scope.go

     1  // Copyright 2013 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 Scopes.
     6  
     7  package types2
     8  
     9  import (
    10  	"cmd/compile/internal/syntax"
    11  	"fmt"
    12  	"io"
    13  	"sort"
    14  	"strings"
    15  	"sync"
    16  )
    17  
    18  // A Scope maintains a set of objects and links to its containing
    19  // (parent) and contained (children) scopes. Objects may be inserted
    20  // and looked up by name. The zero value for Scope is a ready-to-use
    21  // empty scope.
    22  type Scope struct {
    23  	parent   *Scope
    24  	children []*Scope
    25  	number   int               // parent.children[number-1] is this scope; 0 if there is no parent
    26  	elems    map[string]Object // lazily allocated
    27  	pos, end syntax.Pos        // scope extent; may be invalid
    28  	comment  string            // for debugging only
    29  	isFunc   bool              // set if this is a function scope (internal use only)
    30  }
    31  
    32  // NewScope returns a new, empty scope contained in the given parent
    33  // scope, if any. The comment is for debugging only.
    34  func NewScope(parent *Scope, pos, end syntax.Pos, comment string) *Scope {
    35  	s := &Scope{parent, nil, 0, nil, pos, end, comment, false}
    36  	// don't add children to Universe scope!
    37  	if parent != nil && parent != Universe {
    38  		parent.children = append(parent.children, s)
    39  		s.number = len(parent.children)
    40  	}
    41  	return s
    42  }
    43  
    44  // Parent returns the scope's containing (parent) scope.
    45  func (s *Scope) Parent() *Scope { return s.parent }
    46  
    47  // Len returns the number of scope elements.
    48  func (s *Scope) Len() int { return len(s.elems) }
    49  
    50  // Names returns the scope's element names in sorted order.
    51  func (s *Scope) Names() []string {
    52  	names := make([]string, len(s.elems))
    53  	i := 0
    54  	for name := range s.elems {
    55  		names[i] = name
    56  		i++
    57  	}
    58  	sort.Strings(names)
    59  	return names
    60  }
    61  
    62  // NumChildren returns the number of scopes nested in s.
    63  func (s *Scope) NumChildren() int { return len(s.children) }
    64  
    65  // Child returns the i'th child scope for 0 <= i < NumChildren().
    66  func (s *Scope) Child(i int) *Scope { return s.children[i] }
    67  
    68  // Lookup returns the object in scope s with the given name if such an
    69  // object exists; otherwise the result is nil.
    70  func (s *Scope) Lookup(name string) Object {
    71  	obj := resolve(name, s.elems[name])
    72  	// Hijack Lookup for "any": with gotypesalias=1, we want the Universe to
    73  	// return an Alias for "any", and with gotypesalias=0 we want to return
    74  	// the legacy representation of aliases.
    75  	//
    76  	// This is rather tricky, but works out after auditing of the usage of
    77  	// s.elems. The only external API to access scope elements is Lookup.
    78  	//
    79  	// TODO: remove this once gotypesalias=0 is no longer supported.
    80  	if obj == universeAnyAlias && !aliasAny() {
    81  		return universeAnyNoAlias
    82  	}
    83  	return obj
    84  }
    85  
    86  // LookupParent follows the parent chain of scopes starting with s until
    87  // it finds a scope where Lookup(name) returns a non-nil object, and then
    88  // returns that scope and object. If a valid position pos is provided,
    89  // only objects that were declared at or before pos are considered.
    90  // If no such scope and object exists, the result is (nil, nil).
    91  //
    92  // Note that obj.Parent() may be different from the returned scope if the
    93  // object was inserted into the scope and already had a parent at that
    94  // time (see Insert). This can only happen for dot-imported objects
    95  // whose scope is the scope of the package that exported them.
    96  func (s *Scope) LookupParent(name string, pos syntax.Pos) (*Scope, Object) {
    97  	for ; s != nil; s = s.parent {
    98  		if obj := s.Lookup(name); obj != nil && (!pos.IsKnown() || cmpPos(obj.scopePos(), pos) <= 0) {
    99  			return s, obj
   100  		}
   101  	}
   102  	return nil, nil
   103  }
   104  
   105  // Insert attempts to insert an object obj into scope s.
   106  // If s already contains an alternative object alt with
   107  // the same name, Insert leaves s unchanged and returns alt.
   108  // Otherwise it inserts obj, sets the object's parent scope
   109  // if not already set, and returns nil.
   110  func (s *Scope) Insert(obj Object) Object {
   111  	name := obj.Name()
   112  	if alt := s.Lookup(name); alt != nil {
   113  		return alt
   114  	}
   115  	s.insert(name, obj)
   116  	if obj.Parent() == nil {
   117  		obj.setParent(s)
   118  	}
   119  	return nil
   120  }
   121  
   122  // InsertLazy is like Insert, but allows deferring construction of the
   123  // inserted object until it's accessed with Lookup. The Object
   124  // returned by resolve must have the same name as given to InsertLazy.
   125  // If s already contains an alternative object with the same name,
   126  // InsertLazy leaves s unchanged and returns false. Otherwise it
   127  // records the binding and returns true. The object's parent scope
   128  // will be set to s after resolve is called.
   129  func (s *Scope) InsertLazy(name string, resolve func() Object) bool {
   130  	if s.elems[name] != nil {
   131  		return false
   132  	}
   133  	s.insert(name, &lazyObject{parent: s, resolve: resolve})
   134  	return true
   135  }
   136  
   137  func (s *Scope) insert(name string, obj Object) {
   138  	if s.elems == nil {
   139  		s.elems = make(map[string]Object)
   140  	}
   141  	s.elems[name] = obj
   142  }
   143  
   144  // Squash merges s with its parent scope p by adding all
   145  // objects of s to p, adding all children of s to the
   146  // children of p, and removing s from p's children.
   147  // The function f is called for each object obj in s which
   148  // has an object alt in p. s should be discarded after
   149  // having been squashed.
   150  func (s *Scope) Squash(err func(obj, alt Object)) {
   151  	p := s.parent
   152  	assert(p != nil)
   153  	for name, obj := range s.elems {
   154  		obj = resolve(name, obj)
   155  		obj.setParent(nil)
   156  		if alt := p.Insert(obj); alt != nil {
   157  			err(obj, alt)
   158  		}
   159  	}
   160  
   161  	j := -1 // index of s in p.children
   162  	for i, ch := range p.children {
   163  		if ch == s {
   164  			j = i
   165  			break
   166  		}
   167  	}
   168  	assert(j >= 0)
   169  	k := len(p.children) - 1
   170  	p.children[j] = p.children[k]
   171  	p.children = p.children[:k]
   172  
   173  	p.children = append(p.children, s.children...)
   174  
   175  	s.children = nil
   176  	s.elems = nil
   177  }
   178  
   179  // Pos and End describe the scope's source code extent [pos, end).
   180  // The results are guaranteed to be valid only if the type-checked
   181  // AST has complete position information. The extent is undefined
   182  // for Universe and package scopes.
   183  func (s *Scope) Pos() syntax.Pos { return s.pos }
   184  func (s *Scope) End() syntax.Pos { return s.end }
   185  
   186  // Contains reports whether pos is within the scope's extent.
   187  // The result is guaranteed to be valid only if the type-checked
   188  // AST has complete position information.
   189  func (s *Scope) Contains(pos syntax.Pos) bool {
   190  	return cmpPos(s.pos, pos) <= 0 && cmpPos(pos, s.end) < 0
   191  }
   192  
   193  // Innermost returns the innermost (child) scope containing
   194  // pos. If pos is not within any scope, the result is nil.
   195  // The result is also nil for the Universe scope.
   196  // The result is guaranteed to be valid only if the type-checked
   197  // AST has complete position information.
   198  func (s *Scope) Innermost(pos syntax.Pos) *Scope {
   199  	// Package scopes do not have extents since they may be
   200  	// discontiguous, so iterate over the package's files.
   201  	if s.parent == Universe {
   202  		for _, s := range s.children {
   203  			if inner := s.Innermost(pos); inner != nil {
   204  				return inner
   205  			}
   206  		}
   207  	}
   208  
   209  	if s.Contains(pos) {
   210  		for _, s := range s.children {
   211  			if s.Contains(pos) {
   212  				return s.Innermost(pos)
   213  			}
   214  		}
   215  		return s
   216  	}
   217  	return nil
   218  }
   219  
   220  // WriteTo writes a string representation of the scope to w,
   221  // with the scope elements sorted by name.
   222  // The level of indentation is controlled by n >= 0, with
   223  // n == 0 for no indentation.
   224  // If recurse is set, it also writes nested (children) scopes.
   225  func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
   226  	const ind = ".  "
   227  	indn := strings.Repeat(ind, n)
   228  
   229  	fmt.Fprintf(w, "%s%s scope %p {\n", indn, s.comment, s)
   230  
   231  	indn1 := indn + ind
   232  	for _, name := range s.Names() {
   233  		fmt.Fprintf(w, "%s%s\n", indn1, s.Lookup(name))
   234  	}
   235  
   236  	if recurse {
   237  		for _, s := range s.children {
   238  			s.WriteTo(w, n+1, recurse)
   239  		}
   240  	}
   241  
   242  	fmt.Fprintf(w, "%s}\n", indn)
   243  }
   244  
   245  // String returns a string representation of the scope, for debugging.
   246  func (s *Scope) String() string {
   247  	var buf strings.Builder
   248  	s.WriteTo(&buf, 0, false)
   249  	return buf.String()
   250  }
   251  
   252  // A lazyObject represents an imported Object that has not been fully
   253  // resolved yet by its importer.
   254  type lazyObject struct {
   255  	parent  *Scope
   256  	resolve func() Object
   257  	obj     Object
   258  	once    sync.Once
   259  }
   260  
   261  // resolve returns the Object represented by obj, resolving lazy
   262  // objects as appropriate.
   263  func resolve(name string, obj Object) Object {
   264  	if lazy, ok := obj.(*lazyObject); ok {
   265  		lazy.once.Do(func() {
   266  			obj := lazy.resolve()
   267  
   268  			if _, ok := obj.(*lazyObject); ok {
   269  				panic("recursive lazy object")
   270  			}
   271  			if obj.Name() != name {
   272  				panic("lazy object has unexpected name")
   273  			}
   274  
   275  			if obj.Parent() == nil {
   276  				obj.setParent(lazy.parent)
   277  			}
   278  			lazy.obj = obj
   279  		})
   280  
   281  		obj = lazy.obj
   282  	}
   283  	return obj
   284  }
   285  
   286  // stub implementations so *lazyObject implements Object and we can
   287  // store them directly into Scope.elems.
   288  func (*lazyObject) Parent() *Scope                     { panic("unreachable") }
   289  func (*lazyObject) Pos() syntax.Pos                    { panic("unreachable") }
   290  func (*lazyObject) Pkg() *Package                      { panic("unreachable") }
   291  func (*lazyObject) Name() string                       { panic("unreachable") }
   292  func (*lazyObject) Type() Type                         { panic("unreachable") }
   293  func (*lazyObject) Exported() bool                     { panic("unreachable") }
   294  func (*lazyObject) Id() string                         { panic("unreachable") }
   295  func (*lazyObject) String() string                     { panic("unreachable") }
   296  func (*lazyObject) order() uint32                      { panic("unreachable") }
   297  func (*lazyObject) color() color                       { panic("unreachable") }
   298  func (*lazyObject) setType(Type)                       { panic("unreachable") }
   299  func (*lazyObject) setOrder(uint32)                    { panic("unreachable") }
   300  func (*lazyObject) setColor(color color)               { panic("unreachable") }
   301  func (*lazyObject) setParent(*Scope)                   { panic("unreachable") }
   302  func (*lazyObject) sameId(*Package, string, bool) bool { panic("unreachable") }
   303  func (*lazyObject) scopePos() syntax.Pos               { panic("unreachable") }
   304  func (*lazyObject) setScopePos(syntax.Pos)             { panic("unreachable") }
   305
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