What version of Go are you using (go version)?

$ go version
go version devel +0b4bca4654 Fri Nov 30 14:46:17 2018 -0500 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

Linux x86_64

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/usr/local/google/home/thanm/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/ssd2/go1"
GOPROXY=""
GORACE=""
GOROOT="/ssd2/go"
GOTMPDIR=""
GOTOOLDIR="/ssd2/go/pkg/tool/linux_amd64"
GCCGO="/ssd/gcc-trunk2/cross/bin/gccgo"
CC="gcc"
CXX="g++"
...

What did you do?

If you compile the attached Go code with an older version of gccgo (not tip) that uses V2 export data, then try to import the export data using go/internal/gccgoimporter, the importer will crash with

panic: import error /tmp/167944616/issueXXX.o:10:1 (byte offset = 917): internal error: unexpected fixup required for issueXXX.FooServer

The code in the importer is written to allow for possible circular type references (a reference to struct type T that takes place somewhere inside the body or definition of T, before T is finalized); this is handled by making a note of the reference and generating a fixup that is applied later. The fixup scheme is not needed for the most recent version of gccgo export data (V3), but it is needed for older verisons such as V1. The example link illustrates a case where it is also needed for V2 export data.

`
package server

import (
"context"
"errors"
)

type A struct {
x int
}

func (a *A) AMethod(y int) *Server {
return nil
}

// FooServer is a server that provides Foo services
type FooServer Server

func (f *FooServer) WriteEvents(ctx context.Context, x int) error {
return errors.New("hey!")
}

type Server struct {
FooServer *FooServer
user string
ctx context.Context
}

func New(sctx context.Context, u string) (*Server, error) {
s := &Server{user: u, ctx: sctx}
s.FooServer = (*FooServer)(s)
return s, nil
}
`

What did you expect to see?

Import succeeded.

What did you see instead?

Import fails with assertion. Here is a representative stack trace (I'm forcing the import by adding this as a test case to the gccgoimporter test suite):

`=== RUN TestObjImporter
--- FAIL: TestObjImporter (0.41s)
importer_test.go:145: gccgo version 9.0
panic: import error /tmp/542355319/issueXXX.o:10:1 (byte offset = 917): internal error: unexpected fixup required for issueXXX.FooServer [recovered]
panic: import error /tmp/542355319/issueXXX.o:10:1 (byte offset = 917): internal error: unexpected fixup required for issueXXX.FooServer

goroutine 5 [running]:
testing.tRunner.func1(0xc000154100)
/go/src/testing/testing.go:827 +0x387
panic(0x58c1a0, 0xc000172180)
/go/src/runtime/panic.go:513 +0x1b7
go/internal/gccgoimporter.(*parser).error(0xc000175380, 0x579300, 0xc00018e190)
/go/src/go/internal/gccgoimporter/parser.go:86 +0x21e
go/internal/gccgoimporter.(*parser).errorf(0xc000175380, 0x5b9cd0, 0x30, 0xc0002b0598, 0x1, 0x1)
/go/src/go/internal/gccgoimporter/parser.go:90 +0xbc
go/internal/gccgoimporter.(*parser).parseNamedType(0xc000175380, 0xc0003ce9d0, 0x1, 0x1, 0x8, 0x1)
/go/src/go/internal/gccgoimporter/parser.go:530 +0x663
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce9d0, 0x1, 0x1, 0xc0003ce9d0, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:794 +0x367
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x10000c0003ce901, 0xc00018e170)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseType(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x1, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:882 +0x69
go/internal/gccgoimporter.(*parser).parsePointerType(0xc000175380, 0xc00017c190, 0xc0003ce9b0, 0x1, 0x1, 0x1, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:785 +0x168
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce9b0, 0x1, 0x1, 0xc0003ce9b0, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:812 +0x434
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0xc0003ce9a0, 0x9)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseType(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x6, 0x60)
/go/src/go/internal/gccgoimporter/parser.go:882 +0x69
go/internal/gccgoimporter.(*parser).parseField(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x1)
/go/src/go/internal/gccgoimporter/parser.go:241 +0x78
go/internal/gccgoimporter.(*parser).parseStructType(0xc000175380, 0xc00017c190, 0xc0003ce978, 0x1, 0x1, 0x1, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:665 +0x166
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce978, 0x1, 0x1, 0xc0003ce978, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:805 +0x2b9
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x6, 0xc0003ce959)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseType(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x1, 0x8)
/go/src/go/internal/gccgoimporter/parser.go:882 +0x69
go/internal/gccgoimporter.(*parser).parseNamedType(0xc000175380, 0xc0003ce960, 0x1, 0x1, 0x8, 0x1)
/go/src/go/internal/gccgoimporter/parser.go:526 +0x17c
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce960, 0x1, 0x1, 0xc0003ce960, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:794 +0x367
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x10000c0003ce901, 0xc00018e140)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseType(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x1, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:882 +0x69
go/internal/gccgoimporter.(*parser).parsePointerType(0xc000175380, 0xc00017c190, 0xc0003ce948, 0x1, 0x1, 0x1, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:785 +0x168
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce948, 0x1, 0x1, 0xc0003ce948, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:812 +0x434
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x1, 0xc000175380)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseResultList(0xc000175380, 0xc00017c190, 0xc00016c0e0)
/go/src/go/internal/gccgoimporter/parser.go:708 +0x8f
go/internal/gccgoimporter.(*parser).parseNamedType(0xc000175380, 0xc0003ce8c0, 0x1, 0x1, 0x8, 0x1)
/go/src/go/internal/gccgoimporter/parser.go:557 +0x2fc
go/internal/gccgoimporter.(*parser).parseTypeSpec(0xc000175380, 0xc00017c190, 0xc0003ce8c0, 0x1, 0x1, 0xc0003ce8c0, 0x0)
/go/src/go/internal/gccgoimporter/parser.go:794 +0x367
go/internal/gccgoimporter.(*parser).parseTypeAfterAngle(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0x3c, 0xffffffffffffffff)
/go/src/go/internal/gccgoimporter/parser.go:903 +0x571
go/internal/gccgoimporter.(*parser).parseType(0xc000175380, 0xc00017c190, 0x0, 0x0, 0x0, 0xc00017c2d0, 0x100)
/go/src/go/internal/gccgoimporter/parser.go:882 +0x69
go/internal/gccgoimporter.(*parser).parseDirective(0xc000175380)
/go/src/go/internal/gccgoimporter/parser.go:1190 +0x36b
go/internal/gccgoimporter.(*parser).parsePackage(0xc000175380, 0xc000170980)
/go/src/go/internal/gccgoimporter/parser.go:1213 +0x2c
go/internal/gccgoimporter.GetImporter.func1(0xc00016ed20, 0x5b05a9, 0x8, 0x5af36a, 0x1, 0x0, 0x0, 0x0, 0x0)
/go/src/go/internal/gccgoimporter/importer.go:202 +0x3f8
go/internal/gccgoimporter.runImporterTest(0xc000154100, 0xc0000fca50, 0xc0000fca20, 0xc0002b1808)
/go/src/go/internal/gccgoimporter/importer_test.go:25 +0x7b
go/internal/gccgoimporter.TestObjImporter(0xc000154100)
/go/src/go/internal/gccgoimporter/importer_test.go:184 +0xb38
testing.tRunner(0xc000154100, 0x5bba48)
/go/src/testing/testing.go:862 +0xbf
created by testing.(*T).Run
/go/src/testing/testing.go:913 +0x34d
FAIL go/internal/gccgoimporter 0.446s
`