s1036.go raw

   1  package s1036
   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  	"honnef.co/go/tools/pattern"
  11  
  12  	"golang.org/x/tools/go/analysis"
  13  	"golang.org/x/tools/go/analysis/passes/inspect"
  14  )
  15  
  16  var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
  17  	Analyzer: &analysis.Analyzer{
  18  		Name:     "S1036",
  19  		Run:      run,
  20  		Requires: []*analysis.Analyzer{inspect.Analyzer},
  21  	},
  22  	Doc: &lint.RawDocumentation{
  23  		Title: `Unnecessary guard around map access`,
  24  
  25  		Text: `
  26  When accessing a map key that doesn't exist yet, one receives a zero
  27  value. Often, the zero value is a suitable value, for example when
  28  using append or doing integer math.
  29  
  30  The following
  31  
  32      if _, ok := m["foo"]; ok {
  33          m["foo"] = append(m["foo"], "bar")
  34      } else {
  35          m["foo"] = []string{"bar"}
  36      }
  37  
  38  can be simplified to
  39  
  40      m["foo"] = append(m["foo"], "bar")
  41  
  42  and
  43  
  44      if _, ok := m2["k"]; ok {
  45          m2["k"] += 4
  46      } else {
  47          m2["k"] = 4
  48      }
  49  
  50  can be simplified to
  51  
  52      m["k"] += 4
  53  `,
  54  		Since:   "2020.1",
  55  		MergeIf: lint.MergeIfAny,
  56  	},
  57  })
  58  
  59  var Analyzer = SCAnalyzer.Analyzer
  60  
  61  var checkUnnecessaryGuardQ = pattern.MustParse(`
  62  	(Or
  63  		(IfStmt
  64  			(AssignStmt [(Ident "_") ok@(Ident _)] ":=" indexexpr@(IndexExpr _ _))
  65  			ok
  66  			set@(AssignStmt indexexpr "=" (CallExpr (Builtin "append") indexexpr:values))
  67  			(AssignStmt indexexpr "=" (CompositeLit _ values)))
  68  		(IfStmt
  69  			(AssignStmt [(Ident "_") ok] ":=" indexexpr@(IndexExpr _ _))
  70  			ok
  71  			set@(AssignStmt indexexpr "+=" value)
  72  			(AssignStmt indexexpr "=" value))
  73  		(IfStmt
  74  			(AssignStmt [(Ident "_") ok] ":=" indexexpr@(IndexExpr _ _))
  75  			ok
  76  			set@(IncDecStmt indexexpr "++")
  77  			(AssignStmt indexexpr "=" (IntegerLiteral "1"))))`)
  78  
  79  func run(pass *analysis.Pass) (interface{}, error) {
  80  	fn := func(node ast.Node) {
  81  		if m, ok := code.Match(pass, checkUnnecessaryGuardQ, node); ok {
  82  			if code.MayHaveSideEffects(pass, m.State["indexexpr"].(ast.Expr), nil) {
  83  				return
  84  			}
  85  			report.Report(pass, node, "unnecessary guard around map access",
  86  				report.ShortRange(),
  87  				report.Fixes(edit.Fix("simplify map access", edit.ReplaceWithNode(pass.Fset, node, m.State["set"].(ast.Node)))))
  88  		}
  89  	}
  90  	code.Preorder(pass, fn, (*ast.IfStmt)(nil))
  91  	return nil, nil
  92  }
  93