methodset.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 method sets.
     6  
     7  package types
     8  
     9  import (
    10  	"fmt"
    11  	"sort"
    12  	"strings"
    13  )
    14  
    15  // A MethodSet is an ordered set of concrete or abstract (interface) methods;
    16  // a method is a [MethodVal] selection, and they are ordered by ascending m.Obj().Id().
    17  // The zero value for a MethodSet is a ready-to-use empty method set.
    18  type MethodSet struct {
    19  	list []*Selection
    20  }
    21  
    22  func (s *MethodSet) String() string {
    23  	if s.Len() == 0 {
    24  		return "MethodSet {}"
    25  	}
    26  
    27  	var buf strings.Builder
    28  	fmt.Fprintln(&buf, "MethodSet {")
    29  	for _, f := range s.list {
    30  		fmt.Fprintf(&buf, "\t%s\n", f)
    31  	}
    32  	fmt.Fprintln(&buf, "}")
    33  	return buf.String()
    34  }
    35  
    36  // Len returns the number of methods in s.
    37  func (s *MethodSet) Len() int { return len(s.list) }
    38  
    39  // At returns the i'th method in s for 0 <= i < s.Len().
    40  func (s *MethodSet) At(i int) *Selection { return s.list[i] }
    41  
    42  // Lookup returns the method with matching package and name, or nil if not found.
    43  func (s *MethodSet) Lookup(pkg *Package, name string) *Selection {
    44  	if s.Len() == 0 {
    45  		return nil
    46  	}
    47  
    48  	key := Id(pkg, name)
    49  	i := sort.Search(len(s.list), func(i int) bool {
    50  		m := s.list[i]
    51  		return m.obj.Id() >= key
    52  	})
    53  	if i < len(s.list) {
    54  		m := s.list[i]
    55  		if m.obj.Id() == key {
    56  			return m
    57  		}
    58  	}
    59  	return nil
    60  }
    61  
    62  // Shared empty method set.
    63  var emptyMethodSet MethodSet
    64  
    65  // Note: NewMethodSet is intended for external use only as it
    66  //       requires interfaces to be complete. It may be used
    67  //       internally if LookupFieldOrMethod completed the same
    68  //       interfaces beforehand.
    69  
    70  // NewMethodSet returns the method set for the given type T.
    71  // It always returns a non-nil method set, even if it is empty.
    72  func NewMethodSet(T Type) *MethodSet {
    73  	// WARNING: The code in this function is extremely subtle - do not modify casually!
    74  	//          This function and lookupFieldOrMethod should be kept in sync.
    75  
    76  	// TODO(rfindley) confirm that this code is in sync with lookupFieldOrMethod
    77  	//                with respect to type params.
    78  
    79  	// Methods cannot be associated with a named pointer type.
    80  	// (spec: "The type denoted by T is called the receiver base type;
    81  	// it must not be a pointer or interface type and it must be declared
    82  	// in the same package as the method.").
    83  	if t := asNamed(T); t != nil && isPointer(t) {
    84  		return &emptyMethodSet
    85  	}
    86  
    87  	// method set up to the current depth, allocated lazily
    88  	var base methodSet
    89  
    90  	typ, isPtr := deref(T)
    91  
    92  	// *typ where typ is an interface has no methods.
    93  	if isPtr && IsInterface(typ) {
    94  		return &emptyMethodSet
    95  	}
    96  
    97  	// Start with typ as single entry at shallowest depth.
    98  	current := []embeddedType{{typ, nil, isPtr, false}}
    99  
   100  	// seen tracks named types that we have seen already, allocated lazily.
   101  	// Used to avoid endless searches in case of recursive types.
   102  	//
   103  	// We must use a lookup on identity rather than a simple map[*Named]bool as
   104  	// instantiated types may be identical but not equal.
   105  	var seen instanceLookup
   106  
   107  	// collect methods at current depth
   108  	for len(current) > 0 {
   109  		var next []embeddedType // embedded types found at current depth
   110  
   111  		// field and method sets at current depth, indexed by names (Id's), and allocated lazily
   112  		var fset map[string]bool // we only care about the field names
   113  		var mset methodSet
   114  
   115  		for _, e := range current {
   116  			typ := e.typ
   117  
   118  			// If we have a named type, we may have associated methods.
   119  			// Look for those first.
   120  			if named := asNamed(typ); named != nil {
   121  				if alt := seen.lookup(named); alt != nil {
   122  					// We have seen this type before, at a more shallow depth
   123  					// (note that multiples of this type at the current depth
   124  					// were consolidated before). The type at that depth shadows
   125  					// this same type at the current depth, so we can ignore
   126  					// this one.
   127  					continue
   128  				}
   129  				seen.add(named)
   130  
   131  				for i := 0; i < named.NumMethods(); i++ {
   132  					mset = mset.addOne(named.Method(i), concat(e.index, i), e.indirect, e.multiples)
   133  				}
   134  			}
   135  
   136  			switch t := under(typ).(type) {
   137  			case *Struct:
   138  				for i, f := range t.fields {
   139  					if fset == nil {
   140  						fset = make(map[string]bool)
   141  					}
   142  					fset[f.Id()] = true
   143  
   144  					// Embedded fields are always of the form T or *T where
   145  					// T is a type name. If typ appeared multiple times at
   146  					// this depth, f.Type appears multiple times at the next
   147  					// depth.
   148  					if f.embedded {
   149  						typ, isPtr := deref(f.typ)
   150  						// TODO(gri) optimization: ignore types that can't
   151  						// have fields or methods (only Named, Struct, and
   152  						// Interface types need to be considered).
   153  						next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
   154  					}
   155  				}
   156  
   157  			case *Interface:
   158  				mset = mset.add(t.typeSet().methods, e.index, true, e.multiples)
   159  			}
   160  		}
   161  
   162  		// Add methods and collisions at this depth to base if no entries with matching
   163  		// names exist already.
   164  		for k, m := range mset {
   165  			if _, found := base[k]; !found {
   166  				// Fields collide with methods of the same name at this depth.
   167  				if fset[k] {
   168  					m = nil // collision
   169  				}
   170  				if base == nil {
   171  					base = make(methodSet)
   172  				}
   173  				base[k] = m
   174  			}
   175  		}
   176  
   177  		// Add all (remaining) fields at this depth as collisions (since they will
   178  		// hide any method further down) if no entries with matching names exist already.
   179  		for k := range fset {
   180  			if _, found := base[k]; !found {
   181  				if base == nil {
   182  					base = make(methodSet)
   183  				}
   184  				base[k] = nil // collision
   185  			}
   186  		}
   187  
   188  		current = consolidateMultiples(next)
   189  	}
   190  
   191  	if len(base) == 0 {
   192  		return &emptyMethodSet
   193  	}
   194  
   195  	// collect methods
   196  	var list []*Selection
   197  	for _, m := range base {
   198  		if m != nil {
   199  			m.recv = T
   200  			list = append(list, m)
   201  		}
   202  	}
   203  	// sort by unique name
   204  	sort.Slice(list, func(i, j int) bool {
   205  		return list[i].obj.Id() < list[j].obj.Id()
   206  	})
   207  	return &MethodSet{list}
   208  }
   209  
   210  // A methodSet is a set of methods and name collisions.
   211  // A collision indicates that multiple methods with the
   212  // same unique id, or a field with that id appeared.
   213  type methodSet map[string]*Selection // a nil entry indicates a name collision
   214  
   215  // Add adds all functions in list to the method set s.
   216  // If multiples is set, every function in list appears multiple times
   217  // and is treated as a collision.
   218  func (s methodSet) add(list []*Func, index []int, indirect bool, multiples bool) methodSet {
   219  	if len(list) == 0 {
   220  		return s
   221  	}
   222  	for i, f := range list {
   223  		s = s.addOne(f, concat(index, i), indirect, multiples)
   224  	}
   225  	return s
   226  }
   227  
   228  func (s methodSet) addOne(f *Func, index []int, indirect bool, multiples bool) methodSet {
   229  	if s == nil {
   230  		s = make(methodSet)
   231  	}
   232  	key := f.Id()
   233  	// if f is not in the set, add it
   234  	if !multiples {
   235  		// TODO(gri) A found method may not be added because it's not in the method set
   236  		// (!indirect && f.hasPtrRecv()). A 2nd method on the same level may be in the method
   237  		// set and may not collide with the first one, thus leading to a false positive.
   238  		// Is that possible? Investigate.
   239  		if _, found := s[key]; !found && (indirect || !f.hasPtrRecv()) {
   240  			s[key] = &Selection{MethodVal, nil, f, index, indirect}
   241  			return s
   242  		}
   243  	}
   244  	s[key] = nil // collision
   245  	return s
   246  }
   247
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