nilfunc.go

Documentation: golang.org/x/tools/go/analysis/passes/nilfunc

     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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