sa4026.go (2497B)
1 package sa4026 2 3 import ( 4 "fmt" 5 "go/types" 6 7 "honnef.co/go/tools/analysis/code" 8 "honnef.co/go/tools/analysis/edit" 9 "honnef.co/go/tools/analysis/lint" 10 "honnef.co/go/tools/analysis/report" 11 "honnef.co/go/tools/pattern" 12 13 "golang.org/x/tools/go/analysis" 14 ) 15 16 var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{ 17 Analyzer: &analysis.Analyzer{ 18 Name: "SA4026", 19 Run: run, 20 Requires: code.RequiredAnalyzers, 21 }, 22 Doc: &lint.RawDocumentation{ 23 Title: "Go constants cannot express negative zero", 24 Text: `In IEEE 754 floating point math, zero has a sign and can be positive 25 or negative. This can be useful in certain numerical code. 26 27 Go constants, however, cannot express negative zero. This means that 28 the literals \'-0.0\' and \'0.0\' have the same ideal value (zero) and 29 will both represent positive zero at runtime. 30 31 To explicitly and reliably create a negative zero, you can use the 32 \'math.Copysign\' function: \'math.Copysign(0, -1)\'.`, 33 Since: "2021.1", 34 Severity: lint.SeverityWarning, 35 MergeIf: lint.MergeIfAny, 36 }, 37 }) 38 39 var Analyzer = SCAnalyzer.Analyzer 40 41 var negativeZeroFloatQ = pattern.MustParse(` 42 (Or 43 (UnaryExpr 44 "-" 45 (BasicLit "FLOAT" "0.0")) 46 47 (UnaryExpr 48 "-" 49 (CallExpr conv@(Object (Or "float32" "float64")) lit@(Or (BasicLit "INT" "0") (BasicLit "FLOAT" "0.0")))) 50 51 (CallExpr 52 conv@(Object (Or "float32" "float64")) 53 (UnaryExpr "-" lit@(BasicLit "INT" "0"))))`) 54 55 func run(pass *analysis.Pass) (any, error) { 56 for node, m := range code.Matches(pass, negativeZeroFloatQ) { 57 if conv, ok := m.State["conv"].(*types.TypeName); ok { 58 var replacement string 59 // TODO(dh): how does this handle type aliases? 60 if conv.Name() == "float32" { 61 replacement = `float32(math.Copysign(0, -1))` 62 } else { 63 replacement = `math.Copysign(0, -1)` 64 } 65 report.Report(pass, node, 66 fmt.Sprintf("in Go, the floating-point expression '%s' is the same as '%s(%s)', it does not produce a negative zero", 67 report.Render(pass, node), 68 conv.Name(), 69 report.Render(pass, m.State["lit"])), 70 report.Fixes(edit.Fix("Use math.Copysign to create negative zero", edit.ReplaceWithString(node, replacement)))) 71 } else { 72 const replacement = `math.Copysign(0, -1)` 73 report.Report(pass, node, 74 "in Go, the floating-point literal '-0.0' is the same as '0.0', it does not produce a negative zero", 75 report.Fixes(edit.Fix("Use math.Copysign to create negative zero", edit.ReplaceWithString(node, replacement)))) 76 } 77 } 78 return nil, nil 79 }