x/tools/gopls: panic in go/types

[brunetto]

gopls version: v0.6.9
gopls flags:
update flags: proxy
extension version: 0.24.0
go version: 1.16.3
environment: Visual Studio Code darwin
initialization error: undefined
manual restart count: 0
total start count: 1

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

It seems I was defining a type as pointer to an imported type but the type name was the same as the imported package.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x119e3c8]

goroutine 5805 [running]:
go/types.(*Checker).handleBailout(0xc007f30ea0, 0xc00840f808)
	  check.go:245  0x9f
panic(0x190cd00, 0x1fb8350)
	  panic.go:965  0x1b9
go/types.IsInterface(...)
	  predicates.go:76
go/types.(*Checker).rawLookupFieldOrMethod(0xc007f30ea0, 0x1b57338, 0xc00323dcc0, 0xc004975400, 0xc007f6a500, 0xc007f02910, 0x5, 0x0, 0x1, 0x5, ...)
	  lookup.go:86  0x11a8
go/types.(*Checker).lookupFieldOrMethod(0xc007f30ea0, 0x1b57310, 0xc007f6b680, 0xc0052b2500, 0xc007f6a500, 0xc007f02910, 0x5, 0xd5557fb5555fe, 0x34, 0x20, ...)
	  lookup.go:58  0x165
go/types.(*Checker).selector(0xc007f30ea0, 0xc004975440, 0xc007ef8cc0)
	  call.go:433  0x151
go/types.(*Checker).typInternal(0xc007f30ea0, 0x1b62db0, 0xc007ef8cc0, 0x0, 0x10, 0x1926720)
	  typexpr.go:237  0x6f0
go/types.(*Checker).definedType(0xc007f30ea0, 0x1b62db0, 0xc007ef8cc0, 0x0, 0x0, 0x0)
	  typexpr.go:138  0x55
go/types.(*Checker).typ(...)
	  typexpr.go:120
go/types.(*Checker).typInternal(0xc007f30ea0, 0x1b62e40, 0xc007ef8cd8, 0xc007f6b680, 0x48, 0x199e080)
	  typexpr.go:279  0x925
go/types.(*Checker).definedType(0xc007f30ea0, 0x1b62e40, 0xc007ef8cd8, 0xc007f6b680, 0x0, 0x0)
	  typexpr.go:138  0x55
go/types.(*Checker).typeDecl(0xc007f30ea0, 0xc007f6a780, 0x1b62e40, 0xc007ef8cd8, 0x0, 0x0)
	  decl.go:648  0x22e
go/types.(*Checker).objDecl(0xc007f30ea0, 0x1b75608, 0xc007f6a780, 0x0)
	  decl.go:192  0x7e6
go/types.(*Checker).packageObjects(0xc007f30ea0)
	  resolver.go:537  0x3a9
go/types.(*Checker).checkFiles(0xc007f30ea0, 0xc007d4cd50, 0x1, 0x1, 0x0, 0x0)
	  check.go:265  0xb9
go/types.(*Checker).Files(...)
	  check.go:250
golang.org/x/tools/internal/lsp/cache.typeCheck(0x1b64598, 0xc005c25480, 0xc0004c1110, 0xc000fb6e00, 0x2, 0xc0011aa120, 0x0, 0x0, 0x0)
	  check.go:431  0x1193
golang.org/x/tools/internal/lsp/cache.(*snapshot).buildPackageHandle.func1(0x1b64598, 0xc005c25480, 0x1b52e40, 0xc0004c1110, 0xc00051e740, 0x2)
	  check.go:101  0x1bc
golang.org/x/tools/internal/memoize.(*Handle).run.func1(0xc00445fec0, 0x1b64598, 0xc005c25480, 0xc000ceb920, 0x1b52e40, 0xc0004c1110, 0xc00119f6e0)
	  memoize.go:322  0xab
created by golang.org/x/tools/internal/memoize.(*Handle).run
	  memoize.go:315  0x185
[Error - 7:01:37 PM] 

[stamblerre]

Thanks for reporting this issue! It looks like the nil pointer happens here, but I think this has actually been fixed at master (

go/src/go/types/type.go

Line 881 in fca51ba

func under(t Type) Type {

).

/cc @findleyr for confirmation

[findleyr]

Thanks for the report, this is interesting. I would not be surprised if this has been fixed, but also that code should not panic. If I understand your description, you were doing something like this:

type foo *foo.Bar

Is that correct?

CC @griesemer

[griesemer]

The specific code pattern:

type foo *foo.Bar

doesn't cause a panic (neither in go/types nor the compiler, nor types2). I also tried

package p

import "fmt"

type fmt *fmt.Stringer

for good measure, and we also get the expected error repors.

We'd need more info to reproduce this crash, I think.

[brunetto]

Hi,
I tried this and I got a gopls crash immediately:

package main

func main() {}

type fmt *fmt.Stringer

What more info can I provide to help?

[griesemer]

Whatever the bug was in the type checkers, this is not reproducible at tip.

[stamblerre]

Thanks for confirming that, @griesemer.
Looks like the fix will be available when Go 1.17 is released. Sorry about the inconvenience!