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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  // TODO(gri) Provide scopes with a name or other mechanism so that
    19  //           objects can use that information for better printing.
    20  
    21  // A Scope maintains a set of objects and links to its containing
    22  // (parent) and contained (children) scopes. Objects may be inserted
    23  // and looked up by name. The zero value for Scope is a ready-to-use
    24  // empty scope.
    25  type Scope struct {
    26  	parent   *Scope
    27  	children []*Scope
    28  	elems    map[string]Object // lazily allocated
    29  	pos, end token.Pos         // scope extent; may be invalid
    30  	comment  string            // for debugging only
    31  	isFunc   bool              // set if this is a function scope (internal use only)
    32  }
    33  
    34  // NewScope returns a new, empty scope contained in the given parent
    35  // scope, if any. The comment is for debugging only.
    36  func NewScope(parent *Scope, pos, end token.Pos, comment string) *Scope {
    37  	s := &Scope{parent, nil, nil, pos, end, comment, false}
    38  	// don't add children to Universe scope!
    39  	if parent != nil && parent != Universe {
    40  		parent.children = append(parent.children, s)
    41  	}
    42  	return s
    43  }
    44  
    45  // Parent returns the scope's containing (parent) scope.
    46  func (s *Scope) Parent() *Scope { return s.parent }
    47  
    48  // Len() returns the number of scope elements.
    49  func (s *Scope) Len() int { return len(s.elems) }
    50  
    51  // Names returns the scope's element names in sorted order.
    52  func (s *Scope) Names() []string {
    53  	names := make([]string, len(s.elems))
    54  	i := 0
    55  	for name := range s.elems {
    56  		names[i] = name
    57  		i++
    58  	}
    59  	sort.Strings(names)
    60  	return names
    61  }
    62  
    63  // NumChildren() returns the number of scopes nested in s.
    64  func (s *Scope) NumChildren() int { return len(s.children) }
    65  
    66  // Child returns the i'th child scope for 0 <= i < NumChildren().
    67  func (s *Scope) Child(i int) *Scope { return s.children[i] }
    68  
    69  // Lookup returns the object in scope s with the given name if such an
    70  // object exists; otherwise the result is nil.
    71  func (s *Scope) Lookup(name string) Object {
    72  	return s.elems[name]
    73  }
    74  
    75  // LookupParent follows the parent chain of scopes starting with s until
    76  // it finds a scope where Lookup(name) returns a non-nil object, and then
    77  // returns that scope and object. If a valid position pos is provided,
    78  // only objects that were declared at or before pos are considered.
    79  // If no such scope and object exists, the result is (nil, nil).
    80  //
    81  // Note that obj.Parent() may be different from the returned scope if the
    82  // object was inserted into the scope and already had a parent at that
    83  // time (see Insert, below). This can only happen for dot-imported objects
    84  // whose scope is the scope of the package that exported them.
    85  func (s *Scope) LookupParent(name string, pos token.Pos) (*Scope, Object) {
    86  	for ; s != nil; s = s.parent {
    87  		if obj := s.elems[name]; obj != nil && (!pos.IsValid() || obj.scopePos() <= pos) {
    88  			return s, obj
    89  		}
    90  	}
    91  	return nil, nil
    92  }
    93  
    94  // Insert attempts to insert an object obj into scope s.
    95  // If s already contains an alternative object alt with
    96  // the same name, Insert leaves s unchanged and returns alt.
    97  // Otherwise it inserts obj, sets the object's parent scope
    98  // if not already set, and returns nil.
    99  func (s *Scope) Insert(obj Object) Object {
   100  	name := obj.Name()
   101  	if alt := s.elems[name]; alt != nil {
   102  		return alt
   103  	}
   104  	if s.elems == nil {
   105  		s.elems = make(map[string]Object)
   106  	}
   107  	s.elems[name] = obj
   108  	if obj.Parent() == nil {
   109  		obj.setParent(s)
   110  	}
   111  	return nil
   112  }
   113  
   114  // Pos and End describe the scope's source code extent [pos, end).
   115  // The results are guaranteed to be valid only if the type-checked
   116  // AST has complete position information. The extent is undefined
   117  // for Universe and package scopes.
   118  func (s *Scope) Pos() token.Pos { return s.pos }
   119  func (s *Scope) End() token.Pos { return s.end }
   120  
   121  // Contains returns true if pos is within the scope's extent.
   122  // The result is guaranteed to be valid only if the type-checked
   123  // AST has complete position information.
   124  func (s *Scope) Contains(pos token.Pos) bool {
   125  	return s.pos <= pos && pos < s.end
   126  }
   127  
   128  // Innermost returns the innermost (child) scope containing
   129  // pos. If pos is not within any scope, the result is nil.
   130  // The result is also nil for the Universe scope.
   131  // The result is guaranteed to be valid only if the type-checked
   132  // AST has complete position information.
   133  func (s *Scope) Innermost(pos token.Pos) *Scope {
   134  	// Package scopes do not have extents since they may be
   135  	// discontiguous, so iterate over the package's files.
   136  	if s.parent == Universe {
   137  		for _, s := range s.children {
   138  			if inner := s.Innermost(pos); inner != nil {
   139  				return inner
   140  			}
   141  		}
   142  	}
   143  
   144  	if s.Contains(pos) {
   145  		for _, s := range s.children {
   146  			if s.Contains(pos) {
   147  				return s.Innermost(pos)
   148  			}
   149  		}
   150  		return s
   151  	}
   152  	return nil
   153  }
   154  
   155  // WriteTo writes a string representation of the scope to w,
   156  // with the scope elements sorted by name.
   157  // The level of indentation is controlled by n >= 0, with
   158  // n == 0 for no indentation.
   159  // If recurse is set, it also writes nested (children) scopes.
   160  func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
   161  	const ind = ".  "
   162  	indn := strings.Repeat(ind, n)
   163  
   164  	fmt.Fprintf(w, "%s%s scope %p {", indn, s.comment, s)
   165  	if len(s.elems) == 0 {
   166  		fmt.Fprintf(w, "}\n")
   167  		return
   168  	}
   169  
   170  	fmt.Fprintln(w)
   171  	indn1 := indn + ind
   172  	for _, name := range s.Names() {
   173  		fmt.Fprintf(w, "%s%s\n", indn1, s.elems[name])
   174  	}
   175  
   176  	if recurse {
   177  		for _, s := range s.children {
   178  			fmt.Fprintln(w)
   179  			s.WriteTo(w, n+1, recurse)
   180  		}
   181  	}
   182  
   183  	fmt.Fprintf(w, "%s}", indn)
   184  }
   185  
   186  // String returns a string representation of the scope, for debugging.
   187  func (s *Scope) String() string {
   188  	var buf bytes.Buffer
   189  	s.WriteTo(&buf, 0, false)
   190  	return buf.String()
   191  }
   192  

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