Source file src/go/types/scope.go

Documentation: go/types

     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 types
     8  
     9  import (
    10  	"bytes"
    11  	"fmt"
    12  	"go/token"
    13  	"io"
    14  	"sort"
    15  	"strings"
    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  	elems    map[string]Object // lazily allocated
    26  	pos, end token.Pos         // scope extent; may be invalid
    27  	comment  string            // for debugging only
    28  	isFunc   bool              // set if this is a function scope (internal use only)
    29  }
    30  
    31  // NewScope returns a new, empty scope contained in the given parent
    32  // scope, if any. The comment is for debugging only.
    33  func NewScope(parent *Scope, pos, end token.Pos, comment string) *Scope {
    34  	s := &Scope{parent, nil, nil, pos, end, comment, false}
    35  	// don't add children to Universe scope!
    36  	if parent != nil && parent != Universe {
    37  		parent.children = append(parent.children, s)
    38  	}
    39  	return s
    40  }
    41  
    42  // Parent returns the scope's containing (parent) scope.
    43  func (s *Scope) Parent() *Scope { return s.parent }
    44  
    45  // Len returns the number of scope elements.
    46  func (s *Scope) Len() int { return len(s.elems) }
    47  
    48  // Names returns the scope's element names in sorted order.
    49  func (s *Scope) Names() []string {
    50  	names := make([]string, len(s.elems))
    51  	i := 0
    52  	for name := range s.elems {
    53  		names[i] = name
    54  		i++
    55  	}
    56  	sort.Strings(names)
    57  	return names
    58  }
    59  
    60  // NumChildren returns the number of scopes nested in s.
    61  func (s *Scope) NumChildren() int { return len(s.children) }
    62  
    63  // Child returns the i'th child scope for 0 <= i < NumChildren().
    64  func (s *Scope) Child(i int) *Scope { return s.children[i] }
    65  
    66  // Lookup returns the object in scope s with the given name if such an
    67  // object exists; otherwise the result is nil.
    68  func (s *Scope) Lookup(name string) Object {
    69  	return s.elems[name]
    70  }
    71  
    72  // LookupParent follows the parent chain of scopes starting with s until
    73  // it finds a scope where Lookup(name) returns a non-nil object, and then
    74  // returns that scope and object. If a valid position pos is provided,
    75  // only objects that were declared at or before pos are considered.
    76  // If no such scope and object exists, the result is (nil, nil).
    77  //
    78  // Note that obj.Parent() may be different from the returned scope if the
    79  // object was inserted into the scope and already had a parent at that
    80  // time (see Insert, below). This can only happen for dot-imported objects
    81  // whose scope is the scope of the package that exported them.
    82  func (s *Scope) LookupParent(name string, pos token.Pos) (*Scope, Object) {
    83  	for ; s != nil; s = s.parent {
    84  		if obj := s.elems[name]; obj != nil && (!pos.IsValid() || obj.scopePos() <= pos) {
    85  			return s, obj
    86  		}
    87  	}
    88  	return nil, nil
    89  }
    90  
    91  // Insert attempts to insert an object obj into scope s.
    92  // If s already contains an alternative object alt with
    93  // the same name, Insert leaves s unchanged and returns alt.
    94  // Otherwise it inserts obj, sets the object's parent scope
    95  // if not already set, and returns nil.
    96  func (s *Scope) Insert(obj Object) Object {
    97  	name := obj.Name()
    98  	if alt := s.elems[name]; alt != nil {
    99  		return alt
   100  	}
   101  	if s.elems == nil {
   102  		s.elems = make(map[string]Object)
   103  	}
   104  	s.elems[name] = obj
   105  	if obj.Parent() == nil {
   106  		obj.setParent(s)
   107  	}
   108  	return nil
   109  }
   110  
   111  // Pos and End describe the scope's source code extent [pos, end).
   112  // The results are guaranteed to be valid only if the type-checked
   113  // AST has complete position information. The extent is undefined
   114  // for Universe and package scopes.
   115  func (s *Scope) Pos() token.Pos { return s.pos }
   116  func (s *Scope) End() token.Pos { return s.end }
   117  
   118  // Contains reports whether pos is within the scope's extent.
   119  // The result is guaranteed to be valid only if the type-checked
   120  // AST has complete position information.
   121  func (s *Scope) Contains(pos token.Pos) bool {
   122  	return s.pos <= pos && pos < s.end
   123  }
   124  
   125  // Innermost returns the innermost (child) scope containing
   126  // pos. If pos is not within any scope, the result is nil.
   127  // The result is also nil for the Universe scope.
   128  // The result is guaranteed to be valid only if the type-checked
   129  // AST has complete position information.
   130  func (s *Scope) Innermost(pos token.Pos) *Scope {
   131  	// Package scopes do not have extents since they may be
   132  	// discontiguous, so iterate over the package's files.
   133  	if s.parent == Universe {
   134  		for _, s := range s.children {
   135  			if inner := s.Innermost(pos); inner != nil {
   136  				return inner
   137  			}
   138  		}
   139  	}
   140  
   141  	if s.Contains(pos) {
   142  		for _, s := range s.children {
   143  			if s.Contains(pos) {
   144  				return s.Innermost(pos)
   145  			}
   146  		}
   147  		return s
   148  	}
   149  	return nil
   150  }
   151  
   152  // WriteTo writes a string representation of the scope to w,
   153  // with the scope elements sorted by name.
   154  // The level of indentation is controlled by n >= 0, with
   155  // n == 0 for no indentation.
   156  // If recurse is set, it also writes nested (children) scopes.
   157  func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
   158  	const ind = ".  "
   159  	indn := strings.Repeat(ind, n)
   160  
   161  	fmt.Fprintf(w, "%s%s scope %p {\n", indn, s.comment, s)
   162  
   163  	indn1 := indn + ind
   164  	for _, name := range s.Names() {
   165  		fmt.Fprintf(w, "%s%s\n", indn1, s.elems[name])
   166  	}
   167  
   168  	if recurse {
   169  		for _, s := range s.children {
   170  			s.WriteTo(w, n+1, recurse)
   171  		}
   172  	}
   173  
   174  	fmt.Fprintf(w, "%s}\n", indn)
   175  }
   176  
   177  // String returns a string representation of the scope, for debugging.
   178  func (s *Scope) String() string {
   179  	var buf bytes.Buffer
   180  	s.WriteTo(&buf, 0, false)
   181  	return buf.String()
   182  }
   183  

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