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  	"slices"
    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  	slices.Sort(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 { return resolve(name, s.elems[name]) }
    71  
    72  // lookupIgnoringCase returns the objects in scope s whose names match
    73  // the given name ignoring case. If exported is set, only exported names
    74  // are returned.
    75  func (s *Scope) lookupIgnoringCase(name string, exported bool) []Object {
    76  	var matches []Object
    77  	for _, n := range s.Names() {
    78  		if (!exported || isExported(n)) && strings.EqualFold(n, name) {
    79  			matches = append(matches, s.Lookup(n))
    80  		}
    81  	}
    82  	return matches
    83  }
    84  
    85  // Insert attempts to insert an object obj into scope s.
    86  // If s already contains an alternative object alt with
    87  // the same name, Insert leaves s unchanged and returns alt.
    88  // Otherwise it inserts obj, sets the object's parent scope
    89  // if not already set, and returns nil.
    90  func (s *Scope) Insert(obj Object) Object {
    91  	name := obj.Name()
    92  	if alt := s.Lookup(name); alt != nil {
    93  		return alt
    94  	}
    95  	s.insert(name, obj)
    96  	// TODO(gri) Can we always set the parent to s (or is there
    97  	// a need to keep the original parent or some race condition)?
    98  	// If we can, than we may not need environment.lookupScope
    99  	// which is only there so that we get the correct scope for
   100  	// marking "used" dot-imported packages.
   101  	if obj.Parent() == nil {
   102  		obj.setParent(s)
   103  	}
   104  	return nil
   105  }
   106  
   107  // InsertLazy is like Insert, but allows deferring construction of the
   108  // inserted object until it's accessed with Lookup. The Object
   109  // returned by resolve must have the same name as given to InsertLazy.
   110  // If s already contains an alternative object with the same name,
   111  // InsertLazy leaves s unchanged and returns false. Otherwise it
   112  // records the binding and returns true. The object's parent scope
   113  // will be set to s after resolve is called.
   114  func (s *Scope) InsertLazy(name string, resolve func() Object) bool {
   115  	if s.elems[name] != nil {
   116  		return false
   117  	}
   118  	s.insert(name, &lazyObject{parent: s, resolve: resolve})
   119  	return true
   120  }
   121  
   122  func (s *Scope) insert(name string, obj Object) {
   123  	if s.elems == nil {
   124  		s.elems = make(map[string]Object)
   125  	}
   126  	s.elems[name] = obj
   127  }
   128  
   129  // WriteTo writes a string representation of the scope to w,
   130  // with the scope elements sorted by name.
   131  // The level of indentation is controlled by n >= 0, with
   132  // n == 0 for no indentation.
   133  // If recurse is set, it also writes nested (children) scopes.
   134  func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
   135  	const ind = ".  "
   136  	indn := strings.Repeat(ind, n)
   137  
   138  	fmt.Fprintf(w, "%s%s scope %p {\n", indn, s.comment, s)
   139  
   140  	indn1 := indn + ind
   141  	for _, name := range s.Names() {
   142  		fmt.Fprintf(w, "%s%s\n", indn1, s.Lookup(name))
   143  	}
   144  
   145  	if recurse {
   146  		for _, s := range s.children {
   147  			s.WriteTo(w, n+1, recurse)
   148  		}
   149  	}
   150  
   151  	fmt.Fprintf(w, "%s}\n", indn)
   152  }
   153  
   154  // String returns a string representation of the scope, for debugging.
   155  func (s *Scope) String() string {
   156  	var buf strings.Builder
   157  	s.WriteTo(&buf, 0, false)
   158  	return buf.String()
   159  }
   160  
   161  // A lazyObject represents an imported Object that has not been fully
   162  // resolved yet by its importer.
   163  type lazyObject struct {
   164  	parent  *Scope
   165  	resolve func() Object
   166  	obj     Object
   167  	once    sync.Once
   168  }
   169  
   170  // resolve returns the Object represented by obj, resolving lazy
   171  // objects as appropriate.
   172  func resolve(name string, obj Object) Object {
   173  	if lazy, ok := obj.(*lazyObject); ok {
   174  		lazy.once.Do(func() {
   175  			obj := lazy.resolve()
   176  
   177  			if _, ok := obj.(*lazyObject); ok {
   178  				panic("recursive lazy object")
   179  			}
   180  			if obj.Name() != name {
   181  				panic("lazy object has unexpected name")
   182  			}
   183  
   184  			if obj.Parent() == nil {
   185  				obj.setParent(lazy.parent)
   186  			}
   187  			lazy.obj = obj
   188  		})
   189  
   190  		obj = lazy.obj
   191  	}
   192  	return obj
   193  }
   194  
   195  // stub implementations so *lazyObject implements Object and we can
   196  // store them directly into Scope.elems.
   197  func (*lazyObject) Parent() *Scope                     { panic("unreachable") }
   198  func (*lazyObject) Pos() syntax.Pos                    { panic("unreachable") }
   199  func (*lazyObject) Pkg() *Package                      { panic("unreachable") }
   200  func (*lazyObject) Name() string                       { panic("unreachable") }
   201  func (*lazyObject) Type() Type                         { panic("unreachable") }
   202  func (*lazyObject) Exported() bool                     { panic("unreachable") }
   203  func (*lazyObject) Id() string                         { panic("unreachable") }
   204  func (*lazyObject) String() string                     { panic("unreachable") }
   205  func (*lazyObject) order() uint32                      { panic("unreachable") }
   206  func (*lazyObject) setType(Type)                       { panic("unreachable") }
   207  func (*lazyObject) setOrder(uint32)                    { panic("unreachable") }
   208  func (*lazyObject) setParent(*Scope)                   { panic("unreachable") }
   209  func (*lazyObject) sameId(*Package, string, bool) bool { panic("unreachable") }
   210  func (*lazyObject) scopePos() syntax.Pos               { panic("unreachable") }
   211  func (*lazyObject) setScopePos(syntax.Pos)             { panic("unreachable") }
   212
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