go/internal/gccgoimporter: fix bug reading V1 export data

Fix a bug in the reading of elderly export data. In such export data
when reading type information it's possible to encounter a named type N1
defined as a typedef of some other named type N2 at a point when the
underying type of N1 has not yet been finalized. Handle this case by
generating a fixup, then process fixups at the end of parsing to
set the correct underlying type.

Fixes #29006.

Change-Id: I6a505c897bd95eb161ee04637bb6eebad9f20d52
Reviewed-on: https://go-review.googlesource.com/c/151997
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/go/internal/gccgoimporter/importer_test.go

@@ -86,6 +86,7 @@ var importerTests = [...]importerTest{
 	{pkgpath: "aliases", name: "C0", want: "type C0 struct{f1 C1; f2 C1}"},
 	{pkgpath: "escapeinfo", name: "NewT", want: "func NewT(data []byte) *T"},
 	{pkgpath: "issue27856", name: "M", want: "type M struct{E F}"},
+	{pkgpath: "v1reflect", name: "Type", want: "type Type interface{Align() int; AssignableTo(u Type) bool; Bits() int; ChanDir() ChanDir; Elem() Type; Field(i int) StructField; FieldAlign() int; FieldByIndex(index []int) StructField; FieldByName(name string) (StructField, bool); FieldByNameFunc(match func(string) bool) (StructField, bool); Implements(u Type) bool; In(i int) Type; IsVariadic() bool; Key() Type; Kind() Kind; Len() int; Method(int) Method; MethodByName(string) (Method, bool); Name() string; NumField() int; NumIn() int; NumMethod() int; NumOut() int; Out(i int) Type; PkgPath() string; Size() uintptr; String() string; common() *commonType; rawString() string; runtimeType() *runtimeType; uncommon() *uncommonType}"},
 }
 
 func TestGoxImporter(t *testing.T) {

src/go/internal/gccgoimporter/parser.go

@@ -29,9 +29,30 @@ type parser struct {
 	imports  map[string]*types.Package // package path -> package object
 	typeList []types.Type              // type number -> type
 	typeData []string                  // unparsed type data (v3 and later)
+	fixups   []fixupRecord             // fixups to apply at end of parsing
 	initdata InitData                  // package init priority data
 }
 
+// When reading V1 export data it's possible to encounter a defined
+// type N1 with an underlying defined type N2 while we are still
+// reading in that defined type N2; see issue #29006 for an instance
+// of this. Example:
+//
+//   type N1 N2
+//   type N2 struct {
+//      ...
+//      p *N1
+//   }
+//
+// To handle such cases, the parser generates a fixup record (below) and
+// delays setting of N1's underlying type until parsing is complete, at
+// which point fixups are applied.
+
+type fixupRecord struct {
+	toUpdate *types.Named // type to modify when fixup is processed
+	target   types.Type   // type that was incomplete when fixup was created
+}
+
 func (p *parser) init(filename string, src io.Reader, imports map[string]*types.Package) {
 	p.scanner = new(scanner.Scanner)
 	p.initScanner(filename, src)
@@ -504,8 +525,16 @@ func (p *parser) parseNamedType(nlist []int) types.Type {
 
 	underlying := p.parseType(pkg)
 	if nt.Underlying() == nil {
+		if underlying.Underlying() == nil {
+			if p.version != "v1" {
+				p.errorf("internal error: unexpected fixup required for %v", nt)
+			}
+			fix := fixupRecord{toUpdate: nt, target: underlying}
+			p.fixups = append(p.fixups, fix)
+		} else {
 			nt.SetUnderlying(underlying.Underlying())
 		}
+	}
 
 	if p.tok == '\n' {
 		p.next()
@@ -1175,6 +1204,13 @@ func (p *parser) parsePackage() *types.Package {
 	for p.tok != scanner.EOF {
 		p.parseDirective()
 	}
+	for _, f := range p.fixups {
+		if f.target.Underlying() == nil {
+			p.errorf("internal error: fixup can't be applied, loop required")
+		}
+		f.toUpdate.SetUnderlying(f.target.Underlying())
+	}
+	p.fixups = nil
 	for _, typ := range p.typeList {
 		if it, ok := typ.(*types.Interface); ok {
 			it.Complete()