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

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