s1018.go raw

   1  package s1018
   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/go/types/typeutil"
  12  	"honnef.co/go/tools/pattern"
  13  
  14  	"golang.org/x/tools/go/analysis"
  15  	"golang.org/x/tools/go/analysis/passes/inspect"
  16  )
  17  
  18  var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
  19  	Analyzer: &analysis.Analyzer{
  20  		Name:     "S1018",
  21  		Run:      run,
  22  		Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer},
  23  	},
  24  	Doc: &lint.RawDocumentation{
  25  		Title: `Use \"copy\" for sliding elements`,
  26  		Text: `\'copy()\' permits using the same source and destination slice, even with
  27  overlapping ranges. This makes it ideal for sliding elements in a
  28  slice.`,
  29  
  30  		Before: `
  31  for i := 0; i < n; i++ {
  32      bs[i] = bs[offset+i]
  33  }`,
  34  		After:   `copy(bs[:n], bs[offset:])`,
  35  		Since:   "2017.1",
  36  		MergeIf: lint.MergeIfAny,
  37  	},
  38  })
  39  
  40  var Analyzer = SCAnalyzer.Analyzer
  41  
  42  var (
  43  	checkLoopSlideQ = pattern.MustParse(`
  44  		(ForStmt
  45  			(AssignStmt initvar@(Ident _) _ (IntegerLiteral "0"))
  46  			(BinaryExpr initvar "<" limit@(Ident _))
  47  			(IncDecStmt initvar "++")
  48  			[(AssignStmt
  49  				(IndexExpr slice@(Ident _) initvar)
  50  				"="
  51  				(IndexExpr slice (BinaryExpr offset@(Ident _) "+" initvar)))])`)
  52  	checkLoopSlideR = pattern.MustParse(`
  53  		(CallExpr
  54  			(Ident "copy")
  55  			[(SliceExpr slice nil limit nil)
  56  				(SliceExpr slice offset nil nil)])`)
  57  )
  58  
  59  func run(pass *analysis.Pass) (interface{}, error) {
  60  	// TODO(dh): detect bs[i+offset] in addition to bs[offset+i]
  61  	// TODO(dh): consider merging this function with LintLoopCopy
  62  	// TODO(dh): detect length that is an expression, not a variable name
  63  	// TODO(dh): support sliding to a different offset than the beginning of the slice
  64  
  65  	fn := func(node ast.Node) {
  66  		loop := node.(*ast.ForStmt)
  67  		m, edits, ok := code.MatchAndEdit(pass, checkLoopSlideQ, checkLoopSlideR, loop)
  68  		if !ok {
  69  			return
  70  		}
  71  		typ := pass.TypesInfo.TypeOf(m.State["slice"].(*ast.Ident))
  72  		// The pattern probably needs a core type, but All is fine, too. Either way we only accept slices.
  73  		if !typeutil.All(typ, typeutil.IsSlice) {
  74  			return
  75  		}
  76  
  77  		report.Report(pass, loop, "should use copy() instead of loop for sliding slice elements",
  78  			report.ShortRange(),
  79  			report.FilterGenerated(),
  80  			report.Fixes(edit.Fix("use copy() instead of loop", edits...)))
  81  	}
  82  	code.Preorder(pass, fn, (*ast.ForStmt)(nil))
  83  	return nil, nil
  84  }
  85