go/types: assertion failure in expr.go:978 (Checker.rawExpr)

[griesemer]

To reproduce:

1. On top of commit e6d9eda2fc13786c55292429b510128252ad8817, apply
   https://go-review.googlesource.com/#/c/43512/:
   git fetch https://go.googlesource.com/go refs/changes/12/43512/8 && git cherry-pick FETCH_HEAD

2. cd $GOROOT/src; GOOS=linux GOARCH=s390x CGO_ENABLED=0 go tool vet -unsafeptr=false -source archive/zip

Crash (after augmenting go/types to print a bit more information):

vet: import failed: type-checking package "fmt" failed (/Users/gri/go/src/fmt/print.go:10:2: could not import os (type-checking package "os" failed (/Users/gri/go/src/os/dir_unix.go:12:2: could not import syscall (type-checking package "syscall" failed (/Users/gri/go/src/syscall/zerrors_linux_s390x.go:889:2: PR_CAP_AMBIENT redeclared in this block)))))
vet: import failed: type-checking package "fmt" failed (/Users/gri/go/src/fmt/print.go:10:2: could not import os (type-checking package "os" failed (/Users/gri/go/src/os/dir_unix.go:12:2: could not import syscall (type-checking package "syscall" failed (/Users/gri/go/src/syscall/zerrors_linux_s390x.go:889:2: PR_CAP_AMBIENT redeclared in this block)))))
vet: import failed: type-checking package "net/http" failed (/Users/gri/go/src/net/http/client.go:13:2: could not import crypto/tls (type-checking package "crypto/tls" failed (/Users/gri/go/src/crypto/tls/cipher_suites.go:15:2: could not import crypto/x509 (type-checking package "crypto/x509" failed (/Users/gri/go/src/crypto/x509/pem_decrypt.go:16:2: could not import encoding/hex (type-checking package "encoding/hex" failed (/Users/gri/go/src/encoding/hex/hex.go:11:2: could not import fmt (type-checking package "fmt" failed (/Users/gri/go/src/fmt/print.go:10:2: could not import os (type-checking package "os" failed (/Users/gri/go/src/os/dir_unix.go:12:2: could not import syscall (type-checking package "syscall" failed (/Users/gri/go/src/syscall/zerrors_linux_s390x.go:889:2: PR_CAP_AMBIENT redeclared in this block)))))))))))))
vet: import failed: type-checking package "net/http" failed (/Users/gri/go/src/net/http/client.go:13:2: could not import crypto/tls (type-checking package "crypto/tls" failed (/Users/gri/go/src/crypto/tls/cipher_suites.go:15:2: could not import crypto/x509 (type-checking package "crypto/x509" failed (/Users/gri/go/src/crypto/x509/pem_decrypt.go:16:2: could not import encoding/hex (type-checking package "encoding/hex" failed (/Users/gri/go/src/encoding/hex/hex.go:11:2: could not import fmt (type-checking package "fmt" failed (/Users/gri/go/src/fmt/print.go:10:2: could not import os (type-checking package "os" failed (/Users/gri/go/src/os/dir_unix.go:12:2: could not import syscall (type-checking package "syscall" failed (/Users/gri/go/src/syscall/zerrors_linux_s390x.go:889:2: PR_CAP_AMBIENT redeclared in this block)))))))))))))
PANIC archive/zip/reader_test.go:372:17: time.Parse (kind = 1)
panic: archive/zip/reader_test.go:372:17: &{time Parse} (kind = 1)
 [recovered]
	panic: archive/zip/reader_test.go:372:17: &{time Parse} (kind = 1)


goroutine 1 [running]:
go/types.(*Checker).handleBailout(0xc4200fe540, 0xc42133d580)
	/Users/gri/go/src/go/types/check.go:225 +0xa4
panic(0x1274a20, 0xc420bb8080)
	/Users/gri/go/src/runtime/panic.go:491 +0x283
go/types.(*Checker).rawExpr(0xc4200fe540, 0xc4207238c0, 0x1418be0, 0xc4201e69a0, 0x0, 0x0, 0xc42133afa0)
	/Users/gri/go/src/go/types/expr.go:978 +0x6dd
go/types.(*Checker).exprOrType(0xc4200fe540, 0xc4207238c0, 0x1418be0, 0xc4201e69a0)
	/Users/gri/go/src/go/types/expr.go:1576 +0x5f
go/types.(*Checker).call(0xc4200fe540, 0xc4207238c0, 0xc4201e4840, 0x0)
	/Users/gri/go/src/go/types/call.go:15 +0x66
go/types.(*Checker).exprInternal(0xc4200fe540, 0xc4207238c0, 0x14184a0, 0xc4201e4840, 0x0, 0x0, 0xc42133b6d0)
	/Users/gri/go/src/go/types/expr.go:1427 +0x1d21
go/types.(*Checker).rawExpr(0xc4200fe540, 0xc4207238c0, 0x14184a0, 0xc4201e4840, 0x0, 0x0, 0x0)
	/Users/gri/go/src/go/types/expr.go:959 +0x84
go/types.(*Checker).multiExpr(0xc4200fe540, 0xc4207238c0, 0x14184a0, 0xc4201e4840)
	/Users/gri/go/src/go/types/expr.go:1533 +0x62
go/types.(*Checker).initVars.func1(0xc4207238c0, 0x0)
	/Users/gri/go/src/go/types/assignments.go:206 +0x5d
go/types.unpack(0xc42133ba00, 0x1, 0x1, 0x1076c84, 0xc420193c9a, 0x0)
	/Users/gri/go/src/go/types/call.go:140 +0x6a
go/types.(*Checker).initVars(0xc4200fe540, 0xc420bb8040, 0x2, 0x2, 0xc4201e29d0, 0x1, 0x1, 0x0)
	/Users/gri/go/src/go/types/assignments.go:206 +0xf9
go/types.(*Checker).shortVarDecl(0xc4200fe540, 0xb77f, 0xc4201e6940, 0x2, 0x2, 0xc4201e29d0, 0x1, 0x1)
	/Users/gri/go/src/go/types/assignments.go:316 +0x878
go/types.(*Checker).stmt(0xc4200fe540, 0x0, 0x14182a0, 0xc4201e4880)
	/Users/gri/go/src/go/types/stmt.go:391 +0x3763
go/types.(*Checker).stmtList(0xc4200fe540, 0x0, 0xc4201e4ac0, 0x3, 0x4)
	/Users/gri/go/src/go/types/stmt.go:110 +0x88
go/types.(*Checker).stmt(0xc4200fe540, 0x0, 0x1418420, 0xc4201e84b0)
	/Users/gri/go/src/go/types/stmt.go:477 +0x4041
go/types.(*Checker).stmt(0xc4200fe540, 0x0, 0x14188e0, 0xc4201e4b00)
	/Users/gri/go/src/go/types/stmt.go:489 +0x424a
go/types.(*Checker).stmtList(0xc4200fe540, 0x0, 0xc4201de200, 0x12, 0x20)
	/Users/gri/go/src/go/types/stmt.go:110 +0x88
go/types.(*Checker).funcBody(0xc4200fe540, 0xc421cb6cc0, 0xc420193c30, 0xc, 0xc420a2ce40, 0xc4201e8ff0)
	/Users/gri/go/src/go/types/stmt.go:42 +0x18d
go/types.(*Checker).functionBodies(0xc4200fe540)
	/Users/gri/go/src/go/types/resolver.go:476 +0xdb
go/types.(*Checker).checkFiles(0xc4200fe540, 0xc42020ac80, 0x7, 0x8, 0x0, 0x0)
	/Users/gri/go/src/go/types/check.go:241 +0xcb
go/types.(*Checker).Files(0xc4200fe540, 0xc42020ac80, 0x7, 0x8, 0xc420dc54d0, 0x0)
	/Users/gri/go/src/go/types/check.go:230 +0x49
go/types.(*Config).Check(0xc421158580, 0xc42008cbd0, 0x3, 0xc42008f4c0, 0xc42020ac80, 0x7, 0x8, 0xc4205371d0, 0x111e70d, 0x12b89e0, ...)
	/Users/gri/go/src/go/types/api.go:351 +0x1b3
main.(*Package).check(0xc420272600, 0xc42008f4c0, 0xc42020ac80, 0x7, 0x8, 0x0, 0xc420288580)
	/Users/gri/go/src/cmd/vet/types.go:93 +0x37d
main.doPackage(0x7fff5fbffb51, 0xb, 0xc4200a8b80, 0x7, 0x8, 0x0, 0x0)
	/Users/gri/go/src/cmd/vet/main.go:351 +0x919
main.doPackageDir(0x7fff5fbffb51, 0xb)
	/Users/gri/go/src/cmd/vet/main.go:293 +0x586
main.visit(0x7fff5fbffb51, 0xb, 0x1419de0, 0xc4200856c0, 0x0, 0x0, 0x0, 0x0)
	/Users/gri/go/src/cmd/vet/main.go:386 +0xe6
path/filepath.walk(0x7fff5fbffb51, 0xb, 0x1419de0, 0xc4200856c0, 0x12e4c20, 0x0, 0xc420045e70)
	/Users/gri/go/src/path/filepath/path.go:356 +0x81
path/filepath.Walk(0x7fff5fbffb51, 0xb, 0x12e4c20, 0xc, 0xc4200855f0)
	/Users/gri/go/src/path/filepath/path.go:403 +0x11d
main.walkDir(0x7fff5fbffb51, 0xb)
	/Users/gri/go/src/cmd/vet/main.go:401 +0x41
main.main()
	/Users/gri/go/src/cmd/vet/main.go:249 +0x3c2

[griesemer]

Simpler reproducer:

1. Apply the following patch (basically, add an type-check error to the syscall package):

diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go
index 5cbabf7896..0104023356 100644
--- a/src/syscall/exec_linux.go
+++ b/src/syscall/exec_linux.go
@@ -11,6 +11,9 @@ import (
        "unsafe"
 )
 
+const foo = 0
+const foo = 0
+
 // SysProcIDMap holds Container ID to Host ID mappings used for User Namespaces in Linux.
 // See user_namespaces(7).
 type SysProcIDMap struct {

2. Run GOOS=linux go tool vet -source $GOROOT/src/io

[bradfitz]

Now that we know how to work around this for Go 1.9 for the vetall builder (it was finding a real bug, but crashing instead of reporting it), I'm moving this to Go 1.10.

But feel free to fix sooner if it's easy.

[griesemer]

There's a trivial fix, but it's perhaps too aggressive: The problem is that the vet is using a source importer with go/types (it has to). The source importer fails to import the syscall package because it has a bug, yet go/type continues to use that partially type-checked syscall package (to be able to do some type-checking, per #16088 as requested by @alandonovan). The simple solution is to not use an incomplete package, and then the crash disappears. Still checking if there's a softer approach.

[gopherbot]

CL https://golang.org/cl/47074 mentions this issue.

[griesemer]

See also #16088 .