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cmd/compile: able to use interface with type constraints #51578

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dsnet opened this issue Mar 9, 2022 · 5 comments
Closed

cmd/compile: able to use interface with type constraints #51578

dsnet opened this issue Mar 9, 2022 · 5 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
Milestone
Go1.18

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@dsnet
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dsnet commented Mar 9, 2022 •
edited

I'm a little behind on the latest with generics, but my understanding is that interfaces with type sets can currently only be used as type constraints.

If so, I would expect the following to not compile:

type TypeSet interface{ int | string }

func main() {
	t := reflect.TypeOf((*TypeSet)(nil)).Elem()
	fmt.Println(t)
	fmt.Println(t.Kind())
	fmt.Println(t.NumMethod())

	v := reflect.New(t).Elem()
	v.Set(reflect.ValueOf([]byte("hello"))) // this should panic
	fmt.Println(v.Elem().Type())
}

However, not only does it compile, it also executes with incorrect results:

main.TypeSet
interface
0
[]uint8

The v.Set(reflect.ValueOf([]byte("hello"))) is expected to panic since the underlying interface is specified to only hold int or string.

\cc @mdempsky @griesemer @ianlancetaylor
@griesemer griesemer self-assigned this Mar 9, 2022
@griesemer griesemer added NeedsFix The path to resolution is known, but the work has not been done. release-blocker labels Mar 9, 2022
@griesemer griesemer added this to the Go1.18 milestone Mar 9, 2022
@griesemer
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griesemer commented Mar 9, 2022 •
edited

The declaration

type TypeSet interface{ int | string }

is ok, but one shouldn't be able to use this type in the conversion of nil. This is a simple oversight. Fix forthcoming.

@dsnet
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dsnet commented Mar 9, 2022

Also, compiling with GOEXPERIMENT=unified produces an internal compiler error:

<unknown line number>: internal compiler error: panic: unexpected type: 10

goroutine 1 [running]:
runtime/debug.Stack()
	/usr/local/go.tip/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt({0x222d0?, 0xc0?}, {0xd0a13b, 0x9}, {0xc0005b63c8, 0x1, 0x1})
	/usr/local/go.tip/src/cmd/compile/internal/base/print.go:227 +0x1d7
cmd/compile/internal/base.Fatalf(...)
	/usr/local/go.tip/src/cmd/compile/internal/base/print.go:196
cmd/compile/internal/gc.handlePanic()
	/usr/local/go.tip/src/cmd/compile/internal/gc/main.go:48 +0x85
panic({0xc79220, 0xc00010b410})
	/usr/local/go.tip/src/runtime/panic.go:838 +0x207
cmd/compile/internal/noder.(*reader).doTyp(0xc0000b9a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:415 +0x2bd
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0000360c0, {0xc0005b6690?, 0xf2?}, 0xc000137c20, 0x1)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:350 +0x171
cmd/compile/internal/noder.(*reader).typWrapped(0xc0000b98c0, 0x1?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:322 +0x45
cmd/compile/internal/noder.(*reader).typ(...)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:316
cmd/compile/internal/noder.(*reader).interfaceType(0xc0000b98c0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:467 +0x285
cmd/compile/internal/noder.(*reader).doTyp(0xc0000b98c0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:445 +0x249
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0000360c0, {0xc0005b68d0?, 0xff?}, 0xc000137c20, 0x0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:350 +0x171
cmd/compile/internal/noder.(*reader).typWrapped(0xc0000b9600, 0xc0?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:322 +0x45
cmd/compile/internal/noder.(*pkgReader).objIdx(0xc0000360c0, 0x6?, {0x0, 0x0, 0x0}, {0x13afe60, 0x0, 0x0})
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:661 +0x5d2
cmd/compile/internal/noder.(*reader).obj(0xc0000b91e0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:564 +0x1ee
cmd/compile/internal/noder.(*reader).doTyp(0xc0000b91e0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:421 +0x59
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0000360c0, {0xc0000b9080?, 0xc0?}, 0xc000136140, 0x1)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:350 +0x171
cmd/compile/internal/noder.(*reader).typWrapped(0xc0000b9080, 0x80?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:322 +0x45
cmd/compile/internal/noder.(*reader).typ(0x7fa308fb7d30?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:316 +0x1e
cmd/compile/internal/noder.(*reader).doTyp(0xc0000b9080)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:437 +0x145
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0000360c0, {0xc000429a20?, 0x80?}, 0xc000136140, 0x1)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:350 +0x171
cmd/compile/internal/noder.(*reader).typWrapped(0xc000429a20, 0x20?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:322 +0x45
cmd/compile/internal/noder.(*reader).typ(0x4eadc2?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:316 +0x1e
cmd/compile/internal/noder.(*reader).expr(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1668 +0xcb7
cmd/compile/internal/noder.(*reader).exprs(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1768 +0x8d
cmd/compile/internal/noder.(*reader).expr(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1663 +0xe85
cmd/compile/internal/noder.(*reader).expr(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1656 +0xd5b
cmd/compile/internal/noder.(*reader).exprs(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1768 +0x8d
cmd/compile/internal/noder.(*reader).exprList(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1758 +0x2f
cmd/compile/internal/noder.(*reader).stmt1(0xc000429a20?, 0x30?, 0xc0005b77e0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1222 +0xba
cmd/compile/internal/noder.(*reader).stmts(0xc000429a20)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:1199 +0xa5
cmd/compile/internal/noder.(*reader).funcBody.func1()
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:984 +0x52
cmd/compile/internal/ir.WithFunc(0x586?, 0xb7?)
	/usr/local/go.tip/src/cmd/compile/internal/ir/func.go:293 +0xab
cmd/compile/internal/noder.(*reader).funcBody(0xc000429a20, 0xc0004298c0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:977 +0xaf
cmd/compile/internal/noder.pkgReaderIndex.funcBody({0xc0000360c0?, 0xc00013f928?, 0xc000136140?}, 0xc000700000?)
	/usr/local/go.tip/src/cmd/compile/internal/noder/reader.go:970 +0x3c
cmd/compile/internal/noder.readBodies(0xc0001746c0)
	/usr/local/go.tip/src/cmd/compile/internal/noder/unified.go:150 +0xca
cmd/compile/internal/noder.unified({0xc00011c430?, 0x0?, 0x2?})
	/usr/local/go.tip/src/cmd/compile/internal/noder/unified.go:119 +0x42a
cmd/compile/internal/noder.LoadPackage({0xc000124100, 0x1, 0x0?})
	/usr/local/go.tip/src/cmd/compile/internal/noder/noder.go:73 +0x2b4
cmd/compile/internal/gc.Main(0xd398b0)
	/usr/local/go.tip/src/cmd/compile/internal/gc/main.go:190 +0xb13
main.main()
	/usr/local/go.tip/src/cmd/compile/main.go:55 +0xdd

@griesemer
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Simpler reproducer:

var _ = (*interface{int})(nil)

should not be permitted.

@gopherbot
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Change https://go.dev/cl/391275 mentions this issue: go/types, types2: pointer base types cannot be type constraints

@dmitshur dmitshur mentioned this issue Mar 10, 2022
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@gopherbot
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Change https://go.dev/cl/391357 mentions this issue: [release-branch.go1.18] go/types, types2: pointer base types cannot be type constraints

gopherbot pushed a commit that referenced this issue Mar 11, 2022
@griesemer @dmitshur
[release-branch.go1.18] go/types, types2: pointer base types cannot b…
a0c7e26 
…e type constraints

Pointer types may appear in expressions *P and we don't know if
we have an indirection (P is a pointer value) or a pointer type
(P is a type) until we type-check P. Don't forget to check that
a type P must be an ordinary (not a constraint) type in this
special case.

Fixes #51578.

Change-Id: If782cc6dd2a602a498574c78c99e40c3b72274a5
Reviewed-on: https://go-review.googlesource.com/c/go/+/391275
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 3a5e3d8)
Reviewed-on: https://go-review.googlesource.com/c/go/+/391357
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
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