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types2: adjust types reported for shift expressions with constant RHS to match go/types #47410

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findleyr opened this issue Jul 26, 2021 · 7 comments
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@findleyr
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@findleyr findleyr commented Jul 26, 2021

As discussed in #47243, go/types should preserve the type of untyped constants on the RHS of a shift expression.

However, it does this inconsistently for integral vs non-integral types. Consider

  var s int
  var _ = s << 1
  var _ = s << 2.

In 1.16 (and probably earlier), go/types reports the type of 1 as untyped int, but the type of 2. as uint. It should preserve the type of 2. as untyped float.

https://play.golang.org/p/aZZ48onPW2z

We're going to preserve this behavior for 1.17, but should try to fix it for 1.18.

CC @griesemer

@findleyr findleyr added this to the Go1.18 milestone Jul 26, 2021
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@gopherbot gopherbot commented Jul 26, 2021

Change https://golang.org/cl/337529 mentions this issue: go/types: preserve untyped constants on the RHS of a shift expression

gopherbot pushed a commit that referenced this issue Jul 27, 2021
CL 291316 fixed go/types to verify that untyped shift counts are
representable by uint, but as a side effect also converted their types
to uint.

Rearrange the logic to keep the check for representability, but not
actually convert untyped integer constants. Untyped non-integer
constants are still converted, to preserve the behavior of 1.16. This
behavior for non-integer types is a bug, filed as #47410.

Updates #47410
Fixes #47243

Change-Id: I5eab4aab35b97f932fccdee2d4a18623ee2ccad5
Reviewed-on: https://go-review.googlesource.com/c/go/+/337529
Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
@seankhliao seankhliao added the NeedsFix label Jul 28, 2021
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@gopherbot gopherbot commented Jul 28, 2021

Change https://golang.org/cl/338195 mentions this issue: [dev.typeparams] cmd/compile/internal/types2: preserve untyped constants on the RHS of a shift expression

steeve pushed a commit to znly/go that referenced this issue Aug 19, 2021
CL 291316 fixed go/types to verify that untyped shift counts are
representable by uint, but as a side effect also converted their types
to uint.

Rearrange the logic to keep the check for representability, but not
actually convert untyped integer constants. Untyped non-integer
constants are still converted, to preserve the behavior of 1.16. This
behavior for non-integer types is a bug, filed as golang#47410.

Updates golang#47410
Fixes golang#47243

Change-Id: I5eab4aab35b97f932fccdee2d4a18623ee2ccad5
Reviewed-on: https://go-review.googlesource.com/c/go/+/337529
Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
@griesemer griesemer self-assigned this Jan 18, 2022
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jan 28, 2022

@griesemer This is in the 1.18 milestone; time to move to 1.19? Thanks.

@griesemer
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@griesemer griesemer commented Jan 29, 2022

There's a pending CL with failures. It's on my list to investigate.

@griesemer
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@griesemer griesemer commented Jan 29, 2022

The issue here is what type is reported through the API but in contrast to go/types the current API works for the compiler. Eventually we want types2 to match go/types in this respect but it doesn't seem important to do this for 1.18.

@griesemer griesemer removed this from the Go1.18 milestone Jan 29, 2022
@griesemer griesemer added this to the Go1.19 milestone Jan 29, 2022
@griesemer griesemer changed the title go/types: inconsistent types reported for shift expressions with constant RHS types2: adjust types reported for shift expressions with constant RHS to match go/types Jan 29, 2022
@griesemer griesemer changed the title types2: adjust types reported for shift expressions with constant RHS to match go/types types2: adjust types reported for shift expressions with constant RHS to match go/types Jan 29, 2022
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@gopherbot gopherbot commented Mar 30, 2022

Change https://go.dev/cl/396775 mentions this issue: go/types: don't report errors for untyped int shifts on Go < 1.13

gopherbot pushed a commit that referenced this issue Apr 2, 2022
CL 337529 introduced upfront type-checking of constant shift operands,
to avoid converting their type to uint (per the spec). However, it
had an oversight in that the checks intended for non-constant operands
still ran after the explicit checking of constant operands. As a
result, there are at least two bugs:
 - When GoVersion is < 1.13, we report spurious errors for untyped
   constant shift operands.
 - When the operand is an untyped float constant, we still convert to
   uint (this was a known bug reported in #47410).

Looking at this now, it seems clear that we can avoid both of these bugs
by simply not running the additional checks in the case of a constant
operand. However, this should be considered with some care, as shifts
are notoriously tricky.

Updates #47410
Fixes #52031

Change-Id: Ia489cc5470b92a8187d3de0423d05b309daf47bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/396775
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
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@gopherbot gopherbot commented Apr 2, 2022

Change https://go.dev/cl/397680 mentions this issue: [release-branch.go1.18] go/types: don't report errors for untyped int shifts on Go < 1.13

gopherbot pushed a commit that referenced this issue Apr 6, 2022
… shifts on Go < 1.13

CL 337529 introduced upfront type-checking of constant shift operands,
to avoid converting their type to uint (per the spec). However, it
had an oversight in that the checks intended for non-constant operands
still ran after the explicit checking of constant operands. As a
result, there are at least two bugs:
 - When GoVersion is < 1.13, we report spurious errors for untyped
   constant shift operands.
 - When the operand is an untyped float constant, we still convert to
   uint (this was a known bug reported in #47410).

Looking at this now, it seems clear that we can avoid both of these bugs
by simply not running the additional checks in the case of a constant
operand. However, this should be considered with some care, as shifts
are notoriously tricky.

While cherry-picking, the new test file is updated to use the go1_12
package name, following our convention for specifying language version
in the release branch.

Fixes #52032

Change-Id: Ia489cc5470b92a8187d3de0423d05b309daf47bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/396775
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 8a816d5)
Reviewed-on: https://go-review.googlesource.com/c/go/+/397680
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