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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  // funcInfo stores the information required for type-checking a function.
    43  type funcInfo struct {
    44  	name string    // for debugging/tracing only
    45  	decl *declInfo // for cycle detection
    46  	sig  *Signature
    47  	body *ast.BlockStmt
    48  }
    49  
    50  // A context represents the context within which an object is type-checked.
    51  type context struct {
    52  	decl          *declInfo      // package-level declaration whose init expression/function body is checked
    53  	scope         *Scope         // top-most scope for lookups
    54  	iota          constant.Value // value of iota in a constant declaration; nil otherwise
    55  	sig           *Signature     // function signature if inside a function; nil otherwise
    56  	hasLabel      bool           // set if a function makes use of labels (only ~1% of functions); unused outside functions
    57  	hasCallOrRecv bool           // set if an expression contains a function call or channel receive operation
    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 object 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[string][]*Func    // maps type names to associated methods
    90  	untyped  map[ast.Expr]exprInfo // map of expressions without final type
    91  	funcs    []funcInfo            // list of functions to type-check
    92  	delayed  []func()              // delayed checks requiring fully setup types
    93  
    94  	// context within which the current object is type-checked
    95  	// (valid only for the duration of type-checking a specific object)
    96  	context
    97  	pos token.Pos // if valid, identifiers are looked up as if at position pos (used by Eval)
    98  
    99  	// debugging
   100  	indent int // indentation for tracing
   101  }
   102  
   103  // addUnusedImport adds the position of a dot-imported package
   104  // pkg to the map of dot imports for the given file scope.
   105  func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, pos token.Pos) {
   106  	mm := check.unusedDotImports
   107  	if mm == nil {
   108  		mm = make(map[*Scope]map[*Package]token.Pos)
   109  		check.unusedDotImports = mm
   110  	}
   111  	m := mm[scope]
   112  	if m == nil {
   113  		m = make(map[*Package]token.Pos)
   114  		mm[scope] = m
   115  	}
   116  	m[pkg] = pos
   117  }
   118  
   119  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
   120  func (check *Checker) addDeclDep(to Object) {
   121  	from := check.decl
   122  	if from == nil {
   123  		return // not in a package-level init expression
   124  	}
   125  	if _, found := check.objMap[to]; !found {
   126  		return // to is not a package-level object
   127  	}
   128  	from.addDep(to)
   129  }
   130  
   131  func (check *Checker) assocMethod(tname string, meth *Func) {
   132  	m := check.methods
   133  	if m == nil {
   134  		m = make(map[string][]*Func)
   135  		check.methods = m
   136  	}
   137  	m[tname] = append(m[tname], meth)
   138  }
   139  
   140  func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
   141  	m := check.untyped
   142  	if m == nil {
   143  		m = make(map[ast.Expr]exprInfo)
   144  		check.untyped = m
   145  	}
   146  	m[e] = exprInfo{lhs, mode, typ, val}
   147  }
   148  
   149  func (check *Checker) later(name string, decl *declInfo, sig *Signature, body *ast.BlockStmt) {
   150  	check.funcs = append(check.funcs, funcInfo{name, decl, sig, body})
   151  }
   152  
   153  func (check *Checker) delay(f func()) {
   154  	check.delayed = append(check.delayed, f)
   155  }
   156  
   157  // NewChecker returns a new Checker instance for a given package.
   158  // Package files may be added incrementally via checker.Files.
   159  func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
   160  	// make sure we have a configuration
   161  	if conf == nil {
   162  		conf = new(Config)
   163  	}
   164  
   165  	// make sure we have an info struct
   166  	if info == nil {
   167  		info = new(Info)
   168  	}
   169  
   170  	return &Checker{
   171  		conf:   conf,
   172  		fset:   fset,
   173  		pkg:    pkg,
   174  		Info:   info,
   175  		objMap: make(map[Object]*declInfo),
   176  		impMap: make(map[importKey]*Package),
   177  	}
   178  }
   179  
   180  // initFiles initializes the files-specific portion of checker.
   181  // The provided files must all belong to the same package.
   182  func (check *Checker) initFiles(files []*ast.File) {
   183  	// start with a clean slate (check.Files may be called multiple times)
   184  	check.files = nil
   185  	check.unusedDotImports = nil
   186  
   187  	check.firstErr = nil
   188  	check.methods = nil
   189  	check.untyped = nil
   190  	check.funcs = nil
   191  	check.delayed = nil
   192  
   193  	// determine package name and collect valid files
   194  	pkg := check.pkg
   195  	for _, file := range files {
   196  		switch name := file.Name.Name; pkg.name {
   197  		case "":
   198  			if name != "_" {
   199  				pkg.name = name
   200  			} else {
   201  				check.errorf(file.Name.Pos(), "invalid package name _")
   202  			}
   203  			fallthrough
   204  
   205  		case name:
   206  			check.files = append(check.files, file)
   207  
   208  		default:
   209  			check.errorf(file.Package, "package %s; expected %s", name, pkg.name)
   210  			// ignore this file
   211  		}
   212  	}
   213  }
   214  
   215  // A bailout panic is used for early termination.
   216  type bailout struct{}
   217  
   218  func (check *Checker) handleBailout(err *error) {
   219  	switch p := recover().(type) {
   220  	case nil, bailout:
   221  		// normal return or early exit
   222  		*err = check.firstErr
   223  	default:
   224  		// re-panic
   225  		panic(p)
   226  	}
   227  }
   228  
   229  // Files checks the provided files as part of the checker's package.
   230  func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
   231  
   232  func (check *Checker) checkFiles(files []*ast.File) (err error) {
   233  	defer check.handleBailout(&err)
   234  
   235  	check.initFiles(files)
   236  
   237  	check.collectObjects()
   238  
   239  	check.packageObjects(check.resolveOrder())
   240  
   241  	check.functionBodies()
   242  
   243  	check.initOrder()
   244  
   245  	if !check.conf.DisableUnusedImportCheck {
   246  		check.unusedImports()
   247  	}
   248  
   249  	// perform delayed checks
   250  	for _, f := range check.delayed {
   251  		f()
   252  	}
   253  
   254  	check.recordUntyped()
   255  
   256  	check.pkg.complete = true
   257  	return
   258  }
   259  
   260  func (check *Checker) recordUntyped() {
   261  	if !debug && check.Types == nil {
   262  		return // nothing to do
   263  	}
   264  
   265  	for x, info := range check.untyped {
   266  		if debug && isTyped(info.typ) {
   267  			check.dump("%s: %s (type %s) is typed", x.Pos(), x, info.typ)
   268  			unreachable()
   269  		}
   270  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
   271  	}
   272  }
   273  
   274  func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
   275  	assert(x != nil)
   276  	assert(typ != nil)
   277  	if mode == invalid {
   278  		return // omit
   279  	}
   280  	assert(typ != nil)
   281  	if mode == constant_ {
   282  		assert(val != nil)
   283  		assert(typ == Typ[Invalid] || isConstType(typ))
   284  	}
   285  	if m := check.Types; m != nil {
   286  		m[x] = TypeAndValue{mode, typ, val}
   287  	}
   288  }
   289  
   290  func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
   291  	// f must be a (possibly parenthesized) identifier denoting a built-in
   292  	// (built-ins in package unsafe always produce a constant result and
   293  	// we don't record their signatures, so we don't see qualified idents
   294  	// here): record the signature for f and possible children.
   295  	for {
   296  		check.recordTypeAndValue(f, builtin, sig, nil)
   297  		switch p := f.(type) {
   298  		case *ast.Ident:
   299  			return // we're done
   300  		case *ast.ParenExpr:
   301  			f = p.X
   302  		default:
   303  			unreachable()
   304  		}
   305  	}
   306  }
   307  
   308  func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
   309  	assert(x != nil)
   310  	if a[0] == nil || a[1] == nil {
   311  		return
   312  	}
   313  	assert(isTyped(a[0]) && isTyped(a[1]) && isBoolean(a[1]))
   314  	if m := check.Types; m != nil {
   315  		for {
   316  			tv := m[x]
   317  			assert(tv.Type != nil) // should have been recorded already
   318  			pos := x.Pos()
   319  			tv.Type = NewTuple(
   320  				NewVar(pos, check.pkg, "", a[0]),
   321  				NewVar(pos, check.pkg, "", a[1]),
   322  			)
   323  			m[x] = tv
   324  			// if x is a parenthesized expression (p.X), update p.X
   325  			p, _ := x.(*ast.ParenExpr)
   326  			if p == nil {
   327  				break
   328  			}
   329  			x = p.X
   330  		}
   331  	}
   332  }
   333  
   334  func (check *Checker) recordDef(id *ast.Ident, obj Object) {
   335  	assert(id != nil)
   336  	if m := check.Defs; m != nil {
   337  		m[id] = obj
   338  	}
   339  }
   340  
   341  func (check *Checker) recordUse(id *ast.Ident, obj Object) {
   342  	assert(id != nil)
   343  	assert(obj != nil)
   344  	if m := check.Uses; m != nil {
   345  		m[id] = obj
   346  	}
   347  }
   348  
   349  func (check *Checker) recordImplicit(node ast.Node, obj Object) {
   350  	assert(node != nil)
   351  	assert(obj != nil)
   352  	if m := check.Implicits; m != nil {
   353  		m[node] = obj
   354  	}
   355  }
   356  
   357  func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
   358  	assert(obj != nil && (recv == nil || len(index) > 0))
   359  	check.recordUse(x.Sel, obj)
   360  	if m := check.Selections; m != nil {
   361  		m[x] = &Selection{kind, recv, obj, index, indirect}
   362  	}
   363  }
   364  
   365  func (check *Checker) recordScope(node ast.Node, scope *Scope) {
   366  	assert(node != nil)
   367  	assert(scope != nil)
   368  	if m := check.Scopes; m != nil {
   369  		m[node] = scope
   370  	}
   371  }
   372  

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