go/ast: deprecate Object

The following declarations related to syntactic object resolution
are now deprecated:
- Ident.Obj
- Object
- Scope
- File.{Scope,Unresolved}
- Importer
- Package, NewPackage
New programs should use the type checker instead.

Updates golang/go#52463
Updates golang/go#48141

Change-Id: I82b315f49b1341c11ae20dcbf81106084bd2ba86
Reviewed-on: https://go-review.googlesource.com/c/go/+/504915
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>

api/go1.21.txt

@@ -167,7 +167,12 @@ pkg errors, var ErrUnsupported error #41198
 pkg flag, func BoolFunc(string, string, func(string) error) #53747
 pkg flag, method (*FlagSet) BoolFunc(string, string, func(string) error) #53747
 pkg go/ast, func IsGenerated(*File) bool #28089
+pkg go/ast, func NewPackage //deprecated #52463
 pkg go/ast, type File struct, GoVersion string #59033
+pkg go/ast, type Importer //deprecated #52463
+pkg go/ast, type Object //deprecated #52463
+pkg go/ast, type Package //deprecated #52463
+pkg go/ast, type Scope //deprecated #52463
 pkg go/build/constraint, func GoVersion(Expr) string #59033
 pkg go/build, type Directive struct #56986
 pkg go/build, type Directive struct, Pos token.Position #56986

src/go/ast/ast.go

@@ -287,7 +287,7 @@ type (
 	Ident struct {
 		NamePos token.Pos // identifier position
 		Name    string    // identifier name
-		Obj     *Object   // denoted object; or nil
+		Obj     *Object   // denoted object, or nil. Deprecated: see Object.
 	}
 
 	// An Ellipsis node stands for the "..." type in a
@@ -1042,9 +1042,9 @@ type File struct {
 	Decls   []Decl        // top-level declarations; or nil
 
 	FileStart, FileEnd token.Pos       // start and end of entire file
-	Scope              *Scope          // package scope (this file only)
+	Scope              *Scope          // package scope (this file only). Deprecated: see Object
 	Imports            []*ImportSpec   // imports in this file
-	Unresolved         []*Ident        // unresolved identifiers in this file
+	Unresolved         []*Ident        // unresolved identifiers in this file. Deprecated: see Object
 	Comments           []*CommentGroup // list of all comments in the source file
 	GoVersion          string          // minimum Go version required by //go:build or // +build directives
 }
@@ -1064,6 +1064,8 @@ func (f *File) End() token.Pos {
 
 // A Package node represents a set of source files
 // collectively building a Go package.
+//
+// Deprecated: use the type checker [go/types] instead; see [Object].
 type Package struct {
 	Name    string             // package name
 	Scope   *Scope             // package scope across all files

src/go/ast/resolve.go

@@ -60,6 +60,8 @@ func resolve(scope *Scope, ident *Ident) bool {
 // Importer should load the package data for the given path into
 // a new *Object (pkg), record pkg in the imports map, and then
 // return pkg.
+//
+// Deprecated: use the type checker [go/types] instead; see [Object].
 type Importer func(imports map[string]*Object, path string) (pkg *Object, err error)
 
 // NewPackage creates a new Package node from a set of File nodes. It resolves
@@ -70,6 +72,8 @@ type Importer func(imports map[string]*Object, path string) (pkg *Object, err er
 // belong to different packages, one package name is selected and files with
 // different package names are reported and then ignored.
 // The result is a package node and a scanner.ErrorList if there were errors.
+//
+// Deprecated: use the type checker [go/types] instead; see [Object].
 func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, universe *Scope) (*Package, error) {
 	var p pkgBuilder
 	p.fset = fset

src/go/ast/scope.go

@@ -15,6 +15,8 @@ import (
 // A Scope maintains the set of named language entities declared
 // in the scope and a link to the immediately surrounding (outer)
 // scope.
+//
+// Deprecated: use the type checker [go/types] instead; see [Object].
 type Scope struct {
 	Outer   *Scope
 	Objects map[string]*Object
@@ -69,6 +71,19 @@ func (s *Scope) String() string {
 //	Kind    Data type         Data value
 //	Pkg     *Scope            package scope
 //	Con     int               iota for the respective declaration
+//
+// Deprecated: The relationship between Idents and Objects cannot be
+// correctly computed without type information. For example, the
+// expression T{K: 0} may denote a struct, map, slice, or array
+// literal, depending on the type of T. If T is a struct, then K
+// refers to a field of T, whereas for the other types it refers to a
+// value in the environment.
+//
+// New programs should set the [parser.SkipObjectResolution] parser
+// flag to disable syntactic object resolution (which also saves CPU
+// and memory), and instead use the type checker [go/types] if object
+// resolution is desired. See the Defs, Uses, and Implicits fields of
+// the [types.Info] struct for details.
 type Object struct {
 	Kind ObjKind
 	Name string // declared name

src/go/parser/interface.go

@@ -53,7 +53,7 @@ const (
 	Trace                                             // print a trace of parsed productions
 	DeclarationErrors                                 // report declaration errors
 	SpuriousErrors                                    // same as AllErrors, for backward-compatibility
-	SkipObjectResolution                              // don't resolve identifiers to objects - see ParseFile
+	SkipObjectResolution                              // skip deprecated identifier resolution; see ParseFile
 	AllErrors            = SpuriousErrors             // report all errors (not just the first 10 on different lines)
 )
 
@@ -66,10 +66,12 @@ const (
 // for the src parameter must be string, []byte, or io.Reader.
 // If src == nil, ParseFile parses the file specified by filename.
 //
-// The mode parameter controls the amount of source text parsed and other
+// The mode parameter controls the amount of source text parsed and
-// optional parser functionality. If the SkipObjectResolution mode bit is set,
+// other optional parser functionality. If the SkipObjectResolution
-// the object resolution phase of parsing will be skipped, causing File.Scope,
+// mode bit is set (recommended), the object resolution phase of
-// File.Unresolved, and all Ident.Obj fields to be nil.
+// parsing will be skipped, causing File.Scope, File.Unresolved, and
+// all Ident.Obj fields to be nil. Those fields are deprecated; see
+// [ast.Object] for details.
 //
 // Position information is recorded in the file set fset, which must not be
 // nil.