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Source file src/go/types/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  	"go/ast"
    12  	"go/constant"
    13  	"go/token"
    14  )
    15  
    16  // debugging/development support
    17  const (
    18  	debug = false // leave on during development
    19  	trace = false // turn on for detailed type resolution traces
    20  )
    21  
    22  // If Strict is set, the type-checker enforces additional
    23  // rules not specified by the Go 1 spec, but which will
    24  // catch guaranteed run-time errors if the respective
    25  // code is executed. In other words, programs passing in
    26  // Strict mode are Go 1 compliant, but not all Go 1 programs
    27  // will pass in Strict mode. The additional rules are:
    28  //
    29  // - A type assertion x.(T) where T is an interface type
    30  //   is invalid if any (statically known) method that exists
    31  //   for both x and T have different signatures.
    32  //
    33  const strict = false
    34  
    35  // exprInfo stores information about an untyped expression.
    36  type exprInfo struct {
    37  	isLhs bool // expression is lhs operand of a shift with delayed type-check
    38  	mode  operandMode
    39  	typ   *Basic
    40  	val   constant.Value // constant value; or nil (if not a constant)
    41  }
    42  
    43  // A context represents the context within which an object is type-checked.
    44  type context struct {
    45  	decl          *declInfo              // package-level declaration whose init expression/function body is checked
    46  	scope         *Scope                 // top-most scope for lookups
    47  	pos           token.Pos              // if valid, identifiers are looked up as if at position pos (used by Eval)
    48  	iota          constant.Value         // value of iota in a constant declaration; nil otherwise
    49  	errpos        positioner             // if set, identifier position of a constant with inherited initializer
    50  	sig           *Signature             // function signature if inside a function; nil otherwise
    51  	isPanic       map[*ast.CallExpr]bool // set of panic call expressions (used for termination check)
    52  	hasLabel      bool                   // set if a function makes use of labels (only ~1% of functions); unused outside functions
    53  	hasCallOrRecv bool                   // set if an expression contains a function call or channel receive operation
    54  }
    55  
    56  // lookup looks up name in the current context and returns the matching object, or nil.
    57  func (ctxt *context) lookup(name string) Object {
    58  	_, obj := ctxt.scope.LookupParent(name, ctxt.pos)
    59  	return obj
    60  }
    61  
    62  // An importKey identifies an imported package by import path and source directory
    63  // (directory containing the file containing the import). In practice, the directory
    64  // may always be the same, or may not matter. Given an (import path, directory), an
    65  // importer must always return the same package (but given two different import paths,
    66  // an importer may still return the same package by mapping them to the same package
    67  // paths).
    68  type importKey struct {
    69  	path, dir string
    70  }
    71  
    72  // A Checker maintains the state of the type checker.
    73  // It must be created with NewChecker.
    74  type Checker struct {
    75  	// package information
    76  	// (initialized by NewChecker, valid for the life-time of checker)
    77  	conf *Config
    78  	fset *token.FileSet
    79  	pkg  *Package
    80  	*Info
    81  	objMap map[Object]*declInfo       // maps package-level objects and (non-interface) methods to declaration info
    82  	impMap map[importKey]*Package     // maps (import path, source directory) to (complete or fake) package
    83  	posMap map[*Interface][]token.Pos // maps interface types to lists of embedded interface positions
    84  	pkgCnt map[string]int             // counts number of imported packages with a given name (for better error messages)
    85  
    86  	// information collected during type-checking of a set of package files
    87  	// (initialized by Files, valid only for the duration of check.Files;
    88  	// maps and lists are allocated on demand)
    89  	files            []*ast.File                             // package files
    90  	unusedDotImports map[*Scope]map[*Package]*ast.ImportSpec // unused dot-imported packages
    91  
    92  	firstErr error                 // first error encountered
    93  	methods  map[*TypeName][]*Func // maps package scope type names to associated non-blank (non-interface) methods
    94  	untyped  map[ast.Expr]exprInfo // map of expressions without final type
    95  	delayed  []func()              // stack of delayed action segments; segments are processed in FIFO order
    96  	finals   []func()              // list of final actions; processed at the end of type-checking the current set of files
    97  	objPath  []Object              // path of object dependencies during type inference (for cycle reporting)
    98  
    99  	// context within which the current object is type-checked
   100  	// (valid only for the duration of type-checking a specific object)
   101  	context
   102  
   103  	// debugging
   104  	indent int // indentation for tracing
   105  }
   106  
   107  // addUnusedImport adds the position of a dot-imported package
   108  // pkg to the map of dot imports for the given file scope.
   109  func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, spec *ast.ImportSpec) {
   110  	mm := check.unusedDotImports
   111  	if mm == nil {
   112  		mm = make(map[*Scope]map[*Package]*ast.ImportSpec)
   113  		check.unusedDotImports = mm
   114  	}
   115  	m := mm[scope]
   116  	if m == nil {
   117  		m = make(map[*Package]*ast.ImportSpec)
   118  		mm[scope] = m
   119  	}
   120  	m[pkg] = spec
   121  }
   122  
   123  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   124  func (check *Checker) addDeclDep(to Object) {
   125  	from := check.decl
   126  	if from == nil {
   127  		return // not in a package-level init expression
   128  	}
   129  	if _, found := check.objMap[to]; !found {
   130  		return // to is not a package-level object
   131  	}
   132  	from.addDep(to)
   133  }
   134  
   135  func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   136  	m := check.untyped
   137  	if m == nil {
   138  		m = make(map[ast.Expr]exprInfo)
   139  		check.untyped = m
   140  	}
   141  	m[e] = exprInfo{lhs, mode, typ, val}
   142  }
   143  
   144  // later pushes f on to the stack of actions that will be processed later;
   145  // either at the end of the current statement, or in case of a local constant
   146  // or variable declaration, before the constant or variable is in scope
   147  // (so that f still sees the scope before any new declarations).
   148  func (check *Checker) later(f func()) {
   149  	check.delayed = append(check.delayed, f)
   150  }
   151  
   152  // atEnd adds f to the list of actions processed at the end
   153  // of type-checking, before initialization order computation.
   154  // Actions added by atEnd are processed after any actions
   155  // added by later.
   156  func (check *Checker) atEnd(f func()) {
   157  	check.finals = append(check.finals, f)
   158  }
   159  
   160  // push pushes obj onto the object path and returns its index in the path.
   161  func (check *Checker) push(obj Object) int {
   162  	check.objPath = append(check.objPath, obj)
   163  	return len(check.objPath) - 1
   164  }
   165  
   166  // pop pops and returns the topmost object from the object path.
   167  func (check *Checker) pop() Object {
   168  	i := len(check.objPath) - 1
   169  	obj := check.objPath[i]
   170  	check.objPath[i] = nil
   171  	check.objPath = check.objPath[:i]
   172  	return obj
   173  }
   174  
   175  // NewChecker returns a new Checker instance for a given package.
   176  // Package files may be added incrementally via checker.Files.
   177  func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
   178  	// make sure we have a configuration
   179  	if conf == nil {
   180  		conf = new(Config)
   181  	}
   182  
   183  	// make sure we have an info struct
   184  	if info == nil {
   185  		info = new(Info)
   186  	}
   187  
   188  	return &Checker{
   189  		conf:   conf,
   190  		fset:   fset,
   191  		pkg:    pkg,
   192  		Info:   info,
   193  		objMap: make(map[Object]*declInfo),
   194  		impMap: make(map[importKey]*Package),
   195  		posMap: make(map[*Interface][]token.Pos),
   196  		pkgCnt: make(map[string]int),
   197  	}
   198  }
   199  
   200  // initFiles initializes the files-specific portion of checker.
   201  // The provided files must all belong to the same package.
   202  func (check *Checker) initFiles(files []*ast.File) {
   203  	// start with a clean slate (check.Files may be called multiple times)
   204  	check.files = nil
   205  	check.unusedDotImports = nil
   206  
   207  	check.firstErr = nil
   208  	check.methods = nil
   209  	check.untyped = nil
   210  	check.delayed = nil
   211  	check.finals = nil
   212  
   213  	// determine package name and collect valid files
   214  	pkg := check.pkg
   215  	for _, file := range files {
   216  		switch name := file.Name.Name; pkg.name {
   217  		case "":
   218  			if name != "_" {
   219  				pkg.name = name
   220  			} else {
   221  				check.errorf(file.Name, _BlankPkgName, "invalid package name _")
   222  			}
   223  			fallthrough
   224  
   225  		case name:
   226  			check.files = append(check.files, file)
   227  
   228  		default:
   229  			check.errorf(atPos(file.Package), _MismatchedPkgName, "package %s; expected %s", name, pkg.name)
   230  			// ignore this file
   231  		}
   232  	}
   233  }
   234  
   235  // A bailout panic is used for early termination.
   236  type bailout struct{}
   237  
   238  func (check *Checker) handleBailout(err *error) {
   239  	switch p := recover().(type) {
   240  	case nil, bailout:
   241  		// normal return or early exit
   242  		*err = check.firstErr
   243  	default:
   244  		// re-panic
   245  		panic(p)
   246  	}
   247  }
   248  
   249  // Files checks the provided files as part of the checker's package.
   250  func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
   251  
   252  var errBadCgo = errors.New("cannot use FakeImportC and go115UsesCgo together")
   253  
   254  func (check *Checker) checkFiles(files []*ast.File) (err error) {
   255  	if check.conf.FakeImportC && check.conf.go115UsesCgo {
   256  		return errBadCgo
   257  	}
   258  
   259  	defer check.handleBailout(&err)
   260  
   261  	check.initFiles(files)
   262  
   263  	check.collectObjects()
   264  
   265  	check.packageObjects()
   266  
   267  	check.processDelayed(0) // incl. all functions
   268  	check.processFinals()
   269  
   270  	check.initOrder()
   271  
   272  	if !check.conf.DisableUnusedImportCheck {
   273  		check.unusedImports()
   274  	}
   275  
   276  	check.recordUntyped()
   277  
   278  	check.pkg.complete = true
   279  	return
   280  }
   281  
   282  // processDelayed processes all delayed actions pushed after top.
   283  func (check *Checker) processDelayed(top int) {
   284  	// If each delayed action pushes a new action, the
   285  	// stack will continue to grow during this loop.
   286  	// However, it is only processing functions (which
   287  	// are processed in a delayed fashion) that may
   288  	// add more actions (such as nested functions), so
   289  	// this is a sufficiently bounded process.
   290  	for i := top; i < len(check.delayed); i++ {
   291  		check.delayed[i]() // may append to check.delayed
   292  	}
   293  	assert(top <= len(check.delayed)) // stack must not have shrunk
   294  	check.delayed = check.delayed[:top]
   295  }
   296  
   297  func (check *Checker) processFinals() {
   298  	n := len(check.finals)
   299  	for _, f := range check.finals {
   300  		f() // must not append to check.finals
   301  	}
   302  	if len(check.finals) != n {
   303  		panic("internal error: final action list grew")
   304  	}
   305  }
   306  
   307  func (check *Checker) recordUntyped() {
   308  	if !debug && check.Types == nil {
   309  		return // nothing to do
   310  	}
   311  
   312  	for x, info := range check.untyped {
   313  		if debug && isTyped(info.typ) {
   314  			check.dump("%v: %s (type %s) is typed", x.Pos(), x, info.typ)
   315  			unreachable()
   316  		}
   317  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
   318  	}
   319  }
   320  
   321  func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
   322  	assert(x != nil)
   323  	assert(typ != nil)
   324  	if mode == invalid {
   325  		return // omit
   326  	}
   327  	if mode == constant_ {
   328  		assert(val != nil)
   329  		assert(typ == Typ[Invalid] || isConstType(typ))
   330  	}
   331  	if m := check.Types; m != nil {
   332  		m[x] = TypeAndValue{mode, typ, val}
   333  	}
   334  }
   335  
   336  func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
   337  	// f must be a (possibly parenthesized) identifier denoting a built-in
   338  	// (built-ins in package unsafe always produce a constant result and
   339  	// we don't record their signatures, so we don't see qualified idents
   340  	// here): record the signature for f and possible children.
   341  	for {
   342  		check.recordTypeAndValue(f, builtin, sig, nil)
   343  		switch p := f.(type) {
   344  		case *ast.Ident:
   345  			return // we're done
   346  		case *ast.ParenExpr:
   347  			f = p.X
   348  		default:
   349  			unreachable()
   350  		}
   351  	}
   352  }
   353  
   354  func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
   355  	assert(x != nil)
   356  	if a[0] == nil || a[1] == nil {
   357  		return
   358  	}
   359  	assert(isTyped(a[0]) && isTyped(a[1]) && (isBoolean(a[1]) || a[1] == universeError))
   360  	if m := check.Types; m != nil {
   361  		for {
   362  			tv := m[x]
   363  			assert(tv.Type != nil) // should have been recorded already
   364  			pos := x.Pos()
   365  			tv.Type = NewTuple(
   366  				NewVar(pos, check.pkg, "", a[0]),
   367  				NewVar(pos, check.pkg, "", a[1]),
   368  			)
   369  			m[x] = tv
   370  			// if x is a parenthesized expression (p.X), update p.X
   371  			p, _ := x.(*ast.ParenExpr)
   372  			if p == nil {
   373  				break
   374  			}
   375  			x = p.X
   376  		}
   377  	}
   378  }
   379  
   380  func (check *Checker) recordDef(id *ast.Ident, obj Object) {
   381  	assert(id != nil)
   382  	if m := check.Defs; m != nil {
   383  		m[id] = obj
   384  	}
   385  }
   386  
   387  func (check *Checker) recordUse(id *ast.Ident, obj Object) {
   388  	assert(id != nil)
   389  	assert(obj != nil)
   390  	if m := check.Uses; m != nil {
   391  		m[id] = obj
   392  	}
   393  }
   394  
   395  func (check *Checker) recordImplicit(node ast.Node, obj Object) {
   396  	assert(node != nil)
   397  	assert(obj != nil)
   398  	if m := check.Implicits; m != nil {
   399  		m[node] = obj
   400  	}
   401  }
   402  
   403  func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
   404  	assert(obj != nil && (recv == nil || len(index) > 0))
   405  	check.recordUse(x.Sel, obj)
   406  	if m := check.Selections; m != nil {
   407  		m[x] = &Selection{kind, recv, obj, index, indirect}
   408  	}
   409  }
   410  
   411  func (check *Checker) recordScope(node ast.Node, scope *Scope) {
   412  	assert(node != nil)
   413  	assert(scope != nil)
   414  	if m := check.Scopes; m != nil {
   415  		m[node] = scope
   416  	}
   417  }
   418  

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