copylock.go

Documentation: cmd/vendor/golang.org/x/tools/go/analysis/passes/copylock

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package copylock defines an Analyzer that checks for locks
     6  // erroneously passed by value.
     7  package copylock
     8  
     9  import (
    10  	"bytes"
    11  	"fmt"
    12  	"go/ast"
    13  	"go/token"
    14  	"go/types"
    15  
    16  	"golang.org/x/tools/go/analysis"
    17  	"golang.org/x/tools/go/analysis/passes/inspect"
    18  	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
    19  	"golang.org/x/tools/go/ast/astutil"
    20  	"golang.org/x/tools/go/ast/inspector"
    21  	"golang.org/x/tools/internal/typeparams"
    22  )
    23  
    24  const Doc = `check for locks erroneously passed by value
    25  
    26  Inadvertently copying a value containing a lock, such as sync.Mutex or
    27  sync.WaitGroup, may cause both copies to malfunction. Generally such
    28  values should be referred to through a pointer.`
    29  
    30  var Analyzer = &analysis.Analyzer{
    31  	Name:             "copylocks",
    32  	Doc:              Doc,
    33  	URL:              "https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/copylocks",
    34  	Requires:         []*analysis.Analyzer{inspect.Analyzer},
    35  	RunDespiteErrors: true,
    36  	Run:              run,
    37  }
    38  
    39  func run(pass *analysis.Pass) (interface{}, error) {
    40  	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
    41  
    42  	nodeFilter := []ast.Node{
    43  		(*ast.AssignStmt)(nil),
    44  		(*ast.CallExpr)(nil),
    45  		(*ast.CompositeLit)(nil),
    46  		(*ast.FuncDecl)(nil),
    47  		(*ast.FuncLit)(nil),
    48  		(*ast.GenDecl)(nil),
    49  		(*ast.RangeStmt)(nil),
    50  		(*ast.ReturnStmt)(nil),
    51  	}
    52  	inspect.Preorder(nodeFilter, func(node ast.Node) {
    53  		switch node := node.(type) {
    54  		case *ast.RangeStmt:
    55  			checkCopyLocksRange(pass, node)
    56  		case *ast.FuncDecl:
    57  			checkCopyLocksFunc(pass, node.Name.Name, node.Recv, node.Type)
    58  		case *ast.FuncLit:
    59  			checkCopyLocksFunc(pass, "func", nil, node.Type)
    60  		case *ast.CallExpr:
    61  			checkCopyLocksCallExpr(pass, node)
    62  		case *ast.AssignStmt:
    63  			checkCopyLocksAssign(pass, node)
    64  		case *ast.GenDecl:
    65  			checkCopyLocksGenDecl(pass, node)
    66  		case *ast.CompositeLit:
    67  			checkCopyLocksCompositeLit(pass, node)
    68  		case *ast.ReturnStmt:
    69  			checkCopyLocksReturnStmt(pass, node)
    70  		}
    71  	})
    72  	return nil, nil
    73  }
    74  
    75  // checkCopyLocksAssign checks whether an assignment
    76  // copies a lock.
    77  func checkCopyLocksAssign(pass *analysis.Pass, as *ast.AssignStmt) {
    78  	for i, x := range as.Rhs {
    79  		if path := lockPathRhs(pass, x); path != nil {
    80  			pass.ReportRangef(x, "assignment copies lock value to %v: %v", analysisutil.Format(pass.Fset, as.Lhs[i]), path)
    81  		}
    82  	}
    83  }
    84  
    85  // checkCopyLocksGenDecl checks whether lock is copied
    86  // in variable declaration.
    87  func checkCopyLocksGenDecl(pass *analysis.Pass, gd *ast.GenDecl) {
    88  	if gd.Tok != token.VAR {
    89  		return
    90  	}
    91  	for _, spec := range gd.Specs {
    92  		valueSpec := spec.(*ast.ValueSpec)
    93  		for i, x := range valueSpec.Values {
    94  			if path := lockPathRhs(pass, x); path != nil {
    95  				pass.ReportRangef(x, "variable declaration copies lock value to %v: %v", valueSpec.Names[i].Name, path)
    96  			}
    97  		}
    98  	}
    99  }
   100  
   101  // checkCopyLocksCompositeLit detects lock copy inside a composite literal
   102  func checkCopyLocksCompositeLit(pass *analysis.Pass, cl *ast.CompositeLit) {
   103  	for _, x := range cl.Elts {
   104  		if node, ok := x.(*ast.KeyValueExpr); ok {
   105  			x = node.Value
   106  		}
   107  		if path := lockPathRhs(pass, x); path != nil {
   108  			pass.ReportRangef(x, "literal copies lock value from %v: %v", analysisutil.Format(pass.Fset, x), path)
   109  		}
   110  	}
   111  }
   112  
   113  // checkCopyLocksReturnStmt detects lock copy in return statement
   114  func checkCopyLocksReturnStmt(pass *analysis.Pass, rs *ast.ReturnStmt) {
   115  	for _, x := range rs.Results {
   116  		if path := lockPathRhs(pass, x); path != nil {
   117  			pass.ReportRangef(x, "return copies lock value: %v", path)
   118  		}
   119  	}
   120  }
   121  
   122  // checkCopyLocksCallExpr detects lock copy in the arguments to a function call
   123  func checkCopyLocksCallExpr(pass *analysis.Pass, ce *ast.CallExpr) {
   124  	var id *ast.Ident
   125  	switch fun := ce.Fun.(type) {
   126  	case *ast.Ident:
   127  		id = fun
   128  	case *ast.SelectorExpr:
   129  		id = fun.Sel
   130  	}
   131  	if fun, ok := pass.TypesInfo.Uses[id].(*types.Builtin); ok {
   132  		switch fun.Name() {
   133  		case "new", "len", "cap", "Sizeof", "Offsetof", "Alignof":
   134  			return
   135  		}
   136  	}
   137  	for _, x := range ce.Args {
   138  		if path := lockPathRhs(pass, x); path != nil {
   139  			pass.ReportRangef(x, "call of %s copies lock value: %v", analysisutil.Format(pass.Fset, ce.Fun), path)
   140  		}
   141  	}
   142  }
   143  
   144  // checkCopyLocksFunc checks whether a function might
   145  // inadvertently copy a lock, by checking whether
   146  // its receiver, parameters, or return values
   147  // are locks.
   148  func checkCopyLocksFunc(pass *analysis.Pass, name string, recv *ast.FieldList, typ *ast.FuncType) {
   149  	if recv != nil && len(recv.List) > 0 {
   150  		expr := recv.List[0].Type
   151  		if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
   152  			pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
   153  		}
   154  	}
   155  
   156  	if typ.Params != nil {
   157  		for _, field := range typ.Params.List {
   158  			expr := field.Type
   159  			if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
   160  				pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
   161  			}
   162  		}
   163  	}
   164  
   165  	// Don't check typ.Results. If T has a Lock field it's OK to write
   166  	//     return T{}
   167  	// because that is returning the zero value. Leave result checking
   168  	// to the return statement.
   169  }
   170  
   171  // checkCopyLocksRange checks whether a range statement
   172  // might inadvertently copy a lock by checking whether
   173  // any of the range variables are locks.
   174  func checkCopyLocksRange(pass *analysis.Pass, r *ast.RangeStmt) {
   175  	checkCopyLocksRangeVar(pass, r.Tok, r.Key)
   176  	checkCopyLocksRangeVar(pass, r.Tok, r.Value)
   177  }
   178  
   179  func checkCopyLocksRangeVar(pass *analysis.Pass, rtok token.Token, e ast.Expr) {
   180  	if e == nil {
   181  		return
   182  	}
   183  	id, isId := e.(*ast.Ident)
   184  	if isId && id.Name == "_" {
   185  		return
   186  	}
   187  
   188  	var typ types.Type
   189  	if rtok == token.DEFINE {
   190  		if !isId {
   191  			return
   192  		}
   193  		obj := pass.TypesInfo.Defs[id]
   194  		if obj == nil {
   195  			return
   196  		}
   197  		typ = obj.Type()
   198  	} else {
   199  		typ = pass.TypesInfo.Types[e].Type
   200  	}
   201  
   202  	if typ == nil {
   203  		return
   204  	}
   205  	if path := lockPath(pass.Pkg, typ, nil); path != nil {
   206  		pass.Reportf(e.Pos(), "range var %s copies lock: %v", analysisutil.Format(pass.Fset, e), path)
   207  	}
   208  }
   209  
   210  type typePath []string
   211  
   212  // String pretty-prints a typePath.
   213  func (path typePath) String() string {
   214  	n := len(path)
   215  	var buf bytes.Buffer
   216  	for i := range path {
   217  		if i > 0 {
   218  			fmt.Fprint(&buf, " contains ")
   219  		}
   220  		// The human-readable path is in reverse order, outermost to innermost.
   221  		fmt.Fprint(&buf, path[n-i-1])
   222  	}
   223  	return buf.String()
   224  }
   225  
   226  func lockPathRhs(pass *analysis.Pass, x ast.Expr) typePath {
   227  	x = astutil.Unparen(x) // ignore parens on rhs
   228  
   229  	if _, ok := x.(*ast.CompositeLit); ok {
   230  		return nil
   231  	}
   232  	if _, ok := x.(*ast.CallExpr); ok {
   233  		// A call may return a zero value.
   234  		return nil
   235  	}
   236  	if star, ok := x.(*ast.StarExpr); ok {
   237  		if _, ok := astutil.Unparen(star.X).(*ast.CallExpr); ok {
   238  			// A call may return a pointer to a zero value.
   239  			return nil
   240  		}
   241  	}
   242  	return lockPath(pass.Pkg, pass.TypesInfo.Types[x].Type, nil)
   243  }
   244  
   245  // lockPath returns a typePath describing the location of a lock value
   246  // contained in typ. If there is no contained lock, it returns nil.
   247  //
   248  // The seen map is used to short-circuit infinite recursion due to type cycles.
   249  func lockPath(tpkg *types.Package, typ types.Type, seen map[types.Type]bool) typePath {
   250  	if typ == nil || seen[typ] {
   251  		return nil
   252  	}
   253  	if seen == nil {
   254  		seen = make(map[types.Type]bool)
   255  	}
   256  	seen[typ] = true
   257  
   258  	if tpar, ok := typ.(*types.TypeParam); ok {
   259  		terms, err := typeparams.StructuralTerms(tpar)
   260  		if err != nil {
   261  			return nil // invalid type
   262  		}
   263  		for _, term := range terms {
   264  			subpath := lockPath(tpkg, term.Type(), seen)
   265  			if len(subpath) > 0 {
   266  				if term.Tilde() {
   267  					// Prepend a tilde to our lock path entry to clarify the resulting
   268  					// diagnostic message. Consider the following example:
   269  					//
   270  					//  func _[Mutex interface{ ~sync.Mutex; M() }](m Mutex) {}
   271  					//
   272  					// Here the naive error message will be something like "passes lock
   273  					// by value: Mutex contains sync.Mutex". This is misleading because
   274  					// the local type parameter doesn't actually contain sync.Mutex,
   275  					// which lacks the M method.
   276  					//
   277  					// With tilde, it is clearer that the containment is via an
   278  					// approximation element.
   279  					subpath[len(subpath)-1] = "~" + subpath[len(subpath)-1]
   280  				}
   281  				return append(subpath, typ.String())
   282  			}
   283  		}
   284  		return nil
   285  	}
   286  
   287  	for {
   288  		atyp, ok := typ.Underlying().(*types.Array)
   289  		if !ok {
   290  			break
   291  		}
   292  		typ = atyp.Elem()
   293  	}
   294  
   295  	ttyp, ok := typ.Underlying().(*types.Tuple)
   296  	if ok {
   297  		for i := 0; i < ttyp.Len(); i++ {
   298  			subpath := lockPath(tpkg, ttyp.At(i).Type(), seen)
   299  			if subpath != nil {
   300  				return append(subpath, typ.String())
   301  			}
   302  		}
   303  		return nil
   304  	}
   305  
   306  	// We're only interested in the case in which the underlying
   307  	// type is a struct. (Interfaces and pointers are safe to copy.)
   308  	styp, ok := typ.Underlying().(*types.Struct)
   309  	if !ok {
   310  		return nil
   311  	}
   312  
   313  	// We're looking for cases in which a pointer to this type
   314  	// is a sync.Locker, but a value is not. This differentiates
   315  	// embedded interfaces from embedded values.
   316  	if types.Implements(types.NewPointer(typ), lockerType) && !types.Implements(typ, lockerType) {
   317  		return []string{typ.String()}
   318  	}
   319  
   320  	// In go1.10, sync.noCopy did not implement Locker.
   321  	// (The Unlock method was added only in CL 121876.)
   322  	// TODO(adonovan): remove workaround when we drop go1.10.
   323  	if analysisutil.IsNamedType(typ, "sync", "noCopy") {
   324  		return []string{typ.String()}
   325  	}
   326  
   327  	nfields := styp.NumFields()
   328  	for i := 0; i < nfields; i++ {
   329  		ftyp := styp.Field(i).Type()
   330  		subpath := lockPath(tpkg, ftyp, seen)
   331  		if subpath != nil {
   332  			return append(subpath, typ.String())
   333  		}
   334  	}
   335  
   336  	return nil
   337  }
   338  
   339  var lockerType *types.Interface
   340  
   341  // Construct a sync.Locker interface type.
   342  func init() {
   343  	nullary := types.NewSignature(nil, nil, nil, false) // func()
   344  	methods := []*types.Func{
   345  		types.NewFunc(token.NoPos, nil, "Lock", nullary),
   346  		types.NewFunc(token.NoPos, nil, "Unlock", nullary),
   347  	}
   348  	lockerType = types.NewInterface(methods, nil).Complete()
   349  }
   350
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