check.go

     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 types2
     8  
     9  import (
    10  	"cmd/compile/internal/syntax"
    11  	"errors"
    12  	"fmt"
    13  	"go/constant"
    14  	"internal/godebug"
    15  	. "internal/types/errors"
    16  )
    17  
    18  // nopos indicates an unknown position
    19  var nopos syntax.Pos
    20  
    21  // debugging/development support
    22  const debug = false // leave on during development
    23  
    24  // gotypesalias controls the use of Alias types.
    25  var gotypesalias = godebug.New("#gotypesalias")
    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           syntax.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        syntax.Pos                // if valid, 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[*syntax.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 poser, format string, args ...interface{}) {
    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    poser
    90  	format string
    91  	args   []interface{}
    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  
   100  	// If enableAlias is set, alias declarations produce an Alias type.
   101  	// Otherwise the alias information is only in the type name, which
   102  	// points directly to the actual (aliased) type.
   103  	enableAlias bool
   104  
   105  	conf *Config
   106  	ctxt *Context // context for de-duplicating instances
   107  	pkg  *Package
   108  	*Info
   109  	version goVersion              // accepted language version
   110  	nextID  uint64                 // unique Id for type parameters (first valid Id is 1)
   111  	objMap  map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
   112  	impMap  map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
   113  	valids  instanceLookup         // valid *Named (incl. instantiated) types per the validType check
   114  
   115  	// pkgPathMap maps package names to the set of distinct import paths we've
   116  	// seen for that name, anywhere in the import graph. It is used for
   117  	// disambiguating package names in error messages.
   118  	//
   119  	// pkgPathMap is allocated lazily, so that we don't pay the price of building
   120  	// it on the happy path. seenPkgMap tracks the packages that we've already
   121  	// walked.
   122  	pkgPathMap map[string]map[string]bool
   123  	seenPkgMap map[*Package]bool
   124  
   125  	// information collected during type-checking of a set of package files
   126  	// (initialized by Files, valid only for the duration of check.Files;
   127  	// maps and lists are allocated on demand)
   128  	files         []*syntax.File              // list of package files
   129  	versions      map[*syntax.PosBase]string  // maps file bases to version strings (each file has an entry)
   130  	imports       []*PkgName                  // list of imported packages
   131  	dotImportMap  map[dotImportKey]*PkgName   // maps dot-imported objects to the package they were dot-imported through
   132  	recvTParamMap map[*syntax.Name]*TypeParam // maps blank receiver type parameters to their type
   133  	brokenAliases map[*TypeName]bool          // set of aliases with broken (not yet determined) types
   134  	unionTypeSets map[*Union]*_TypeSet        // computed type sets for union types
   135  	mono          monoGraph                   // graph for detecting non-monomorphizable instantiation loops
   136  
   137  	firstErr error                    // first error encountered
   138  	methods  map[*TypeName][]*Func    // maps package scope type names to associated non-blank (non-interface) methods
   139  	untyped  map[syntax.Expr]exprInfo // map of expressions without final type
   140  	delayed  []action                 // stack of delayed action segments; segments are processed in FIFO order
   141  	objPath  []Object                 // path of object dependencies during type inference (for cycle reporting)
   142  	cleaners []cleaner                // list of types that may need a final cleanup at the end of type-checking
   143  
   144  	// environment within which the current object is type-checked (valid only
   145  	// for the duration of type-checking a specific object)
   146  	environment
   147  
   148  	// debugging
   149  	indent int // indentation for tracing
   150  }
   151  
   152  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   153  func (check *Checker) addDeclDep(to Object) {
   154  	from := check.decl
   155  	if from == nil {
   156  		return // not in a package-level init expression
   157  	}
   158  	if _, found := check.objMap[to]; !found {
   159  		return // to is not a package-level object
   160  	}
   161  	from.addDep(to)
   162  }
   163  
   164  // Note: The following three alias-related functions are only used
   165  //       when Alias types are not enabled.
   166  
   167  // brokenAlias records that alias doesn't have a determined type yet.
   168  // It also sets alias.typ to Typ[Invalid].
   169  // Not used if check.enableAlias is set.
   170  func (check *Checker) brokenAlias(alias *TypeName) {
   171  	assert(!check.enableAlias)
   172  	if check.brokenAliases == nil {
   173  		check.brokenAliases = make(map[*TypeName]bool)
   174  	}
   175  	check.brokenAliases[alias] = true
   176  	alias.typ = Typ[Invalid]
   177  }
   178  
   179  // validAlias records that alias has the valid type typ (possibly Typ[Invalid]).
   180  func (check *Checker) validAlias(alias *TypeName, typ Type) {
   181  	assert(!check.enableAlias)
   182  	delete(check.brokenAliases, alias)
   183  	alias.typ = typ
   184  }
   185  
   186  // isBrokenAlias reports whether alias doesn't have a determined type yet.
   187  func (check *Checker) isBrokenAlias(alias *TypeName) bool {
   188  	assert(!check.enableAlias)
   189  	return check.brokenAliases[alias]
   190  }
   191  
   192  func (check *Checker) rememberUntyped(e syntax.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   193  	m := check.untyped
   194  	if m == nil {
   195  		m = make(map[syntax.Expr]exprInfo)
   196  		check.untyped = m
   197  	}
   198  	m[e] = exprInfo{lhs, mode, typ, val}
   199  }
   200  
   201  // later pushes f on to the stack of actions that will be processed later;
   202  // either at the end of the current statement, or in case of a local constant
   203  // or variable declaration, before the constant or variable is in scope
   204  // (so that f still sees the scope before any new declarations).
   205  // later returns the pushed action so one can provide a description
   206  // via action.describef for debugging, if desired.
   207  func (check *Checker) later(f func()) *action {
   208  	i := len(check.delayed)
   209  	check.delayed = append(check.delayed, action{f: f})
   210  	return &check.delayed[i]
   211  }
   212  
   213  // push pushes obj onto the object path and returns its index in the path.
   214  func (check *Checker) push(obj Object) int {
   215  	check.objPath = append(check.objPath, obj)
   216  	return len(check.objPath) - 1
   217  }
   218  
   219  // pop pops and returns the topmost object from the object path.
   220  func (check *Checker) pop() Object {
   221  	i := len(check.objPath) - 1
   222  	obj := check.objPath[i]
   223  	check.objPath[i] = nil
   224  	check.objPath = check.objPath[:i]
   225  	return obj
   226  }
   227  
   228  type cleaner interface {
   229  	cleanup()
   230  }
   231  
   232  // needsCleanup records objects/types that implement the cleanup method
   233  // which will be called at the end of type-checking.
   234  func (check *Checker) needsCleanup(c cleaner) {
   235  	check.cleaners = append(check.cleaners, c)
   236  }
   237  
   238  // NewChecker returns a new Checker instance for a given package.
   239  // Package files may be added incrementally via checker.Files.
   240  func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
   241  	// make sure we have a configuration
   242  	if conf == nil {
   243  		conf = new(Config)
   244  	}
   245  
   246  	// make sure we have an info struct
   247  	if info == nil {
   248  		info = new(Info)
   249  	}
   250  
   251  	// Note: clients may call NewChecker with the Unsafe package, which is
   252  	// globally shared and must not be mutated. Therefore NewChecker must not
   253  	// mutate *pkg.
   254  	//
   255  	// (previously, pkg.goVersion was mutated here: go.dev/issue/61212)
   256  
   257  	return &Checker{
   258  		enableAlias: gotypesalias.Value() == "1",
   259  		conf:        conf,
   260  		ctxt:        conf.Context,
   261  		pkg:         pkg,
   262  		Info:        info,
   263  		version:     asGoVersion(conf.GoVersion),
   264  		objMap:      make(map[Object]*declInfo),
   265  		impMap:      make(map[importKey]*Package),
   266  	}
   267  }
   268  
   269  // initFiles initializes the files-specific portion of checker.
   270  // The provided files must all belong to the same package.
   271  func (check *Checker) initFiles(files []*syntax.File) {
   272  	// start with a clean slate (check.Files may be called multiple times)
   273  	check.files = nil
   274  	check.imports = nil
   275  	check.dotImportMap = nil
   276  
   277  	check.firstErr = nil
   278  	check.methods = nil
   279  	check.untyped = nil
   280  	check.delayed = nil
   281  	check.objPath = nil
   282  	check.cleaners = nil
   283  
   284  	// determine package name and collect valid files
   285  	pkg := check.pkg
   286  	for _, file := range files {
   287  		switch name := file.PkgName.Value; pkg.name {
   288  		case "":
   289  			if name != "_" {
   290  				pkg.name = name
   291  			} else {
   292  				check.error(file.PkgName, BlankPkgName, "invalid package name _")
   293  			}
   294  			fallthrough
   295  
   296  		case name:
   297  			check.files = append(check.files, file)
   298  
   299  		default:
   300  			check.errorf(file, MismatchedPkgName, "package %s; expected %s", name, pkg.name)
   301  			// ignore this file
   302  		}
   303  	}
   304  
   305  	// reuse Info.FileVersions if provided
   306  	versions := check.Info.FileVersions
   307  	if versions == nil {
   308  		versions = make(map[*syntax.PosBase]string)
   309  	}
   310  	check.versions = versions
   311  
   312  	pkgVersionOk := check.version.isValid()
   313  	downgradeOk := check.version.cmp(go1_21) >= 0
   314  
   315  	// determine Go version for each file
   316  	for _, file := range check.files {
   317  		// use unaltered Config.GoVersion by default
   318  		// (This version string may contain dot-release numbers as in go1.20.1,
   319  		// unlike file versions which are Go language versions only, if valid.)
   320  		v := check.conf.GoVersion
   321  		// use the file version, if applicable
   322  		// (file versions are either the empty string or of the form go1.dd)
   323  		if pkgVersionOk {
   324  			fileVersion := asGoVersion(file.GoVersion)
   325  			if fileVersion.isValid() {
   326  				cmp := fileVersion.cmp(check.version)
   327  				// Go 1.21 introduced the feature of setting the go.mod
   328  				// go line to an early version of Go and allowing //go:build lines
   329  				// to “upgrade” (cmp > 0) the Go version in a given file.
   330  				// We can do that backwards compatibly.
   331  				//
   332  				// Go 1.21 also introduced the feature of allowing //go:build lines
   333  				// to “downgrade” (cmp < 0) the Go version in a given file.
   334  				// That can't be done compatibly in general, since before the
   335  				// build lines were ignored and code got the module's Go version.
   336  				// To work around this, downgrades are only allowed when the
   337  				// module's Go version is Go 1.21 or later.
   338  				//
   339  				// If there is no valid check.version, then we don't really know what
   340  				// Go version to apply.
   341  				// Legacy tools may do this, and they historically have accepted everything.
   342  				// Preserve that behavior by ignoring //go:build constraints entirely in that
   343  				// case (!pkgVersionOk).
   344  				if cmp > 0 || cmp < 0 && downgradeOk {
   345  					v = file.GoVersion
   346  				}
   347  			}
   348  		}
   349  		versions[base(file.Pos())] = v // base(file.Pos()) may be nil for tests
   350  	}
   351  }
   352  
   353  // A bailout panic is used for early termination.
   354  type bailout struct{}
   355  
   356  func (check *Checker) handleBailout(err *error) {
   357  	switch p := recover().(type) {
   358  	case nil, bailout:
   359  		// normal return or early exit
   360  		*err = check.firstErr
   361  	default:
   362  		// re-panic
   363  		panic(p)
   364  	}
   365  }
   366  
   367  // Files checks the provided files as part of the checker's package.
   368  func (check *Checker) Files(files []*syntax.File) error { return check.checkFiles(files) }
   369  
   370  var errBadCgo = errors.New("cannot use FakeImportC and go115UsesCgo together")
   371  
   372  func (check *Checker) checkFiles(files []*syntax.File) (err error) {
   373  	if check.pkg == Unsafe {
   374  		// Defensive handling for Unsafe, which cannot be type checked, and must
   375  		// not be mutated. See https://go.dev/issue/61212 for an example of where
   376  		// Unsafe is passed to NewChecker.
   377  		return nil
   378  	}
   379  
   380  	// Note: NewChecker doesn't return an error, so we need to check the version here.
   381  	if check.version.cmp(go_current) > 0 {
   382  		return fmt.Errorf("package requires newer Go version %v", check.version)
   383  	}
   384  	if check.conf.FakeImportC && check.conf.go115UsesCgo {
   385  		return errBadCgo
   386  	}
   387  
   388  	defer check.handleBailout(&err)
   389  
   390  	print := func(msg string) {
   391  		if check.conf.Trace {
   392  			fmt.Println()
   393  			fmt.Println(msg)
   394  		}
   395  	}
   396  
   397  	print("== initFiles ==")
   398  	check.initFiles(files)
   399  
   400  	print("== collectObjects ==")
   401  	check.collectObjects()
   402  
   403  	print("== packageObjects ==")
   404  	check.packageObjects()
   405  
   406  	print("== processDelayed ==")
   407  	check.processDelayed(0) // incl. all functions
   408  
   409  	print("== cleanup ==")
   410  	check.cleanup()
   411  
   412  	print("== initOrder ==")
   413  	check.initOrder()
   414  
   415  	if !check.conf.DisableUnusedImportCheck {
   416  		print("== unusedImports ==")
   417  		check.unusedImports()
   418  	}
   419  
   420  	print("== recordUntyped ==")
   421  	check.recordUntyped()
   422  
   423  	if check.firstErr == nil {
   424  		// TODO(mdempsky): Ensure monomorph is safe when errors exist.
   425  		check.monomorph()
   426  	}
   427  
   428  	check.pkg.goVersion = check.conf.GoVersion
   429  	check.pkg.complete = true
   430  
   431  	// no longer needed - release memory
   432  	check.imports = nil
   433  	check.dotImportMap = nil
   434  	check.pkgPathMap = nil
   435  	check.seenPkgMap = nil
   436  	check.recvTParamMap = nil
   437  	check.brokenAliases = nil
   438  	check.unionTypeSets = nil
   439  	check.ctxt = nil
   440  
   441  	// TODO(gri) There's more memory we should release at this point.
   442  
   443  	return
   444  }
   445  
   446  // processDelayed processes all delayed actions pushed after top.
   447  func (check *Checker) processDelayed(top int) {
   448  	// If each delayed action pushes a new action, the
   449  	// stack will continue to grow during this loop.
   450  	// However, it is only processing functions (which
   451  	// are processed in a delayed fashion) that may
   452  	// add more actions (such as nested functions), so
   453  	// this is a sufficiently bounded process.
   454  	for i := top; i < len(check.delayed); i++ {
   455  		a := &check.delayed[i]
   456  		if check.conf.Trace {
   457  			if a.desc != nil {
   458  				check.trace(a.desc.pos.Pos(), "-- "+a.desc.format, a.desc.args...)
   459  			} else {
   460  				check.trace(nopos, "-- delayed %p", a.f)
   461  			}
   462  		}
   463  		a.f() // may append to check.delayed
   464  		if check.conf.Trace {
   465  			fmt.Println()
   466  		}
   467  	}
   468  	assert(top <= len(check.delayed)) // stack must not have shrunk
   469  	check.delayed = check.delayed[:top]
   470  }
   471  
   472  // cleanup runs cleanup for all collected cleaners.
   473  func (check *Checker) cleanup() {
   474  	// Don't use a range clause since Named.cleanup may add more cleaners.
   475  	for i := 0; i < len(check.cleaners); i++ {
   476  		check.cleaners[i].cleanup()
   477  	}
   478  	check.cleaners = nil
   479  }
   480  
   481  func (check *Checker) record(x *operand) {
   482  	// convert x into a user-friendly set of values
   483  	// TODO(gri) this code can be simplified
   484  	var typ Type
   485  	var val constant.Value
   486  	switch x.mode {
   487  	case invalid:
   488  		typ = Typ[Invalid]
   489  	case novalue:
   490  		typ = (*Tuple)(nil)
   491  	case constant_:
   492  		typ = x.typ
   493  		val = x.val
   494  	default:
   495  		typ = x.typ
   496  	}
   497  	assert(x.expr != nil && typ != nil)
   498  
   499  	if isUntyped(typ) {
   500  		// delay type and value recording until we know the type
   501  		// or until the end of type checking
   502  		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
   503  	} else {
   504  		check.recordTypeAndValue(x.expr, x.mode, typ, val)
   505  	}
   506  }
   507  
   508  func (check *Checker) recordUntyped() {
   509  	if !debug && !check.recordTypes() {
   510  		return // nothing to do
   511  	}
   512  
   513  	for x, info := range check.untyped {
   514  		if debug && isTyped(info.typ) {
   515  			check.dump("%v: %s (type %s) is typed", atPos(x), x, info.typ)
   516  			unreachable()
   517  		}
   518  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
   519  	}
   520  }
   521  
   522  func (check *Checker) recordTypeAndValue(x syntax.Expr, mode operandMode, typ Type, val constant.Value) {
   523  	assert(x != nil)
   524  	assert(typ != nil)
   525  	if mode == invalid {
   526  		return // omit
   527  	}
   528  	if mode == constant_ {
   529  		assert(val != nil)
   530  		// We check allBasic(typ, IsConstType) here as constant expressions may be
   531  		// recorded as type parameters.
   532  		assert(!isValid(typ) || allBasic(typ, IsConstType))
   533  	}
   534  	if m := check.Types; m != nil {
   535  		m[x] = TypeAndValue{mode, typ, val}
   536  	}
   537  	if check.StoreTypesInSyntax {
   538  		tv := TypeAndValue{mode, typ, val}
   539  		stv := syntax.TypeAndValue{Type: typ, Value: val}
   540  		if tv.IsVoid() {
   541  			stv.SetIsVoid()
   542  		}
   543  		if tv.IsType() {
   544  			stv.SetIsType()
   545  		}
   546  		if tv.IsBuiltin() {
   547  			stv.SetIsBuiltin()
   548  		}
   549  		if tv.IsValue() {
   550  			stv.SetIsValue()
   551  		}
   552  		if tv.IsNil() {
   553  			stv.SetIsNil()
   554  		}
   555  		if tv.Addressable() {
   556  			stv.SetAddressable()
   557  		}
   558  		if tv.Assignable() {
   559  			stv.SetAssignable()
   560  		}
   561  		if tv.HasOk() {
   562  			stv.SetHasOk()
   563  		}
   564  		x.SetTypeInfo(stv)
   565  	}
   566  }
   567  
   568  func (check *Checker) recordBuiltinType(f syntax.Expr, sig *Signature) {
   569  	// f must be a (possibly parenthesized, possibly qualified)
   570  	// identifier denoting a built-in (including unsafe's non-constant
   571  	// functions Add and Slice): record the signature for f and possible
   572  	// children.
   573  	for {
   574  		check.recordTypeAndValue(f, builtin, sig, nil)
   575  		switch p := f.(type) {
   576  		case *syntax.Name, *syntax.SelectorExpr:
   577  			return // we're done
   578  		case *syntax.ParenExpr:
   579  			f = p.X
   580  		default:
   581  			unreachable()
   582  		}
   583  	}
   584  }
   585  
   586  // recordCommaOkTypes updates recorded types to reflect that x is used in a commaOk context
   587  // (and therefore has tuple type).
   588  func (check *Checker) recordCommaOkTypes(x syntax.Expr, a []*operand) {
   589  	assert(x != nil)
   590  	assert(len(a) == 2)
   591  	if a[0].mode == invalid {
   592  		return
   593  	}
   594  	t0, t1 := a[0].typ, a[1].typ
   595  	assert(isTyped(t0) && isTyped(t1) && (isBoolean(t1) || t1 == universeError))
   596  	if m := check.Types; m != nil {
   597  		for {
   598  			tv := m[x]
   599  			assert(tv.Type != nil) // should have been recorded already
   600  			pos := x.Pos()
   601  			tv.Type = NewTuple(
   602  				NewVar(pos, check.pkg, "", t0),
   603  				NewVar(pos, check.pkg, "", t1),
   604  			)
   605  			m[x] = tv
   606  			// if x is a parenthesized expression (p.X), update p.X
   607  			p, _ := x.(*syntax.ParenExpr)
   608  			if p == nil {
   609  				break
   610  			}
   611  			x = p.X
   612  		}
   613  	}
   614  	if check.StoreTypesInSyntax {
   615  		// Note: this loop is duplicated because the type of tv is different.
   616  		// Above it is types2.TypeAndValue, here it is syntax.TypeAndValue.
   617  		for {
   618  			tv := x.GetTypeInfo()
   619  			assert(tv.Type != nil) // should have been recorded already
   620  			pos := x.Pos()
   621  			tv.Type = NewTuple(
   622  				NewVar(pos, check.pkg, "", t0),
   623  				NewVar(pos, check.pkg, "", t1),
   624  			)
   625  			x.SetTypeInfo(tv)
   626  			p, _ := x.(*syntax.ParenExpr)
   627  			if p == nil {
   628  				break
   629  			}
   630  			x = p.X
   631  		}
   632  	}
   633  }
   634  
   635  // recordInstance records instantiation information into check.Info, if the
   636  // Instances map is non-nil. The given expr must be an ident, selector, or
   637  // index (list) expr with ident or selector operand.
   638  //
   639  // TODO(rfindley): the expr parameter is fragile. See if we can access the
   640  // instantiated identifier in some other way.
   641  func (check *Checker) recordInstance(expr syntax.Expr, targs []Type, typ Type) {
   642  	ident := instantiatedIdent(expr)
   643  	assert(ident != nil)
   644  	assert(typ != nil)
   645  	if m := check.Instances; m != nil {
   646  		m[ident] = Instance{newTypeList(targs), typ}
   647  	}
   648  }
   649  
   650  func instantiatedIdent(expr syntax.Expr) *syntax.Name {
   651  	var selOrIdent syntax.Expr
   652  	switch e := expr.(type) {
   653  	case *syntax.IndexExpr:
   654  		selOrIdent = e.X
   655  	case *syntax.SelectorExpr, *syntax.Name:
   656  		selOrIdent = e
   657  	}
   658  	switch x := selOrIdent.(type) {
   659  	case *syntax.Name:
   660  		return x
   661  	case *syntax.SelectorExpr:
   662  		return x.Sel
   663  	}
   664  	panic("instantiated ident not found")
   665  }
   666  
   667  func (check *Checker) recordDef(id *syntax.Name, obj Object) {
   668  	assert(id != nil)
   669  	if m := check.Defs; m != nil {
   670  		m[id] = obj
   671  	}
   672  }
   673  
   674  func (check *Checker) recordUse(id *syntax.Name, obj Object) {
   675  	assert(id != nil)
   676  	assert(obj != nil)
   677  	if m := check.Uses; m != nil {
   678  		m[id] = obj
   679  	}
   680  }
   681  
   682  func (check *Checker) recordImplicit(node syntax.Node, obj Object) {
   683  	assert(node != nil)
   684  	assert(obj != nil)
   685  	if m := check.Implicits; m != nil {
   686  		m[node] = obj
   687  	}
   688  }
   689  
   690  func (check *Checker) recordSelection(x *syntax.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
   691  	assert(obj != nil && (recv == nil || len(index) > 0))
   692  	check.recordUse(x.Sel, obj)
   693  	if m := check.Selections; m != nil {
   694  		m[x] = &Selection{kind, recv, obj, index, indirect}
   695  	}
   696  }
   697  
   698  func (check *Checker) recordScope(node syntax.Node, scope *Scope) {
   699  	assert(node != nil)
   700  	assert(scope != nil)
   701  	if m := check.Scopes; m != nil {
   702  		m[node] = scope
   703  	}
   704  }
   705
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