Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa9006/sa9006.go

@@ -0,0 +1,100 @@
+package sa9006
+
+import (
+	"fmt"
+	"go/ast"
+	"go/types"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/pattern"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA9006",
+		Run:      run,
+		Requires: code.RequiredAnalyzers,
+	},
+	Doc: &lint.RawDocumentation{
+		Title: `Dubious bit shifting of a fixed size integer value`,
+		Text: `Bit shifting a value past its size will always clear the value.
+
+For instance:
+
+    v := int8(42)
+    v >>= 8
+
+will always result in 0.
+
+This check flags bit shifting operations on fixed size integer values only.
+That is, int, uint and uintptr are never flagged to avoid potential false
+positives in somewhat exotic but valid bit twiddling tricks:
+
+    // Clear any value above 32 bits if integers are more than 32 bits.
+    func f(i int) int {
+        v := i >> 32
+        v = v << 32
+        return i-v
+    }`,
+		Since:    "2020.2",
+		Severity: lint.SeverityWarning,
+		// Technically this should be MergeIfAll, because the type of
+		// v might be different for different build tags. Practically,
+		// don't write code that depends on that.
+		MergeIf: lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+var (
+	checkFixedLengthTypeShiftQ = pattern.MustParse(`
+		(Or
+			(AssignStmt _ (Or ">>=" "<<=") _)
+			(BinaryExpr _ (Or ">>" "<<") _))
+	`)
+)
+
+func run(pass *analysis.Pass) (any, error) {
+	isDubiousShift := func(x, y ast.Expr) (int64, int64, bool) {
+		typ, ok := pass.TypesInfo.TypeOf(x).Underlying().(*types.Basic)
+		if !ok {
+			return 0, 0, false
+		}
+		switch typ.Kind() {
+		case types.Int8, types.Int16, types.Int32, types.Int64,
+			types.Uint8, types.Uint16, types.Uint32, types.Uint64:
+			// We're only interested in fixed–size types.
+		default:
+			return 0, 0, false
+		}
+
+		const bitsInByte = 8
+		typeBits := pass.TypesSizes.Sizeof(typ) * bitsInByte
+
+		shiftLength, ok := code.ExprToInt(pass, y)
+		if !ok {
+			return 0, 0, false
+		}
+
+		return typeBits, shiftLength, shiftLength >= typeBits
+	}
+
+	for node := range code.Matches(pass, checkFixedLengthTypeShiftQ) {
+		switch e := node.(type) {
+		case *ast.AssignStmt:
+			if size, shift, yes := isDubiousShift(e.Lhs[0], e.Rhs[0]); yes {
+				report.Report(pass, e, fmt.Sprintf("shifting %d-bit value by %d bits will always clear it", size, shift))
+			}
+		case *ast.BinaryExpr:
+			if size, shift, yes := isDubiousShift(e.X, e.Y); yes {
+				report.Report(pass, e, fmt.Sprintf("shifting %d-bit value by %d bits will always clear it", size, shift))
+			}
+		}
+	}
+
+	return nil, nil
+}