{ |
| 26 | Name: "errorsas", |
| 27 | Doc: Doc, |
| 28 | Requires: []*analysis.Analyzer{inspect.Analyzer}, |
| 29 | Run: run, |
| 30 | } |
| 31 | |
| 32 | func run(pass *analysis.Pass) (interface{}, error) { |
| 33 | switch pass.Pkg.Path() { |
| 34 | case "errors", "errors_test": |
| 35 | // These packages know how to use their own APIs. |
| 36 | // Sometimes they are testing what happens to incorrect programs. |
| 37 | return nil, nil |
| 38 | } |
| 39 | |
| 40 | inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector) |
| 41 | |
| 42 | nodeFilter := []ast.Node{ |
| 43 | (*ast.CallExpr)(nil), |
| 44 | } |
| 45 | inspect.Preorder(nodeFilter, func(n ast.Node) { |
| 46 | call := n.(*ast.CallExpr) |
| 47 | fn := typeutil.StaticCallee(pass.TypesInfo, call) |
| 48 | if fn == nil { |
| 49 | return // not a static call |
| 50 | } |
| 51 | if len(call.Args) < 2 { |
| 52 | return // not enough arguments, e.g. called with return values of another function |
| 53 | } |
| 54 | if fn.FullName() != "errors.As" { |
| 55 | return |
| 56 | } |
| 57 | if err := checkAsTarget(pass, call.Args[1]); err != nil { |
| 58 | pass.ReportRangef(call, "%v", err) |
| 59 | } |
| 60 | }) |
| 61 | return nil, nil |
| 62 | } |
| 63 | |
| 64 | var errorType = types.Universe.Lookup("error").Type() |
| 65 | |
| 66 | // pointerToInterfaceOrError reports whether the type of e is a pointer to an interface or a type implementing error, |
| 67 | // or is the empty interface. |
| 68 | |
| 69 | // checkAsTarget reports an error if the second argument to errors.As is invalid. |
| 70 | func checkAsTarget(pass *analysis.Pass, e ast.Expr) error { |
| 71 | t := pass.TypesInfo.Types[e].Type |
| 72 | if it, ok := t.Underlying().(*types.Interface); ok && it.NumMethods() == 0 { |
| 73 | // A target of interface{} is always allowed, since it often indicates |
| 74 | // a value forwarded from another source. |
| 75 | return nil |
| 76 | } |
| 77 | pt, ok := t.Underlying().(*types.Pointer) |
| 78 | if !ok { |
| 79 | 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") |
| 80 | } |
| 81 | if pt.Elem() == errorType { |
| 82 | return errors.New("second argument to errors.As should not be *error") |
| 83 | } |
| 84 | _, ok = pt.Elem().Underlying().(*types.Interface) |
| 85 | if ok || types.Implements(pt.Elem(), errorType.Underlying().(*types.Interface)) { |
| 86 | return nil |
| 87 | } |
| 88 | 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") |
| 89 | } |
| 90 |
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