github.com/amarpal/go-tools@v0.0.0-20240422043104-40142f59f616/staticcheck/sa4000/sa4000.go (about)

     1  package sa4000
     2  
     3  import (
     4  	"fmt"
     5  	"go/ast"
     6  	"go/token"
     7  	"go/types"
     8  	"reflect"
     9  
    10  	"github.com/amarpal/go-tools/analysis/code"
    11  	"github.com/amarpal/go-tools/analysis/facts/generated"
    12  	"github.com/amarpal/go-tools/analysis/lint"
    13  	"github.com/amarpal/go-tools/analysis/report"
    14  	"github.com/amarpal/go-tools/go/types/typeutil"
    15  
    16  	"golang.org/x/tools/go/analysis"
    17  	"golang.org/x/tools/go/analysis/passes/inspect"
    18  )
    19  
    20  var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
    21  	Analyzer: &analysis.Analyzer{
    22  		Name:     "SA4000",
    23  		Run:      run,
    24  		Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer},
    25  	},
    26  	Doc: &lint.Documentation{
    27  		Title:    `Binary operator has identical expressions on both sides`,
    28  		Since:    "2017.1",
    29  		Severity: lint.SeverityWarning,
    30  		MergeIf:  lint.MergeIfAny,
    31  	},
    32  })
    33  
    34  var Analyzer = SCAnalyzer.Analyzer
    35  
    36  func run(pass *analysis.Pass) (interface{}, error) {
    37  	var isFloat func(T types.Type) bool
    38  	isFloat = func(T types.Type) bool {
    39  		tset := typeutil.NewTypeSet(T)
    40  		if len(tset.Terms) == 0 {
    41  			// no terms, so floats are a possibility
    42  			return true
    43  		}
    44  		return tset.Any(func(term *types.Term) bool {
    45  			switch typ := term.Type().Underlying().(type) {
    46  			case *types.Basic:
    47  				kind := typ.Kind()
    48  				return kind == types.Float32 || kind == types.Float64
    49  			case *types.Array:
    50  				return isFloat(typ.Elem())
    51  			case *types.Struct:
    52  				for i := 0; i < typ.NumFields(); i++ {
    53  					if !isFloat(typ.Field(i).Type()) {
    54  						return false
    55  					}
    56  				}
    57  				return true
    58  			default:
    59  				return false
    60  			}
    61  		})
    62  	}
    63  
    64  	// TODO(dh): this check ignores the existence of side-effects and
    65  	// happily flags fn() == fn() – so far, we've had nobody complain
    66  	// about a false positive, and it's caught several bugs in real
    67  	// code.
    68  	//
    69  	// We special case functions from the math/rand package. Someone ran
    70  	// into the following false positive: "rand.Intn(2) - rand.Intn(2), which I wrote to generate values {-1, 0, 1} with {0.25, 0.5, 0.25} probability."
    71  	fn := func(node ast.Node) {
    72  		op := node.(*ast.BinaryExpr)
    73  		switch op.Op {
    74  		case token.EQL, token.NEQ:
    75  		case token.SUB, token.QUO, token.AND, token.REM, token.OR, token.XOR, token.AND_NOT,
    76  			token.LAND, token.LOR, token.LSS, token.GTR, token.LEQ, token.GEQ:
    77  		default:
    78  			// For some ops, such as + and *, it can make sense to
    79  			// have identical operands
    80  			return
    81  		}
    82  
    83  		if isFloat(pass.TypesInfo.TypeOf(op.X)) {
    84  			// 'float <op> float' makes sense for several operators.
    85  			// We've tried keeping an exact list of operators to allow, but floats keep surprising us. Let's just give up instead.
    86  			return
    87  		}
    88  
    89  		if reflect.TypeOf(op.X) != reflect.TypeOf(op.Y) {
    90  			return
    91  		}
    92  		if report.Render(pass, op.X) != report.Render(pass, op.Y) {
    93  			return
    94  		}
    95  		l1, ok1 := op.X.(*ast.BasicLit)
    96  		l2, ok2 := op.Y.(*ast.BasicLit)
    97  		if ok1 && ok2 && l1.Kind == token.INT && l2.Kind == l1.Kind && l1.Value == "0" && l2.Value == l1.Value && code.IsGenerated(pass, l1.Pos()) {
    98  			// cgo generates the following function call:
    99  			// _cgoCheckPointer(_cgoBase0, 0 == 0) – it uses 0 == 0
   100  			// instead of true in case the user shadowed the
   101  			// identifier. Ideally we'd restrict this exception to
   102  			// calls of _cgoCheckPointer, but it's not worth the
   103  			// hassle of keeping track of the stack. <lit> <op> <lit>
   104  			// are very rare to begin with, and we're mostly checking
   105  			// for them to catch typos such as 1 == 1 where the user
   106  			// meant to type i == 1. The odds of a false negative for
   107  			// 0 == 0 are slim.
   108  			return
   109  		}
   110  
   111  		if expr, ok := op.X.(*ast.CallExpr); ok {
   112  			call := code.CallName(pass, expr)
   113  			switch call {
   114  			case "math/rand.Int",
   115  				"math/rand.Int31",
   116  				"math/rand.Int31n",
   117  				"math/rand.Int63",
   118  				"math/rand.Int63n",
   119  				"math/rand.Intn",
   120  				"math/rand.Uint32",
   121  				"math/rand.Uint64",
   122  				"math/rand.ExpFloat64",
   123  				"math/rand.Float32",
   124  				"math/rand.Float64",
   125  				"math/rand.NormFloat64",
   126  				"(*math/rand.Rand).Int",
   127  				"(*math/rand.Rand).Int31",
   128  				"(*math/rand.Rand).Int31n",
   129  				"(*math/rand.Rand).Int63",
   130  				"(*math/rand.Rand).Int63n",
   131  				"(*math/rand.Rand).Intn",
   132  				"(*math/rand.Rand).Uint32",
   133  				"(*math/rand.Rand).Uint64",
   134  				"(*math/rand.Rand).ExpFloat64",
   135  				"(*math/rand.Rand).Float32",
   136  				"(*math/rand.Rand).Float64",
   137  				"(*math/rand.Rand).NormFloat64":
   138  				return
   139  			}
   140  		}
   141  
   142  		report.Report(pass, op, fmt.Sprintf("identical expressions on the left and right side of the '%s' operator", op.Op))
   143  	}
   144  	code.Preorder(pass, fn, (*ast.BinaryExpr)(nil))
   145  	return nil, nil
   146  }