Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4018/sa4018.go

@@ -0,0 +1,61 @@
+package sa4018
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"reflect"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/facts/generated"
+	"honnef.co/go/tools/analysis/facts/purity"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA4018",
+		Run:      run,
+		Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer, purity.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `Self-assignment of variables`,
+		Since:    "2017.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	pure := pass.ResultOf[purity.Analyzer].(purity.Result)
+
+	fn := func(node ast.Node) {
+		assign := node.(*ast.AssignStmt)
+		if assign.Tok != token.ASSIGN || len(assign.Lhs) != len(assign.Rhs) {
+			return
+		}
+		for i, lhs := range assign.Lhs {
+			rhs := assign.Rhs[i]
+			if reflect.TypeOf(lhs) != reflect.TypeOf(rhs) {
+				continue
+			}
+			if code.MayHaveSideEffects(pass, lhs, pure) || code.MayHaveSideEffects(pass, rhs, pure) {
+				continue
+			}
+
+			rlh := report.Render(pass, lhs)
+			rrh := report.Render(pass, rhs)
+			if rlh == rrh {
+				report.Report(pass, assign, fmt.Sprintf("self-assignment of %s to %s", rrh, rlh), report.FilterGenerated())
+			}
+		}
+	}
+	code.Preorder(pass, fn, (*ast.AssignStmt)(nil))
+	return nil, nil
+}