Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4016/sa4016.go

@@ -0,0 +1,116 @@
+package sa4016
+
+import (
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"go/types"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/go/ast/astutil"
+	"honnef.co/go/tools/go/types/typeutil"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA4016",
+		Run:      run,
+		Requires: []*analysis.Analyzer{inspect.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `Certain bitwise operations, such as \'x ^ 0\', do not do anything useful`,
+		Since:    "2017.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny, // MergeIfAny if we only flag literals, not named constants
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	fn := func(node ast.Node) {
+		binop := node.(*ast.BinaryExpr)
+		if !typeutil.All(pass.TypesInfo.TypeOf(binop), func(term *types.Term) bool {
+			b, ok := term.Type().Underlying().(*types.Basic)
+			if !ok {
+				return false
+			}
+			return (b.Info() & types.IsInteger) != 0
+		}) {
+			return
+		}
+		switch binop.Op {
+		case token.AND, token.OR, token.XOR:
+		default:
+			// we do not flag shifts because too often, x<<0 is part
+			// of a pattern, x<<0, x<<8, x<<16, ...
+			return
+		}
+		if y, ok := binop.Y.(*ast.Ident); ok {
+			obj, ok := pass.TypesInfo.ObjectOf(y).(*types.Const)
+			if !ok {
+				return
+			}
+			if obj.Pkg() != pass.Pkg {
+				// identifier was dot-imported
+				return
+			}
+			if v, _ := constant.Int64Val(obj.Val()); v != 0 {
+				return
+			}
+			path, _ := astutil.PathEnclosingInterval(code.File(pass, obj), obj.Pos(), obj.Pos())
+			if len(path) < 2 {
+				return
+			}
+			spec, ok := path[1].(*ast.ValueSpec)
+			if !ok {
+				return
+			}
+			if len(spec.Names) != 1 || len(spec.Values) != 1 {
+				// TODO(dh): we could support this
+				return
+			}
+			ident, ok := spec.Values[0].(*ast.Ident)
+			if !ok {
+				return
+			}
+			if !isIota(pass.TypesInfo.ObjectOf(ident)) {
+				return
+			}
+			switch binop.Op {
+			case token.AND:
+				report.Report(pass, node,
+					fmt.Sprintf("%s always equals 0; %s is defined as iota and has value 0, maybe %s is meant to be 1 << iota?", report.Render(pass, binop), report.Render(pass, binop.Y), report.Render(pass, binop.Y)))
+			case token.OR, token.XOR:
+				report.Report(pass, node,
+					fmt.Sprintf("%s always equals %s; %s is defined as iota and has value 0, maybe %s is meant to be 1 << iota?", report.Render(pass, binop), report.Render(pass, binop.X), report.Render(pass, binop.Y), report.Render(pass, binop.Y)))
+			}
+		} else if code.IsIntegerLiteral(pass, binop.Y, constant.MakeInt64(0)) {
+			switch binop.Op {
+			case token.AND:
+				report.Report(pass, node, fmt.Sprintf("%s always equals 0", report.Render(pass, binop)))
+			case token.OR, token.XOR:
+				report.Report(pass, node, fmt.Sprintf("%s always equals %s", report.Render(pass, binop), report.Render(pass, binop.X)))
+			}
+		}
+	}
+	code.Preorder(pass, fn, (*ast.BinaryExpr)(nil))
+	return nil, nil
+}
+
+func isIota(obj types.Object) bool {
+	if obj.Name() != "iota" {
+		return false
+	}
+	c, ok := obj.(*types.Const)
+	if !ok {
+		return false
+	}
+	return c.Pkg() == nil
+}