copylock.go

Documentation: 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/inspector"
    20  	"golang.org/x/tools/internal/typeparams"
    21  )
    22  
    23  const Doc = `check for locks erroneously passed by value
    24  
    25  Inadvertently copying a value containing a lock, such as sync.Mutex or
    26  sync.WaitGroup, may cause both copies to malfunction. Generally such
    27  values should be referred to through a pointer.`
    28  
    29  var Analyzer = &analysis.Analyzer{
    30  	Name:             "copylocks",
    31  	Doc:              Doc,
    32  	Requires:         []*analysis.Analyzer{inspect.Analyzer},
    33  	RunDespiteErrors: true,
    34  	Run:              run,
    35  }
    36  
    37  func run(pass *analysis.Pass) (interface{}, error) {
    38  	inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
    39  
    40  	nodeFilter := []ast.Node{
    41  		(*ast.AssignStmt)(nil),
    42  		(*ast.CallExpr)(nil),
    43  		(*ast.CompositeLit)(nil),
    44  		(*ast.FuncDecl)(nil),
    45  		(*ast.FuncLit)(nil),
    46  		(*ast.GenDecl)(nil),
    47  		(*ast.RangeStmt)(nil),
    48  		(*ast.ReturnStmt)(nil),
    49  	}
    50  	inspect.Preorder(nodeFilter, func(node ast.Node) {
    51  		switch node := node.(type) {
    52  		case *ast.RangeStmt:
    53  			checkCopyLocksRange(pass, node)
    54  		case *ast.FuncDecl:
    55  			checkCopyLocksFunc(pass, node.Name.Name, node.Recv, node.Type)
    56  		case *ast.FuncLit:
    57  			checkCopyLocksFunc(pass, "func", nil, node.Type)
    58  		case *ast.CallExpr:
    59  			checkCopyLocksCallExpr(pass, node)
    60  		case *ast.AssignStmt:
    61  			checkCopyLocksAssign(pass, node)
    62  		case *ast.GenDecl:
    63  			checkCopyLocksGenDecl(pass, node)
    64  		case *ast.CompositeLit:
    65  			checkCopyLocksCompositeLit(pass, node)
    66  		case *ast.ReturnStmt:
    67  			checkCopyLocksReturnStmt(pass, node)
    68  		}
    69  	})
    70  	return nil, nil
    71  }
    72  
    73  // checkCopyLocksAssign checks whether an assignment
    74  // copies a lock.
    75  func checkCopyLocksAssign(pass *analysis.Pass, as *ast.AssignStmt) {
    76  	for i, x := range as.Rhs {
    77  		if path := lockPathRhs(pass, x); path != nil {
    78  			pass.ReportRangef(x, "assignment copies lock value to %v: %v", analysisutil.Format(pass.Fset, as.Lhs[i]), path)
    79  		}
    80  	}
    81  }
    82  
    83  // checkCopyLocksGenDecl checks whether lock is copied
    84  // in variable declaration.
    85  func checkCopyLocksGenDecl(pass *analysis.Pass, gd *ast.GenDecl) {
    86  	if gd.Tok != token.VAR {
    87  		return
    88  	}
    89  	for _, spec := range gd.Specs {
    90  		valueSpec := spec.(*ast.ValueSpec)
    91  		for i, x := range valueSpec.Values {
    92  			if path := lockPathRhs(pass, x); path != nil {
    93  				pass.ReportRangef(x, "variable declaration copies lock value to %v: %v", valueSpec.Names[i].Name, path)
    94  			}
    95  		}
    96  	}
    97  }
    98  
    99  // checkCopyLocksCompositeLit detects lock copy inside a composite literal
   100  func checkCopyLocksCompositeLit(pass *analysis.Pass, cl *ast.CompositeLit) {
   101  	for _, x := range cl.Elts {
   102  		if node, ok := x.(*ast.KeyValueExpr); ok {
   103  			x = node.Value
   104  		}
   105  		if path := lockPathRhs(pass, x); path != nil {
   106  			pass.ReportRangef(x, "literal copies lock value from %v: %v", analysisutil.Format(pass.Fset, x), path)
   107  		}
   108  	}
   109  }
   110  
   111  // checkCopyLocksReturnStmt detects lock copy in return statement
   112  func checkCopyLocksReturnStmt(pass *analysis.Pass, rs *ast.ReturnStmt) {
   113  	for _, x := range rs.Results {
   114  		if path := lockPathRhs(pass, x); path != nil {
   115  			pass.ReportRangef(x, "return copies lock value: %v", path)
   116  		}
   117  	}
   118  }
   119  
   120  // checkCopyLocksCallExpr detects lock copy in the arguments to a function call
   121  func checkCopyLocksCallExpr(pass *analysis.Pass, ce *ast.CallExpr) {
   122  	var id *ast.Ident
   123  	switch fun := ce.Fun.(type) {
   124  	case *ast.Ident:
   125  		id = fun
   126  	case *ast.SelectorExpr:
   127  		id = fun.Sel
   128  	}
   129  	if fun, ok := pass.TypesInfo.Uses[id].(*types.Builtin); ok {
   130  		switch fun.Name() {
   131  		case "new", "len", "cap", "Sizeof", "Offsetof", "Alignof":
   132  			return
   133  		}
   134  	}
   135  	for _, x := range ce.Args {
   136  		if path := lockPathRhs(pass, x); path != nil {
   137  			pass.ReportRangef(x, "call of %s copies lock value: %v", analysisutil.Format(pass.Fset, ce.Fun), path)
   138  		}
   139  	}
   140  }
   141  
   142  // checkCopyLocksFunc checks whether a function might
   143  // inadvertently copy a lock, by checking whether
   144  // its receiver, parameters, or return values
   145  // are locks.
   146  func checkCopyLocksFunc(pass *analysis.Pass, name string, recv *ast.FieldList, typ *ast.FuncType) {
   147  	if recv != nil && len(recv.List) > 0 {
   148  		expr := recv.List[0].Type
   149  		if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
   150  			pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
   151  		}
   152  	}
   153  
   154  	if typ.Params != nil {
   155  		for _, field := range typ.Params.List {
   156  			expr := field.Type
   157  			if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
   158  				pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
   159  			}
   160  		}
   161  	}
   162  
   163  	// Don't check typ.Results. If T has a Lock field it's OK to write
   164  	//     return T{}
   165  	// because that is returning the zero value. Leave result checking
   166  	// to the return statement.
   167  }
   168  
   169  // checkCopyLocksRange checks whether a range statement
   170  // might inadvertently copy a lock by checking whether
   171  // any of the range variables are locks.
   172  func checkCopyLocksRange(pass *analysis.Pass, r *ast.RangeStmt) {
   173  	checkCopyLocksRangeVar(pass, r.Tok, r.Key)
   174  	checkCopyLocksRangeVar(pass, r.Tok, r.Value)
   175  }
   176  
   177  func checkCopyLocksRangeVar(pass *analysis.Pass, rtok token.Token, e ast.Expr) {
   178  	if e == nil {
   179  		return
   180  	}
   181  	id, isId := e.(*ast.Ident)
   182  	if isId && id.Name == "_" {
   183  		return
   184  	}
   185  
   186  	var typ types.Type
   187  	if rtok == token.DEFINE {
   188  		if !isId {
   189  			return
   190  		}
   191  		obj := pass.TypesInfo.Defs[id]
   192  		if obj == nil {
   193  			return
   194  		}
   195  		typ = obj.Type()
   196  	} else {
   197  		typ = pass.TypesInfo.Types[e].Type
   198  	}
   199  
   200  	if typ == nil {
   201  		return
   202  	}
   203  	if path := lockPath(pass.Pkg, typ, nil); path != nil {
   204  		pass.Reportf(e.Pos(), "range var %s copies lock: %v", analysisutil.Format(pass.Fset, e), path)
   205  	}
   206  }
   207  
   208  type typePath []string
   209  
   210  // String pretty-prints a typePath.
   211  func (path typePath) String() string {
   212  	n := len(path)
   213  	var buf bytes.Buffer
   214  	for i := range path {
   215  		if i > 0 {
   216  			fmt.Fprint(&buf, " contains ")
   217  		}
   218  		// The human-readable path is in reverse order, outermost to innermost.
   219  		fmt.Fprint(&buf, path[n-i-1])
   220  	}
   221  	return buf.String()
   222  }
   223  
   224  func lockPathRhs(pass *analysis.Pass, x ast.Expr) typePath {
   225  	if _, ok := x.(*ast.CompositeLit); ok {
   226  		return nil
   227  	}
   228  	if _, ok := x.(*ast.CallExpr); ok {
   229  		// A call may return a zero value.
   230  		return nil
   231  	}
   232  	if star, ok := x.(*ast.StarExpr); ok {
   233  		if _, ok := star.X.(*ast.CallExpr); ok {
   234  			// A call may return a pointer to a zero value.
   235  			return nil
   236  		}
   237  	}
   238  	return lockPath(pass.Pkg, pass.TypesInfo.Types[x].Type, nil)
   239  }
   240  
   241  // lockPath returns a typePath describing the location of a lock value
   242  // contained in typ. If there is no contained lock, it returns nil.
   243  //
   244  // The seenTParams map is used to short-circuit infinite recursion via type
   245  // parameters.
   246  func lockPath(tpkg *types.Package, typ types.Type, seenTParams map[*typeparams.TypeParam]bool) typePath {
   247  	if typ == nil {
   248  		return nil
   249  	}
   250  
   251  	if tpar, ok := typ.(*typeparams.TypeParam); ok {
   252  		if seenTParams == nil {
   253  			// Lazily allocate seenTParams, since the common case will not involve
   254  			// any type parameters.
   255  			seenTParams = make(map[*typeparams.TypeParam]bool)
   256  		}
   257  		if seenTParams[tpar] {
   258  			return nil
   259  		}
   260  		seenTParams[tpar] = true
   261  		terms, err := typeparams.StructuralTerms(tpar)
   262  		if err != nil {
   263  			return nil // invalid type
   264  		}
   265  		for _, term := range terms {
   266  			subpath := lockPath(tpkg, term.Type(), seenTParams)
   267  			if len(subpath) > 0 {
   268  				if term.Tilde() {
   269  					// Prepend a tilde to our lock path entry to clarify the resulting
   270  					// diagnostic message. Consider the following example:
   271  					//
   272  					//  func _[Mutex interface{ ~sync.Mutex; M() }](m Mutex) {}
   273  					//
   274  					// Here the naive error message will be something like "passes lock
   275  					// by value: Mutex contains sync.Mutex". This is misleading because
   276  					// the local type parameter doesn't actually contain sync.Mutex,
   277  					// which lacks the M method.
   278  					//
   279  					// With tilde, it is clearer that the containment is via an
   280  					// approximation element.
   281  					subpath[len(subpath)-1] = "~" + subpath[len(subpath)-1]
   282  				}
   283  				return append(subpath, typ.String())
   284  			}
   285  		}
   286  		return nil
   287  	}
   288  
   289  	for {
   290  		atyp, ok := typ.Underlying().(*types.Array)
   291  		if !ok {
   292  			break
   293  		}
   294  		typ = atyp.Elem()
   295  	}
   296  
   297  	ttyp, ok := typ.Underlying().(*types.Tuple)
   298  	if ok {
   299  		for i := 0; i < ttyp.Len(); i++ {
   300  			subpath := lockPath(tpkg, ttyp.At(i).Type(), seenTParams)
   301  			if subpath != nil {
   302  				return append(subpath, typ.String())
   303  			}
   304  		}
   305  		return nil
   306  	}
   307  
   308  	// We're only interested in the case in which the underlying
   309  	// type is a struct. (Interfaces and pointers are safe to copy.)
   310  	styp, ok := typ.Underlying().(*types.Struct)
   311  	if !ok {
   312  		return nil
   313  	}
   314  
   315  	// We're looking for cases in which a pointer to this type
   316  	// is a sync.Locker, but a value is not. This differentiates
   317  	// embedded interfaces from embedded values.
   318  	if types.Implements(types.NewPointer(typ), lockerType) && !types.Implements(typ, lockerType) {
   319  		return []string{typ.String()}
   320  	}
   321  
   322  	// In go1.10, sync.noCopy did not implement Locker.
   323  	// (The Unlock method was added only in CL 121876.)
   324  	// TODO(adonovan): remove workaround when we drop go1.10.
   325  	if named, ok := typ.(*types.Named); ok &&
   326  		named.Obj().Name() == "noCopy" &&
   327  		named.Obj().Pkg().Path() == "sync" {
   328  		return []string{typ.String()}
   329  	}
   330  
   331  	nfields := styp.NumFields()
   332  	for i := 0; i < nfields; i++ {
   333  		ftyp := styp.Field(i).Type()
   334  		subpath := lockPath(tpkg, ftyp, seenTParams)
   335  		if subpath != nil {
   336  			return append(subpath, typ.String())
   337  		}
   338  	}
   339  
   340  	return nil
   341  }
   342  
   343  var lockerType *types.Interface
   344  
   345  // Construct a sync.Locker interface type.
   346  func init() {
   347  	nullary := types.NewSignature(nil, nil, nil, false) // func()
   348  	methods := []*types.Func{
   349  		types.NewFunc(token.NoPos, nil, "Lock", nullary),
   350  		types.NewFunc(token.NoPos, nil, "Unlock", nullary),
   351  	}
   352  	lockerType = types.NewInterface(methods, nil).Complete()
   353  }
   354
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