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josharian opened this issue Oct 25, 2018 · 8 comments
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cmd/compile: nil type word in interface #28390

josharian opened this issue Oct 25, 2018 · 8 comments
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FrozenDueToAge release-blocker
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Go1.12

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@josharian
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Originally reported by @shuLhan on golang-dev.

The following code panics due to a nil type word:

package main

import (
	"fmt"
)

type A struct {
	K int
	S string
	M map[string]string
}

func newA(k int, s string) (a A) {
	a.K = k
	a.S = s
	a.M = make(map[string]string)
	a.M[s] = s
	return
}

func proxy() (x int, a A) {
	return 1, newA(2, "3")
}

func consume(x int, a interface{}) {
	fmt.Println(x)
	fmt.Println(a)
}

func main() {
	consume(proxy())
}

Introduced by CL 114797.
@josharian josharian added this to the Go1.12 milestone Oct 25, 2018
@josharian josharian self-assigned this Oct 25, 2018
@josharian
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I'm really surprised that this didn't fail anywhere else in all.bash.

In any case, testing a fix now.

@gopherbot
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Change https://golang.org/cl/144598 mentions this issue: cmd/compile: convert arguments as needed

@cherrymui
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I'm really surprised that this didn't fail anywhere else in all.bash.

I guess it only triggers in the form of f(g()) where g returns multiple results and some of the results need conversion? That is probably quite rare...

@josharian
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Actually, g() is inlined in the code above, so it isn't (really) of the form f(g()).

@tandr
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tandr commented Oct 25, 2018 •
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if this regression is reproducible on Go 1.11.1 (as reported in golang-nuts), it seems to be appropriate to have it cherrypicked for go1.11.2 as a target. (IMHO)

@josharian
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Do you have a link handy for the 1.11.1 reproduction report? I can’t reproduce locally with 1.11.1. And the code in question is very much new to 1.12...

@cherrymui
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I don't think it is reproducible with Go 1.11. I can only reproduce it with tip, and the culprit CL is pretty recent, past Go 1.11.

@tandr do you have a link to golang-nuts report?

@tandr
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tandr commented Oct 25, 2018 •
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D'oh, my bad... I misread the https://groups.google.com/forum/#!topic/golang-dev/3Fy0M5dlc-w -- it is NOT reproducible on 1.11.1 (first email in a thread - https://groups.google.com/d/msg/golang-dev/3Fy0M5dlc-w/s5ZdqvfOBwAJ )

Terrible sorry for the noise

@josharian josharian mentioned this issue Oct 27, 2018
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