go/ast resolver: properly maintain map of package global imports

- add Data field to ast.Object
- for package objects, the Data field holds the package scope
- resolve several TODOs

R=rsc
CC=golang-dev
https://golang.org/cl/4538069

7 files changed, 131 insertions, 95 deletions

diff --git a/src/pkg/go/ast/ast.go b/src/pkg/go/ast/ast.go
index d7221b3321..31602ec850 100644
--- a/src/pkg/go/ast/ast.go
+++ b/src/pkg/go/ast/ast.go
@@ -945,10 +945,10 @@ func (f *File) End() token.Pos {
 // collectively building a Go package.
 //
 type Package struct {
-	Name    string            // package name
-	Scope   *Scope            // package scope across all files
-	Imports map[string]*Scope // map of import path -> package scope
-	Files   map[string]*File  // Go source files by filename
+	Name    string             // package name
+	Scope   *Scope             // package scope across all files
+	Imports map[string]*Object // map of package id -> package object
+	Files   map[string]*File   // Go source files by filename
 }
 
 
diff --git a/src/pkg/go/ast/resolve.go b/src/pkg/go/ast/resolve.go
index a2ff620dae..ecd2e8a7c3 100644
--- a/src/pkg/go/ast/resolve.go
+++ b/src/pkg/go/ast/resolve.go
@@ -58,11 +58,16 @@ func resolve(scope *Scope, ident *Ident) bool {
 }
 
 
-// NewPackage uses an Importer to resolve imports. Given an importPath,
-// an importer returns the imported package's name, its scope of exported
-// objects, and an error, if any.
-//
-type Importer func(path string) (name string, scope *Scope, err os.Error)
+// An Importer resolves import paths to package Objects.
+// The imports map records the packages already imported,
+// indexed by package id (canonical import path).
+// An Importer must determine the canonical import path and
+// check the map to see if it is already present in the imports map.
+// If so, the Importer can return the map entry.  Otherwise, the
+// 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.
+type Importer func(imports map[string]*Object, path string) (pkg *Object, err os.Error)
 
 
 // NewPackage creates a new Package node from a set of File nodes. It resolves
@@ -97,14 +102,8 @@ func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer,
 		}
 	}
 
-	// imports maps import paths to package names and scopes
-	// TODO(gri): Eventually we like to get to the import scope from
-	//            a package object. Then we can have a map path -> Obj.
-	type importedPkg struct {
-		name  string
-		scope *Scope
-	}
-	imports := make(map[string]*importedPkg)
+	// package global mapping of imported package ids to package objects
+	imports := make(map[string]*Object)
 
 	// complete file scopes with imports and resolve identifiers
 	for _, file := range files {
@@ -118,41 +117,41 @@ func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer,
 		importErrors := false
 		fileScope := NewScope(pkgScope)
 		for _, spec := range file.Imports {
-			// add import to global map of imports
+			if importer == nil {
+				importErrors = true
+				continue
+			}
 			path, _ := strconv.Unquote(string(spec.Path.Value))
-			pkg := imports[path]
-			if pkg == nil {
-				if importer == nil {
-					importErrors = true
-					continue
-				}
-				name, scope, err := importer(path)
-				if err != nil {
-					p.errorf(spec.Path.Pos(), "could not import %s (%s)", path, err)
-					importErrors = true
-					continue
-				}
-				pkg = &importedPkg{name, scope}
-				imports[path] = pkg
-				// TODO(gri) If a local package name != "." is provided,
-				// global identifier resolution could proceed even if the
-				// import failed. Consider adjusting the logic here a bit.
+			pkg, err := importer(imports, path)
+			if err != nil {
+				p.errorf(spec.Path.Pos(), "could not import %s (%s)", path, err)
+				importErrors = true
+				continue
 			}
+			// TODO(gri) If a local package name != "." is provided,
+			// global identifier resolution could proceed even if the
+			// import failed. Consider adjusting the logic here a bit.
+
 			// local name overrides imported package name
-			name := pkg.name
+			name := pkg.Name
 			if spec.Name != nil {
 				name = spec.Name.Name
 			}
+
 			// add import to file scope
 			if name == "." {
 				// merge imported scope with file scope
-				for _, obj := range pkg.scope.Objects {
+				for _, obj := range pkg.Data.(*Scope).Objects {
 					p.declare(fileScope, pkgScope, obj)
 				}
 			} else {
 				// declare imported package object in file scope
+				// (do not re-use pkg in the file scope but create
+				// a new object instead; the Decl field is different
+				// for different files)
 				obj := NewObj(Pkg, name)
 				obj.Decl = spec
+				obj.Data = pkg.Data
 				p.declare(fileScope, pkgScope, obj)
 			}
 		}
@@ -178,11 +177,5 @@ func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer,
 		pkgScope.Outer = universe // reset universe scope
 	}
 
-	// collect all import paths and respective package scopes
-	importedScopes := make(map[string]*Scope)
-	for path, pkg := range imports {
-		importedScopes[path] = pkg.scope
-	}
-
-	return &Package{pkgName, pkgScope, importedScopes, files}, p.GetError(scanner.Sorted)
+	return &Package{pkgName, pkgScope, imports, files}, p.GetError(scanner.Sorted)
 }
diff --git a/src/pkg/go/ast/scope.go b/src/pkg/go/ast/scope.go
index 830d88aef4..b966f786fb 100644
--- a/src/pkg/go/ast/scope.go
+++ b/src/pkg/go/ast/scope.go
@@ -70,13 +70,24 @@ func (s *Scope) String() string {
 // ----------------------------------------------------------------------------
 // Objects
 
+// TODO(gri) Consider replacing the Object struct with an interface
+//           and a corresponding set of object implementations.
+
 // An Object describes a named language entity such as a package,
 // constant, type, variable, function (incl. methods), or label.
 //
+// The Data fields contains object-specific data:
+//
+//	Kind    Data type    Data value
+//	Pkg	*Scope       package scope
+//	Con     int          iota for the respective declaration
+//	Con     != nil       constant value
+//
 type Object struct {
 	Kind ObjKind
 	Name string      // declared name
 	Decl interface{} // corresponding Field, XxxSpec, FuncDecl, or LabeledStmt; or nil
+	Data interface{} // object-specific data; or nil
 	Type interface{} // place holder for type information; may be nil
 }
 
diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index 2bc550bac7..da1e0390b6 100644
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -131,13 +131,14 @@ func (p *parser) closeLabelScope() {
 }
 
 
-func (p *parser) declare(decl interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+func (p *parser) declare(decl, data interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
 	for _, ident := range idents {
 		assert(ident.Obj == nil, "identifier already declared or resolved")
 		obj := ast.NewObj(kind, ident.Name)
 		// remember the corresponding declaration for redeclaration
 		// errors and global variable resolution/typechecking phase
 		obj.Decl = decl
+		obj.Data = data
 		ident.Obj = obj
 		if ident.Name != "_" {
 			if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
@@ -596,7 +597,7 @@ func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
 	p.expectSemi() // call before accessing p.linecomment
 
 	field := &ast.Field{doc, idents, typ, tag, p.lineComment}
-	p.declare(field, scope, ast.Var, idents...)
+	p.declare(field, nil, scope, ast.Var, idents...)
 
 	return field
 }
@@ -707,7 +708,7 @@ func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params [
 		params = append(params, field)
 		// Go spec: The scope of an identifier denoting a function
 		// parameter or result variable is the function body.
-		p.declare(field, scope, ast.Var, idents...)
+		p.declare(field, nil, scope, ast.Var, idents...)
 		if p.tok == token.COMMA {
 			p.next()
 		}
@@ -719,7 +720,7 @@ func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params [
 			params = append(params, field)
 			// Go spec: The scope of an identifier denoting a function
 			// parameter or result variable is the function body.
-			p.declare(field, scope, ast.Var, idents...)
+			p.declare(field, nil, scope, ast.Var, idents...)
 			if p.tok != token.COMMA {
 				break
 			}
@@ -823,7 +824,7 @@ func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
 	p.expectSemi() // call before accessing p.linecomment
 
 	spec := &ast.Field{doc, idents, typ, nil, p.lineComment}
-	p.declare(spec, scope, ast.Fun, idents...)
+	p.declare(spec, nil, scope, ast.Fun, idents...)
 
 	return spec
 }
@@ -1477,7 +1478,7 @@ func (p *parser) parseSimpleStmt(labelOk bool) ast.Stmt {
 			// in which it is declared and excludes the body of any nested
 			// function.
 			stmt := &ast.LabeledStmt{label, colon, p.parseStmt()}
-			p.declare(stmt, p.labelScope, ast.Lbl, label)
+			p.declare(stmt, nil, p.labelScope, ast.Lbl, label)
 			return stmt
 		}
 		p.error(x[0].Pos(), "illegal label declaration")
@@ -2001,7 +2002,7 @@ func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
 	// the end of the innermost containing block.
 	// (Global identifiers are resolved in a separate phase after parsing.)
 	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
-	p.declare(spec, p.topScope, ast.Con, idents...)
+	p.declare(spec, iota, p.topScope, ast.Con, idents...)
 
 	return spec
 }
@@ -2019,7 +2020,7 @@ func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	// containing block.
 	// (Global identifiers are resolved in a separate phase after parsing.)
 	spec := &ast.TypeSpec{doc, ident, nil, nil}
-	p.declare(spec, p.topScope, ast.Typ, ident)
+	p.declare(spec, nil, p.topScope, ast.Typ, ident)
 
 	spec.Type = p.parseType()
 	p.expectSemi() // call before accessing p.linecomment
@@ -2048,7 +2049,7 @@ func parseVarSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	// the end of the innermost containing block.
 	// (Global identifiers are resolved in a separate phase after parsing.)
 	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
-	p.declare(spec, p.topScope, ast.Var, idents...)
+	p.declare(spec, nil, p.topScope, ast.Var, idents...)
 
 	return spec
 }
@@ -2140,7 +2141,7 @@ func (p *parser) parseFuncDecl() *ast.FuncDecl {
 		// init() functions cannot be referred to and there may
 		// be more than one - don't put them in the pkgScope
 		if ident.Name != "init" {
-			p.declare(decl, p.pkgScope, ast.Fun, ident)
+			p.declare(decl, nil, p.pkgScope, ast.Fun, ident)
 		}
 	}
 
diff --git a/src/pkg/go/types/gcimporter.go b/src/pkg/go/types/gcimporter.go
index 5acaf8ceaf..377c45ad65 100644
--- a/src/pkg/go/types/gcimporter.go
+++ b/src/pkg/go/types/gcimporter.go
@@ -74,15 +74,14 @@ func findPkg(path string) (filename, id string) {
 // object/archive file and populates its scope with the results.
 type gcParser struct {
 	scanner scanner.Scanner
-	tok     int                   // current token
-	lit     string                // literal string; only valid for Ident, Int, String tokens
-	id      string                // package id of imported package
-	scope   *ast.Scope            // scope of imported package; alias for deps[id]
-	deps    map[string]*ast.Scope // package id -> package scope
+	tok     int                    // current token
+	lit     string                 // literal string; only valid for Ident, Int, String tokens
+	id      string                 // package id of imported package
+	imports map[string]*ast.Object // package id -> package object
 }
 
 
-func (p *gcParser) init(filename, id string, src io.Reader) {
+func (p *gcParser) init(filename, id string, src io.Reader, imports map[string]*ast.Object) {
 	p.scanner.Init(src)
 	p.scanner.Error = func(_ *scanner.Scanner, msg string) { p.error(msg) }
 	p.scanner.Mode = scanner.ScanIdents | scanner.ScanInts | scanner.ScanStrings | scanner.ScanComments | scanner.SkipComments
@@ -90,8 +89,7 @@ func (p *gcParser) init(filename, id string, src io.Reader) {
 	p.scanner.Filename = filename // for good error messages
 	p.next()
 	p.id = id
-	p.scope = ast.NewScope(nil)
-	p.deps = map[string]*ast.Scope{"unsafe": Unsafe, id: p.scope}
+	p.imports = imports
 }
 
 
@@ -110,9 +108,9 @@ func (p *gcParser) next() {
 
 
 // GcImporter implements the ast.Importer signature.
-func GcImporter(path string) (name string, scope *ast.Scope, err os.Error) {
+func GcImporter(imports map[string]*ast.Object, path string) (pkg *ast.Object, err os.Error) {
 	if path == "unsafe" {
-		return path, Unsafe, nil
+		return Unsafe, nil
 	}
 
 	defer func() {
@@ -130,6 +128,10 @@ func GcImporter(path string) (name string, scope *ast.Scope, err os.Error) {
 		return
 	}
 
+	if pkg = imports[id]; pkg != nil {
+		return // package was imported before
+	}
+
 	buf, err := ExportData(filename)
 	if err != nil {
 		return
@@ -137,13 +139,12 @@ func GcImporter(path string) (name string, scope *ast.Scope, err os.Error) {
 	defer buf.Close()
 
 	if trace {
-		fmt.Printf("importing %s\n", filename)
+		fmt.Printf("importing %s (%s)\n", id, filename)
 	}
 
 	var p gcParser
-	p.init(filename, id, buf)
-	name, scope = p.parseExport()
-
+	p.init(filename, id, buf, imports)
+	pkg = p.parseExport()
 	return
 }
 
@@ -214,21 +215,31 @@ func (p *gcParser) expectKeyword(keyword string) {
 
 // ImportPath = string_lit .
 //
-func (p *gcParser) parsePkgId() *ast.Scope {
+func (p *gcParser) parsePkgId() *ast.Object {
 	id, err := strconv.Unquote(p.expect(scanner.String))
 	if err != nil {
 		p.error(err)
 	}
 
-	scope := p.scope // id == "" stands for the imported package id
-	if id != "" {
-		if scope = p.deps[id]; scope == nil {
-			scope = ast.NewScope(nil)
-			p.deps[id] = scope
-		}
+	switch id {
+	case "":
+		// id == "" stands for the imported package id
+		// (only known at time of package installation)
+		id = p.id
+	case "unsafe":
+		// package unsafe is not in the imports map - handle explicitly
+		return Unsafe
+	}
+
+	pkg := p.imports[id]
+	if pkg == nil {
+		scope = ast.NewScope(nil)
+		pkg = ast.NewObj(ast.Pkg, "")
+		pkg.Data = scope
+		p.imports[id] = pkg
 	}
 
-	return scope
+	return pkg
 }
 
 
@@ -253,13 +264,14 @@ func (p *gcParser) parseDotIdent() string {
 // ExportedName = ImportPath "." dotIdentifier .
 //
 func (p *gcParser) parseExportedName(kind ast.ObjKind) *ast.Object {
-	scope := p.parsePkgId()
+	pkg := p.parsePkgId()
 	p.expect('.')
 	name := p.parseDotIdent()
 
 	// a type may have been declared before - if it exists
 	// already in the respective package scope, return that
 	// type
+	scope := pkg.Data.(*ast.Scope)
 	if kind == ast.Typ {
 		if obj := scope.Lookup(name); obj != nil {
 			assert(obj.Kind == ast.Typ)
@@ -598,9 +610,10 @@ func (p *gcParser) parseImportDecl() {
 	// The identifier has no semantic meaning in the import data.
 	// It exists so that error messages can print the real package
 	// name: binary.ByteOrder instead of "encoding/binary".ByteOrder.
-	// TODO(gri): Save package id -> package name mapping.
-	p.expect(scanner.Ident)
-	p.parsePkgId()
+	name := p.expect(scanner.Ident)
+	pkg := p.parsePkgId()
+	assert(pkg.Name == "" || pkg.Name == name)
+	pkg.Name = name
 }
 
 
@@ -701,7 +714,7 @@ func (p *gcParser) parseConstDecl() {
 	if obj.Type == nil {
 		obj.Type = typ
 	}
-	_ = x // TODO(gri) store x somewhere
+	obj.Data = x
 }
 
 
@@ -710,12 +723,18 @@ func (p *gcParser) parseConstDecl() {
 func (p *gcParser) parseTypeDecl() {
 	p.expectKeyword("type")
 	obj := p.parseExportedName(ast.Typ)
+
+	// The type object may have been imported before and thus already
+	// have a type associated with it. We still need to parse the type
+	// structure, but throw it away if the object already has a type.
+	// This ensures that all imports refer to the same type object for
+	// a given type declaration.
 	typ := p.parseType()
 
-	name := obj.Type.(*Name)
-	assert(name.Underlying == nil)
-	assert(Underlying(typ) == typ)
-	name.Underlying = typ
+	if name := obj.Type.(*Name); name.Underlying == nil {
+		assert(Underlying(typ) == typ)
+		name.Underlying = typ
+	}
 }
 
 
@@ -780,7 +799,7 @@ func (p *gcParser) parseDecl() {
 // Export        = "PackageClause { Decl } "$$" .
 // PackageClause = "package" identifier [ "safe" ] "\n" .
 //
-func (p *gcParser) parseExport() (string, *ast.Scope) {
+func (p *gcParser) parseExport() *ast.Object {
 	p.expectKeyword("package")
 	name := p.expect(scanner.Ident)
 	if p.tok != '\n' {
@@ -791,6 +810,11 @@ func (p *gcParser) parseExport() (string, *ast.Scope) {
 	}
 	p.expect('\n')
 
+	assert(p.imports[p.id] == nil)
+	pkg := ast.NewObj(ast.Pkg, name)
+	pkg.Data = ast.NewScope(nil)
+	p.imports[p.id] = pkg
+
 	for p.tok != '$' && p.tok != scanner.EOF {
 		p.parseDecl()
 	}
@@ -805,5 +829,5 @@ func (p *gcParser) parseExport() (string, *ast.Scope) {
 		p.errorf("expected no scanner errors, got %d", n)
 	}
 
-	return name, p.scope
+	return pkg
 }
diff --git a/src/pkg/go/types/gcimporter_test.go b/src/pkg/go/types/gcimporter_test.go
index 556e761df2..50e70f29c5 100644
--- a/src/pkg/go/types/gcimporter_test.go
+++ b/src/pkg/go/types/gcimporter_test.go
@@ -6,6 +6,7 @@ package types
 
 import (
 	"exec"
+	"go/ast"
 	"io/ioutil"
 	"path/filepath"
 	"runtime"
@@ -57,8 +58,12 @@ func compile(t *testing.T, dirname, filename string) {
 }
 
 
+// Use the same global imports map for all tests. The effect is
+// as if all tested packages were imported into a single package.
+var imports = make(map[string]*ast.Object)
+
 func testPath(t *testing.T, path string) bool {
-	_, _, err := GcImporter(path)
+	_, err := GcImporter(imports, path)
 	if err != nil {
 		t.Errorf("testPath(%s): %s", path, err)
 		return false
diff --git a/src/pkg/go/types/universe.go b/src/pkg/go/types/universe.go
index 2a54a8ac12..96005cff5e 100644
--- a/src/pkg/go/types/universe.go
+++ b/src/pkg/go/types/universe.go
@@ -11,9 +11,9 @@ import "go/ast"
 
 
 var (
-	scope, // current scope to use for initialization
-	Universe,
-	Unsafe *ast.Scope
+	scope    *ast.Scope // current scope to use for initialization
+	Universe *ast.Scope
+	Unsafe   *ast.Object // package unsafe
 )
 
 
@@ -56,8 +56,8 @@ var (
 
 
 func init() {
-	Universe = ast.NewScope(nil)
-	scope = Universe
+	scope = ast.NewScope(nil)
+	Universe = scope
 
 	Bool = defType("bool")
 	defType("byte") // TODO(gri) should be an alias for uint8
@@ -98,8 +98,10 @@ func init() {
 	defFun("real")
 	defFun("recover")
 
-	Unsafe = ast.NewScope(nil)
-	scope = Unsafe
+	scope = ast.NewScope(nil)
+	Unsafe = ast.NewObj(ast.Pkg, "unsafe")
+	Unsafe.Data = scope
+
 	defType("Pointer")
 
 	defFun("Alignof")