src

Go monorepo.
git clone git://code.dwrz.net/src
Log | Files | Refs

sa5002.go (2109B)

      1 package sa5002
      2 
      3 import (
      4 	"go/ast"
      5 	"go/constant"
      6 	"go/types"
      7 
      8 	"honnef.co/go/tools/analysis/code"
      9 	"honnef.co/go/tools/analysis/lint"
     10 	"honnef.co/go/tools/analysis/report"
     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:     "SA5002",
     19 		Run:      run,
     20 		Requires: []*analysis.Analyzer{inspect.Analyzer},
     21 	},
     22 	Doc: &lint.RawDocumentation{
     23 		Title:    `The empty for loop (\"for {}\") spins and can block the scheduler`,
     24 		Since:    "2017.1",
     25 		Severity: lint.SeverityWarning,
     26 		MergeIf:  lint.MergeIfAny,
     27 	},
     28 })
     29 
     30 var Analyzer = SCAnalyzer.Analyzer
     31 
     32 func run(pass *analysis.Pass) (any, error) {
     33 	fn := func(node ast.Node) {
     34 		loop := node.(*ast.ForStmt)
     35 		if len(loop.Body.List) != 0 || loop.Post != nil {
     36 			return
     37 		}
     38 
     39 		if loop.Init != nil {
     40 			// TODO(dh): this isn't strictly necessary, it just makes
     41 			// the check easier.
     42 			return
     43 		}
     44 		// An empty loop is bad news in two cases: 1) The loop has no
     45 		// condition. In that case, it's just a loop that spins
     46 		// forever and as fast as it can, keeping a core busy. 2) The
     47 		// loop condition only consists of variable or field reads and
     48 		// operators on those. The only way those could change their
     49 		// value is with unsynchronised access, which constitutes a
     50 		// data race.
     51 		//
     52 		// If the condition contains any function calls, its behaviour
     53 		// is dynamic and the loop might terminate. Similarly for
     54 		// channel receives.
     55 
     56 		if loop.Cond != nil {
     57 			if code.MayHaveSideEffects(pass, loop.Cond, nil) {
     58 				return
     59 			}
     60 			if ident, ok := loop.Cond.(*ast.Ident); ok {
     61 				if k, ok := pass.TypesInfo.ObjectOf(ident).(*types.Const); ok {
     62 					if !constant.BoolVal(k.Val()) {
     63 						// don't flag `for false {}` loops. They're a debug aid.
     64 						return
     65 					}
     66 				}
     67 			}
     68 			report.Report(pass, loop, "loop condition never changes or has a race condition")
     69 		}
     70 		report.Report(pass, loop, "this loop will spin, using 100% CPU", report.ShortRange())
     71 	}
     72 	code.Preorder(pass, fn, (*ast.ForStmt)(nil))
     73 	return nil, nil
     74 }