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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  	"go/ast"
    11  	"go/constant"
    12  	"go/token"
    13  )
    14  
    15  // debugging/development support
    16  const (
    17  	debug = false // leave on during development
    18  	trace = false // turn on for detailed type resolution traces
    19  )
    20  
    21  // If Strict is set, the type-checker enforces additional
    22  // rules not specified by the Go 1 spec, but which will
    23  // catch guaranteed run-time errors if the respective
    24  // code is executed. In other words, programs passing in
    25  // Strict mode are Go 1 compliant, but not all Go 1 programs
    26  // will pass in Strict mode. The additional rules are:
    27  //
    28  // - A type assertion x.(T) where T is an interface type
    29  //   is invalid if any (statically known) method that exists
    30  //   for both x and T have different signatures.
    31  //
    32  const strict = false
    33  
    34  // exprInfo stores information about an untyped expression.
    35  type exprInfo struct {
    36  	isLhs bool // expression is lhs operand of a shift with delayed type-check
    37  	mode  operandMode
    38  	typ   *Basic
    39  	val   constant.Value // constant value; or nil (if not a constant)
    40  }
    41  
    42  // A context represents the context within which an object is type-checked.
    43  type context struct {
    44  	decl          *declInfo              // package-level declaration whose init expression/function body is checked
    45  	scope         *Scope                 // top-most scope for lookups
    46  	pos           token.Pos              // if valid, identifiers are looked up as if at position pos (used by Eval)
    47  	iota          constant.Value         // value of iota in a constant declaration; nil otherwise
    48  	sig           *Signature             // function signature if inside a function; nil otherwise
    49  	isPanic       map[*ast.CallExpr]bool // set of panic call expressions (used for termination check)
    50  	hasLabel      bool                   // set if a function makes use of labels (only ~1% of functions); unused outside functions
    51  	hasCallOrRecv bool                   // set if an expression contains a function call or channel receive operation
    52  }
    53  
    54  // lookup looks up name in the current context and returns the matching object, or nil.
    55  func (ctxt *context) lookup(name string) Object {
    56  	_, obj := ctxt.scope.LookupParent(name, ctxt.pos)
    57  	return obj
    58  }
    59  
    60  // An importKey identifies an imported package by import path and source directory
    61  // (directory containing the file containing the import). In practice, the directory
    62  // may always be the same, or may not matter. Given an (import path, directory), an
    63  // importer must always return the same package (but given two different import paths,
    64  // an importer may still return the same package by mapping them to the same package
    65  // paths).
    66  type importKey struct {
    67  	path, dir string
    68  }
    69  
    70  // A Checker maintains the state of the type checker.
    71  // It must be created with NewChecker.
    72  type Checker struct {
    73  	// package information
    74  	// (initialized by NewChecker, valid for the life-time of checker)
    75  	conf *Config
    76  	fset *token.FileSet
    77  	pkg  *Package
    78  	*Info
    79  	objMap map[Object]*declInfo   // maps package-level objects and (non-interface) methods to declaration info
    80  	impMap map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
    81  
    82  	// information collected during type-checking of a set of package files
    83  	// (initialized by Files, valid only for the duration of check.Files;
    84  	// maps and lists are allocated on demand)
    85  	files            []*ast.File                       // package files
    86  	unusedDotImports map[*Scope]map[*Package]token.Pos // positions of unused dot-imported packages for each file scope
    87  
    88  	firstErr error                 // first error encountered
    89  	methods  map[*TypeName][]*Func // maps package scope type names to associated non-blank, non-interface methods
    90  	// TODO(gri) move interfaces up to the group of fields persistent across check.Files invocations (see also comment in Checker.initFiles)
    91  	interfaces map[*TypeName]*ifaceInfo // maps interface type names to corresponding interface infos
    92  	untyped    map[ast.Expr]exprInfo    // map of expressions without final type
    93  	delayed    []func()                 // stack of delayed actions
    94  	objPath    []Object                 // path of object dependencies during type inference (for cycle reporting)
    95  
    96  	// context within which the current object is type-checked
    97  	// (valid only for the duration of type-checking a specific object)
    98  	context
    99  
   100  	// debugging
   101  	indent int // indentation for tracing
   102  }
   103  
   104  // addUnusedImport adds the position of a dot-imported package
   105  // pkg to the map of dot imports for the given file scope.
   106  func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, pos token.Pos) {
   107  	mm := check.unusedDotImports
   108  	if mm == nil {
   109  		mm = make(map[*Scope]map[*Package]token.Pos)
   110  		check.unusedDotImports = mm
   111  	}
   112  	m := mm[scope]
   113  	if m == nil {
   114  		m = make(map[*Package]token.Pos)
   115  		mm[scope] = m
   116  	}
   117  	m[pkg] = pos
   118  }
   119  
   120  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   121  func (check *Checker) addDeclDep(to Object) {
   122  	from := check.decl
   123  	if from == nil {
   124  		return // not in a package-level init expression
   125  	}
   126  	if _, found := check.objMap[to]; !found {
   127  		return // to is not a package-level object
   128  	}
   129  	from.addDep(to)
   130  }
   131  
   132  func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   133  	m := check.untyped
   134  	if m == nil {
   135  		m = make(map[ast.Expr]exprInfo)
   136  		check.untyped = m
   137  	}
   138  	m[e] = exprInfo{lhs, mode, typ, val}
   139  }
   140  
   141  // later pushes f on to the stack of actions that will be processed later;
   142  // either at the end of the current statement, or in case of a local constant
   143  // or variable declaration, before the constant or variable is in scope
   144  // (so that f still sees the scope before any new declarations).
   145  func (check *Checker) later(f func()) {
   146  	check.delayed = append(check.delayed, f)
   147  }
   148  
   149  // push pushes obj onto the object path and returns its index in the path.
   150  func (check *Checker) push(obj Object) int {
   151  	check.objPath = append(check.objPath, obj)
   152  	return len(check.objPath) - 1
   153  }
   154  
   155  // pop pops and returns the topmost object from the object path.
   156  func (check *Checker) pop() Object {
   157  	i := len(check.objPath) - 1
   158  	obj := check.objPath[i]
   159  	check.objPath[i] = nil
   160  	check.objPath = check.objPath[:i]
   161  	return obj
   162  }
   163  
   164  // NewChecker returns a new Checker instance for a given package.
   165  // Package files may be added incrementally via checker.Files.
   166  func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
   167  	// make sure we have a configuration
   168  	if conf == nil {
   169  		conf = new(Config)
   170  	}
   171  
   172  	// make sure we have an info struct
   173  	if info == nil {
   174  		info = new(Info)
   175  	}
   176  
   177  	return &Checker{
   178  		conf:   conf,
   179  		fset:   fset,
   180  		pkg:    pkg,
   181  		Info:   info,
   182  		objMap: make(map[Object]*declInfo),
   183  		impMap: make(map[importKey]*Package),
   184  	}
   185  }
   186  
   187  // initFiles initializes the files-specific portion of checker.
   188  // The provided files must all belong to the same package.
   189  func (check *Checker) initFiles(files []*ast.File) {
   190  	// start with a clean slate (check.Files may be called multiple times)
   191  	check.files = nil
   192  	check.unusedDotImports = nil
   193  
   194  	check.firstErr = nil
   195  	check.methods = nil
   196  	// Don't clear the interfaces cache! It's important that we don't recompute
   197  	// ifaceInfos repeatedly (due to multiple check.Files calls) because when
   198  	// they are recomputed, they are not used in the context of their original
   199  	// declaration (because those types are already type-checked, typically) and
   200  	// then they will get the wrong receiver types, which matters for go/types
   201  	// clients. It is also safe to not reset the interfaces cache because files
   202  	// added to a package cannot change (add methods to) existing interface types;
   203  	// they can only add new interfaces. See also the respective comment in
   204  	// checker.infoFromTypeName (interfaces.go). Was bug - see issue #29029.
   205  	check.untyped = nil
   206  	check.delayed = nil
   207  
   208  	// determine package name and collect valid files
   209  	pkg := check.pkg
   210  	for _, file := range files {
   211  		switch name := file.Name.Name; pkg.name {
   212  		case "":
   213  			if name != "_" {
   214  				pkg.name = name
   215  			} else {
   216  				check.errorf(file.Name.Pos(), "invalid package name _")
   217  			}
   218  			fallthrough
   219  
   220  		case name:
   221  			check.files = append(check.files, file)
   222  
   223  		default:
   224  			check.errorf(file.Package, "package %s; expected %s", name, pkg.name)
   225  			// ignore this file
   226  		}
   227  	}
   228  }
   229  
   230  // A bailout panic is used for early termination.
   231  type bailout struct{}
   232  
   233  func (check *Checker) handleBailout(err *error) {
   234  	switch p := recover().(type) {
   235  	case nil, bailout:
   236  		// normal return or early exit
   237  		*err = check.firstErr
   238  	default:
   239  		// re-panic
   240  		panic(p)
   241  	}
   242  }
   243  
   244  // Files checks the provided files as part of the checker's package.
   245  func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
   246  
   247  func (check *Checker) checkFiles(files []*ast.File) (err error) {
   248  	defer check.handleBailout(&err)
   249  
   250  	check.initFiles(files)
   251  
   252  	check.collectObjects()
   253  
   254  	check.packageObjects()
   255  
   256  	check.processDelayed(0) // incl. all functions
   257  
   258  	check.initOrder()
   259  
   260  	if !check.conf.DisableUnusedImportCheck {
   261  		check.unusedImports()
   262  	}
   263  
   264  	check.recordUntyped()
   265  
   266  	check.pkg.complete = true
   267  	return
   268  }
   269  
   270  func (check *Checker) recordUntyped() {
   271  	if !debug && check.Types == nil {
   272  		return // nothing to do
   273  	}
   274  
   275  	for x, info := range check.untyped {
   276  		if debug && isTyped(info.typ) {
   277  			check.dump("%v: %s (type %s) is typed", x.Pos(), x, info.typ)
   278  			unreachable()
   279  		}
   280  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
   281  	}
   282  }
   283  
   284  func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
   285  	assert(x != nil)
   286  	assert(typ != nil)
   287  	if mode == invalid {
   288  		return // omit
   289  	}
   290  	assert(typ != nil)
   291  	if mode == constant_ {
   292  		assert(val != nil)
   293  		assert(typ == Typ[Invalid] || isConstType(typ))
   294  	}
   295  	if m := check.Types; m != nil {
   296  		m[x] = TypeAndValue{mode, typ, val}
   297  	}
   298  }
   299  
   300  func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
   301  	// f must be a (possibly parenthesized) identifier denoting a built-in
   302  	// (built-ins in package unsafe always produce a constant result and
   303  	// we don't record their signatures, so we don't see qualified idents
   304  	// here): record the signature for f and possible children.
   305  	for {
   306  		check.recordTypeAndValue(f, builtin, sig, nil)
   307  		switch p := f.(type) {
   308  		case *ast.Ident:
   309  			return // we're done
   310  		case *ast.ParenExpr:
   311  			f = p.X
   312  		default:
   313  			unreachable()
   314  		}
   315  	}
   316  }
   317  
   318  func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
   319  	assert(x != nil)
   320  	if a[0] == nil || a[1] == nil {
   321  		return
   322  	}
   323  	assert(isTyped(a[0]) && isTyped(a[1]) && isBoolean(a[1]))
   324  	if m := check.Types; m != nil {
   325  		for {
   326  			tv := m[x]
   327  			assert(tv.Type != nil) // should have been recorded already
   328  			pos := x.Pos()
   329  			tv.Type = NewTuple(
   330  				NewVar(pos, check.pkg, "", a[0]),
   331  				NewVar(pos, check.pkg, "", a[1]),
   332  			)
   333  			m[x] = tv
   334  			// if x is a parenthesized expression (p.X), update p.X
   335  			p, _ := x.(*ast.ParenExpr)
   336  			if p == nil {
   337  				break
   338  			}
   339  			x = p.X
   340  		}
   341  	}
   342  }
   343  
   344  func (check *Checker) recordDef(id *ast.Ident, obj Object) {
   345  	assert(id != nil)
   346  	if m := check.Defs; m != nil {
   347  		m[id] = obj
   348  	}
   349  }
   350  
   351  func (check *Checker) recordUse(id *ast.Ident, obj Object) {
   352  	assert(id != nil)
   353  	assert(obj != nil)
   354  	if m := check.Uses; m != nil {
   355  		m[id] = obj
   356  	}
   357  }
   358  
   359  func (check *Checker) recordImplicit(node ast.Node, obj Object) {
   360  	assert(node != nil)
   361  	assert(obj != nil)
   362  	if m := check.Implicits; m != nil {
   363  		m[node] = obj
   364  	}
   365  }
   366  
   367  func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
   368  	assert(obj != nil && (recv == nil || len(index) > 0))
   369  	check.recordUse(x.Sel, obj)
   370  	if m := check.Selections; m != nil {
   371  		m[x] = &Selection{kind, recv, obj, index, indirect}
   372  	}
   373  }
   374  
   375  func (check *Checker) recordScope(node ast.Node, scope *Scope) {
   376  	assert(node != nil)
   377  	assert(scope != nil)
   378  	if m := check.Scopes; m != nil {
   379  		m[node] = scope
   380  	}
   381  }
   382  

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