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x/tools/go/ssa: panic with Go 1.17 slice-to-array conversions when converting to a newtype #48281

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ainar-g opened this issue Sep 9, 2021 · 2 comments
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x/tools/go/ssa: panic with Go 1.17 slice-to-array conversions when converting to a newtype #48281

ainar-g opened this issue Sep 9, 2021 · 2 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. Tools This label describes issues relating to any tools in the x/tools repository.
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Unreleased

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@ainar-g
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ainar-g commented Sep 9, 2021

This is probably related to #46987. Consider this code:

package main

import (
	"fmt"
)

type arr [2]int

func main() {
	s := []int{1, 2, 3, 4}
	fmt.Println(*(*arr)(s))
}

This program works and produces the intended output with Go 1.17. But checking it with any SSA-based analyser seems to trigger a panic. For example, using nilness:

goroutine 195 [running]:
golang.org/x/tools/go/ssa.emitConv(0xc0000fac80, {0x7c6120, 0xc00049cea0}, {0x7bf368, 0xc000078810})
        /home/ainar/go/pkg/mod/golang.org/x/tools@v0.1.6-0.20210908235426-076821bd2bbc/go/ssa/emit.go:252 +0x8ee
golang.org/x/tools/go/ssa.(*builder).expr0(0x6fe800, 0xc0000fac80, {0x7bfac8, 0xc0001163c0}, {0x7, {0x7bf368, 0xc000078810}, {0x0, 0x0}})
        /home/ainar/go/pkg/mod/golang.org/x/tools@v0.1.6-0.20210908235426-076821bd2bbc/go/ssa/builder.go:573 +0x925
golang.org/x/tools/go/ssa.(*builder).expr(0x0, 0xc0000fac80, {0x7bfac8, 0xc0001163c0})
        /home/ainar/go/pkg/mod/golang.org/x/tools@v0.1.6-0.20210908235426-076821bd2bbc/go/ssa/builder.go:530 +0x19f

But if you replace a newtype with a type alias, it works:

-type arr [2]int
+type arr = [2]int
@gopherbot gopherbot added the Tools This label describes issues relating to any tools in the x/tools repository. label Sep 9, 2021
@gopherbot gopherbot added this to the Unreleased milestone Sep 9, 2021
@cuonglm cuonglm self-assigned this Sep 9, 2021
@cuonglm cuonglm added the NeedsFix The path to resolution is known, but the work has not been done. label Sep 9, 2021
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Change https://golang.org/cl/348511 mentions this issue: go/ssa: fix slice to array ptr conversions for named type

@ainar-g ainar-g mentioned this issue Sep 9, 2021
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@ainar-g
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ainar-g commented Sep 13, 2021

Thanks again for a quick response! I confim that the issue is fixed on the master branch.

ainar-g added a commit to ainar-g/unparam that referenced this issue Sep 15, 2021
@ainar-g
go.mod: update golang.org/x/tools
eae81bc 
Make sure that golang/go#48281 doesn't affect unparam by updating module
golang.org/x/tools to the latest master version.

    go get golang.org/x/tools@master
    go mod tidy

There are no manual changes.
@ainar-g ainar-g mentioned this issue Sep 15, 2021
Merged
mvdan pushed a commit to mvdan/unparam that referenced this issue Sep 15, 2021
@ainar-g @mvdan
go.mod: update golang.org/x/tools
dcc0b62 
Make sure that golang/go#48281 doesn't affect unparam by updating module
golang.org/x/tools to the latest master version.

    go get golang.org/x/tools@master
    go mod tidy

There are no manual changes.
@rsc rsc unassigned cuonglm Jun 23, 2022
@golang golang locked and limited conversation to collaborators Jun 23, 2023
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