Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4012/sa4012.go

@@ -0,0 +1,51 @@
+package sa4012
+
+import (
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/go/ir"
+	"honnef.co/go/tools/go/ir/irutil"
+	"honnef.co/go/tools/internal/passes/buildir"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA4012",
+		Run:      run,
+		Requires: []*analysis.Analyzer{buildir.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `Comparing a value against NaN even though no value is equal to NaN`,
+		Since:    "2017.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	isNaN := func(v ir.Value) bool {
+		call, ok := v.(*ir.Call)
+		if !ok {
+			return false
+		}
+		return irutil.IsCallTo(call.Common(), "math.NaN")
+	}
+	for _, fn := range pass.ResultOf[buildir.Analyzer].(*buildir.IR).SrcFuncs {
+		for _, block := range fn.Blocks {
+			for _, ins := range block.Instrs {
+				ins, ok := ins.(*ir.BinOp)
+				if !ok {
+					continue
+				}
+				if isNaN(irutil.Flatten(ins.X)) || isNaN(irutil.Flatten(ins.Y)) {
+					report.Report(pass, ins, "no value is equal to NaN, not even NaN itself")
+				}
+			}
+		}
+	}
+	return nil, nil
+}