go/types: add doc strings to various undocumented exported objects

Fixes #22747.

Change-Id: I498cb29f18bd9b59b13dc2ddc3a613cc12ac2a14
Reviewed-on: https://go-review.googlesource.com/110975Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/go/types/object.go

@@ -81,13 +81,31 @@ type object struct {
 	scopePos_ token.Pos
 }
 
+// Parent returns the scope in which the object is declared.
+// The result is nil for methods and struct fields.
 func (obj *object) Parent() *Scope { return obj.parent }
+
+// Pos returns the declaration position of the object's identifier.
 func (obj *object) Pos() token.Pos { return obj.pos }
+
+// Pkg returns the package to which the object belongs.
+// The result is nil for labels and objects in the Universe scope.
 func (obj *object) Pkg() *Package { return obj.pkg }
+
+// Name returns the object's (package-local, unqualified) name.
 func (obj *object) Name() string { return obj.name }
+
+// Type returns the object's type.
 func (obj *object) Type() Type { return obj.typ }
+
+// Exported reports whether the object is exported (starts with a capital letter).
+// It doesn't take into account whether the object is in a local (function) scope
+// or not.
 func (obj *object) Exported() bool { return ast.IsExported(obj.name) }
+
+// Id is a wrapper for Id(obj.Pkg(), obj.Name()).
 func (obj *object) Id() string { return Id(obj.pkg, obj.name) }
+
 func (obj *object) String() string      { panic("abstract") }
 func (obj *object) order() uint32       { return obj.order_ }
 func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
@@ -149,10 +167,12 @@ func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.V
 	return &Const{object{nil, pos, pkg, name, typ, 0, token.NoPos}, val, false}
 }
 
+// Val returns the constant's value.
 func (obj *Const) Val() constant.Value { return obj.val }
+
 func (*Const) isDependency() {} // a constant may be a dependency of an initialization expression
 
-// A TypeName represents a name for a (named or alias) type.
+// A TypeName represents a name for a (defined or alias) type.
 type TypeName struct {
 	object
 }

src/go/types/universe.go

@@ -12,9 +12,15 @@ import (
 	"strings"
 )
 
+// The Universe scope contains all predeclared objects of Go.
+// It is the outermost scope of any chain of nested scopes.
+var Universe *Scope
+
+// The Unsafe package is the package returned by an importer
+// for the import path "unsafe".
+var Unsafe *Package
+
 var (
-	Universe     *Scope
-	Unsafe       *Package
 	universeIota *Const
 	universeByte *Basic // uint8 alias, but has name "byte"
 	universeRune *Basic // int32 alias, but has name "rune"