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cmd/go2go: segfault in go2go playground #39693

davidthomas426 opened this issue Jun 18, 2020 · 3 comments

cmd/go2go: segfault in go2go playground #39693

davidthomas426 opened this issue Jun 18, 2020 · 3 comments


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@davidthomas426 davidthomas426 commented Jun 18, 2020

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

go2go playground

What did you do?

Even more pared down:

Just trying out generics for the first time. Used a type list in an interface, but I got the syntax wrong.

What did you expect to see?

Syntax error, like in this link:

type checking failed for main
prog.go2:4:2: int is not an interface
prog.go2:4:7: float64 is not an interface

Go build failed.

What did you see instead?

Seg fault and panic

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x40 pc=0x56ca7a]

goroutine 1 [running]:
go/types.(*Checker).handleBailout(0xc00007c6c0, 0xc0000c9be0)
	/usr/local/go-faketime/src/go/types/check.go:251 +0x98
panic(0x64d840, 0x8048d0)
	/usr/local/go-faketime/src/runtime/panic.go:969 +0x175
go/types.(*Interface).Complete(0x0, 0x0)
	/usr/local/go-faketime/src/go/types/type.go:608 +0x3a
go/types.(*Interface).Complete(0xc000084700, 0xc000084700)
	/usr/local/go-faketime/src/go/types/type.go:637 +0x265
go/types.(*TypeParam).Bound(0xc000072740, 0xc000072740)
	/usr/local/go-faketime/src/go/types/type.go:819 +0x47
go/types.optype(0x6de060, 0xc000072740, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/type.go:831 +0x4e
go/types.(*TypeParam).Interface(0xc000072740, 0x6daa60)
	/usr/local/go-faketime/src/go/types/type.go:848 +0x37
go/types.(*Checker).varType(0xc00007c6c0, 0x6daa60, 0xc00000c320, 0xc0000c9460, 0x56d1ff)
	/usr/local/go-faketime/src/go/types/typexpr.go:131 +0x6d
go/types.(*Checker).collectParams(0xc00007c6c0, 0xc0000f3220, 0xc000010ba0, 0x0, 0x0, 0xc00000e201, 0x0, 0x0, 0x0, 0x6dda00)
	/usr/local/go-faketime/src/go/types/typexpr.go:691 +0x4c9
go/types.(*Checker).funcType(0xc00007c6c0, 0xc0000f4840, 0x0, 0xc00000c460)
	/usr/local/go-faketime/src/go/types/typexpr.go:326 +0x8c7
go/types.(*Checker).funcDecl(0xc00007c6c0, 0xc0000f30e0, 0xc0000f4780)
	/usr/local/go-faketime/src/go/types/decl.go:779 +0xc5
go/types.(*Checker).objDecl(0xc00007c6c0, 0x6de7e0, 0xc0000f30e0, 0x0)
	/usr/local/go-faketime/src/go/types/decl.go:200 +0xb85
	/usr/local/go-faketime/src/go/types/resolver.go:644 +0x3a9
go/types.(*Checker).checkFiles(0xc00007c6c0, 0xc00003dcb8, 0x1, 0x1, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/check.go:280 +0x118
go/types.(*Config).Check(0xc0000725c0, 0xc00001a3e0, 0x4, 0xc000072240, 0xc00003dcb8, 0x1, 0x1, 0xc000055360, 0x0, 0x4b6d2f, ...)
	/usr/local/go-faketime/src/go/types/api.go:387 +0x188
go/go2go.RewriteBuffer(0xc0000553b0, 0x7ffebe9a2dd8, 0x1e, 0xc0000b8000, 0xad, 0x2ad, 0x0, 0xc000010a50, 0xc000010a20, 0xc0000109f0, ...)
	/usr/local/go-faketime/src/go/go2go/go2go.go:127 +0x24f
main.translateFile(0xc0000553b0, 0x7ffebe9a2dd8, 0x1e)
	/usr/local/go-faketime/src/cmd/go2go/translate.go:26 +0xa9
	/usr/local/go-faketime/src/cmd/go2go/main.go:64 +0x2ea

Go build failed.
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@griesemer griesemer commented Jun 18, 2020

Thanks. Clearly a bug in the type checker.

This works, as you probably have found out by now:

@griesemer griesemer self-assigned this Jun 18, 2020
@griesemer griesemer added the NeedsFix label Jun 18, 2020
@griesemer griesemer added this to the Unreleased milestone Jun 18, 2020
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@gopherbot gopherbot commented Jun 19, 2020

Change mentions this issue: [dev.go2go] go/types: don't panic if an embedded type is not an interface

gopherbot pushed a commit that referenced this issue Jun 19, 2020

Fixes #39693.

Change-Id: I7f2a4dd95edac3365a9b41b66afcd0015b5b836c
Reviewed-by: Robert Griesemer <>
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@griesemer griesemer commented Jun 19, 2020

Fixed in dev.go2go.

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