s1010.go raw

   1  package s1010
   2  
   3  import (
   4  	"go/ast"
   5  
   6  	"honnef.co/go/tools/analysis/code"
   7  	"honnef.co/go/tools/analysis/edit"
   8  	"honnef.co/go/tools/analysis/facts/generated"
   9  	"honnef.co/go/tools/analysis/lint"
  10  	"honnef.co/go/tools/analysis/report"
  11  	"honnef.co/go/tools/pattern"
  12  
  13  	"golang.org/x/tools/go/analysis"
  14  	"golang.org/x/tools/go/analysis/passes/inspect"
  15  )
  16  
  17  var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
  18  	Analyzer: &analysis.Analyzer{
  19  		Name:     "S1010",
  20  		Run:      run,
  21  		Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer},
  22  	},
  23  	Doc: &lint.RawDocumentation{
  24  		Title: `Omit default slice index`,
  25  		Text: `When slicing, the second index defaults to the length of the value,
  26  making \'s[n:len(s)]\' and \'s[n:]\' equivalent.`,
  27  		Since:   "2017.1",
  28  		MergeIf: lint.MergeIfAny,
  29  	},
  30  })
  31  
  32  var Analyzer = SCAnalyzer.Analyzer
  33  
  34  var checkSlicingQ = pattern.MustParse(`(SliceExpr x@(Object _) low (CallExpr (Builtin "len") [x]) nil)`)
  35  
  36  func run(pass *analysis.Pass) (interface{}, error) {
  37  	fn := func(node ast.Node) {
  38  		if _, ok := code.Match(pass, checkSlicingQ, node); ok {
  39  			expr := node.(*ast.SliceExpr)
  40  			report.Report(pass, expr.High,
  41  				"should omit second index in slice, s[a:len(s)] is identical to s[a:]",
  42  				report.FilterGenerated(),
  43  				report.Fixes(edit.Fix("simplify slice expression", edit.Delete(expr.High))))
  44  		}
  45  	}
  46  	code.Preorder(pass, fn, (*ast.SliceExpr)(nil))
  47  	return nil, nil
  48  }
  49