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cmd/compile: slice bounds out of range panic on generic code #49497

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rogpeppe opened this issue Nov 10, 2021 · 2 comments
Closed

cmd/compile: slice bounds out of range panic on generic code #49497

rogpeppe opened this issue Nov 10, 2021 · 2 comments
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@rogpeppe
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@rogpeppe rogpeppe commented Nov 10, 2021

go version devel go1.18-17980dff36 Wed Nov 10 05:08:25 2021 +0000 linux/amd64

What did you do?

Run testscript on the following txtar file:

go test
-- go.mod --
module example.com/m

go 1.18
-- m.go --
package m

func F[T any]() A[T] {
	panic("unreachable")
}

type A[T any] struct {
	b B[T]
}

func (a A[T]) M() C[T] {
	return C[T]{
		B: a.b,
	}
}

type B[T any] struct{}

type C[T any] struct {
	B B[T]
}
-- m_test.go --
package m_test

import (
	"testing"

	"example.com/m"
)

func TestF(t *testing.T) {
	m.F[string]()
}

I see a panic with the following stack trace:

panic: runtime error: slice bounds out of range [:-1]

goroutine 1 [running]:
cmd/compile/internal/typecheck.genericTypeName(...)
	/home/rogpeppe/go/src/cmd/compile/internal/typecheck/subr.go:1402
cmd/compile/internal/typecheck.(*Tsubster).typ1(0xc0005afd68, 0xc0005ae1c0)
	/home/rogpeppe/go/src/cmd/compile/internal/typecheck/subr.go:1106 +0x13dd
cmd/compile/internal/typecheck.(*Tsubster).Typ(0x59728b?, 0x4?)
	/home/rogpeppe/go/src/cmd/compile/internal/typecheck/subr.go:1046 +0x25
cmd/compile/internal/noder.(*subster).node.func1({0xe892b8, 0xc00068d520?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:903 +0x305
cmd/compile/internal/ir.(*KeyExpr).editChildren(0xc000374180, 0xc000684c30)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/node_gen.go:792 +0x62
cmd/compile/internal/ir.EditChildren(...)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/visit.go:185
cmd/compile/internal/noder.(*subster).node.func1({0xe88e08, 0xc000374060?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:955 +0x52f
cmd/compile/internal/ir.editNodes(...)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/node_gen.go:1521
cmd/compile/internal/ir.(*CompLitExpr).editChildren(0xc0005b2080, 0xc000684c30)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/node_gen.go:405 +0x171
cmd/compile/internal/ir.EditChildren(...)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/visit.go:185
cmd/compile/internal/noder.(*subster).node.func1({0xe880c0, 0xc0005b2000?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:955 +0x52f
cmd/compile/internal/ir.editNodes(...)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/node_gen.go:1521
cmd/compile/internal/ir.(*ReturnStmt).editChildren(0xe89830?, 0xc000684c30)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/node_gen.go:1056 +0xa2
cmd/compile/internal/ir.EditChildren(...)
	/home/rogpeppe/go/src/cmd/compile/internal/ir/visit.go:185
cmd/compile/internal/noder.(*subster).node.func1({0xe89830, 0xc0004e3130?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:955 +0x52f
cmd/compile/internal/noder.(*subster).node(0xc0005afd50, {0xe89830, 0xc0004e3130})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:1171 +0xa5
cmd/compile/internal/noder.(*subster).list(0xc00000fda0?, {0xc0005464c0, 0x1, 0xc00051cfa0?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:1426 +0x8e
cmd/compile/internal/noder.(*genInst).genericSubst(0x1382d60, 0xc0004e31d0, 0xc00068dc70, {0xc00000fd18, 0x1, 0x1}, 0x1, 0xc000684ae0)
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:803 +0xce6
cmd/compile/internal/noder.(*genInst).getInstantiation(0x1382d60, 0xc00068dc70, {0xc00000fc70, 0x1, 0x7fed55649418?}, 0x39?)
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:680 +0x298
cmd/compile/internal/noder.(*genInst).instantiateMethods(0x40cdc5?)
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:577 +0x24e
cmd/compile/internal/noder.(*genInst).buildInstantiations(0x1382d60, 0x1)
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:60 +0x3a
cmd/compile/internal/noder.BuildInstantiations(...)
	/home/rogpeppe/go/src/cmd/compile/internal/noder/stencil.go:47
cmd/compile/internal/noder.(*irgen).generate(0xc00016a240, {0xc00000e420, 0x1, 0x203000?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/irgen.go:320 +0x3db
cmd/compile/internal/noder.check2({0xc00000e420, 0x1, 0x1})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/irgen.go:92 +0x16d
cmd/compile/internal/noder.LoadPackage({0xc00001e220, 0x1, 0x0?})
	/home/rogpeppe/go/src/cmd/compile/internal/noder/noder.go:90 +0x335
cmd/compile/internal/gc.Main(0xd42fd0)
	/home/rogpeppe/go/src/cmd/compile/internal/gc/main.go:191 +0xb13
main.main()
	/home/rogpeppe/go/src/cmd/compile/main.go:55 +0xdd

If I change the name of the field C.B to C.b, it doesn't panic.

@danscales danscales self-assigned this Nov 10, 2021
@danscales
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@danscales danscales commented Nov 10, 2021

Yes, it looks to be a confusion on the name 'B' during import of package m into m_test. I'll investigate further.

@danscales danscales added the NeedsInvestigation label Nov 10, 2021
@danscales danscales added this to the Go1.18 milestone Nov 10, 2021
@gopherbot
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@gopherbot gopherbot commented Nov 10, 2021

Change https://golang.org/cl/363074 mentions this issue: cmd/compile: don't do Resolve on OKEY identifiers during import

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