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cmd/dist: remove precompiled .a files from binary distributions [freeze exception] #47257

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jayconrod opened this issue Jul 16, 2021 · 60 comments
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@jayconrod
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The downloadable archives at https://golang.org/dl/ currently contain precompiled .a files for all packages in the standard library. Each archive has a set of .a files for one platform, plus another set for -race builds.

These files take up quite a bit of space, and they're fast to rebuild on demand. We should consider removing them from binary Go distributions.

For example, in 1.17rc1 on darwin/amd64, the whole distribution uncompressed is 435M. The pkg/darwin_amd64 directory is 97M (22%), and the pkg/darwin_amd64_race directory is 109M (25%). Compressed as a zip file with default settings, the archive is 135M. Without .a files, it's 86M (63%).

After #40042 was fixed, the C compiler version is included in the cache key for each package that uses cgo. That means that if no C compiler is installed on the system, or if a different C compiler version is installed (very common), go build and other commands will rebuild packages that depend on cgo instead of using the versions installed in $GOROOT/pkg. As of 1.17rc1, there are 27 packages in std that use cgo directly or indirectly, most prominently, net. The precompiled files for these packages are almost never used unless the installed C compiler exactly matches the version used to build the Go distribution.

Note that the fix for #40042 is causing builds to fail on systems without a C compiler installed (#47215), so it may be partially or completely rolled back in 1.17. If we implement this proposal, we'd have the same problem, so we may want to think about changing the default value of CGO_ENABLED (#47251).

cc @rsc @bcmills @matloob

@jayconrod jayconrod added this to the Proposal milestone Jul 16, 2021
@mvdan
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mvdan commented Jul 17, 2021

Another reason to do this is that internet speeds vary wildly. To some people, downloading an extra 50MiB is a split second, but to many others it's staring at their screen for an extra minute. I don't have an ETA for FTTH reaching my building in the UK, for example :)

CPU speeds and compile times also vary, but I think the lower bound is much less worrying - even with a five-year-old thin laptop, one should be able to build the standard library in 10-20s.

@ianlancetaylor
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I think it's pretty important that a Go binary installation work on a system with no C compiler installed. And at least in the past on macOS Go programs would only work if using the cgo version of the net package. So I think we at least need to provide the .a files for the standard library packages that use cgo, which I think is currently net and os/user.

@bcmills
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bcmills commented Jul 19, 2021

I think it's pretty important that a Go binary installation work on a system with no C compiler installed. And at least in the past on macOS Go programs would only work if using the cgo version of the net package.

Does that imply that on macOS it already isn't possible to build a working Go program that depends on net with CGO_ENABLED=0?

If so, that would imply that without a working C compiler it also isn't possible to build programs that depend on both net and some third-party package whose source files vary based on the cgo build constraint: the cgo constraint is met if CGO_ENABLED=1 even if the C compiler is present. So that would force users to choose between two options:

  1. Build with CGO_ENABLED=1 and get build errors due to attempting to compile third-party //go:build cgo files without a working C compiler.
  2. Build with CGO_ENABLED=0, and get the appropriate source files for third-party packages but a non-working net package.

I think we could resolve that in one of three ways:

  1. Change the net package to not require a C compiler on macOS.
  2. Change cmd/go to build the net package on macOS using a C compiler even if CGO_ENABLED=0.
  3. Declare that a C compiler is required in order to build Go programs that depend on net on macOS.

@bcmills
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bcmills commented Jul 19, 2021

On further consideration, I don't think option (2) above is viable. There are too many other ways to invalidate cache entries, such as by setting (or not setting) -trimpath, and those will also cause the precompiled libraries not to be used.

And I believe our builders already invalidate the cache for libraries bundled in the macOS release, because they build using a non-default value for CGO_CFLAGS (see #33598, #46347, #46292).

@rsc
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rsc commented Jul 19, 2021

@ianlancetaylor

I think it's pretty important that a Go binary installation work on a system with no C compiler installed.

I would agree with you a priori, but as I understand the current state of the world, the introduction of the build cache broke this case many releases back, with no complaints (or at least not enough that we've tried to fix it). The .a files that ship do not actually have the right cache keys embedded inside them to be used by essentially any out-of-the-box install of Go. Instead, they get recomputed (in the cache only, not in the install location) the first time you build something.

Assuming I am right about that (I have not done the experiment myself), then I think it is OK to just drop the .a files entirely and not worry about the "cgo without C compiler" case anymore.

@jayconrod
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I would agree with you a priori, but as I understand the current state of the world, the introduction of the build cache broke this case many releases back, with no complaints (or at least not enough that we've tried to fix it). The .a files that ship do not actually have the right cache keys embedded inside them to be used by essentially any out-of-the-box install of Go. Instead, they get recomputed (in the cache only, not in the install location) the first time you build something.

@rsc I was under this impression too until looking at #47215 last week. The C compiler version only became part of the cache key in #40042. So this is true for 1.17rc1, but not for 1.16 or lower. If neither CC nor CGO_CFLAGS are explicitly set, the go command will happily use the precompiled runtime/cgo.a, even if no C compiler is installed. We're looking at a narrow rollback of this in CL 335409.

(@bcmills pointed out cases where the cache keys don't match on macOS, but they do match on Linux, and that's the platform I'm most worried about, since a lot of folks are building in Docker without installing a C compiler).

@jayconrod
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  1. Change the net package to not require a C compiler on macOS.

I wonder how viable this is?

I know very little about the guts of the net package. Reading https://pkg.go.dev/net#hdr-Name_Resolution, it looks like there are Go and cgo implementation for name resolution. When cgo is available, they're both compiled in and selected dynamically (GODEBUG=netdns=go or GODEBUG=netdns=cgo can pick one at run-time). On macOS, the cgo version seems to be preferred.

But does the cgo version actually need to be written with cgo? On macOS at least, we link dynamically with /usr/lib/libSystem.B.dylib even with CGO_ENABLED=0, so we don't need the external linker. CL 227037 leads me to believe it's possible to call C code from Go with assembly trampolines. (This is mostly a thought experiment; I don't want to re-implement net or awaken Cthulhu).

@ianlancetaylor
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@jayconrod I think you are correct that with our current implementation we could call the macOS libraries directly without having to use cgo. The same is true on AIX and Solaris, for that matter.

@jfesler
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jfesler commented Jul 19, 2021

re CGO_ENABLED=0 GOOS=darwin: #12524 (comment)

@jfesler
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jfesler commented Jul 19, 2021

CGO_ENABLED=0 is effectively the same as cross-compiled, and same headaches: netdns's go is simply inadequate, at least for use cases where DNS queries are routed based on domain name to different resolvers by the operating system. /etc/resolv.conf does not adequately describe the OS DNS routing behavior; there's no good way for netdns to ever do this correctly.

@rsc
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rsc commented Jul 21, 2021

I think we can plausibly check in the relevant cgo-generated pieces for the few stdlib packages that need cgo.
Then we wouldn't need a special case for "install runtime/cgo.a but no other .a files".

@rsc rsc changed the title proposal: remove precompiled .a files from binary distributions proposal: cmd/dist: remove precompiled .a files from binary distributions Jul 28, 2021
@rsc
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rsc commented Jul 28, 2021

My suggestion here would be to define that go install x only ever installs binaries, never .a files.
That would change this from being about cmd/dist and the Go distribution to being about cmd/go.
The distributions would shrink as a side effect, and the meaning of go install would become clearer.

@jayconrod
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Agreed that go install should no longer install .a files.

I think the main technical blocker is being able to build net with its current netcgo functionality without actually needing cgo. That seems like it can be done either by checking in pre-generated cgo code or by linking against C code directly with //go:cgo_import_dynamic. Not sure exactly what it will look like, but it seems plausible and probably a good change to make anyway.

For a broad go install change, I'm a bit worried about -buildmode=shared and -linkshared. Not sure those work at all in module mode currently, so it would be good to have a plan to deprecate or fix.

@rsc
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rsc commented Aug 4, 2021

Yes, buildmode=shared is dead and has been for a long time. Anyone using it must not be using modules.
We could potentially do a special case in buildmode=shared for just the standard library, but I don't see how to make more than that work (and even that is a bit iffy).

/cc @mwhudson

@rsc
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rsc commented Aug 4, 2021

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

@rsc
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rsc commented Aug 11, 2021

@mwhudson, do you know of any existing uses of -buildmode=shared and -linkshared anymore?
We believe they have been broken since modules are introduced and are thinking about removing them.
Thanks!

@mwhudson
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I'm not aware of any used for those buildmodes currently, no. Never quite got to the point of them being genuinely useful before our requirements shifted a bit unfortunately.

@rsc
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rsc commented Aug 18, 2021

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

@iskarian
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iskarian commented Aug 24, 2021

My suggestion here would be to define that go install x only ever installs binaries, never .a files.
That would change this from being about cmd/dist and the Go distribution to being about cmd/go.
The distributions would shrink as a side effect, and the meaning of go install would become clearer.

Would this removal leave any method of installing .a files aside from build -o file.a?

(Context: For reproducible builds we often use isolated build environments where the build cache cannot be persisted between builds. Options for reusing build artifacts currently are, in order of ease:

  1. Use install in GOPATH-mode and save the installed archives in build output;
  2. Build/install in module-aware mode and use more-opaque and possibly-brittle methods to determine which parts of the build cache to save in build output; or
  3. Use build -o file.a for each package, which requires getting the build order the same as cmd/go so the actionID portion of BuildIDs match.

My concern is that this change would remove option 1, without adding any facility for making 2 or 3 less brittle.)

gopherbot pushed a commit that referenced this issue Dec 2, 2022
…r all of std

gcimporter.TestImportTypeparamTests still needs to create full export
data because it loads lots of source files from GOROOT/test that
expect to be able to import arbitrary subsets of the standard library,
so we now skip it in short mode.

On a clean build cache, this reduces
'go test -short cmd/compile/internal/importer go/internal/gcimporter'
on my machine from 21–28s per test to <6s per test.

Updates #56967.
Updates #47257.

Change-Id: I8fd80293ab135e0d2d213529b74e0ca6429cdfc7
Reviewed-on: https://go-review.googlesource.com/c/go/+/454498
Run-TryBot: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
gopherbot pushed a commit to golang/tools that referenced this issue Dec 2, 2022
This fixes tests failing on the Android builders on Go 1.20 after CL
454499. Previously the tests were skipped in the 'compile' helper
function, but as of that CL they fail before reaching that point due
to missing export data for packages in std.

Updates golang/go#56967.
Updates golang/go#47257.

Change-Id: Ief953b6dbc54c8e0b1f71fc18a0d6ab212caf308
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454500
gopls-CI: kokoro <[email protected]>
Reviewed-by: Jamal Carvalho <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
@gopherbot
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Change https://go.dev/cl/461676 mentions this issue: cmd/dist: skip building std for the host when cross-compiling

@gopherbot
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Change https://go.dev/cl/462636 mentions this issue: [internal-branch.go1.20-vendor] internal/gcimporter: fix TestImportStdLib

@gopherbot
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Change https://go.dev/cl/462637 mentions this issue: [internal-branch.go1.20-vendor] internal/gcimporter: load cached export data for packages individually

@gopherbot
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Change https://go.dev/cl/462638 mentions this issue: [internal-branch.go1.20-vendor] internal/gcimporter: skip tests earlier when 'go build' is not available

gopherbot pushed a commit to golang/tools that referenced this issue Jan 18, 2023
…dLib

The test attempted to find all stdlib packages by scanning
pkg/$GOOS_$GOARCH for .a files and then tried to import all of them.
Now that .a files are no longer being placed there, the test is a
noop. Fix this by using go list std (and filtering out testonly
packages) and trying to import all of those to recreate what the test
intended to do.

This also removes a dependency on the pkg/$GOOS_$GOARCH directory
which will stop being produced by dist in CL 453496.

Updates golang/go#47257

Change-Id: Idfa0cbb21093776183ce193eb5363a9727bf77ef
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454118
Run-TryBot: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
gopls-CI: kokoro <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
(cherry picked from commit 0379b73)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/462636
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Russ Cox <[email protected]>
gopherbot pushed a commit to golang/tools that referenced this issue Jan 18, 2023
…rt data for packages individually

In short tests, also avoid creating export data for all of std.

This change applies the same improvements made to the equivalent std
packages in CL 454497 and CL 454498. (It may even fix the reverse
builders that are currently timing out in x/tools, although I suspect
there is still a bit of work to do for those.)

Updates golang/go#56967.
Updates golang/go#47257.

Change-Id: I82e72557da5f917203637513122932c7942a98e9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454499
Auto-Submit: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
gopls-CI: kokoro <[email protected]>
(cherry picked from commit f540ee6)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/462637
Reviewed-by: Russ Cox <[email protected]>
gopherbot pushed a commit to golang/tools that referenced this issue Jan 18, 2023
…er when 'go build' is not available

This fixes tests failing on the Android builders on Go 1.20 after CL
454499. Previously the tests were skipped in the 'compile' helper
function, but as of that CL they fail before reaching that point due
to missing export data for packages in std.

Updates golang/go#56967.
Updates golang/go#47257.

Change-Id: Ief953b6dbc54c8e0b1f71fc18a0d6ab212caf308
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454500
gopls-CI: kokoro <[email protected]>
Reviewed-by: Jamal Carvalho <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
(cherry picked from commit bdcd082)
Reviewed-on: https://go-review.googlesource.com/c/tools/+/462638
Reviewed-by: Russ Cox <[email protected]>
gopherbot pushed a commit that referenced this issue Jan 30, 2023
Since packages in "std" no longer have install targets, checking them
for staleness is somewhat meaningless: if they are not cached they
will be rebuilt anyway, and without installed archives against which
we can compare them the staleness check will not detect builder skew.

It would still be meaningful to check "cmd" for staleness, but
(especially on sharded VM-based builders) that is a fairly expensive
operation relative to its benefit. If we are really interested in
detecting builder skew and/or build reproducibility, we could instead
add a "misc" test (similar to "misc/reboot", or perhaps even a part of
that test) that verifies that bootstrapped binaries are reproducible.

For #57734.
Updates #47257.
Updates #56896.

Change-Id: I8683ee81aefe8fb59cce9484453df9729bdc587c
Reviewed-on: https://go-review.googlesource.com/c/go/+/452775
Run-TryBot: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
gopherbot pushed a commit that referenced this issue Jan 30, 2023
The purpose of building the host toolchain is so that we can use it to
build and test the target configuration.

The host configuration should already be tested separately (with its
own builder), so we do not need to build the parts of that
configuration that are not relevant to the task of building and
testing the target configuration.

Updates #47257.

Change-Id: I814778d2d65b1f2887c9419232b5bfd4068f58af
Reviewed-on: https://go-review.googlesource.com/c/go/+/461676
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
@gopherbot
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Change https://go.dev/cl/464736 mentions this issue: internal/abi: avoid rebuilding all of std in TestFuncPCCompileError

gopherbot pushed a commit that referenced this issue Feb 2, 2023
Instead, have the caller pass in an explicit list of the packages
(if any) they need.

After #47257, a builder running a test does not necessarily have the
entire standard library already cached, especially when running tests
in sharded mode. testenv.WriteImportcfg used to write an importcfg for
the entire standard library — which required rebuilding the entire
standard library — even though most tests need only a tiny subset.

This reduces the time to test internal/abi with a cold build cache on
my workstation from ~16s to ~0.05s.

It somewhat increases the time for 'go test go/internal/gcimporter'
with a cold cache, from ~43s to ~54s, presumably due to decreased
parallelism in rebuilding the standard library and increased overhead
in re-resolving the import map. However, 'go test -short' running time
remains stable (~5.5s before and after).

Fixes #58248.

Change-Id: I9be6b61ae6e28b75b53af85207c281bb93b9346f
Reviewed-on: https://go-review.googlesource.com/c/go/+/464736
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 12, 2023
Since packages in "std" no longer have install targets, checking them
for staleness is somewhat meaningless: if they are not cached they
will be rebuilt anyway, and without installed archives against which
we can compare them the staleness check will not detect builder skew.

It would still be meaningful to check "cmd" for staleness, but
(especially on sharded VM-based builders) that is a fairly expensive
operation relative to its benefit. If we are really interested in
detecting builder skew and/or build reproducibility, we could instead
add a "misc" test (similar to "misc/reboot", or perhaps even a part of
that test) that verifies that bootstrapped binaries are reproducible.

For golang#57734.
Updates golang#47257.
Updates golang#56896.

Change-Id: I8683ee81aefe8fb59cce9484453df9729bdc587c
Reviewed-on: https://go-review.googlesource.com/c/go/+/452775
Run-TryBot: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 12, 2023
The purpose of building the host toolchain is so that we can use it to
build and test the target configuration.

The host configuration should already be tested separately (with its
own builder), so we do not need to build the parts of that
configuration that are not relevant to the task of building and
testing the target configuration.

Updates golang#47257.

Change-Id: I814778d2d65b1f2887c9419232b5bfd4068f58af
Reviewed-on: https://go-review.googlesource.com/c/go/+/461676
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 12, 2023
Instead, have the caller pass in an explicit list of the packages
(if any) they need.

After golang#47257, a builder running a test does not necessarily have the
entire standard library already cached, especially when running tests
in sharded mode. testenv.WriteImportcfg used to write an importcfg for
the entire standard library — which required rebuilding the entire
standard library — even though most tests need only a tiny subset.

This reduces the time to test internal/abi with a cold build cache on
my workstation from ~16s to ~0.05s.

It somewhat increases the time for 'go test go/internal/gcimporter'
with a cold cache, from ~43s to ~54s, presumably due to decreased
parallelism in rebuilding the standard library and increased overhead
in re-resolving the import map. However, 'go test -short' running time
remains stable (~5.5s before and after).

Fixes golang#58248.

Change-Id: I9be6b61ae6e28b75b53af85207c281bb93b9346f
Reviewed-on: https://go-review.googlesource.com/c/go/+/464736
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
rinchsan pushed a commit to rinchsan/gosimports that referenced this issue Feb 19, 2023
…l compile' does not exist

Now that .a files are no longer being preinstalled for
standard-library packages (#47257), tests that require the export data
from those files must have access to 'go list -export' in order to
generate and load export data from the Go build cache.

`go list -export` does not work without a Go compiler, so assume that
tests that need the 'go' command also need the compiler.

This may cause the tests currently failing on the android-.*-emu
builders to instead be skipped, since the test harness does not copy
the compiler to the execution environment.

For golang/go#47257.

Change-Id: Ie82ab09ac8165a01fc1d3a083b1e86226efc469d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/451597
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
gopls-CI: kokoro <[email protected]>
kirederik added a commit to syntasso/kratix that referenced this issue Jun 15, 2023
1.19.10 includes a change on linked libraries that's messing up our manager binary

see golang/go#47257 and golang/go#57328
(issues are closed, but the error is the same)
@rsc rsc removed this from Proposals Dec 4, 2023
@golang golang locked and limited conversation to collaborators Feb 2, 2024
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