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spec: unclear whether error should be reported for non-comparable switch expression in empty switch #43200

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griesemer opened this issue Dec 15, 2020 · 5 comments
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spec: unclear whether error should be reported for non-comparable switch expression in empty switch #43200

griesemer opened this issue Dec 15, 2020 · 5 comments
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FrozenDueToAge NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made.
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Go1.17

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@griesemer
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For:

var a struct{ _ func() }
switch a {
}

the compiler reports an error:

cannot switch on a (type struct { _ func() }) (struct containing func() cannot be compared)

Since there's no case in the switch statement, this might be considered ok. The spec is not explicitly stating that this is invalid.

See also #43110.
@griesemer griesemer added the NeedsDecision Feedback is required from experts, contributors, and/or the community before a change can be made. label Dec 15, 2020
@griesemer griesemer added this to the Go1.17 milestone Dec 15, 2020
@griesemer griesemer self-assigned this Dec 15, 2020
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Change https://golang.org/cl/278132 mentions this issue: [dev.typeparams] cmd/compile/internal/types2: report error for invalid (but empty) expr switch

gopherbot pushed a commit that referenced this issue Dec 15, 2020
@griesemer
[dev.typeparams] cmd/compile/internal/types2: report error for invali…
14e4267 
…d (but empty) expr switch

Enable one more errorcheck test.

Updates #43110.
Updates #43200.

Change-Id: Ib7b971d5e9989c65320579f75d65266bbbbeec53
Reviewed-on: https://go-review.googlesource.com/c/go/+/278132
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
@griesemer
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cc: @ianlancetaylor for input on what gccgo does.

@ianlancetaylor
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gccgo says

foo7.go:5:16: error: cannot switch on value whose type that may not be compared
    5 |         switch a {
      |                ^

So the message needs a little work but it has the same behavior.

@gopherbot
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Change https://golang.org/cl/278452 mentions this issue: compiler: correct grammar in error message

gopherbot pushed a commit to golang/gofrontend that referenced this issue Dec 15, 2020
@ianlancetaylor
compiler: correct grammar in error message
5260373 
For golang/go#43200

Change-Id: I7f102bfdd5a2578e59292be4c84e11df107f65c6
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/278452
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
sebhub pushed a commit to RTEMS/gnu-mirror-gcc that referenced this issue Dec 16, 2020
@ianlancetaylor
compiler: correct grammar in error message
5aba026 
For golang/go#43200

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/278452
@griesemer griesemer mentioned this issue Apr 14, 2021
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Change https://golang.org/cl/314411 mentions this issue: spec: clarify conditions for switch expression value

@golang golang locked and limited conversation to collaborators Apr 28, 2022
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