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Source file src/cmd/vet/nilfunc.go

Documentation: cmd/vet

  // Copyright 2013 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.
  
  /*
  This file contains the code to check for useless function comparisons.
  A useless comparison is one like f == nil as opposed to f() == nil.
  */
  
  package main
  
  import (
  	"go/ast"
  	"go/token"
  	"go/types"
  )
  
  func init() {
  	register("nilfunc",
  		"check for comparisons between functions and nil",
  		checkNilFuncComparison,
  		binaryExpr)
  }
  
  func checkNilFuncComparison(f *File, node ast.Node) {
  	e := node.(*ast.BinaryExpr)
  
  	// Only want == or != comparisons.
  	if e.Op != token.EQL && e.Op != token.NEQ {
  		return
  	}
  
  	// Only want comparisons with a nil identifier on one side.
  	var e2 ast.Expr
  	switch {
  	case f.isNil(e.X):
  		e2 = e.Y
  	case f.isNil(e.Y):
  		e2 = e.X
  	default:
  		return
  	}
  
  	// Only want identifiers or selector expressions.
  	var obj types.Object
  	switch v := e2.(type) {
  	case *ast.Ident:
  		obj = f.pkg.uses[v]
  	case *ast.SelectorExpr:
  		obj = f.pkg.uses[v.Sel]
  	default:
  		return
  	}
  
  	// Only want functions.
  	if _, ok := obj.(*types.Func); !ok {
  		return
  	}
  
  	f.Badf(e.Pos(), "comparison of function %v %v nil is always %v", obj.Name(), e.Op, e.Op == token.NEQ)
  }
  
  // isNil reports whether the provided expression is the built-in nil
  // identifier.
  func (f *File) isNil(e ast.Expr) bool {
  	return f.pkg.types[e].Type == types.Typ[types.UntypedNil]
  }
  

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