check.go

Documentation: go/types

     1  // Copyright 2011 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  // This file implements the Check function, which drives type-checking.
     6  
     7  package types
     8  
     9  import (
    10  	"errors"
    11  	"fmt"
    12  	"go/ast"
    13  	"go/constant"
    14  	"go/token"
    15  )
    16  
    17  // debugging/development support
    18  const (
    19  	debug = false // leave on during development
    20  	trace = false // turn on for detailed type resolution traces
    21  
    22  	// TODO(rfindley): add compiler error message handling from types2, guarded
    23  	// behind this flag, so that we can keep the code in sync.
    24  	compilerErrorMessages = false // match compiler error messages
    25  )
    26  
    27  // exprInfo stores information about an untyped expression.
    28  type exprInfo struct {
    29  	isLhs bool // expression is lhs operand of a shift with delayed type-check
    30  	mode  operandMode
    31  	typ   *Basic
    32  	val   constant.Value // constant value; or nil (if not a constant)
    33  }
    34  
    35  // An environment represents the environment within which an object is
    36  // type-checked.
    37  type environment struct {
    38  	decl          *declInfo              // package-level declaration whose init expression/function body is checked
    39  	scope         *Scope                 // top-most scope for lookups
    40  	pos           token.Pos              // if valid, identifiers are looked up as if at position pos (used by Eval)
    41  	iota          constant.Value         // value of iota in a constant declaration; nil otherwise
    42  	errpos        positioner             // if set, identifier position of a constant with inherited initializer
    43  	inTParamList  bool                   // set if inside a type parameter list
    44  	sig           *Signature             // function signature if inside a function; nil otherwise
    45  	isPanic       map[*ast.CallExpr]bool // set of panic call expressions (used for termination check)
    46  	hasLabel      bool                   // set if a function makes use of labels (only ~1% of functions); unused outside functions
    47  	hasCallOrRecv bool                   // set if an expression contains a function call or channel receive operation
    48  }
    49  
    50  // lookup looks up name in the current environment and returns the matching object, or nil.
    51  func (env *environment) lookup(name string) Object {
    52  	_, obj := env.scope.LookupParent(name, env.pos)
    53  	return obj
    54  }
    55  
    56  // An importKey identifies an imported package by import path and source directory
    57  // (directory containing the file containing the import). In practice, the directory
    58  // may always be the same, or may not matter. Given an (import path, directory), an
    59  // importer must always return the same package (but given two different import paths,
    60  // an importer may still return the same package by mapping them to the same package
    61  // paths).
    62  type importKey struct {
    63  	path, dir string
    64  }
    65  
    66  // A dotImportKey describes a dot-imported object in the given scope.
    67  type dotImportKey struct {
    68  	scope *Scope
    69  	name  string
    70  }
    71  
    72  // An action describes a (delayed) action.
    73  type action struct {
    74  	f    func()      // action to be executed
    75  	desc *actionDesc // action description; may be nil, requires debug to be set
    76  }
    77  
    78  // If debug is set, describef sets a printf-formatted description for action a.
    79  // Otherwise, it is a no-op.
    80  func (a *action) describef(pos positioner, format string, args ...any) {
    81  	if debug {
    82  		a.desc = &actionDesc{pos, format, args}
    83  	}
    84  }
    85  
    86  // An actionDesc provides information on an action.
    87  // For debugging only.
    88  type actionDesc struct {
    89  	pos    positioner
    90  	format string
    91  	args   []any
    92  }
    93  
    94  // A Checker maintains the state of the type checker.
    95  // It must be created with NewChecker.
    96  type Checker struct {
    97  	// package information
    98  	// (initialized by NewChecker, valid for the life-time of checker)
    99  	conf *Config
   100  	ctxt *Context // context for de-duplicating instances
   101  	fset *token.FileSet
   102  	pkg  *Package
   103  	*Info
   104  	version version                // accepted language version
   105  	nextID  uint64                 // unique Id for type parameters (first valid Id is 1)
   106  	objMap  map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
   107  	impMap  map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
   108  	valids  instanceLookup         // valid *Named (incl. instantiated) types per the validType check
   109  
   110  	// pkgPathMap maps package names to the set of distinct import paths we've
   111  	// seen for that name, anywhere in the import graph. It is used for
   112  	// disambiguating package names in error messages.
   113  	//
   114  	// pkgPathMap is allocated lazily, so that we don't pay the price of building
   115  	// it on the happy path. seenPkgMap tracks the packages that we've already
   116  	// walked.
   117  	pkgPathMap map[string]map[string]bool
   118  	seenPkgMap map[*Package]bool
   119  
   120  	// information collected during type-checking of a set of package files
   121  	// (initialized by Files, valid only for the duration of check.Files;
   122  	// maps and lists are allocated on demand)
   123  	files         []*ast.File               // package files
   124  	imports       []*PkgName                // list of imported packages
   125  	dotImportMap  map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
   126  	recvTParamMap map[*ast.Ident]*TypeParam // maps blank receiver type parameters to their type
   127  	brokenAliases map[*TypeName]bool        // set of aliases with broken (not yet determined) types
   128  	unionTypeSets map[*Union]*_TypeSet      // computed type sets for union types
   129  	mono          monoGraph                 // graph for detecting non-monomorphizable instantiation loops
   130  
   131  	firstErr error                 // first error encountered
   132  	methods  map[*TypeName][]*Func // maps package scope type names to associated non-blank (non-interface) methods
   133  	untyped  map[ast.Expr]exprInfo // map of expressions without final type
   134  	delayed  []action              // stack of delayed action segments; segments are processed in FIFO order
   135  	objPath  []Object              // path of object dependencies during type inference (for cycle reporting)
   136  	cleaners []cleaner             // list of types that may need a final cleanup at the end of type-checking
   137  
   138  	// environment within which the current object is type-checked (valid only
   139  	// for the duration of type-checking a specific object)
   140  	environment
   141  
   142  	// debugging
   143  	indent int // indentation for tracing
   144  }
   145  
   146  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   147  func (check *Checker) addDeclDep(to Object) {
   148  	from := check.decl
   149  	if from == nil {
   150  		return // not in a package-level init expression
   151  	}
   152  	if _, found := check.objMap[to]; !found {
   153  		return // to is not a package-level object
   154  	}
   155  	from.addDep(to)
   156  }
   157  
   158  // brokenAlias records that alias doesn't have a determined type yet.
   159  // It also sets alias.typ to Typ[Invalid].
   160  func (check *Checker) brokenAlias(alias *TypeName) {
   161  	if check.brokenAliases == nil {
   162  		check.brokenAliases = make(map[*TypeName]bool)
   163  	}
   164  	check.brokenAliases[alias] = true
   165  	alias.typ = Typ[Invalid]
   166  }
   167  
   168  // validAlias records that alias has the valid type typ (possibly Typ[Invalid]).
   169  func (check *Checker) validAlias(alias *TypeName, typ Type) {
   170  	delete(check.brokenAliases, alias)
   171  	alias.typ = typ
   172  }
   173  
   174  // isBrokenAlias reports whether alias doesn't have a determined type yet.
   175  func (check *Checker) isBrokenAlias(alias *TypeName) bool {
   176  	return alias.typ == Typ[Invalid] && check.brokenAliases[alias]
   177  }
   178  
   179  func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   180  	m := check.untyped
   181  	if m == nil {
   182  		m = make(map[ast.Expr]exprInfo)
   183  		check.untyped = m
   184  	}
   185  	m[e] = exprInfo{lhs, mode, typ, val}
   186  }
   187  
   188  // later pushes f on to the stack of actions that will be processed later;
   189  // either at the end of the current statement, or in case of a local constant
   190  // or variable declaration, before the constant or variable is in scope
   191  // (so that f still sees the scope before any new declarations).
   192  // later returns the pushed action so one can provide a description
   193  // via action.describef for debugging, if desired.
   194  func (check *Checker) later(f func()) *action {
   195  	i := len(check.delayed)
   196  	check.delayed = append(check.delayed, action{f: f})
   197  	return &check.delayed[i]
   198  }
   199  
   200  // push pushes obj onto the object path and returns its index in the path.
   201  func (check *Checker) push(obj Object) int {
   202  	check.objPath = append(check.objPath, obj)
   203  	return len(check.objPath) - 1
   204  }
   205  
   206  // pop pops and returns the topmost object from the object path.
   207  func (check *Checker) pop() Object {
   208  	i := len(check.objPath) - 1
   209  	obj := check.objPath[i]
   210  	check.objPath[i] = nil
   211  	check.objPath = check.objPath[:i]
   212  	return obj
   213  }
   214  
   215  type cleaner interface {
   216  	cleanup()
   217  }
   218  
   219  // needsCleanup records objects/types that implement the cleanup method
   220  // which will be called at the end of type-checking.
   221  func (check *Checker) needsCleanup(c cleaner) {
   222  	check.cleaners = append(check.cleaners, c)
   223  }
   224  
   225  // NewChecker returns a new Checker instance for a given package.
   226  // Package files may be added incrementally via checker.Files.
   227  func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
   228  	// make sure we have a configuration
   229  	if conf == nil {
   230  		conf = new(Config)
   231  	}
   232  
   233  	// make sure we have an info struct
   234  	if info == nil {
   235  		info = new(Info)
   236  	}
   237  
   238  	version, err := parseGoVersion(conf.GoVersion)
   239  	if err != nil {
   240  		panic(fmt.Sprintf("invalid Go version %q (%v)", conf.GoVersion, err))
   241  	}
   242  
   243  	return &Checker{
   244  		conf:    conf,
   245  		ctxt:    conf.Context,
   246  		fset:    fset,
   247  		pkg:     pkg,
   248  		Info:    info,
   249  		version: version,
   250  		objMap:  make(map[Object]*declInfo),
   251  		impMap:  make(map[importKey]*Package),
   252  	}
   253  }
   254  
   255  // initFiles initializes the files-specific portion of checker.
   256  // The provided files must all belong to the same package.
   257  func (check *Checker) initFiles(files []*ast.File) {
   258  	// start with a clean slate (check.Files may be called multiple times)
   259  	check.files = nil
   260  	check.imports = nil
   261  	check.dotImportMap = nil
   262  
   263  	check.firstErr = nil
   264  	check.methods = nil
   265  	check.untyped = nil
   266  	check.delayed = nil
   267  	check.objPath = nil
   268  	check.cleaners = nil
   269  
   270  	// determine package name and collect valid files
   271  	pkg := check.pkg
   272  	for _, file := range files {
   273  		switch name := file.Name.Name; pkg.name {
   274  		case "":
   275  			if name != "_" {
   276  				pkg.name = name
   277  			} else {
   278  				check.errorf(file.Name, _BlankPkgName, "invalid package name _")
   279  			}
   280  			fallthrough
   281  
   282  		case name:
   283  			check.files = append(check.files, file)
   284  
   285  		default:
   286  			check.errorf(atPos(file.Package), _MismatchedPkgName, "package %s; expected %s", name, pkg.name)
   287  			// ignore this file
   288  		}
   289  	}
   290  }
   291  
   292  // A bailout panic is used for early termination.
   293  type bailout struct{}
   294  
   295  func (check *Checker) handleBailout(err *error) {
   296  	switch p := recover().(type) {
   297  	case nil, bailout:
   298  		// normal return or early exit
   299  		*err = check.firstErr
   300  	default:
   301  		// re-panic
   302  		panic(p)
   303  	}
   304  }
   305  
   306  // Files checks the provided files as part of the checker's package.
   307  func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
   308  
   309  var errBadCgo = errors.New("cannot use FakeImportC and go115UsesCgo together")
   310  
   311  func (check *Checker) checkFiles(files []*ast.File) (err error) {
   312  	if check.conf.FakeImportC && check.conf.go115UsesCgo {
   313  		return errBadCgo
   314  	}
   315  
   316  	defer check.handleBailout(&err)
   317  
   318  	print := func(msg string) {
   319  		if trace {
   320  			fmt.Println()
   321  			fmt.Println(msg)
   322  		}
   323  	}
   324  
   325  	print("== initFiles ==")
   326  	check.initFiles(files)
   327  
   328  	print("== collectObjects ==")
   329  	check.collectObjects()
   330  
   331  	print("== packageObjects ==")
   332  	check.packageObjects()
   333  
   334  	print("== processDelayed ==")
   335  	check.processDelayed(0) // incl. all functions
   336  
   337  	print("== cleanup ==")
   338  	check.cleanup()
   339  
   340  	print("== initOrder ==")
   341  	check.initOrder()
   342  
   343  	if !check.conf.DisableUnusedImportCheck {
   344  		print("== unusedImports ==")
   345  		check.unusedImports()
   346  	}
   347  
   348  	print("== recordUntyped ==")
   349  	check.recordUntyped()
   350  
   351  	if check.firstErr == nil {
   352  		// TODO(mdempsky): Ensure monomorph is safe when errors exist.
   353  		check.monomorph()
   354  	}
   355  
   356  	check.pkg.complete = true
   357  
   358  	// no longer needed - release memory
   359  	check.imports = nil
   360  	check.dotImportMap = nil
   361  	check.pkgPathMap = nil
   362  	check.seenPkgMap = nil
   363  	check.recvTParamMap = nil
   364  	check.brokenAliases = nil
   365  	check.unionTypeSets = nil
   366  	check.ctxt = nil
   367  
   368  	// TODO(rFindley) There's more memory we should release at this point.
   369  
   370  	return
   371  }
   372  
   373  // processDelayed processes all delayed actions pushed after top.
   374  func (check *Checker) processDelayed(top int) {
   375  	// If each delayed action pushes a new action, the
   376  	// stack will continue to grow during this loop.
   377  	// However, it is only processing functions (which
   378  	// are processed in a delayed fashion) that may
   379  	// add more actions (such as nested functions), so
   380  	// this is a sufficiently bounded process.
   381  	for i := top; i < len(check.delayed); i++ {
   382  		a := &check.delayed[i]
   383  		if trace {
   384  			if a.desc != nil {
   385  				check.trace(a.desc.pos.Pos(), "-- "+a.desc.format, a.desc.args...)
   386  			} else {
   387  				check.trace(token.NoPos, "-- delayed %p", a.f)
   388  			}
   389  		}
   390  		a.f() // may append to check.delayed
   391  		if trace {
   392  			fmt.Println()
   393  		}
   394  	}
   395  	assert(top <= len(check.delayed)) // stack must not have shrunk
   396  	check.delayed = check.delayed[:top]
   397  }
   398  
   399  // cleanup runs cleanup for all collected cleaners.
   400  func (check *Checker) cleanup() {
   401  	// Don't use a range clause since Named.cleanup may add more cleaners.
   402  	for i := 0; i < len(check.cleaners); i++ {
   403  		check.cleaners[i].cleanup()
   404  	}
   405  	check.cleaners = nil
   406  }
   407  
   408  func (check *Checker) record(x *operand) {
   409  	// convert x into a user-friendly set of values
   410  	// TODO(gri) this code can be simplified
   411  	var typ Type
   412  	var val constant.Value
   413  	switch x.mode {
   414  	case invalid:
   415  		typ = Typ[Invalid]
   416  	case novalue:
   417  		typ = (*Tuple)(nil)
   418  	case constant_:
   419  		typ = x.typ
   420  		val = x.val
   421  	default:
   422  		typ = x.typ
   423  	}
   424  	assert(x.expr != nil && typ != nil)
   425  
   426  	if isUntyped(typ) {
   427  		// delay type and value recording until we know the type
   428  		// or until the end of type checking
   429  		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
   430  	} else {
   431  		check.recordTypeAndValue(x.expr, x.mode, typ, val)
   432  	}
   433  }
   434  
   435  func (check *Checker) recordUntyped() {
   436  	if !debug && check.Types == nil {
   437  		return // nothing to do
   438  	}
   439  
   440  	for x, info := range check.untyped {
   441  		if debug && isTyped(info.typ) {
   442  			check.dump("%v: %s (type %s) is typed", x.Pos(), x, info.typ)
   443  			unreachable()
   444  		}
   445  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
   446  	}
   447  }
   448  
   449  func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
   450  	assert(x != nil)
   451  	assert(typ != nil)
   452  	if mode == invalid {
   453  		return // omit
   454  	}
   455  	if mode == constant_ {
   456  		assert(val != nil)
   457  		// We check allBasic(typ, IsConstType) here as constant expressions may be
   458  		// recorded as type parameters.
   459  		assert(typ == Typ[Invalid] || allBasic(typ, IsConstType))
   460  	}
   461  	if m := check.Types; m != nil {
   462  		m[x] = TypeAndValue{mode, typ, val}
   463  	}
   464  }
   465  
   466  func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
   467  	// f must be a (possibly parenthesized, possibly qualified)
   468  	// identifier denoting a built-in (including unsafe's non-constant
   469  	// functions Add and Slice): record the signature for f and possible
   470  	// children.
   471  	for {
   472  		check.recordTypeAndValue(f, builtin, sig, nil)
   473  		switch p := f.(type) {
   474  		case *ast.Ident, *ast.SelectorExpr:
   475  			return // we're done
   476  		case *ast.ParenExpr:
   477  			f = p.X
   478  		default:
   479  			unreachable()
   480  		}
   481  	}
   482  }
   483  
   484  func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
   485  	assert(x != nil)
   486  	if a[0] == nil || a[1] == nil {
   487  		return
   488  	}
   489  	assert(isTyped(a[0]) && isTyped(a[1]) && (isBoolean(a[1]) || a[1] == universeError))
   490  	if m := check.Types; m != nil {
   491  		for {
   492  			tv := m[x]
   493  			assert(tv.Type != nil) // should have been recorded already
   494  			pos := x.Pos()
   495  			tv.Type = NewTuple(
   496  				NewVar(pos, check.pkg, "", a[0]),
   497  				NewVar(pos, check.pkg, "", a[1]),
   498  			)
   499  			m[x] = tv
   500  			// if x is a parenthesized expression (p.X), update p.X
   501  			p, _ := x.(*ast.ParenExpr)
   502  			if p == nil {
   503  				break
   504  			}
   505  			x = p.X
   506  		}
   507  	}
   508  }
   509  
   510  // recordInstance records instantiation information into check.Info, if the
   511  // Instances map is non-nil. The given expr must be an ident, selector, or
   512  // index (list) expr with ident or selector operand.
   513  //
   514  // TODO(rfindley): the expr parameter is fragile. See if we can access the
   515  // instantiated identifier in some other way.
   516  func (check *Checker) recordInstance(expr ast.Expr, targs []Type, typ Type) {
   517  	ident := instantiatedIdent(expr)
   518  	assert(ident != nil)
   519  	assert(typ != nil)
   520  	if m := check.Instances; m != nil {
   521  		m[ident] = Instance{newTypeList(targs), typ}
   522  	}
   523  }
   524  
   525  func instantiatedIdent(expr ast.Expr) *ast.Ident {
   526  	var selOrIdent ast.Expr
   527  	switch e := expr.(type) {
   528  	case *ast.IndexExpr:
   529  		selOrIdent = e.X
   530  	case *ast.IndexListExpr:
   531  		selOrIdent = e.X
   532  	case *ast.SelectorExpr, *ast.Ident:
   533  		selOrIdent = e
   534  	}
   535  	switch x := selOrIdent.(type) {
   536  	case *ast.Ident:
   537  		return x
   538  	case *ast.SelectorExpr:
   539  		return x.Sel
   540  	}
   541  	panic("instantiated ident not found")
   542  }
   543  
   544  func (check *Checker) recordDef(id *ast.Ident, obj Object) {
   545  	assert(id != nil)
   546  	if m := check.Defs; m != nil {
   547  		m[id] = obj
   548  	}
   549  }
   550  
   551  func (check *Checker) recordUse(id *ast.Ident, obj Object) {
   552  	assert(id != nil)
   553  	assert(obj != nil)
   554  	if m := check.Uses; m != nil {
   555  		m[id] = obj
   556  	}
   557  }
   558  
   559  func (check *Checker) recordImplicit(node ast.Node, obj Object) {
   560  	assert(node != nil)
   561  	assert(obj != nil)
   562  	if m := check.Implicits; m != nil {
   563  		m[node] = obj
   564  	}
   565  }
   566  
   567  func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
   568  	assert(obj != nil && (recv == nil || len(index) > 0))
   569  	check.recordUse(x.Sel, obj)
   570  	if m := check.Selections; m != nil {
   571  		m[x] = &Selection{kind, recv, obj, index, indirect}
   572  	}
   573  }
   574  
   575  func (check *Checker) recordScope(node ast.Node, scope *Scope) {
   576  	assert(node != nil)
   577  	assert(scope != nil)
   578  	if m := check.Scopes; m != nil {
   579  		m[node] = scope
   580  	}
   581  }
   582
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