Source file src/go/types/object.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  package types
     6  
     7  import (
     8  	"bytes"
     9  	"fmt"
    10  	"go/constant"
    11  	"go/token"
    12  )
    13  
    14  // An Object describes a named language entity such as a package,
    15  // constant, type, variable, function (incl. methods), or label.
    16  // All objects implement the Object interface.
    17  //
    18  type Object interface {
    19  	Parent() *Scope // scope in which this object is declared; nil for methods and struct fields
    20  	Pos() token.Pos // position of object identifier in declaration
    21  	Pkg() *Package  // package to which this object belongs; nil for labels and objects in the Universe scope
    22  	Name() string   // package local object name
    23  	Type() Type     // object type
    24  	Exported() bool // reports whether the name starts with a capital letter
    25  	Id() string     // object name if exported, qualified name if not exported (see func Id)
    26  
    27  	// String returns a human-readable string of the object.
    28  	String() string
    29  
    30  	// order reflects a package-level object's source order: if object
    31  	// a is before object b in the source, then a.order() < b.order().
    32  	// order returns a value > 0 for package-level objects; it returns
    33  	// 0 for all other objects (including objects in file scopes).
    34  	order() uint32
    35  
    36  	// color returns the object's color.
    37  	color() color
    38  
    39  	// setOrder sets the order number of the object. It must be > 0.
    40  	setOrder(uint32)
    41  
    42  	// setColor sets the object's color. It must not be white.
    43  	setColor(color color)
    44  
    45  	// setParent sets the parent scope of the object.
    46  	setParent(*Scope)
    47  
    48  	// sameId reports whether obj.Id() and Id(pkg, name) are the same.
    49  	sameId(pkg *Package, name string) bool
    50  
    51  	// scopePos returns the start position of the scope of this Object
    52  	scopePos() token.Pos
    53  
    54  	// setScopePos sets the start position of the scope for this Object.
    55  	setScopePos(pos token.Pos)
    56  }
    57  
    58  // Id returns name if it is exported, otherwise it
    59  // returns the name qualified with the package path.
    60  func Id(pkg *Package, name string) string {
    61  	if token.IsExported(name) {
    62  		return name
    63  	}
    64  	// unexported names need the package path for differentiation
    65  	// (if there's no package, make sure we don't start with '.'
    66  	// as that may change the order of methods between a setup
    67  	// inside a package and outside a package - which breaks some
    68  	// tests)
    69  	path := "_"
    70  	// pkg is nil for objects in Universe scope and possibly types
    71  	// introduced via Eval (see also comment in object.sameId)
    72  	if pkg != nil && pkg.path != "" {
    73  		path = pkg.path
    74  	}
    75  	return path + "." + name
    76  }
    77  
    78  // An object implements the common parts of an Object.
    79  type object struct {
    80  	parent    *Scope
    81  	pos       token.Pos
    82  	pkg       *Package
    83  	name      string
    84  	typ       Type
    85  	order_    uint32
    86  	color_    color
    87  	scopePos_ token.Pos
    88  }
    89  
    90  // color encodes the color of an object (see Checker.objDecl for details).
    91  type color uint32
    92  
    93  // An object may be painted in one of three colors.
    94  // Color values other than white or black are considered grey.
    95  const (
    96  	white color = iota
    97  	black
    98  	grey // must be > white and black
    99  )
   100  
   101  func (c color) String() string {
   102  	switch c {
   103  	case white:
   104  		return "white"
   105  	case black:
   106  		return "black"
   107  	default:
   108  		return "grey"
   109  	}
   110  }
   111  
   112  // colorFor returns the (initial) color for an object depending on
   113  // whether its type t is known or not.
   114  func colorFor(t Type) color {
   115  	if t != nil {
   116  		return black
   117  	}
   118  	return white
   119  }
   120  
   121  // Parent returns the scope in which the object is declared.
   122  // The result is nil for methods and struct fields.
   123  func (obj *object) Parent() *Scope { return obj.parent }
   124  
   125  // Pos returns the declaration position of the object's identifier.
   126  func (obj *object) Pos() token.Pos { return obj.pos }
   127  
   128  // Pkg returns the package to which the object belongs.
   129  // The result is nil for labels and objects in the Universe scope.
   130  func (obj *object) Pkg() *Package { return obj.pkg }
   131  
   132  // Name returns the object's (package-local, unqualified) name.
   133  func (obj *object) Name() string { return obj.name }
   134  
   135  // Type returns the object's type.
   136  func (obj *object) Type() Type { return obj.typ }
   137  
   138  // Exported reports whether the object is exported (starts with a capital letter).
   139  // It doesn't take into account whether the object is in a local (function) scope
   140  // or not.
   141  func (obj *object) Exported() bool { return token.IsExported(obj.name) }
   142  
   143  // Id is a wrapper for Id(obj.Pkg(), obj.Name()).
   144  func (obj *object) Id() string { return Id(obj.pkg, obj.name) }
   145  
   146  func (obj *object) String() string      { panic("abstract") }
   147  func (obj *object) order() uint32       { return obj.order_ }
   148  func (obj *object) color() color        { return obj.color_ }
   149  func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
   150  
   151  func (obj *object) setParent(parent *Scope)   { obj.parent = parent }
   152  func (obj *object) setOrder(order uint32)     { assert(order > 0); obj.order_ = order }
   153  func (obj *object) setColor(color color)      { assert(color != white); obj.color_ = color }
   154  func (obj *object) setScopePos(pos token.Pos) { obj.scopePos_ = pos }
   155  
   156  func (obj *object) sameId(pkg *Package, name string) bool {
   157  	// spec:
   158  	// "Two identifiers are different if they are spelled differently,
   159  	// or if they appear in different packages and are not exported.
   160  	// Otherwise, they are the same."
   161  	if name != obj.name {
   162  		return false
   163  	}
   164  	// obj.Name == name
   165  	if obj.Exported() {
   166  		return true
   167  	}
   168  	// not exported, so packages must be the same (pkg == nil for
   169  	// fields in Universe scope; this can only happen for types
   170  	// introduced via Eval)
   171  	if pkg == nil || obj.pkg == nil {
   172  		return pkg == obj.pkg
   173  	}
   174  	// pkg != nil && obj.pkg != nil
   175  	return pkg.path == obj.pkg.path
   176  }
   177  
   178  // A PkgName represents an imported Go package.
   179  // PkgNames don't have a type.
   180  type PkgName struct {
   181  	object
   182  	imported *Package
   183  	used     bool // set if the package was used
   184  }
   185  
   186  // NewPkgName returns a new PkgName object representing an imported package.
   187  // The remaining arguments set the attributes found with all Objects.
   188  func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
   189  	return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, black, token.NoPos}, imported, false}
   190  }
   191  
   192  // Imported returns the package that was imported.
   193  // It is distinct from Pkg(), which is the package containing the import statement.
   194  func (obj *PkgName) Imported() *Package { return obj.imported }
   195  
   196  // A Const represents a declared constant.
   197  type Const struct {
   198  	object
   199  	val constant.Value
   200  }
   201  
   202  // NewConst returns a new constant with value val.
   203  // The remaining arguments set the attributes found with all Objects.
   204  func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
   205  	return &Const{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, val}
   206  }
   207  
   208  // Val returns the constant's value.
   209  func (obj *Const) Val() constant.Value { return obj.val }
   210  
   211  func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
   212  
   213  // A TypeName represents a name for a (defined or alias) type.
   214  type TypeName struct {
   215  	object
   216  }
   217  
   218  // NewTypeName returns a new type name denoting the given typ.
   219  // The remaining arguments set the attributes found with all Objects.
   220  //
   221  // The typ argument may be a defined (Named) type or an alias type.
   222  // It may also be nil such that the returned TypeName can be used as
   223  // argument for NewNamed, which will set the TypeName's type as a side-
   224  // effect.
   225  func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
   226  	return &TypeName{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
   227  }
   228  
   229  // IsAlias reports whether obj is an alias name for a type.
   230  func (obj *TypeName) IsAlias() bool {
   231  	switch t := obj.typ.(type) {
   232  	case nil:
   233  		return false
   234  	case *Basic:
   235  		// unsafe.Pointer is not an alias.
   236  		if obj.pkg == Unsafe {
   237  			return false
   238  		}
   239  		// Any user-defined type name for a basic type is an alias for a
   240  		// basic type (because basic types are pre-declared in the Universe
   241  		// scope, outside any package scope), and so is any type name with
   242  		// a different name than the name of the basic type it refers to.
   243  		// Additionally, we need to look for "byte" and "rune" because they
   244  		// are aliases but have the same names (for better error messages).
   245  		return obj.pkg != nil || t.name != obj.name || t == universeByte || t == universeRune
   246  	case *Named:
   247  		return obj != t.obj
   248  	default:
   249  		return true
   250  	}
   251  }
   252  
   253  // A Variable represents a declared variable (including function parameters and results, and struct fields).
   254  type Var struct {
   255  	object
   256  	embedded bool // if set, the variable is an embedded struct field, and name is the type name
   257  	isField  bool // var is struct field
   258  	used     bool // set if the variable was used
   259  }
   260  
   261  // NewVar returns a new variable.
   262  // The arguments set the attributes found with all Objects.
   263  func NewVar(pos token.Pos, pkg *Package, name string, typ Type) *Var {
   264  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}}
   265  }
   266  
   267  // NewParam returns a new variable representing a function parameter.
   268  func NewParam(pos token.Pos, pkg *Package, name string, typ Type) *Var {
   269  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, used: true} // parameters are always 'used'
   270  }
   271  
   272  // NewField returns a new variable representing a struct field.
   273  // For embedded fields, the name is the unqualified type name
   274  /// under which the field is accessible.
   275  func NewField(pos token.Pos, pkg *Package, name string, typ Type, embedded bool) *Var {
   276  	return &Var{object: object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, embedded: embedded, isField: true}
   277  }
   278  
   279  // Anonymous reports whether the variable is an embedded field.
   280  // Same as Embedded; only present for backward-compatibility.
   281  func (obj *Var) Anonymous() bool { return obj.embedded }
   282  
   283  // Embedded reports whether the variable is an embedded field.
   284  func (obj *Var) Embedded() bool { return obj.embedded }
   285  
   286  // IsField reports whether the variable is a struct field.
   287  func (obj *Var) IsField() bool { return obj.isField }
   288  
   289  func (*Var) isDependency() {} // a variable may be a dependency of an initialization expression
   290  
   291  // A Func represents a declared function, concrete method, or abstract
   292  // (interface) method. Its Type() is always a *Signature.
   293  // An abstract method may belong to many interfaces due to embedding.
   294  type Func struct {
   295  	object
   296  	hasPtrRecv bool // only valid for methods that don't have a type yet
   297  }
   298  
   299  // NewFunc returns a new function with the given signature, representing
   300  // the function's type.
   301  func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
   302  	// don't store a nil signature
   303  	var typ Type
   304  	if sig != nil {
   305  		typ = sig
   306  	}
   307  	return &Func{object{nil, pos, pkg, name, typ, 0, colorFor(typ), token.NoPos}, false}
   308  }
   309  
   310  // FullName returns the package- or receiver-type-qualified name of
   311  // function or method obj.
   312  func (obj *Func) FullName() string {
   313  	var buf bytes.Buffer
   314  	writeFuncName(&buf, obj, nil)
   315  	return buf.String()
   316  }
   317  
   318  // Scope returns the scope of the function's body block.
   319  func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
   320  
   321  func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
   322  
   323  // A Label represents a declared label.
   324  // Labels don't have a type.
   325  type Label struct {
   326  	object
   327  	used bool // set if the label was used
   328  }
   329  
   330  // NewLabel returns a new label.
   331  func NewLabel(pos token.Pos, pkg *Package, name string) *Label {
   332  	return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid], color_: black}, false}
   333  }
   334  
   335  // A Builtin represents a built-in function.
   336  // Builtins don't have a valid type.
   337  type Builtin struct {
   338  	object
   339  	id builtinId
   340  }
   341  
   342  func newBuiltin(id builtinId) *Builtin {
   343  	return &Builtin{object{name: predeclaredFuncs[id].name, typ: Typ[Invalid], color_: black}, id}
   344  }
   345  
   346  // Nil represents the predeclared value nil.
   347  type Nil struct {
   348  	object
   349  }
   350  
   351  func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
   352  	var tname *TypeName
   353  	typ := obj.Type()
   354  
   355  	switch obj := obj.(type) {
   356  	case *PkgName:
   357  		fmt.Fprintf(buf, "package %s", obj.Name())
   358  		if path := obj.imported.path; path != "" && path != obj.name {
   359  			fmt.Fprintf(buf, " (%q)", path)
   360  		}
   361  		return
   362  
   363  	case *Const:
   364  		buf.WriteString("const")
   365  
   366  	case *TypeName:
   367  		tname = obj
   368  		buf.WriteString("type")
   369  
   370  	case *Var:
   371  		if obj.isField {
   372  			buf.WriteString("field")
   373  		} else {
   374  			buf.WriteString("var")
   375  		}
   376  
   377  	case *Func:
   378  		buf.WriteString("func ")
   379  		writeFuncName(buf, obj, qf)
   380  		if typ != nil {
   381  			WriteSignature(buf, typ.(*Signature), qf)
   382  		}
   383  		return
   384  
   385  	case *Label:
   386  		buf.WriteString("label")
   387  		typ = nil
   388  
   389  	case *Builtin:
   390  		buf.WriteString("builtin")
   391  		typ = nil
   392  
   393  	case *Nil:
   394  		buf.WriteString("nil")
   395  		return
   396  
   397  	default:
   398  		panic(fmt.Sprintf("writeObject(%T)", obj))
   399  	}
   400  
   401  	buf.WriteByte(' ')
   402  
   403  	// For package-level objects, qualify the name.
   404  	if obj.Pkg() != nil && obj.Pkg().scope.Lookup(obj.Name()) == obj {
   405  		writePackage(buf, obj.Pkg(), qf)
   406  	}
   407  	buf.WriteString(obj.Name())
   408  
   409  	if typ == nil {
   410  		return
   411  	}
   412  
   413  	if tname != nil {
   414  		// We have a type object: Don't print anything more for
   415  		// basic types since there's no more information (names
   416  		// are the same; see also comment in TypeName.IsAlias).
   417  		if _, ok := typ.(*Basic); ok {
   418  			return
   419  		}
   420  		if tname.IsAlias() {
   421  			buf.WriteString(" =")
   422  		} else {
   423  			typ = typ.Underlying()
   424  		}
   425  	}
   426  
   427  	buf.WriteByte(' ')
   428  	WriteType(buf, typ, qf)
   429  }
   430  
   431  func writePackage(buf *bytes.Buffer, pkg *Package, qf Qualifier) {
   432  	if pkg == nil {
   433  		return
   434  	}
   435  	var s string
   436  	if qf != nil {
   437  		s = qf(pkg)
   438  	} else {
   439  		s = pkg.Path()
   440  	}
   441  	if s != "" {
   442  		buf.WriteString(s)
   443  		buf.WriteByte('.')
   444  	}
   445  }
   446  
   447  // ObjectString returns the string form of obj.
   448  // The Qualifier controls the printing of
   449  // package-level objects, and may be nil.
   450  func ObjectString(obj Object, qf Qualifier) string {
   451  	var buf bytes.Buffer
   452  	writeObject(&buf, obj, qf)
   453  	return buf.String()
   454  }
   455  
   456  func (obj *PkgName) String() string  { return ObjectString(obj, nil) }
   457  func (obj *Const) String() string    { return ObjectString(obj, nil) }
   458  func (obj *TypeName) String() string { return ObjectString(obj, nil) }
   459  func (obj *Var) String() string      { return ObjectString(obj, nil) }
   460  func (obj *Func) String() string     { return ObjectString(obj, nil) }
   461  func (obj *Label) String() string    { return ObjectString(obj, nil) }
   462  func (obj *Builtin) String() string  { return ObjectString(obj, nil) }
   463  func (obj *Nil) String() string      { return ObjectString(obj, nil) }
   464  
   465  func writeFuncName(buf *bytes.Buffer, f *Func, qf Qualifier) {
   466  	if f.typ != nil {
   467  		sig := f.typ.(*Signature)
   468  		if recv := sig.Recv(); recv != nil {
   469  			buf.WriteByte('(')
   470  			if _, ok := recv.Type().(*Interface); ok {
   471  				// gcimporter creates abstract methods of
   472  				// named interfaces using the interface type
   473  				// (not the named type) as the receiver.
   474  				// Don't print it in full.
   475  				buf.WriteString("interface")
   476  			} else {
   477  				WriteType(buf, recv.Type(), qf)
   478  			}
   479  			buf.WriteByte(')')
   480  			buf.WriteByte('.')
   481  		} else if f.pkg != nil {
   482  			writePackage(buf, f.pkg, qf)
   483  		}
   484  	}
   485  	buf.WriteString(f.name)
   486  }
   487  

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