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cmd/go: panics on error during downgrade #31942

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heschik opened this issue May 9, 2019 · 3 comments

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@heschik
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commented May 9, 2019

What version of Go are you using (go version)?

$ go version
go version devel +f0c383b833 Wed May 1 16:53:19 2019 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What did you do?

Note: this used to reproduce both with and without GOPROXY=https://proxy.golang.org but now only reproduces with the mirror. Presumably something changed upstream that hasn't made it to the mirror yet.

$ cd $(mktemp -d)
$ go mod init example.com
$ go mod init example.com
go: creating new go.mod: module example.com
$ go get -u cloud.google.com/go@master
[snip]
$ go get -u cloud.google.com/go@master
go: finding cloud.google.com/go master
go: finding github.com/googleapis/gax-go/v2 v2.0.0
go: github.com/googleapis/gax-go/v2@v2.0.0: unexpected status (https://proxy.golang.org/github.com/googleapis/gax-go/v2/@v/v2.0.0.info): 410 Gone                                                                                            
panic: error loading module requirements

goroutine 1 [running]:
cmd/go/internal/mvs.Downgrade.func2(0xc00024a3c0, 0x1f, 0xc00056a6c0, 0x6)
        /usr/lib/google-golang/src/cmd/go/internal/mvs/mvs.go:317 +0x659
cmd/go/internal/mvs.Downgrade(0xc00028c810, 0xb, 0x0, 0x0, 0xbdf500, 0xc0001d6000, 0xc00044c040, 0x1, 0x1, 0x0, ...)
        /usr/lib/google-golang/src/cmd/go/internal/mvs/mvs.go:349 +0x617
cmd/go/internal/modget.runGet(0xfd0d40, 0xc000020130, 0x1, 0x1)
        /usr/lib/google-golang/src/cmd/go/internal/modget/get.go:446 +0x1ed6
main.main()
        /usr/lib/google-golang/src/cmd/go/main.go:219 +0x837

What did you expect to see?

No panic.

What did you see instead?

Panic.

https://github.com/golang/go/blob/go1.12.5/src/cmd/go/internal/mvs/mvs.go#L317

@lopezator

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commented May 14, 2019

I've got bitten by this also.

go version go1.12.5 darwin/amd64

Also reproducible on tip:

go version devel +45d74aa Tue May 14 00:50:42 2019 +0000 darwin/amd64

Steps to reproduce:

After doing:

mkdir test
go mod init
go get github.com/volatiletech/sqlboiler@v2.5.1

Any of these (among others), fails with the same error:

go get google.golang.org/grpc@c443156028b9fa563e063e9fa8ba7881d467833b

go get google.golang.org/genproto@595979c8a7bf586b2d293fb42246bf91a0b893d9

go get github.com/golang/protobuf@17ce1425424ab154092bbb43af630bd647f3bb0d

go get golang.org/x/net@02ac38e2528ff4adea90f184d71a3faa04b4b1b0

go get golang.org/x/sys@7a4fde3fda8ef580a89dbae8138c26041be14299

go get golang.org/x/text@836efe42bb4aa16aaa17b9c155d8813d336ed720

Error

panic: github.com/googleapis/gax-go/v2@v2.0.0: missing github.com/googleapis/gax-go/go.mod and .../v2/go.mod at revision v2.0.0

goroutine 1 [running]:
cmd/go/internal/mvs.Downgrade.func2(0xc00025e720, 0x1f, 0xc00035121a, 0x6)
	/Users/d.lopez/sdk/gotip/src/cmd/go/internal/mvs/mvs.go:409 +0x676
cmd/go/internal/mvs.Downgrade(0xc0000240c0, 0x33, 0x0, 0x0, 0x1711ec0, 0xc0004c53b0, 0xc0000e7820, 0x1, 0x1, 0x0, ...)
	/Users/d.lopez/sdk/gotip/src/cmd/go/internal/mvs/mvs.go:441 +0x5c7
cmd/go/internal/modget.runGet(0x1a77220, 0xc0000c0050, 0x1, 0x1)
	/Users/d.lopez/sdk/gotip/src/cmd/go/internal/modget/get.go:563 +0x2e8a
main.main()
	/Users/d.lopez/sdk/gotip/src/cmd/go/main.go:188 +0x57f

@bcmills bcmills added this to the Go1.13 milestone May 14, 2019

@jayconrod

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commented May 14, 2019

Oh this is fun.

When we downgrade a module, we consider the full module version graph, excluding newer versions of the downgraded module and anything else that requires newer versions. Then we do MVS on whatever's left.

When we require cloud.google.com/go v0.39.1-0.20190513200544-741d62a9e2a8 (the current master), that implies github.com/googleapis/gax-go/v2 v2.0.4. That requires something that gets excluded, so we try to downgrade to an earlier version. However, gax-go didn't migrate to modules until v2.0.3. v2.0.2 don't have go.mod files, so it's an error to depend on them. They should probably be considered part of the module github.com/googleapis/gax-go with a +incompatible suffix, but we don't see that for v2+ modules.

Even if we stopped returning these versions for the v2 module, GOPROXY will serve them forever. This is an easy mistake to make, and the Go command ought to recover from it when downgrading. Fortunately, this shouldn't affect upgrades or anyone getting the module at latest.

One possible fix: if Reqs.Required returns an error for a previous version of a module during a downgrade, we could silently exclude the version. It's currently hard to distinguish between transient errors (we couldn't reach the repository) and permanent errors (we couldn't parse the go.mod), but I think that's the right thing to do.

@jayconrod jayconrod added the NeedsFix label May 14, 2019

@gopherbot

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commented May 15, 2019

Change https://golang.org/cl/177337 mentions this issue: cmd/go: don't attempt to downgrade to incompatible versions

@gopherbot gopherbot closed this in 06642d8 May 17, 2019

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