Add staticcheck tool

vendor/honnef.co/go/tools/stylecheck/st1015/st1015.go

@@ -0,0 +1,77 @@
+package st1015
+
+import (
+	"go/ast"
+	"go/token"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/facts/generated"
+	"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:     "ST1015",
+		Run:      run,
+		Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:   `A switch's default case should be the first or last case`,
+		Since:   "2019.1",
+		MergeIf: lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	hasFallthrough := func(clause ast.Stmt) bool {
+		// A valid fallthrough statement may be used only as the final non-empty statement in a case clause. Thus we can
+		// easily avoid falsely matching fallthroughs in nested switches by not descending into blocks.
+
+		body := clause.(*ast.CaseClause).Body
+		for i := len(body) - 1; i >= 0; i-- {
+			last := body[i]
+			switch stmt := last.(type) {
+			case *ast.EmptyStmt:
+				// Fallthrough may be followed by empty statements
+			case *ast.BranchStmt:
+				return stmt.Tok == token.FALLTHROUGH
+			default:
+				return false
+			}
+		}
+
+		return false
+	}
+
+	fn := func(node ast.Node) {
+		stmt := node.(*ast.SwitchStmt)
+		list := stmt.Body.List
+		defaultIdx := -1
+		for i, c := range list {
+			if c.(*ast.CaseClause).List == nil {
+				defaultIdx = i
+				break
+			}
+		}
+
+		if defaultIdx == -1 || defaultIdx == 0 || defaultIdx == len(list)-1 {
+			// No default case, or it's the first or last case
+			return
+		}
+
+		if hasFallthrough(list[defaultIdx-1]) || hasFallthrough(list[defaultIdx]) {
+			// We either fall into or out of this case; don't mess with the order
+			return
+		}
+
+		report.Report(pass, list[defaultIdx], "default case should be first or last in switch statement", report.FilterGenerated())
+	}
+	code.Preorder(pass, fn, (*ast.SwitchStmt)(nil))
+	return nil, nil
+}