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go/types: spurious diagnostics for untyped shift operands with GoVersion < go1.13 [1.18 backport] #52032

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gopherbot opened this issue Mar 30, 2022 · 4 comments
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@gopherbot
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@findleyr requested issue #52031 to be considered for backport to the next 1.18 minor release.

@gopherbot please backport to 1.18, this is a newly visible bug with no workaround.

@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Mar 30, 2022
@gopherbot gopherbot added this to the Go1.18.1 milestone Mar 30, 2022
@heschi
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heschi commented Mar 30, 2022

Note that the next minor release is scheduled for next week; if this fix is intended to land for that release it should be prepared soon.

@gopherbot
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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

@cherrymui
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Approved for backport. This affects users with a go version <1.13 set in go.mod file.

@cherrymui cherrymui added NeedsFix The path to resolution is known, but the work has not been done. CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases NeedsFix The path to resolution is known, but the work has not been done. labels Apr 6, 2022
@gopherbot
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Closed by merging 9535031 to release-branch.go1.18.

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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