1 files changed, 535 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/importer/ureader.go b/src/cmd/compile/internal/importer/ureader.go
new file mode 100644
index 0000000..f5c2f41
--- /dev/null
+++ b/src/cmd/compile/internal/importer/ureader.go
@@ -0,0 +1,535 @@
+// Copyright 2021 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 importer
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+	"internal/pkgbits"
+)
+
+type pkgReader struct {
+	pkgbits.PkgDecoder
+
+	ctxt    *types2.Context
+	imports map[string]*types2.Package
+
+	posBases []*syntax.PosBase
+	pkgs     []*types2.Package
+	typs     []types2.Type
+}
+
+func ReadPackage(ctxt *types2.Context, imports map[string]*types2.Package, input pkgbits.PkgDecoder) *types2.Package {
+	pr := pkgReader{
+		PkgDecoder: input,
+
+		ctxt:    ctxt,
+		imports: imports,
+
+		posBases: make([]*syntax.PosBase, input.NumElems(pkgbits.RelocPosBase)),
+		pkgs:     make([]*types2.Package, input.NumElems(pkgbits.RelocPkg)),
+		typs:     make([]types2.Type, input.NumElems(pkgbits.RelocType)),
+	}
+
+	r := pr.newReader(pkgbits.RelocMeta, pkgbits.PublicRootIdx, pkgbits.SyncPublic)
+	pkg := r.pkg()
+	r.Bool() // TODO(mdempsky): Remove; was "has init"
+
+	for i, n := 0, r.Len(); i < n; i++ {
+		// As if r.obj(), but avoiding the Scope.Lookup call,
+		// to avoid eager loading of imports.
+		r.Sync(pkgbits.SyncObject)
+		assert(!r.Bool())
+		r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+		assert(r.Len() == 0)
+	}
+
+	r.Sync(pkgbits.SyncEOF)
+
+	pkg.MarkComplete()
+	return pkg
+}
+
+type reader struct {
+	pkgbits.Decoder
+
+	p *pkgReader
+
+	dict *readerDict
+}
+
+type readerDict struct {
+	bounds []typeInfo
+
+	tparams []*types2.TypeParam
+
+	derived      []derivedInfo
+	derivedTypes []types2.Type
+}
+
+type readerTypeBound struct {
+	derived  bool
+	boundIdx int
+}
+
+func (pr *pkgReader) newReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.NewDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) tempReader(k pkgbits.RelocKind, idx pkgbits.Index, marker pkgbits.SyncMarker) *reader {
+	return &reader{
+		Decoder: pr.TempDecoder(k, idx, marker),
+		p:       pr,
+	}
+}
+
+func (pr *pkgReader) retireReader(r *reader) {
+	pr.RetireDecoder(&r.Decoder)
+}
+
+// @@@ Positions
+
+func (r *reader) pos() syntax.Pos {
+	r.Sync(pkgbits.SyncPos)
+	if !r.Bool() {
+		return syntax.Pos{}
+	}
+
+	// TODO(mdempsky): Delta encoding.
+	posBase := r.posBase()
+	line := r.Uint()
+	col := r.Uint()
+	return syntax.MakePos(posBase, line, col)
+}
+
+func (r *reader) posBase() *syntax.PosBase {
+	return r.p.posBaseIdx(r.Reloc(pkgbits.RelocPosBase))
+}
+
+func (pr *pkgReader) posBaseIdx(idx pkgbits.Index) *syntax.PosBase {
+	if b := pr.posBases[idx]; b != nil {
+		return b
+	}
+	var b *syntax.PosBase
+	{
+		r := pr.tempReader(pkgbits.RelocPosBase, idx, pkgbits.SyncPosBase)
+
+		filename := r.String()
+
+		if r.Bool() {
+			b = syntax.NewTrimmedFileBase(filename, true)
+		} else {
+			pos := r.pos()
+			line := r.Uint()
+			col := r.Uint()
+			b = syntax.NewLineBase(pos, filename, true, line, col)
+		}
+		pr.retireReader(r)
+	}
+
+	pr.posBases[idx] = b
+	return b
+}
+
+// @@@ Packages
+
+func (r *reader) pkg() *types2.Package {
+	r.Sync(pkgbits.SyncPkg)
+	return r.p.pkgIdx(r.Reloc(pkgbits.RelocPkg))
+}
+
+func (pr *pkgReader) pkgIdx(idx pkgbits.Index) *types2.Package {
+	// TODO(mdempsky): Consider using some non-nil pointer to indicate
+	// the universe scope, so we don't need to keep re-reading it.
+	if pkg := pr.pkgs[idx]; pkg != nil {
+		return pkg
+	}
+
+	pkg := pr.newReader(pkgbits.RelocPkg, idx, pkgbits.SyncPkgDef).doPkg()
+	pr.pkgs[idx] = pkg
+	return pkg
+}
+
+func (r *reader) doPkg() *types2.Package {
+	path := r.String()
+	switch path {
+	case "":
+		path = r.p.PkgPath()
+	case "builtin":
+		return nil // universe
+	case "unsafe":
+		return types2.Unsafe
+	}
+
+	if pkg := r.p.imports[path]; pkg != nil {
+		return pkg
+	}
+
+	name := r.String()
+	pkg := types2.NewPackage(path, name)
+	r.p.imports[path] = pkg
+
+	// TODO(mdempsky): The list of imported packages is important for
+	// go/types, but we could probably skip populating it for types2.
+	imports := make([]*types2.Package, r.Len())
+	for i := range imports {
+		imports[i] = r.pkg()
+	}
+	pkg.SetImports(imports)
+
+	return pkg
+}
+
+// @@@ Types
+
+func (r *reader) typ() types2.Type {
+	return r.p.typIdx(r.typInfo(), r.dict)
+}
+
+func (r *reader) typInfo() typeInfo {
+	r.Sync(pkgbits.SyncType)
+	if r.Bool() {
+		return typeInfo{idx: pkgbits.Index(r.Len()), derived: true}
+	}
+	return typeInfo{idx: r.Reloc(pkgbits.RelocType), derived: false}
+}
+
+func (pr *pkgReader) typIdx(info typeInfo, dict *readerDict) types2.Type {
+	idx := info.idx
+	var where *types2.Type
+	if info.derived {
+		where = &dict.derivedTypes[idx]
+		idx = dict.derived[idx].idx
+	} else {
+		where = &pr.typs[idx]
+	}
+
+	if typ := *where; typ != nil {
+		return typ
+	}
+
+	var typ types2.Type
+	{
+		r := pr.tempReader(pkgbits.RelocType, idx, pkgbits.SyncTypeIdx)
+		r.dict = dict
+
+		typ = r.doTyp()
+		assert(typ != nil)
+		pr.retireReader(r)
+	}
+
+	// See comment in pkgReader.typIdx explaining how this happens.
+	if prev := *where; prev != nil {
+		return prev
+	}
+
+	*where = typ
+	return typ
+}
+
+func (r *reader) doTyp() (res types2.Type) {
+	switch tag := pkgbits.CodeType(r.Code(pkgbits.SyncType)); tag {
+	default:
+		base.FatalfAt(src.NoXPos, "unhandled type tag: %v", tag)
+		panic("unreachable")
+
+	case pkgbits.TypeBasic:
+		return types2.Typ[r.Len()]
+
+	case pkgbits.TypeNamed:
+		obj, targs := r.obj()
+		name := obj.(*types2.TypeName)
+		if len(targs) != 0 {
+			t, _ := types2.Instantiate(r.p.ctxt, name.Type(), targs, false)
+			return t
+		}
+		return name.Type()
+
+	case pkgbits.TypeTypeParam:
+		return r.dict.tparams[r.Len()]
+
+	case pkgbits.TypeArray:
+		len := int64(r.Uint64())
+		return types2.NewArray(r.typ(), len)
+	case pkgbits.TypeChan:
+		dir := types2.ChanDir(r.Len())
+		return types2.NewChan(dir, r.typ())
+	case pkgbits.TypeMap:
+		return types2.NewMap(r.typ(), r.typ())
+	case pkgbits.TypePointer:
+		return types2.NewPointer(r.typ())
+	case pkgbits.TypeSignature:
+		return r.signature(nil, nil, nil)
+	case pkgbits.TypeSlice:
+		return types2.NewSlice(r.typ())
+	case pkgbits.TypeStruct:
+		return r.structType()
+	case pkgbits.TypeInterface:
+		return r.interfaceType()
+	case pkgbits.TypeUnion:
+		return r.unionType()
+	}
+}
+
+func (r *reader) structType() *types2.Struct {
+	fields := make([]*types2.Var, r.Len())
+	var tags []string
+	for i := range fields {
+		pos := r.pos()
+		pkg, name := r.selector()
+		ftyp := r.typ()
+		tag := r.String()
+		embedded := r.Bool()
+
+		fields[i] = types2.NewField(pos, pkg, name, ftyp, embedded)
+		if tag != "" {
+			for len(tags) < i {
+				tags = append(tags, "")
+			}
+			tags = append(tags, tag)
+		}
+	}
+	return types2.NewStruct(fields, tags)
+}
+
+func (r *reader) unionType() *types2.Union {
+	terms := make([]*types2.Term, r.Len())
+	for i := range terms {
+		terms[i] = types2.NewTerm(r.Bool(), r.typ())
+	}
+	return types2.NewUnion(terms)
+}
+
+func (r *reader) interfaceType() *types2.Interface {
+	methods := make([]*types2.Func, r.Len())
+	embeddeds := make([]types2.Type, r.Len())
+	implicit := len(methods) == 0 && len(embeddeds) == 1 && r.Bool()
+
+	for i := range methods {
+		pos := r.pos()
+		pkg, name := r.selector()
+		mtyp := r.signature(nil, nil, nil)
+		methods[i] = types2.NewFunc(pos, pkg, name, mtyp)
+	}
+
+	for i := range embeddeds {
+		embeddeds[i] = r.typ()
+	}
+
+	iface := types2.NewInterfaceType(methods, embeddeds)
+	if implicit {
+		iface.MarkImplicit()
+	}
+	return iface
+}
+
+func (r *reader) signature(recv *types2.Var, rtparams, tparams []*types2.TypeParam) *types2.Signature {
+	r.Sync(pkgbits.SyncSignature)
+
+	params := r.params()
+	results := r.params()
+	variadic := r.Bool()
+
+	return types2.NewSignatureType(recv, rtparams, tparams, params, results, variadic)
+}
+
+func (r *reader) params() *types2.Tuple {
+	r.Sync(pkgbits.SyncParams)
+	params := make([]*types2.Var, r.Len())
+	for i := range params {
+		params[i] = r.param()
+	}
+	return types2.NewTuple(params...)
+}
+
+func (r *reader) param() *types2.Var {
+	r.Sync(pkgbits.SyncParam)
+
+	pos := r.pos()
+	pkg, name := r.localIdent()
+	typ := r.typ()
+
+	return types2.NewParam(pos, pkg, name, typ)
+}
+
+// @@@ Objects
+
+func (r *reader) obj() (types2.Object, []types2.Type) {
+	r.Sync(pkgbits.SyncObject)
+
+	assert(!r.Bool())
+
+	pkg, name := r.p.objIdx(r.Reloc(pkgbits.RelocObj))
+	obj := pkg.Scope().Lookup(name)
+
+	targs := make([]types2.Type, r.Len())
+	for i := range targs {
+		targs[i] = r.typ()
+	}
+
+	return obj, targs
+}
+
+func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types2.Package, string) {
+	var objPkg *types2.Package
+	var objName string
+	var tag pkgbits.CodeObj
+	{
+		rname := pr.tempReader(pkgbits.RelocName, idx, pkgbits.SyncObject1)
+
+		objPkg, objName = rname.qualifiedIdent()
+		assert(objName != "")
+
+		tag = pkgbits.CodeObj(rname.Code(pkgbits.SyncCodeObj))
+		pr.retireReader(rname)
+	}
+
+	if tag == pkgbits.ObjStub {
+		base.Assertf(objPkg == nil || objPkg == types2.Unsafe, "unexpected stub package: %v", objPkg)
+		return objPkg, objName
+	}
+
+	objPkg.Scope().InsertLazy(objName, func() types2.Object {
+		dict := pr.objDictIdx(idx)
+
+		r := pr.newReader(pkgbits.RelocObj, idx, pkgbits.SyncObject1)
+		r.dict = dict
+
+		switch tag {
+		default:
+			panic("weird")
+
+		case pkgbits.ObjAlias:
+			pos := r.pos()
+			typ := r.typ()
+			return types2.NewTypeName(pos, objPkg, objName, typ)
+
+		case pkgbits.ObjConst:
+			pos := r.pos()
+			typ := r.typ()
+			val := r.Value()
+			return types2.NewConst(pos, objPkg, objName, typ, val)
+
+		case pkgbits.ObjFunc:
+			pos := r.pos()
+			tparams := r.typeParamNames()
+			sig := r.signature(nil, nil, tparams)
+			return types2.NewFunc(pos, objPkg, objName, sig)
+
+		case pkgbits.ObjType:
+			pos := r.pos()
+
+			return types2.NewTypeNameLazy(pos, objPkg, objName, func(named *types2.Named) (tparams []*types2.TypeParam, underlying types2.Type, methods []*types2.Func) {
+				tparams = r.typeParamNames()
+
+				// TODO(mdempsky): Rewrite receiver types to underlying is an
+				// Interface? The go/types importer does this (I think because
+				// unit tests expected that), but cmd/compile doesn't care
+				// about it, so maybe we can avoid worrying about that here.
+				underlying = r.typ().Underlying()
+
+				methods = make([]*types2.Func, r.Len())
+				for i := range methods {
+					methods[i] = r.method()
+				}
+
+				return
+			})
+
+		case pkgbits.ObjVar:
+			pos := r.pos()
+			typ := r.typ()
+			return types2.NewVar(pos, objPkg, objName, typ)
+		}
+	})
+
+	return objPkg, objName
+}
+
+func (pr *pkgReader) objDictIdx(idx pkgbits.Index) *readerDict {
+	var dict readerDict
+	{
+		r := pr.tempReader(pkgbits.RelocObjDict, idx, pkgbits.SyncObject1)
+
+		if implicits := r.Len(); implicits != 0 {
+			base.Fatalf("unexpected object with %v implicit type parameter(s)", implicits)
+		}
+
+		dict.bounds = make([]typeInfo, r.Len())
+		for i := range dict.bounds {
+			dict.bounds[i] = r.typInfo()
+		}
+
+		dict.derived = make([]derivedInfo, r.Len())
+		dict.derivedTypes = make([]types2.Type, len(dict.derived))
+		for i := range dict.derived {
+			dict.derived[i] = derivedInfo{r.Reloc(pkgbits.RelocType), r.Bool()}
+		}
+
+		pr.retireReader(r)
+	}
+	// function references follow, but reader doesn't need those
+
+	return &dict
+}
+
+func (r *reader) typeParamNames() []*types2.TypeParam {
+	r.Sync(pkgbits.SyncTypeParamNames)
+
+	// Note: This code assumes it only processes objects without
+	// implement type parameters. This is currently fine, because
+	// reader is only used to read in exported declarations, which are
+	// always package scoped.
+
+	if len(r.dict.bounds) == 0 {
+		return nil
+	}
+
+	// Careful: Type parameter lists may have cycles. To allow for this,
+	// we construct the type parameter list in two passes: first we
+	// create all the TypeNames and TypeParams, then we construct and
+	// set the bound type.
+
+	r.dict.tparams = make([]*types2.TypeParam, len(r.dict.bounds))
+	for i := range r.dict.bounds {
+		pos := r.pos()
+		pkg, name := r.localIdent()
+
+		tname := types2.NewTypeName(pos, pkg, name, nil)
+		r.dict.tparams[i] = types2.NewTypeParam(tname, nil)
+	}
+
+	for i, bound := range r.dict.bounds {
+		r.dict.tparams[i].SetConstraint(r.p.typIdx(bound, r.dict))
+	}
+
+	return r.dict.tparams
+}
+
+func (r *reader) method() *types2.Func {
+	r.Sync(pkgbits.SyncMethod)
+	pos := r.pos()
+	pkg, name := r.selector()
+
+	rtparams := r.typeParamNames()
+	sig := r.signature(r.param(), rtparams, nil)
+
+	_ = r.pos() // TODO(mdempsky): Remove; this is a hacker for linker.go.
+	return types2.NewFunc(pos, pkg, name, sig)
+}
+
+func (r *reader) qualifiedIdent() (*types2.Package, string) { return r.ident(pkgbits.SyncSym) }
+func (r *reader) localIdent() (*types2.Package, string)     { return r.ident(pkgbits.SyncLocalIdent) }
+func (r *reader) selector() (*types2.Package, string)       { return r.ident(pkgbits.SyncSelector) }
+
+func (r *reader) ident(marker pkgbits.SyncMarker) (*types2.Package, string) {
+	r.Sync(marker)
+	return r.pkg(), r.String()
+}