| 1 | // Copyright 2013 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 | // Package nilfunc defines an Analyzer that checks for useless |
| 6 | // comparisons against nil. |
| 7 | package nilfunc |
| 8 | |
| 9 | import ( |
| 10 | "go/ast" |
| 11 | "go/token" |
| 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/internal/typeparams" |
| 18 | ) |
| 19 | |
| 20 | const Doc = `check for useless comparisons between functions and nil |
| 21 | |
| 22 | A useless comparison is one like f == nil as opposed to f() == nil.` |
| 23 | |
| 24 | var Analyzer = &analysis.Analyzer{ |
| 25 | Name: "nilfunc", |
| 26 | Doc: Doc, |
| 27 | Requires: []*analysis.Analyzer{inspect.Analyzer}, |
| 28 | Run: run, |
| 29 | } |
| 30 | |
| 31 | func run(pass *analysis.Pass) (interface{}, error) { |
| 32 | inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector) |
| 33 | |
| 34 | nodeFilter := []ast.Node{ |
| 35 | (*ast.BinaryExpr)(nil), |
| 36 | } |
| 37 | inspect.Preorder(nodeFilter, func(n ast.Node) { |
| 38 | e := n.(*ast.BinaryExpr) |
| 39 | |
| 40 | // Only want == or != comparisons. |
| 41 | if e.Op != token.EQL && e.Op != token.NEQ { |
| 42 | return |
| 43 | } |
| 44 | |
| 45 | // Only want comparisons with a nil identifier on one side. |
| 46 | var e2 ast.Expr |
| 47 | switch { |
| 48 | case pass.TypesInfo.Types[e.X].IsNil(): |
| 49 | e2 = e.Y |
| 50 | case pass.TypesInfo.Types[e.Y].IsNil(): |
| 51 | e2 = e.X |
| 52 | default: |
| 53 | return |
| 54 | } |
| 55 | |
| 56 | // Only want identifiers or selector expressions. |
| 57 | var obj types.Object |
| 58 | switch v := e2.(type) { |
| 59 | case *ast.Ident: |
| 60 | obj = pass.TypesInfo.Uses[v] |
| 61 | case *ast.SelectorExpr: |
| 62 | obj = pass.TypesInfo.Uses[v.Sel] |
| 63 | case *ast.IndexExpr, *typeparams.IndexListExpr: |
| 64 | // Check generic functions such as "f[T1,T2]". |
| 65 | x, _, _, _ := typeparams.UnpackIndexExpr(v) |
| 66 | if id, ok := x.(*ast.Ident); ok { |
| 67 | obj = pass.TypesInfo.Uses[id] |
| 68 | } |
| 69 | default: |
| 70 | return |
| 71 | } |
| 72 | |
| 73 | // Only want functions. |
| 74 | if _, ok := obj.(*types.Func); !ok { |
| 75 | return |
| 76 | } |
| 77 | |
| 78 | pass.ReportRangef(e, "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ) |
| 79 | }) |
| 80 | return nil, nil |
| 81 | } |
| 82 |
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