Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4004/sa4004.go

@@ -0,0 +1,159 @@
+package sa4004
+
+import (
+	"go/ast"
+	"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/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:     "SA4004",
+		Run:      run,
+		Requires: []*analysis.Analyzer{inspect.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `The loop exits unconditionally after one iteration`,
+		Since:    "2017.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAll,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	// This check detects some, but not all unconditional loop exits.
+	// We give up in the following cases:
+	//
+	// - a goto anywhere in the loop. The goto might skip over our
+	// return, and we don't check that it doesn't.
+	//
+	// - any nested, unlabelled continue, even if it is in another
+	// loop or closure.
+	fn := func(node ast.Node) {
+		var body *ast.BlockStmt
+		switch fn := node.(type) {
+		case *ast.FuncDecl:
+			body = fn.Body
+		case *ast.FuncLit:
+			body = fn.Body
+		default:
+			lint.ExhaustiveTypeSwitch(node)
+		}
+		if body == nil {
+			return
+		}
+		labels := map[types.Object]ast.Stmt{}
+		ast.Inspect(body, func(node ast.Node) bool {
+			label, ok := node.(*ast.LabeledStmt)
+			if !ok {
+				return true
+			}
+			labels[pass.TypesInfo.ObjectOf(label.Label)] = label.Stmt
+			return true
+		})
+
+		ast.Inspect(body, func(node ast.Node) bool {
+			var loop ast.Node
+			var body *ast.BlockStmt
+			switch node := node.(type) {
+			case *ast.ForStmt:
+				body = node.Body
+				loop = node
+			case *ast.RangeStmt:
+				ok := typeutil.All(pass.TypesInfo.TypeOf(node.X), func(term *types.Term) bool {
+					switch term.Type().Underlying().(type) {
+					case *types.Slice, *types.Chan, *types.Basic, *types.Pointer, *types.Array:
+						return true
+					case *types.Map:
+						// looping once over a map is a valid pattern for
+						// getting an arbitrary element.
+						return false
+					case *types.Signature:
+						// we have no idea what semantics the function implements
+						return false
+					default:
+						lint.ExhaustiveTypeSwitch(term.Type().Underlying())
+						return false
+					}
+				})
+				if !ok {
+					return true
+				}
+				body = node.Body
+				loop = node
+			default:
+				return true
+			}
+			if len(body.List) < 2 {
+				// TODO(dh): is this check needed? when body.List < 2,
+				// then we can't find both an unconditional exit and a
+				// branching statement (if, ...). and we don't flag
+				// unconditional exits if there has been no branching
+				// in the loop body.
+
+				// avoid flagging the somewhat common pattern of using
+				// a range loop to get the first element in a slice,
+				// or the first rune in a string.
+				return true
+			}
+			var unconditionalExit ast.Node
+			hasBranching := false
+			for _, stmt := range body.List {
+				switch stmt := stmt.(type) {
+				case *ast.BranchStmt:
+					switch stmt.Tok {
+					case token.BREAK:
+						if stmt.Label == nil || labels[pass.TypesInfo.ObjectOf(stmt.Label)] == loop {
+							unconditionalExit = stmt
+						}
+					case token.CONTINUE:
+						if stmt.Label == nil || labels[pass.TypesInfo.ObjectOf(stmt.Label)] == loop {
+							unconditionalExit = nil
+							return false
+						}
+					}
+				case *ast.ReturnStmt:
+					unconditionalExit = stmt
+				case *ast.IfStmt, *ast.ForStmt, *ast.RangeStmt, *ast.SwitchStmt, *ast.SelectStmt:
+					hasBranching = true
+				}
+			}
+			if unconditionalExit == nil || !hasBranching {
+				return false
+			}
+			ast.Inspect(body, func(node ast.Node) bool {
+				if branch, ok := node.(*ast.BranchStmt); ok {
+
+					switch branch.Tok {
+					case token.GOTO:
+						unconditionalExit = nil
+						return false
+					case token.CONTINUE:
+						if branch.Label != nil && labels[pass.TypesInfo.ObjectOf(branch.Label)] != loop {
+							return true
+						}
+						unconditionalExit = nil
+						return false
+					}
+				}
+				return true
+			})
+			if unconditionalExit != nil {
+				report.Report(pass, unconditionalExit, "the surrounding loop is unconditionally terminated")
+			}
+			return true
+		})
+	}
+	code.Preorder(pass, fn, (*ast.FuncDecl)(nil), (*ast.FuncLit)(nil))
+	return nil, nil
+}