cmd/compile: crash when masking len builtin with a const of same name

[kwoodhouse93]

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

The playground uses the latest stable release of Go.
The current version is go1.11.1.

Does this issue reproduce with the latest release?

Yes

What did you do?

Minimal example:
https://play.golang.org/p/zVHeuxQmSGD

What did you expect to see?

A compiler error

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x70 pc=0xb7c7ee]

goroutine 1 [running]:
cmd/compile/internal/gc.typecheck1(0xc00034e000, 0x1, 0xca41c5)
	/usr/local/go/src/cmd/compile/internal/gc/typecheck.go:1270 +0x3ece
cmd/compile/internal/gc.typecheck(0xc00034e000, 0x1, 0x3)
	/usr/local/go/src/cmd/compile/internal/gc/typecheck.go:238 +0x6ad
cmd/compile/internal/gc.typecheckslice(0xc0000705a0, 0x1, 0x1, 0x1)
	/usr/local/go/src/cmd/compile/internal/gc/typecheck.go:68 +0x50
cmd/compile/internal/gc.Main(0xcc2180)
	/usr/local/go/src/cmd/compile/internal/gc/main.go:518 +0x2059
main.main()
	/usr/local/go/src/cmd/compile/main.go:51 +0x96

[bmkessler]

This may be a duplicate of #27973

[randall77]

This seems to be fixed at tip.
We could consider a backport to 1.11, but I'm inclined not to for this error, it's pretty obscure.

[ALTree]

The fix was already backported to 1.11.2 (#27399). Please upgrade your 1.11 installation to the latest 1.11.5.

Closing here.

[johanbrandhorst]

Does this mean the playground is also running an old version of Go?

[ALTree]

Does this mean the playground is also running an old version of Go?

Yes: https://play.golang.org/p/1VcPUlPk_3

It's currently on 1.11.1.