github.com/amarpal/go-tools@v0.0.0-20240422043104-40142f59f616/staticcheck/sa5002/sa5002.go (about)

     1  package sa5002
     2  
     3  import (
     4  	"go/ast"
     5  	"go/constant"
     6  	"go/types"
     7  
     8  	"github.com/amarpal/go-tools/analysis/code"
     9  	"github.com/amarpal/go-tools/analysis/lint"
    10  	"github.com/amarpal/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.Documentation{
    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) (interface{}, 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  }