cmd/compile: enable new comparable behavior by default [freeze exception]
#57011
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comparable behavior by default [freeze exception]
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CC @golang/release |
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Approved after offline discussion. In the future, if it looks like there's going to be trouble with the timeline for a feature like this please let us know and we'll try to see if we can smooth things over. |
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Change https://go.dev/cl/454575 mentions this issue: |
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Dec 1, 2022
Ordinary interface types now satisfy comparable constraints. This is a fully backward-compatible change: it simply permits additional code to be valid that wasn't valid before. This change makes the new comparable semantics the default behavior, depending on the Go -lang version. It also renames the flag types2.Config.AltComparableSemantics to types2.Config.OldComparableSemantics and inverts its meaning (or types.Config.oldComparableSemantics respectively). Add new predicate Satisfies (matching the predicate Implements but for constraint satisfaction), per the proposal description. Adjust some existing tests by setting -oldComparableSemantics and add some new tests that verify version-dependent behavior. The compiler flag -oldcomparable may be used to temporarily switch back to the Go 1.18/1.19 behavior should this change cause problems, or to identify that a problem is unrelated to this change. The flag will be removed for Go 1.21. For #52509. For #56548. For #57011. Change-Id: I8b3b3d9d492fc24b0693567055f0053ccb5aeb42 Reviewed-on: https://go-review.googlesource.com/c/go/+/454575 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@google.com> Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
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This change has been submitted. Closing. |
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Proposal #56548 which allows ordinary interfaces to implement
comparablehas been accepted today. We would like to incorporate this into 1.20 as it will directly influence the kind of generic code people will be able to write.The respective change was implemented a while ago in go/types, types2, and the compiler, and could be enabled with a compiler flag:
-altcomparable(see CL 444635 and CL 444636). By default, the feature was disabled.I would like to request a freeze exception to enable the feature by default.
CL 454575 makes the new behavior the default and Go 1.20 version dependent, and provides error messages reporting version issues, and adds more tests.
Safety of the change:
If there are any suspected problems with the change, a) by setting the compiler flag
-oldcomparablewe can confirm if there's an issue related to this change in the first place; and b) if we decide to roll back, all we need to do is to change the flag default (or roll back the CL).Finally, I note that the new behavior for
comparableis in fact the behavior we had implemented until about 6 weeks before the release of Go 1.18, when people perceived an apparent inconsistency (see issue #50646 which was closed on Feb 1, 2022). To err on the side of caution we deliberately restricted what types would satisfycomparable. At this point, and after many proposals and discussions (for a list see #56548), we agreed that the original behavior was in fact what people expect. With the changes here we simply re-establish this original behavior.cc: golang/release
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