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cmd/compile: "any" should be an alias for "interface{}", not a defined type #49665

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cherrymui opened this issue Nov 18, 2021 · 9 comments
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cmd/compile: "any" should be an alias for "interface{}", not a defined type #49665

cherrymui opened this issue Nov 18, 2021 · 9 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker
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Go1.18

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@cherrymui
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The spec says

the predeclared type any is an alias for the empty interface.

I would interpret it as "any" being an alias type, not a defined type, i.e. essentially type any = interface{}.

But it seems the compiler treats "any" as a defined type, for example,

package main

import "fmt"

var x any
var y interface{}

func main() {
	fmt.Printf("%T\n%T\n", &x, &y)
}

This prints

*any
*interface {}

(In contrast, the spec says "byte" is an alias for "uint8", and both byte and uint8 print as "uint8".)
@ianlancetaylor
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CC @griesemer

@ianlancetaylor ianlancetaylor added Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Nov 18, 2021
@ianlancetaylor ianlancetaylor added this to the Go1.18 milestone Nov 18, 2021
@findleyr
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See also #49583. I expected that change to only affect error messages from the type checker, not %T formatting (if indeed this is a consequence of that change).

@findleyr
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CC @danscales @mdempsky

Discussing with @griesemer, the problem may be here:
https://cs.opensource.google/go/go/+/master:src/cmd/compile/internal/types/universe.go;l=113;drc=5344dcae4139de85b9e3d8cea81f9b65fc2bd25f

Should that be TINTER, not TFORW?

@mdempsky
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Yeah, that code is incorrect if any should be an alias.

We should be creating types.AnyType as an anonymous type and then directly declaring it as the name any. That's a little more involved than just changing TFORW to TINTER but not that invasive.

A bit more involved will be finding all the byte / rune logic that specially handles those aliases for error messages and replicate it to handle any too.

@mdempsky
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If we confirm that any should be an alias, not a defined type, I can fix cmd/compile.

@randall77
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@thanm This may be related to the any problem you were trying to fix in DWARF.

@griesemer
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any is definitively and alias for interface{}.

@griesemer
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See also the forthcoming spec (search for predeclared type any).

@mdempsky mdempsky self-assigned this Nov 18, 2021
@mdempsky mdempsky added NeedsFix The path to resolution is known, but the work has not been done. and removed Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Nov 18, 2021
@mdempsky mdempsky changed the title spec, cmd/compile: clarify if "any" is a defined type cmd/compile: "any" should be an alias for "interface{}", not a defined type Nov 18, 2021
@gopherbot
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Change https://golang.org/cl/365354 mentions this issue: cmd/compile: handle anyas alias likebyteandrune``

@golang golang locked and limited conversation to collaborators Jun 23, 2023
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@mdempsky @ianlancetaylor @randall77 @griesemer @gopherbot @cherrymui @findleyr