internal/facts/facts.go - tools - Git at Google

 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package facts defines a serializable set of analysis.Fact.
 //
 // It provides a partial implementation of the Fact-related parts of the
 // analysis.Pass interface for use in analysis drivers such as "go vet"
 // and other build systems.
 //
 // The serial format is unspecified and may change, so the same version
 // of this package must be used for reading and writing serialized facts.
 //
 // The handling of facts in the analysis system parallels the handling
 // of type information in the compiler: during compilation of package P,
 // the compiler emits an export data file that describes the type of
 // every object (named thing) defined in package P, plus every object
 // indirectly reachable from one of those objects. Thus the downstream
 // compiler of package Q need only load one export data file per direct
 // import of Q, and it will learn everything about the API of package P
 // and everything it needs to know about the API of P's dependencies.
 //
 // Similarly, analysis of package P emits a fact set containing facts
 // about all objects exported from P, plus additional facts about only
 // those objects of P's dependencies that are reachable from the API of
 // package P; the downstream analysis of Q need only load one fact set
 // per direct import of Q.
 //
 // The notion of "exportedness" that matters here is that of the
 // compiler. According to the language spec, a method pkg.T.f is
 // unexported simply because its name starts with lowercase. But the
 // compiler must nonetheless export f so that downstream compilations can
 // accurately ascertain whether pkg.T implements an interface pkg.I
 // defined as interface{f()}. Exported thus means "described in export
 // data".
 package facts

 import (
 	"bytes"
 	"encoding/gob"
 	"fmt"
 	"go/types"
 	"io"
 	"log"
 	"reflect"
 	"sort"
 	"sync"

 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/types/objectpath"
 )

 const debug = false

 // A Set is a set of analysis.Facts.
 //
 // Decode creates a Set of facts by reading from the imports of a given
 // package, and Encode writes out the set. Between these operation,
 // the Import and Export methods will query and update the set.
 //
 // All of Set's methods except String are safe to call concurrently.
 type Set struct {
 	pkg *types.Package
 	mu  sync.Mutex
 	m   map[key]analysis.Fact
 }

 type key struct {
 	pkg *types.Package
 	obj types.Object // (object facts only)
 	t   reflect.Type
 }

 // ImportObjectFact implements analysis.Pass.ImportObjectFact.
 func (s *Set) ImportObjectFact(obj types.Object, ptr analysis.Fact) bool {
 	if obj == nil {
 		panic("nil object")
 	}
 	key := key{pkg: obj.Pkg(), obj: obj, t: reflect.TypeOf(ptr)}
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if v, ok := s.m[key]; ok {
 		reflect.ValueOf(ptr).Elem().Set(reflect.ValueOf(v).Elem())
 		return true
 	}
 	return false
 }

 // ExportObjectFact implements analysis.Pass.ExportObjectFact.
 func (s *Set) ExportObjectFact(obj types.Object, fact analysis.Fact) {
 	if obj.Pkg() != s.pkg {
 		log.Panicf("in package %s: ExportObjectFact(%s, %T): can't set fact on object belonging another package",
 			s.pkg, obj, fact)
 	}
 	key := key{pkg: obj.Pkg(), obj: obj, t: reflect.TypeOf(fact)}
 	s.mu.Lock()
 	s.m[key] = fact // clobber any existing entry
 	s.mu.Unlock()
 }

 func (s *Set) AllObjectFacts(filter map[reflect.Type]bool) []analysis.ObjectFact {
 	var facts []analysis.ObjectFact
 	s.mu.Lock()
 	for k, v := range s.m {
 		if k.obj != nil && filter[k.t] {
 			facts = append(facts, analysis.ObjectFact{Object: k.obj, Fact: v})
 		}
 	}
 	s.mu.Unlock()
 	return facts
 }

 // ImportPackageFact implements analysis.Pass.ImportPackageFact.
 func (s *Set) ImportPackageFact(pkg *types.Package, ptr analysis.Fact) bool {
 	if pkg == nil {
 		panic("nil package")
 	}
 	key := key{pkg: pkg, t: reflect.TypeOf(ptr)}
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if v, ok := s.m[key]; ok {
 		reflect.ValueOf(ptr).Elem().Set(reflect.ValueOf(v).Elem())
 		return true
 	}
 	return false
 }

 // ExportPackageFact implements analysis.Pass.ExportPackageFact.
 func (s *Set) ExportPackageFact(fact analysis.Fact) {
 	key := key{pkg: s.pkg, t: reflect.TypeOf(fact)}
 	s.mu.Lock()
 	s.m[key] = fact // clobber any existing entry
 	s.mu.Unlock()
 }

 func (s *Set) AllPackageFacts(filter map[reflect.Type]bool) []analysis.PackageFact {
 	var facts []analysis.PackageFact
 	s.mu.Lock()
 	for k, v := range s.m {
 		if k.obj == nil && filter[k.t] {
 			facts = append(facts, analysis.PackageFact{Package: k.pkg, Fact: v})
 		}
 	}
 	s.mu.Unlock()
 	return facts
 }

 // gobFact is the Gob declaration of a serialized fact.
 type gobFact struct {
 	PkgPath string          // path of package
 	Object  objectpath.Path // optional path of object relative to package itself
 	Fact    analysis.Fact   // type and value of user-defined Fact
 }

 // A Decoder decodes the facts from the direct imports of the package
 // provided to NewEncoder. A single decoder may be used to decode
 // multiple fact sets (e.g. each for a different set of fact types)
 // for the same package. Each call to Decode returns an independent
 // fact set.
 type Decoder struct {
 	pkg        *types.Package
 	getPackage GetPackageFunc
 }

 // NewDecoder returns a fact decoder for the specified package.
 //
 // It uses a brute-force recursive approach to enumerate all objects
 // defined by dependencies of pkg, so that it can learn the set of
 // package paths that may be mentioned in the fact encoding. This does
 // not scale well; use [NewDecoderFunc] where possible.
 func NewDecoder(pkg *types.Package) *Decoder {
 	// Compute the import map for this package.
 	// See the package doc comment.
 	m := importMap(pkg.Imports())
 	getPackageFunc := func(path string) *types.Package { return m[path] }
 	return NewDecoderFunc(pkg, getPackageFunc)
 }

 // NewDecoderFunc returns a fact decoder for the specified package.
 //
 // It calls the getPackage function for the package path string of
 // each dependency (perhaps indirect) that it encounters in the
 // encoding. If the function returns nil, the fact is discarded.
 //
 // This function is preferred over [NewDecoder] when the client is
 // capable of efficient look-up of packages by package path.
 func NewDecoderFunc(pkg *types.Package, getPackage GetPackageFunc) *Decoder {
 	return &Decoder{
 		pkg:        pkg,
 		getPackage: getPackage,
 	}
 }

 // A GetPackageFunc function returns the package denoted by a package path.
 type GetPackageFunc = func(pkgPath string) *types.Package

 // Decode decodes all the facts relevant to the analysis of package
 // pkgPath. The read function reads serialized fact data from an external
 // source for one of pkg's direct imports, identified by package path.
 // The empty file is a valid encoding of an empty fact set.
 //
 // It is the caller's responsibility to call gob.Register on all
 // necessary fact types.
 //
 // Concurrent calls to Decode are safe, so long as the
 // [GetPackageFunc] (if any) is also concurrency-safe.
 func (d *Decoder) Decode(read func(pkgPath string) ([]byte, error)) (*Set, error) {
 	// Read facts from imported packages.
 	// Facts may describe indirectly imported packages, or their objects.
 	m := make(map[key]analysis.Fact) // one big bucket
 	for _, imp := range d.pkg.Imports() {
 		logf := func(format string, args ...interface{}) {
 			if debug {
 				prefix := fmt.Sprintf("in %s, importing %s: ",
 					d.pkg.Path(), imp.Path())
 				log.Print(prefix, fmt.Sprintf(format, args...))
 			}
 		}

 		// Read the gob-encoded facts.
 		data, err := read(imp.Path())
 		if err != nil {
 			return nil, fmt.Errorf("in %s, can't import facts for package %q: %v",
 				d.pkg.Path(), imp.Path(), err)
 		}
 		if len(data) == 0 {
 			continue // no facts
 		}
 		var gobFacts []gobFact
 		if err := gob.NewDecoder(bytes.NewReader(data)).Decode(&gobFacts); err != nil {
 			return nil, fmt.Errorf("decoding facts for %q: %v", imp.Path(), err)
 		}
 		logf("decoded %d facts: %v", len(gobFacts), gobFacts)

 		// Parse each one into a key and a Fact.
 		for _, f := range gobFacts {
 			factPkg := d.getPackage(f.PkgPath) // possibly an indirect dependency
 			if factPkg == nil {
 				// Fact relates to a dependency that was
 				// unused in this translation unit. Skip.
 				logf("no package %q; discarding %v", f.PkgPath, f.Fact)
 				continue
 			}
 			key := key{pkg: factPkg, t: reflect.TypeOf(f.Fact)}
 			if f.Object != "" {
 				// object fact
 				obj, err := objectpath.Object(factPkg, f.Object)
 				if err != nil {
 					// (most likely due to unexported object)
 					// TODO(adonovan): audit for other possibilities.
 					logf("no object for path: %v; discarding %s", err, f.Fact)
 					continue
 				}
 				key.obj = obj
 				logf("read %T fact %s for %v", f.Fact, f.Fact, key.obj)
 			} else {
 				// package fact
 				logf("read %T fact %s for %v", f.Fact, f.Fact, factPkg)
 			}
 			m[key] = f.Fact
 		}
 	}

 	return &Set{pkg: d.pkg, m: m}, nil
 }

 // Encode encodes a set of facts to a memory buffer.
 //
 // It may fail if one of the Facts could not be gob-encoded, but this is
 // a sign of a bug in an Analyzer.
 func (s *Set) Encode() []byte {
 	encoder := new(objectpath.Encoder)

 	// TODO(adonovan): opt: use a more efficient encoding
 	// that avoids repeating PkgPath for each fact.

 	// Gather all facts, including those from imported packages.
 	var gobFacts []gobFact

 	s.mu.Lock()
 	for k, fact := range s.m {
 		if debug {
 			log.Printf("%v => %s\n", k, fact)
 		}

 		// Don't export facts that we imported from another
 		// package, unless they represent fields or methods,
 		// or package-level types.
 		// (Facts about packages, and other package-level
 		// objects, are only obtained from direct imports so
 		// they needn't be reexported.)
 		//
 		// This is analogous to the pruning done by "deep"
 		// export data for types, but not as precise because
 		// we aren't careful about which structs or methods
 		// we rexport: it should be only those referenced
 		// from the API of s.pkg.
 		// TODO(adonovan): opt: be more precise. e.g.
 		// intersect with the set of objects computed by
 		// importMap(s.pkg.Imports()).
 		// TODO(adonovan): opt: implement "shallow" facts.
 		if k.pkg != s.pkg {
 			if k.obj == nil {
 				continue // imported package fact
 			}
 			if _, isType := k.obj.(*types.TypeName); !isType &&
 				k.obj.Parent() == k.obj.Pkg().Scope() {
 				continue // imported fact about package-level non-type object
 			}
 		}

 		var object objectpath.Path
 		if k.obj != nil {
 			path, err := encoder.For(k.obj)
 			if err != nil {
 				if debug {
 					log.Printf("discarding fact %s about %s\n", fact, k.obj)
 				}
 				continue // object not accessible from package API; discard fact
 			}
 			object = path
 		}
 		gobFacts = append(gobFacts, gobFact{
 			PkgPath: k.pkg.Path(),
 			Object:  object,
 			Fact:    fact,
 		})
 	}
 	s.mu.Unlock()

 	// Sort facts by (package, object, type) for determinism.
 	sort.Slice(gobFacts, func(i, j int) bool {
 		x, y := gobFacts[i], gobFacts[j]
 		if x.PkgPath != y.PkgPath {
 			return x.PkgPath < y.PkgPath
 		}
 		if x.Object != y.Object {
 			return x.Object < y.Object
 		}
 		tx := reflect.TypeOf(x.Fact)
 		ty := reflect.TypeOf(y.Fact)
 		if tx != ty {
 			return tx.String() < ty.String()
 		}
 		return false // equal
 	})

 	var buf bytes.Buffer
 	if len(gobFacts) > 0 {
 		if err := gob.NewEncoder(&buf).Encode(gobFacts); err != nil {
 			// Fact encoding should never fail. Identify the culprit.
 			for _, gf := range gobFacts {
 				if err := gob.NewEncoder(io.Discard).Encode(gf); err != nil {
 					fact := gf.Fact
 					pkgpath := reflect.TypeOf(fact).Elem().PkgPath()
 					log.Panicf("internal error: gob encoding of analysis fact %s failed: %v; please report a bug against fact %T in package %q",
 						fact, err, fact, pkgpath)
 				}
 			}
 		}
 	}

 	if debug {
 		log.Printf("package %q: encode %d facts, %d bytes\n",
 			s.pkg.Path(), len(gobFacts), buf.Len())
 	}

 	return buf.Bytes()
 }

 // String is provided only for debugging, and must not be called
 // concurrent with any Import/Export method.
 func (s *Set) String() string {
 	var buf bytes.Buffer
 	buf.WriteString("{")
 	for k, f := range s.m {
 		if buf.Len() > 1 {
 			buf.WriteString(", ")
 		}
 		if k.obj != nil {
 			buf.WriteString(k.obj.String())
 		} else {
 			buf.WriteString(k.pkg.Path())
 		}
 		fmt.Fprintf(&buf, ": %v", f)
 	}
 	buf.WriteString("}")
 	return buf.String()
 }
	// Copyright 2018 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package facts defines a serializable set of analysis.Fact.
	//
	// It provides a partial implementation of the Fact-related parts of the
	// analysis.Pass interface for use in analysis drivers such as "go vet"
	// and other build systems.
	//
	// The serial format is unspecified and may change, so the same version
	// of this package must be used for reading and writing serialized facts.
	//
	// The handling of facts in the analysis system parallels the handling
	// of type information in the compiler: during compilation of package P,
	// the compiler emits an export data file that describes the type of
	// every object (named thing) defined in package P, plus every object
	// indirectly reachable from one of those objects. Thus the downstream
	// compiler of package Q need only load one export data file per direct
	// import of Q, and it will learn everything about the API of package P
	// and everything it needs to know about the API of P's dependencies.
	//
	// Similarly, analysis of package P emits a fact set containing facts
	// about all objects exported from P, plus additional facts about only
	// those objects of P's dependencies that are reachable from the API of
	// package P; the downstream analysis of Q need only load one fact set
	// per direct import of Q.
	//
	// The notion of "exportedness" that matters here is that of the
	// compiler. According to the language spec, a method pkg.T.f is
	// unexported simply because its name starts with lowercase. But the
	// compiler must nonetheless export f so that downstream compilations can
	// accurately ascertain whether pkg.T implements an interface pkg.I
	// defined as interface{f()}. Exported thus means "described in export
	// data".
	package facts

	import (
	"bytes"
	"encoding/gob"
	"fmt"
	"go/types"
	"io"
	"log"
	"reflect"
	"sort"
	"sync"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/types/objectpath"
	)

	const debug = false

	// A Set is a set of analysis.Facts.
	//
	// Decode creates a Set of facts by reading from the imports of a given
	// package, and Encode writes out the set. Between these operation,
	// the Import and Export methods will query and update the set.
	//
	// All of Set's methods except String are safe to call concurrently.
	type Set struct {
	pkg *types.Package
	mu sync.Mutex
	m map[key]analysis.Fact
	}

	type key struct {
	pkg *types.Package
	obj types.Object // (object facts only)
	t reflect.Type
	}

	// ImportObjectFact implements analysis.Pass.ImportObjectFact.
	func (s *Set) ImportObjectFact(obj types.Object, ptr analysis.Fact) bool {
	if obj == nil {
	panic("nil object")
	}
	key := key{pkg: obj.Pkg(), obj: obj, t: reflect.TypeOf(ptr)}
	s.mu.Lock()
	defer s.mu.Unlock()
	if v, ok := s.m[key]; ok {
	reflect.ValueOf(ptr).Elem().Set(reflect.ValueOf(v).Elem())
	return true
	}
	return false
	}

	// ExportObjectFact implements analysis.Pass.ExportObjectFact.
	func (s *Set) ExportObjectFact(obj types.Object, fact analysis.Fact) {
	if obj.Pkg() != s.pkg {
	log.Panicf("in package %s: ExportObjectFact(%s, %T): can't set fact on object belonging another package",
	s.pkg, obj, fact)
	}
	key := key{pkg: obj.Pkg(), obj: obj, t: reflect.TypeOf(fact)}
	s.mu.Lock()
	s.m[key] = fact // clobber any existing entry
	s.mu.Unlock()
	}

	func (s *Set) AllObjectFacts(filter map[reflect.Type]bool) []analysis.ObjectFact {
	var facts []analysis.ObjectFact
	s.mu.Lock()
	for k, v := range s.m {
	if k.obj != nil && filter[k.t] {
	facts = append(facts, analysis.ObjectFact{Object: k.obj, Fact: v})
	}
	}
	s.mu.Unlock()
	return facts
	}

	// ImportPackageFact implements analysis.Pass.ImportPackageFact.
	func (s Set) ImportPackageFact(pkg types.Package, ptr analysis.Fact) bool {
	if pkg == nil {
	panic("nil package")
	}
	key := key{pkg: pkg, t: reflect.TypeOf(ptr)}
	s.mu.Lock()
	defer s.mu.Unlock()
	if v, ok := s.m[key]; ok {
	reflect.ValueOf(ptr).Elem().Set(reflect.ValueOf(v).Elem())
	return true
	}
	return false
	}

	// ExportPackageFact implements analysis.Pass.ExportPackageFact.
	func (s *Set) ExportPackageFact(fact analysis.Fact) {
	key := key{pkg: s.pkg, t: reflect.TypeOf(fact)}
	s.mu.Lock()
	s.m[key] = fact // clobber any existing entry
	s.mu.Unlock()
	}

	func (s *Set) AllPackageFacts(filter map[reflect.Type]bool) []analysis.PackageFact {
	var facts []analysis.PackageFact
	s.mu.Lock()
	for k, v := range s.m {
	if k.obj == nil && filter[k.t] {
	facts = append(facts, analysis.PackageFact{Package: k.pkg, Fact: v})
	}
	}
	s.mu.Unlock()
	return facts
	}

	// gobFact is the Gob declaration of a serialized fact.
	type gobFact struct {
	PkgPath string // path of package
	Object objectpath.Path // optional path of object relative to package itself
	Fact analysis.Fact // type and value of user-defined Fact
	}

	// A Decoder decodes the facts from the direct imports of the package
	// provided to NewEncoder. A single decoder may be used to decode
	// multiple fact sets (e.g. each for a different set of fact types)
	// for the same package. Each call to Decode returns an independent
	// fact set.
	type Decoder struct {
	pkg *types.Package
	getPackage GetPackageFunc
	}

	// NewDecoder returns a fact decoder for the specified package.
	//
	// It uses a brute-force recursive approach to enumerate all objects
	// defined by dependencies of pkg, so that it can learn the set of
	// package paths that may be mentioned in the fact encoding. This does
	// not scale well; use [NewDecoderFunc] where possible.
	func NewDecoder(pkg types.Package) Decoder {
	// Compute the import map for this package.
	// See the package doc comment.
	m := importMap(pkg.Imports())
	getPackageFunc := func(path string) *types.Package { return m[path] }
	return NewDecoderFunc(pkg, getPackageFunc)
	}

	// NewDecoderFunc returns a fact decoder for the specified package.
	//
	// It calls the getPackage function for the package path string of
	// each dependency (perhaps indirect) that it encounters in the
	// encoding. If the function returns nil, the fact is discarded.
	//
	// This function is preferred over [NewDecoder] when the client is
	// capable of efficient look-up of packages by package path.
	func NewDecoderFunc(pkg types.Package, getPackage GetPackageFunc) Decoder {
	return &Decoder{
	pkg: pkg,
	getPackage: getPackage,
	}
	}

	// A GetPackageFunc function returns the package denoted by a package path.
	type GetPackageFunc = func(pkgPath string) *types.Package

	// Decode decodes all the facts relevant to the analysis of package
	// pkgPath. The read function reads serialized fact data from an external
	// source for one of pkg's direct imports, identified by package path.
	// The empty file is a valid encoding of an empty fact set.
	//
	// It is the caller's responsibility to call gob.Register on all
	// necessary fact types.
	//
	// Concurrent calls to Decode are safe, so long as the
	// [GetPackageFunc] (if any) is also concurrency-safe.
	func (d Decoder) Decode(read func(pkgPath string) ([]byte, error)) (Set, error) {
	// Read facts from imported packages.
	// Facts may describe indirectly imported packages, or their objects.
	m := make(map[key]analysis.Fact) // one big bucket
	for _, imp := range d.pkg.Imports() {
	logf := func(format string, args ...interface{}) {
	if debug {
	prefix := fmt.Sprintf("in %s, importing %s: ",
	d.pkg.Path(), imp.Path())
	log.Print(prefix, fmt.Sprintf(format, args...))
	}
	}

	// Read the gob-encoded facts.
	data, err := read(imp.Path())
	if err != nil {
	return nil, fmt.Errorf("in %s, can't import facts for package %q: %v",
	d.pkg.Path(), imp.Path(), err)
	}
	if len(data) == 0 {
	continue // no facts
	}
	var gobFacts []gobFact
	if err := gob.NewDecoder(bytes.NewReader(data)).Decode(&gobFacts); err != nil {
	return nil, fmt.Errorf("decoding facts for %q: %v", imp.Path(), err)
	}
	logf("decoded %d facts: %v", len(gobFacts), gobFacts)

	// Parse each one into a key and a Fact.
	for _, f := range gobFacts {
	factPkg := d.getPackage(f.PkgPath) // possibly an indirect dependency
	if factPkg == nil {
	// Fact relates to a dependency that was
	// unused in this translation unit. Skip.
	logf("no package %q; discarding %v", f.PkgPath, f.Fact)
	continue
	}
	key := key{pkg: factPkg, t: reflect.TypeOf(f.Fact)}
	if f.Object != "" {
	// object fact
	obj, err := objectpath.Object(factPkg, f.Object)
	if err != nil {
	// (most likely due to unexported object)
	// TODO(adonovan): audit for other possibilities.
	logf("no object for path: %v; discarding %s", err, f.Fact)
	continue
	}
	key.obj = obj
	logf("read %T fact %s for %v", f.Fact, f.Fact, key.obj)
	} else {
	// package fact
	logf("read %T fact %s for %v", f.Fact, f.Fact, factPkg)
	}
	m[key] = f.Fact
	}
	}

	return &Set{pkg: d.pkg, m: m}, nil
	}

	// Encode encodes a set of facts to a memory buffer.
	//
	// It may fail if one of the Facts could not be gob-encoded, but this is
	// a sign of a bug in an Analyzer.
	func (s *Set) Encode() []byte {
	encoder := new(objectpath.Encoder)

	// TODO(adonovan): opt: use a more efficient encoding
	// that avoids repeating PkgPath for each fact.

	// Gather all facts, including those from imported packages.
	var gobFacts []gobFact

	s.mu.Lock()
	for k, fact := range s.m {
	if debug {
	log.Printf("%v => %s\n", k, fact)
	}

	// Don't export facts that we imported from another
	// package, unless they represent fields or methods,
	// or package-level types.
	// (Facts about packages, and other package-level
	// objects, are only obtained from direct imports so
	// they needn't be reexported.)
	//
	// This is analogous to the pruning done by "deep"
	// export data for types, but not as precise because
	// we aren't careful about which structs or methods
	// we rexport: it should be only those referenced
	// from the API of s.pkg.
	// TODO(adonovan): opt: be more precise. e.g.
	// intersect with the set of objects computed by
	// importMap(s.pkg.Imports()).
	// TODO(adonovan): opt: implement "shallow" facts.
	if k.pkg != s.pkg {
	if k.obj == nil {
	continue // imported package fact
	}
	if _, isType := k.obj.(*types.TypeName); !isType &&
	k.obj.Parent() == k.obj.Pkg().Scope() {
	continue // imported fact about package-level non-type object
	}
	}

	var object objectpath.Path
	if k.obj != nil {
	path, err := encoder.For(k.obj)
	if err != nil {
	if debug {
	log.Printf("discarding fact %s about %s\n", fact, k.obj)
	}
	continue // object not accessible from package API; discard fact
	}
	object = path
	}
	gobFacts = append(gobFacts, gobFact{
	PkgPath: k.pkg.Path(),
	Object: object,
	Fact: fact,
	})
	}
	s.mu.Unlock()

	// Sort facts by (package, object, type) for determinism.
	sort.Slice(gobFacts, func(i, j int) bool {
	x, y := gobFacts[i], gobFacts[j]
	if x.PkgPath != y.PkgPath {
	return x.PkgPath < y.PkgPath
	}
	if x.Object != y.Object {
	return x.Object < y.Object
	}
	tx := reflect.TypeOf(x.Fact)
	ty := reflect.TypeOf(y.Fact)
	if tx != ty {
	return tx.String() < ty.String()
	}
	return false // equal
	})

	var buf bytes.Buffer
	if len(gobFacts) > 0 {
	if err := gob.NewEncoder(&buf).Encode(gobFacts); err != nil {
	// Fact encoding should never fail. Identify the culprit.
	for _, gf := range gobFacts {
	if err := gob.NewEncoder(io.Discard).Encode(gf); err != nil {
	fact := gf.Fact
	pkgpath := reflect.TypeOf(fact).Elem().PkgPath()
	log.Panicf("internal error: gob encoding of analysis fact %s failed: %v; please report a bug against fact %T in package %q",
	fact, err, fact, pkgpath)
	}
	}
	}
	}

	if debug {
	log.Printf("package %q: encode %d facts, %d bytes\n",
	s.pkg.Path(), len(gobFacts), buf.Len())
	}

	return buf.Bytes()
	}

	// String is provided only for debugging, and must not be called
	// concurrent with any Import/Export method.
	func (s *Set) String() string {
	var buf bytes.Buffer
	buf.WriteString("{")
	for k, f := range s.m {
	if buf.Len() > 1 {
	buf.WriteString(", ")
	}
	if k.obj != nil {
	buf.WriteString(k.obj.String())
	} else {
	buf.WriteString(k.pkg.Path())
	}
	fmt.Fprintf(&buf, ": %v", f)
	}
	buf.WriteString("}")
	return buf.String()
	}