scope.go

Documentation: cmd/compile/internal/types2

     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  	return resolve(name, s.elems[name])
    72  }
    73  
    74  // LookupParent follows the parent chain of scopes starting with s until
    75  // it finds a scope where Lookup(name) returns a non-nil object, and then
    76  // returns that scope and object. If a valid position pos is provided,
    77  // only objects that were declared at or before pos are considered.
    78  // If no such scope and object exists, the result is (nil, nil).
    79  //
    80  // Note that obj.Parent() may be different from the returned scope if the
    81  // object was inserted into the scope and already had a parent at that
    82  // time (see Insert). This can only happen for dot-imported objects
    83  // whose scope is the scope of the package that exported them.
    84  func (s *Scope) LookupParent(name string, pos syntax.Pos) (*Scope, Object) {
    85  	for ; s != nil; s = s.parent {
    86  		if obj := s.Lookup(name); obj != nil && (!pos.IsKnown() || cmpPos(obj.scopePos(), pos) <= 0) {
    87  			return s, obj
    88  		}
    89  	}
    90  	return nil, nil
    91  }
    92  
    93  // Insert attempts to insert an object obj into scope s.
    94  // If s already contains an alternative object alt with
    95  // the same name, Insert leaves s unchanged and returns alt.
    96  // Otherwise it inserts obj, sets the object's parent scope
    97  // if not already set, and returns nil.
    98  func (s *Scope) Insert(obj Object) Object {
    99  	name := obj.Name()
   100  	if alt := s.Lookup(name); alt != nil {
   101  		return alt
   102  	}
   103  	s.insert(name, obj)
   104  	if obj.Parent() == nil {
   105  		obj.setParent(s)
   106  	}
   107  	return nil
   108  }
   109  
   110  // InsertLazy is like Insert, but allows deferring construction of the
   111  // inserted object until it's accessed with Lookup. The Object
   112  // returned by resolve must have the same name as given to InsertLazy.
   113  // If s already contains an alternative object with the same name,
   114  // InsertLazy leaves s unchanged and returns false. Otherwise it
   115  // records the binding and returns true. The object's parent scope
   116  // will be set to s after resolve is called.
   117  func (s *Scope) InsertLazy(name string, resolve func() Object) bool {
   118  	if s.elems[name] != nil {
   119  		return false
   120  	}
   121  	s.insert(name, &lazyObject{parent: s, resolve: resolve})
   122  	return true
   123  }
   124  
   125  func (s *Scope) insert(name string, obj Object) {
   126  	if s.elems == nil {
   127  		s.elems = make(map[string]Object)
   128  	}
   129  	s.elems[name] = obj
   130  }
   131  
   132  // Squash merges s with its parent scope p by adding all
   133  // objects of s to p, adding all children of s to the
   134  // children of p, and removing s from p's children.
   135  // The function f is called for each object obj in s which
   136  // has an object alt in p. s should be discarded after
   137  // having been squashed.
   138  func (s *Scope) Squash(err func(obj, alt Object)) {
   139  	p := s.parent
   140  	assert(p != nil)
   141  	for name, obj := range s.elems {
   142  		obj = resolve(name, obj)
   143  		obj.setParent(nil)
   144  		if alt := p.Insert(obj); alt != nil {
   145  			err(obj, alt)
   146  		}
   147  	}
   148  
   149  	j := -1 // index of s in p.children
   150  	for i, ch := range p.children {
   151  		if ch == s {
   152  			j = i
   153  			break
   154  		}
   155  	}
   156  	assert(j >= 0)
   157  	k := len(p.children) - 1
   158  	p.children[j] = p.children[k]
   159  	p.children = p.children[:k]
   160  
   161  	p.children = append(p.children, s.children...)
   162  
   163  	s.children = nil
   164  	s.elems = nil
   165  }
   166  
   167  // Pos and End describe the scope's source code extent [pos, end).
   168  // The results are guaranteed to be valid only if the type-checked
   169  // AST has complete position information. The extent is undefined
   170  // for Universe and package scopes.
   171  func (s *Scope) Pos() syntax.Pos { return s.pos }
   172  func (s *Scope) End() syntax.Pos { return s.end }
   173  
   174  // Contains reports whether pos is within the scope's extent.
   175  // The result is guaranteed to be valid only if the type-checked
   176  // AST has complete position information.
   177  func (s *Scope) Contains(pos syntax.Pos) bool {
   178  	return cmpPos(s.pos, pos) <= 0 && cmpPos(pos, s.end) < 0
   179  }
   180  
   181  // Innermost returns the innermost (child) scope containing
   182  // pos. If pos is not within any scope, the result is nil.
   183  // The result is also nil for the Universe scope.
   184  // The result is guaranteed to be valid only if the type-checked
   185  // AST has complete position information.
   186  func (s *Scope) Innermost(pos syntax.Pos) *Scope {
   187  	// Package scopes do not have extents since they may be
   188  	// discontiguous, so iterate over the package's files.
   189  	if s.parent == Universe {
   190  		for _, s := range s.children {
   191  			if inner := s.Innermost(pos); inner != nil {
   192  				return inner
   193  			}
   194  		}
   195  	}
   196  
   197  	if s.Contains(pos) {
   198  		for _, s := range s.children {
   199  			if s.Contains(pos) {
   200  				return s.Innermost(pos)
   201  			}
   202  		}
   203  		return s
   204  	}
   205  	return nil
   206  }
   207  
   208  // WriteTo writes a string representation of the scope to w,
   209  // with the scope elements sorted by name.
   210  // The level of indentation is controlled by n >= 0, with
   211  // n == 0 for no indentation.
   212  // If recurse is set, it also writes nested (children) scopes.
   213  func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
   214  	const ind = ".  "
   215  	indn := strings.Repeat(ind, n)
   216  
   217  	fmt.Fprintf(w, "%s%s scope %p {\n", indn, s.comment, s)
   218  
   219  	indn1 := indn + ind
   220  	for _, name := range s.Names() {
   221  		fmt.Fprintf(w, "%s%s\n", indn1, s.Lookup(name))
   222  	}
   223  
   224  	if recurse {
   225  		for _, s := range s.children {
   226  			s.WriteTo(w, n+1, recurse)
   227  		}
   228  	}
   229  
   230  	fmt.Fprintf(w, "%s}\n", indn)
   231  }
   232  
   233  // String returns a string representation of the scope, for debugging.
   234  func (s *Scope) String() string {
   235  	var buf strings.Builder
   236  	s.WriteTo(&buf, 0, false)
   237  	return buf.String()
   238  }
   239  
   240  // A lazyObject represents an imported Object that has not been fully
   241  // resolved yet by its importer.
   242  type lazyObject struct {
   243  	parent  *Scope
   244  	resolve func() Object
   245  	obj     Object
   246  	once    sync.Once
   247  }
   248  
   249  // resolve returns the Object represented by obj, resolving lazy
   250  // objects as appropriate.
   251  func resolve(name string, obj Object) Object {
   252  	if lazy, ok := obj.(*lazyObject); ok {
   253  		lazy.once.Do(func() {
   254  			obj := lazy.resolve()
   255  
   256  			if _, ok := obj.(*lazyObject); ok {
   257  				panic("recursive lazy object")
   258  			}
   259  			if obj.Name() != name {
   260  				panic("lazy object has unexpected name")
   261  			}
   262  
   263  			if obj.Parent() == nil {
   264  				obj.setParent(lazy.parent)
   265  			}
   266  			lazy.obj = obj
   267  		})
   268  
   269  		obj = lazy.obj
   270  	}
   271  	return obj
   272  }
   273  
   274  // stub implementations so *lazyObject implements Object and we can
   275  // store them directly into Scope.elems.
   276  func (*lazyObject) Parent() *Scope                        { panic("unreachable") }
   277  func (*lazyObject) Pos() syntax.Pos                       { panic("unreachable") }
   278  func (*lazyObject) Pkg() *Package                         { panic("unreachable") }
   279  func (*lazyObject) Name() string                          { panic("unreachable") }
   280  func (*lazyObject) Type() Type                            { panic("unreachable") }
   281  func (*lazyObject) Exported() bool                        { panic("unreachable") }
   282  func (*lazyObject) Id() string                            { panic("unreachable") }
   283  func (*lazyObject) String() string                        { panic("unreachable") }
   284  func (*lazyObject) order() uint32                         { panic("unreachable") }
   285  func (*lazyObject) color() color                          { panic("unreachable") }
   286  func (*lazyObject) setType(Type)                          { panic("unreachable") }
   287  func (*lazyObject) setOrder(uint32)                       { panic("unreachable") }
   288  func (*lazyObject) setColor(color color)                  { panic("unreachable") }
   289  func (*lazyObject) setParent(*Scope)                      { panic("unreachable") }
   290  func (*lazyObject) sameId(pkg *Package, name string) bool { panic("unreachable") }
   291  func (*lazyObject) scopePos() syntax.Pos                  { panic("unreachable") }
   292  func (*lazyObject) setScopePos(pos syntax.Pos)            { panic("unreachable") }
   293
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