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  	"fmt"
    12  	"go/constant"
    13  	. "internal/types/errors"
    14  	"os"
    15  	"sync/atomic"
    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  // position tracing for panics during type checking
    25  const tracePos = false // TODO(markfreeman): check performance implications
    26  
    27  // _aliasAny changes the behavior of [Scope.Lookup] for "any" in the
    28  // [Universe] scope.
    29  //
    30  // This is necessary because while Alias creation is controlled by
    31  // [Config.EnableAlias], the representation of "any" is a global. In
    32  // [Scope.Lookup], we select this global representation based on the result of
    33  // [aliasAny], but as a result need to guard against this behavior changing
    34  // during the type checking pass. Therefore we implement the following rule:
    35  // any number of goroutines can type check concurrently with the same
    36  // EnableAlias value, but if any goroutine tries to type check concurrently
    37  // with a different EnableAlias value, we panic.
    38  //
    39  // To achieve this, _aliasAny is a state machine:
    40  //
    41  //	0:        no type checking is occurring
    42  //	negative: type checking is occurring without EnableAlias set
    43  //	positive: type checking is occurring with EnableAlias set
    44  var _aliasAny int32
    45  
    46  func aliasAny() bool {
    47  	return atomic.LoadInt32(&_aliasAny) >= 0 // default true
    48  }
    49  
    50  // exprInfo stores information about an untyped expression.
    51  type exprInfo struct {
    52  	isLhs bool // expression is lhs operand of a shift with delayed type-check
    53  	mode  operandMode
    54  	typ   *Basic
    55  	val   constant.Value // constant value; or nil (if not a constant)
    56  }
    57  
    58  // An environment represents the environment within which an object is
    59  // type-checked.
    60  type environment struct {
    61  	decl          *declInfo                 // package-level declaration whose init expression/function body is checked
    62  	scope         *Scope                    // top-most scope for lookups
    63  	version       goVersion                 // current accepted language version; changes across files
    64  	iota          constant.Value            // value of iota in a constant declaration; nil otherwise
    65  	errpos        syntax.Pos                // if valid, identifier position of a constant with inherited initializer
    66  	inTParamList  bool                      // set if inside a type parameter list
    67  	sig           *Signature                // function signature if inside a function; nil otherwise
    68  	isPanic       map[*syntax.CallExpr]bool // set of panic call expressions (used for termination check)
    69  	hasLabel      bool                      // set if a function makes use of labels (only ~1% of functions); unused outside functions
    70  	hasCallOrRecv bool                      // set if an expression contains a function call or channel receive operation
    71  }
    72  
    73  // lookupScope looks up name in the current environment and if an object
    74  // is found it returns the scope containing the object and the object.
    75  // Otherwise it returns (nil, nil).
    76  //
    77  // Note that obj.Parent() may be different from the returned scope if the
    78  // object was inserted into the scope and already had a parent at that
    79  // time (see Scope.Insert). This can only happen for dot-imported objects
    80  // whose parent is the scope of the package that exported them.
    81  func (env *environment) lookupScope(name string) (*Scope, Object) {
    82  	for s := env.scope; s != nil; s = s.parent {
    83  		if obj := s.Lookup(name); obj != nil {
    84  			return s, obj
    85  		}
    86  	}
    87  	return nil, nil
    88  }
    89  
    90  // lookup is like lookupScope but it only returns the object (or nil).
    91  func (env *environment) lookup(name string) Object {
    92  	_, obj := env.lookupScope(name)
    93  	return obj
    94  }
    95  
    96  // An importKey identifies an imported package by import path and source directory
    97  // (directory containing the file containing the import). In practice, the directory
    98  // may always be the same, or may not matter. Given an (import path, directory), an
    99  // importer must always return the same package (but given two different import paths,
   100  // an importer may still return the same package by mapping them to the same package
   101  // paths).
   102  type importKey struct {
   103  	path, dir string
   104  }
   105  
   106  // A dotImportKey describes a dot-imported object in the given scope.
   107  type dotImportKey struct {
   108  	scope *Scope
   109  	name  string
   110  }
   111  
   112  // An action describes a (delayed) action.
   113  type action struct {
   114  	version goVersion   // applicable language version
   115  	f       func()      // action to be executed
   116  	desc    *actionDesc // action description; may be nil, requires debug to be set
   117  }
   118  
   119  // If debug is set, describef sets a printf-formatted description for action a.
   120  // Otherwise, it is a no-op.
   121  func (a *action) describef(pos poser, format string, args ...interface{}) {
   122  	if debug {
   123  		a.desc = &actionDesc{pos, format, args}
   124  	}
   125  }
   126  
   127  // An actionDesc provides information on an action.
   128  // For debugging only.
   129  type actionDesc struct {
   130  	pos    poser
   131  	format string
   132  	args   []interface{}
   133  }
   134  
   135  // A Checker maintains the state of the type checker.
   136  // It must be created with NewChecker.
   137  type Checker struct {
   138  	// package information
   139  	// (initialized by NewChecker, valid for the life-time of checker)
   140  	conf *Config
   141  	ctxt *Context // context for de-duplicating instances
   142  	pkg  *Package
   143  	*Info
   144  	nextID uint64                 // unique Id for type parameters (first valid Id is 1)
   145  	objMap map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
   146  	impMap map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
   147  	// see TODO in validtype.go
   148  	// valids  instanceLookup      // valid *Named (incl. instantiated) types per the validType check
   149  
   150  	// pkgPathMap maps package names to the set of distinct import paths we've
   151  	// seen for that name, anywhere in the import graph. It is used for
   152  	// disambiguating package names in error messages.
   153  	//
   154  	// pkgPathMap is allocated lazily, so that we don't pay the price of building
   155  	// it on the happy path. seenPkgMap tracks the packages that we've already
   156  	// walked.
   157  	pkgPathMap map[string]map[string]bool
   158  	seenPkgMap map[*Package]bool
   159  
   160  	// information collected during type-checking of a set of package files
   161  	// (initialized by Files, valid only for the duration of check.Files;
   162  	// maps and lists are allocated on demand)
   163  	files         []*syntax.File             // list of package files
   164  	versions      map[*syntax.PosBase]string // maps files to version strings (each file has an entry); shared with Info.FileVersions if present; may be unaltered Config.GoVersion
   165  	imports       []*PkgName                 // list of imported packages
   166  	dotImportMap  map[dotImportKey]*PkgName  // maps dot-imported objects to the package they were dot-imported through
   167  	brokenAliases map[*TypeName]bool         // set of aliases with broken (not yet determined) types
   168  	unionTypeSets map[*Union]*_TypeSet       // computed type sets for union types
   169  	usedVars      map[*Var]bool              // set of used variables
   170  	usedPkgNames  map[*PkgName]bool          // set of used package names
   171  	mono          monoGraph                  // graph for detecting non-monomorphizable instantiation loops
   172  
   173  	firstErr error                    // first error encountered
   174  	methods  map[*TypeName][]*Func    // maps package scope type names to associated non-blank (non-interface) methods
   175  	untyped  map[syntax.Expr]exprInfo // map of expressions without final type
   176  	delayed  []action                 // stack of delayed action segments; segments are processed in FIFO order
   177  	objPath  []Object                 // path of object dependencies during type inference (for cycle reporting)
   178  	cleaners []cleaner                // list of types that may need a final cleanup at the end of type-checking
   179  
   180  	// environment within which the current object is type-checked (valid only
   181  	// for the duration of type-checking a specific object)
   182  	environment
   183  
   184  	// debugging
   185  	posStack []syntax.Pos // stack of source positions seen; used for panic tracing
   186  	indent   int          // indentation for tracing
   187  }
   188  
   189  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   190  func (check *Checker) addDeclDep(to Object) {
   191  	from := check.decl
   192  	if from == nil {
   193  		return // not in a package-level init expression
   194  	}
   195  	if _, found := check.objMap[to]; !found {
   196  		return // to is not a package-level object
   197  	}
   198  	from.addDep(to)
   199  }
   200  
   201  // Note: The following three alias-related functions are only used
   202  //       when Alias types are not enabled.
   203  
   204  // brokenAlias records that alias doesn't have a determined type yet.
   205  // It also sets alias.typ to Typ[Invalid].
   206  // Not used if check.conf.EnableAlias is set.
   207  func (check *Checker) brokenAlias(alias *TypeName) {
   208  	assert(!check.conf.EnableAlias)
   209  	if check.brokenAliases == nil {
   210  		check.brokenAliases = make(map[*TypeName]bool)
   211  	}
   212  	check.brokenAliases[alias] = true
   213  	alias.typ = Typ[Invalid]
   214  }
   215  
   216  // validAlias records that alias has the valid type typ (possibly Typ[Invalid]).
   217  func (check *Checker) validAlias(alias *TypeName, typ Type) {
   218  	assert(!check.conf.EnableAlias)
   219  	delete(check.brokenAliases, alias)
   220  	alias.typ = typ
   221  }
   222  
   223  // isBrokenAlias reports whether alias doesn't have a determined type yet.
   224  func (check *Checker) isBrokenAlias(alias *TypeName) bool {
   225  	assert(!check.conf.EnableAlias)
   226  	return check.brokenAliases[alias]
   227  }
   228  
   229  func (check *Checker) rememberUntyped(e syntax.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   230  	m := check.untyped
   231  	if m == nil {
   232  		m = make(map[syntax.Expr]exprInfo)
   233  		check.untyped = m
   234  	}
   235  	m[e] = exprInfo{lhs, mode, typ, val}
   236  }
   237  
   238  // later pushes f on to the stack of actions that will be processed later;
   239  // either at the end of the current statement, or in case of a local constant
   240  // or variable declaration, before the constant or variable is in scope
   241  // (so that f still sees the scope before any new declarations).
   242  // later returns the pushed action so one can provide a description
   243  // via action.describef for debugging, if desired.
   244  func (check *Checker) later(f func()) *action {
   245  	i := len(check.delayed)
   246  	check.delayed = append(check.delayed, action{version: check.version, f: f})
   247  	return &check.delayed[i]
   248  }
   249  
   250  // push pushes obj onto the object path and returns its index in the path.
   251  func (check *Checker) push(obj Object) int {
   252  	check.objPath = append(check.objPath, obj)
   253  	return len(check.objPath) - 1
   254  }
   255  
   256  // pop pops and returns the topmost object from the object path.
   257  func (check *Checker) pop() Object {
   258  	i := len(check.objPath) - 1
   259  	obj := check.objPath[i]
   260  	check.objPath[i] = nil
   261  	check.objPath = check.objPath[:i]
   262  	return obj
   263  }
   264  
   265  type cleaner interface {
   266  	cleanup()
   267  }
   268  
   269  // needsCleanup records objects/types that implement the cleanup method
   270  // which will be called at the end of type-checking.
   271  func (check *Checker) needsCleanup(c cleaner) {
   272  	check.cleaners = append(check.cleaners, c)
   273  }
   274  
   275  // NewChecker returns a new Checker instance for a given package.
   276  // Package files may be added incrementally via checker.Files.
   277  func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
   278  	// make sure we have a configuration
   279  	if conf == nil {
   280  		conf = new(Config)
   281  	}
   282  
   283  	// make sure we have an info struct
   284  	if info == nil {
   285  		info = new(Info)
   286  	}
   287  
   288  	// Note: clients may call NewChecker with the Unsafe package, which is
   289  	// globally shared and must not be mutated. Therefore NewChecker must not
   290  	// mutate *pkg.
   291  	//
   292  	// (previously, pkg.goVersion was mutated here: go.dev/issue/61212)
   293  
   294  	return &Checker{
   295  		conf:         conf,
   296  		ctxt:         conf.Context,
   297  		pkg:          pkg,
   298  		Info:         info,
   299  		objMap:       make(map[Object]*declInfo),
   300  		impMap:       make(map[importKey]*Package),
   301  		usedVars:     make(map[*Var]bool),
   302  		usedPkgNames: make(map[*PkgName]bool),
   303  	}
   304  }
   305  
   306  // initFiles initializes the files-specific portion of checker.
   307  // The provided files must all belong to the same package.
   308  func (check *Checker) initFiles(files []*syntax.File) {
   309  	// start with a clean slate (check.Files may be called multiple times)
   310  	// TODO(gri): what determines which fields are zeroed out here, vs at the end
   311  	// of checkFiles?
   312  	check.files = nil
   313  	check.imports = nil
   314  	check.dotImportMap = nil
   315  
   316  	check.firstErr = nil
   317  	check.methods = nil
   318  	check.untyped = nil
   319  	check.delayed = nil
   320  	check.objPath = nil
   321  	check.cleaners = nil
   322  
   323  	// We must initialize usedVars and usedPkgNames both here and in NewChecker,
   324  	// because initFiles is not called in the CheckExpr or Eval codepaths, yet we
   325  	// want to free this memory at the end of Files ('used' predicates are
   326  	// only needed in the context of a given file).
   327  	check.usedVars = make(map[*Var]bool)
   328  	check.usedPkgNames = make(map[*PkgName]bool)
   329  
   330  	// determine package name and collect valid files
   331  	pkg := check.pkg
   332  	for _, file := range files {
   333  		switch name := file.PkgName.Value; pkg.name {
   334  		case "":
   335  			if name != "_" {
   336  				pkg.name = name
   337  			} else {
   338  				check.error(file.PkgName, BlankPkgName, "invalid package name _")
   339  			}
   340  			fallthrough
   341  
   342  		case name:
   343  			check.files = append(check.files, file)
   344  
   345  		default:
   346  			check.errorf(file, MismatchedPkgName, "package %s; expected package %s", name, pkg.name)
   347  			// ignore this file
   348  		}
   349  	}
   350  
   351  	// reuse Info.FileVersions if provided
   352  	versions := check.Info.FileVersions
   353  	if versions == nil {
   354  		versions = make(map[*syntax.PosBase]string)
   355  	}
   356  	check.versions = versions
   357  
   358  	pkgVersion := asGoVersion(check.conf.GoVersion)
   359  	if pkgVersion.isValid() && len(files) > 0 && pkgVersion.cmp(go_current) > 0 {
   360  		check.errorf(files[0], TooNew, "package requires newer Go version %v (application built with %v)",
   361  			pkgVersion, go_current)
   362  	}
   363  
   364  	// determine Go version for each file
   365  	for _, file := range check.files {
   366  		// use unaltered Config.GoVersion by default
   367  		// (This version string may contain dot-release numbers as in go1.20.1,
   368  		// unlike file versions which are Go language versions only, if valid.)
   369  		v := check.conf.GoVersion
   370  
   371  		// If the file specifies a version, use max(fileVersion, go1.21).
   372  		if fileVersion := asGoVersion(file.GoVersion); fileVersion.isValid() {
   373  			// Go 1.21 introduced the feature of allowing //go:build lines
   374  			// to sometimes set the Go version in a given file. Versions Go 1.21 and later
   375  			// can be set backwards compatibly as that was the first version
   376  			// files with go1.21 or later build tags could be built with.
   377  			//
   378  			// Set the version to max(fileVersion, go1.21): That will allow a
   379  			// downgrade to a version before go1.22, where the for loop semantics
   380  			// change was made, while being backwards compatible with versions of
   381  			// go before the new //go:build semantics were introduced.
   382  			v = string(versionMax(fileVersion, go1_21))
   383  
   384  			// Report a specific error for each tagged file that's too new.
   385  			// (Normally the build system will have filtered files by version,
   386  			// but clients can present arbitrary files to the type checker.)
   387  			if fileVersion.cmp(go_current) > 0 {
   388  				// Use position of 'package [p]' for types/types2 consistency.
   389  				// (Ideally we would use the //build tag itself.)
   390  				check.errorf(file.PkgName, TooNew, "file requires newer Go version %v", fileVersion)
   391  			}
   392  		}
   393  		versions[file.Pos().FileBase()] = v // file.Pos().FileBase() may be nil for tests
   394  	}
   395  }
   396  
   397  func versionMax(a, b goVersion) goVersion {
   398  	if a.cmp(b) > 0 {
   399  		return a
   400  	}
   401  	return b
   402  }
   403  
   404  // pushPos pushes pos onto the pos stack.
   405  func (check *Checker) pushPos(pos syntax.Pos) {
   406  	check.posStack = append(check.posStack, pos)
   407  }
   408  
   409  // popPos pops from the pos stack.
   410  func (check *Checker) popPos() {
   411  	check.posStack = check.posStack[:len(check.posStack)-1]
   412  }
   413  
   414  // A bailout panic is used for early termination.
   415  type bailout struct{}
   416  
   417  func (check *Checker) handleBailout(err *error) {
   418  	switch p := recover().(type) {
   419  	case nil, bailout:
   420  		// normal return or early exit
   421  		*err = check.firstErr
   422  	default:
   423  		if len(check.posStack) > 0 {
   424  			doPrint := func(ps []syntax.Pos) {
   425  				for i := len(ps) - 1; i >= 0; i-- {
   426  					fmt.Fprintf(os.Stderr, "\t%v\n", ps[i])
   427  				}
   428  			}
   429  
   430  			fmt.Fprintln(os.Stderr, "The following panic happened checking types near:")
   431  			if len(check.posStack) <= 10 {
   432  				doPrint(check.posStack)
   433  			} else {
   434  				// if it's long, truncate the middle; it's least likely to help
   435  				doPrint(check.posStack[len(check.posStack)-5:])
   436  				fmt.Fprintln(os.Stderr, "\t...")
   437  				doPrint(check.posStack[:5])
   438  			}
   439  		}
   440  
   441  		// re-panic
   442  		panic(p)
   443  	}
   444  }
   445  
   446  // Files checks the provided files as part of the checker's package.
   447  func (check *Checker) Files(files []*syntax.File) (err error) {
   448  	if check.pkg == Unsafe {
   449  		// Defensive handling for Unsafe, which cannot be type checked, and must
   450  		// not be mutated. See https://go.dev/issue/61212 for an example of where
   451  		// Unsafe is passed to NewChecker.
   452  		return nil
   453  	}
   454  
   455  	// Avoid early returns here! Nearly all errors can be
   456  	// localized to a piece of syntax and needn't prevent
   457  	// type-checking of the rest of the package.
   458  
   459  	defer check.handleBailout(&err)
   460  	check.checkFiles(files)
   461  	return
   462  }
   463  
   464  // checkFiles type-checks the specified files. Errors are reported as
   465  // a side effect, not by returning early, to ensure that well-formed
   466  // syntax is properly type annotated even in a package containing
   467  // errors.
   468  func (check *Checker) checkFiles(files []*syntax.File) {
   469  	// Ensure that EnableAlias is consistent among concurrent type checking
   470  	// operations. See the documentation of [_aliasAny] for details.
   471  	if check.conf.EnableAlias {
   472  		if atomic.AddInt32(&_aliasAny, 1) <= 0 {
   473  			panic("EnableAlias set while !EnableAlias type checking is ongoing")
   474  		}
   475  		defer atomic.AddInt32(&_aliasAny, -1)
   476  	} else {
   477  		if atomic.AddInt32(&_aliasAny, -1) >= 0 {
   478  			panic("!EnableAlias set while EnableAlias type checking is ongoing")
   479  		}
   480  		defer atomic.AddInt32(&_aliasAny, 1)
   481  	}
   482  
   483  	print := func(msg string) {
   484  		if check.conf.Trace {
   485  			fmt.Println()
   486  			fmt.Println(msg)
   487  		}
   488  	}
   489  
   490  	print("== initFiles ==")
   491  	check.initFiles(files)
   492  
   493  	print("== collectObjects ==")
   494  	check.collectObjects()
   495  
   496  	print("== packageObjects ==")
   497  	check.packageObjects()
   498  
   499  	print("== processDelayed ==")
   500  	check.processDelayed(0) // incl. all functions
   501  
   502  	print("== cleanup ==")
   503  	check.cleanup()
   504  
   505  	print("== initOrder ==")
   506  	check.initOrder()
   507  
   508  	if !check.conf.DisableUnusedImportCheck {
   509  		print("== unusedImports ==")
   510  		check.unusedImports()
   511  	}
   512  
   513  	print("== recordUntyped ==")
   514  	check.recordUntyped()
   515  
   516  	if check.firstErr == nil {
   517  		// TODO(mdempsky): Ensure monomorph is safe when errors exist.
   518  		check.monomorph()
   519  	}
   520  
   521  	check.pkg.goVersion = check.conf.GoVersion
   522  	check.pkg.complete = true
   523  
   524  	// no longer needed - release memory
   525  	check.imports = nil
   526  	check.dotImportMap = nil
   527  	check.pkgPathMap = nil
   528  	check.seenPkgMap = nil
   529  	check.brokenAliases = nil
   530  	check.unionTypeSets = nil
   531  	check.usedVars = nil
   532  	check.usedPkgNames = nil
   533  	check.ctxt = nil
   534  
   535  	// TODO(gri): shouldn't the cleanup above occur after the bailout?
   536  	// TODO(gri) There's more memory we should release at this point.
   537  }
   538  
   539  // processDelayed processes all delayed actions pushed after top.
   540  func (check *Checker) processDelayed(top int) {
   541  	// If each delayed action pushes a new action, the
   542  	// stack will continue to grow during this loop.
   543  	// However, it is only processing functions (which
   544  	// are processed in a delayed fashion) that may
   545  	// add more actions (such as nested functions), so
   546  	// this is a sufficiently bounded process.
   547  	savedVersion := check.version
   548  	for i := top; i < len(check.delayed); i++ {
   549  		a := &check.delayed[i]
   550  		if check.conf.Trace {
   551  			if a.desc != nil {
   552  				check.trace(a.desc.pos.Pos(), "-- "+a.desc.format, a.desc.args...)
   553  			} else {
   554  				check.trace(nopos, "-- delayed %p", a.f)
   555  			}
   556  		}
   557  		check.version = a.version // reestablish the effective Go version captured earlier
   558  		a.f()                     // may append to check.delayed
   559  		if check.conf.Trace {
   560  			fmt.Println()
   561  		}
   562  	}
   563  	assert(top <= len(check.delayed)) // stack must not have shrunk
   564  	check.delayed = check.delayed[:top]
   565  	check.version = savedVersion
   566  }
   567  
   568  // cleanup runs cleanup for all collected cleaners.
   569  func (check *Checker) cleanup() {
   570  	// Don't use a range clause since Named.cleanup may add more cleaners.
   571  	for i := 0; i < len(check.cleaners); i++ {
   572  		check.cleaners[i].cleanup()
   573  	}
   574  	check.cleaners = nil
   575  }
   576  
   577  // types2-specific support for recording type information in the syntax tree.
   578  func (check *Checker) recordTypeAndValueInSyntax(x syntax.Expr, mode operandMode, typ Type, val constant.Value) {
   579  	if check.StoreTypesInSyntax {
   580  		tv := TypeAndValue{mode, typ, val}
   581  		stv := syntax.TypeAndValue{Type: typ, Value: val}
   582  		if tv.IsVoid() {
   583  			stv.SetIsVoid()
   584  		}
   585  		if tv.IsType() {
   586  			stv.SetIsType()
   587  		}
   588  		if tv.IsBuiltin() {
   589  			stv.SetIsBuiltin()
   590  		}
   591  		if tv.IsValue() {
   592  			stv.SetIsValue()
   593  		}
   594  		if tv.IsNil() {
   595  			stv.SetIsNil()
   596  		}
   597  		if tv.Addressable() {
   598  			stv.SetAddressable()
   599  		}
   600  		if tv.Assignable() {
   601  			stv.SetAssignable()
   602  		}
   603  		if tv.HasOk() {
   604  			stv.SetHasOk()
   605  		}
   606  		x.SetTypeInfo(stv)
   607  	}
   608  }
   609  
   610  // types2-specific support for recording type information in the syntax tree.
   611  func (check *Checker) recordCommaOkTypesInSyntax(x syntax.Expr, t0, t1 Type) {
   612  	if check.StoreTypesInSyntax {
   613  		// Note: this loop is duplicated because the type of tv is different.
   614  		// Above it is types2.TypeAndValue, here it is syntax.TypeAndValue.
   615  		for {
   616  			tv := x.GetTypeInfo()
   617  			assert(tv.Type != nil) // should have been recorded already
   618  			pos := x.Pos()
   619  			tv.Type = NewTuple(
   620  				NewParam(pos, check.pkg, "", t0),
   621  				NewParam(pos, check.pkg, "", t1),
   622  			)
   623  			x.SetTypeInfo(tv)
   624  			p, _ := x.(*syntax.ParenExpr)
   625  			if p == nil {
   626  				break
   627  			}
   628  			x = p.X
   629  		}
   630  	}
   631  }
   632  
   633  // instantiatedIdent determines the identifier of the type instantiated in expr.
   634  // Helper function for recordInstance in recording.go.
   635  func instantiatedIdent(expr syntax.Expr) *syntax.Name {
   636  	var selOrIdent syntax.Expr
   637  	switch e := expr.(type) {
   638  	case *syntax.IndexExpr:
   639  		selOrIdent = e.X
   640  	case *syntax.SelectorExpr, *syntax.Name:
   641  		selOrIdent = e
   642  	}
   643  	switch x := selOrIdent.(type) {
   644  	case *syntax.Name:
   645  		return x
   646  	case *syntax.SelectorExpr:
   647  		return x.Sel
   648  	}
   649  
   650  	// extra debugging of go.dev/issue/63933
   651  	panic(sprintf(nil, true, "instantiated ident not found; please report: %s", expr))
   652  }
   653
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