sa5004.go raw

   1  package sa5004
   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/lint"
   9  	"honnef.co/go/tools/analysis/report"
  10  
  11  	"golang.org/x/tools/go/analysis"
  12  	"golang.org/x/tools/go/analysis/passes/inspect"
  13  )
  14  
  15  var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
  16  	Analyzer: &analysis.Analyzer{
  17  		Name:     "SA5004",
  18  		Run:      run,
  19  		Requires: []*analysis.Analyzer{inspect.Analyzer},
  20  	},
  21  	Doc: &lint.RawDocumentation{
  22  		Title:    `\"for { select { ...\" with an empty default branch spins`,
  23  		Since:    "2017.1",
  24  		Severity: lint.SeverityWarning,
  25  		MergeIf:  lint.MergeIfAny,
  26  	},
  27  })
  28  
  29  var Analyzer = SCAnalyzer.Analyzer
  30  
  31  func run(pass *analysis.Pass) (interface{}, error) {
  32  	fn := func(node ast.Node) {
  33  		loop := node.(*ast.ForStmt)
  34  		if len(loop.Body.List) != 1 || loop.Cond != nil || loop.Init != nil {
  35  			return
  36  		}
  37  		sel, ok := loop.Body.List[0].(*ast.SelectStmt)
  38  		if !ok {
  39  			return
  40  		}
  41  		for _, c := range sel.Body.List {
  42  			// FIXME this leaves behind an empty line, and possibly
  43  			// comments in the default branch. We can't easily fix
  44  			// either.
  45  			if comm, ok := c.(*ast.CommClause); ok && comm.Comm == nil && len(comm.Body) == 0 {
  46  				report.Report(pass, comm, "should not have an empty default case in a for+select loop; the loop will spin",
  47  					report.Fixes(edit.Fix("remove empty default branch", edit.Delete(comm))))
  48  				// there can only be one default case
  49  				break
  50  			}
  51  		}
  52  	}
  53  	code.Preorder(pass, fn, (*ast.ForStmt)(nil))
  54  	return nil, nil
  55  }
  56