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cmd/go: go install: don’t fail when go.mod can’t be updated on a read-only system #33326

stapelberg opened this issue Jul 28, 2019 · 0 comments


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commented Jul 28, 2019

$ go version
go version go1.13beta1 linux/amd64

I talked about this issue with @bcmills over GopherCon 2019 and he recommended I file this issue for tracking.

I am using cmd/go in a build environment where the entire system is read-only, but I have a writable copy of the source tree I’m building (e.g. The system provides a read-only module cache (at /ro/gopath/pkg/mod) which contains all the dependencies of the source tree.

I’m using replace directives to enforce that my environment’s module versions are used, which can be different from the versions listed in go.mod/go.sum. See #29410 (comment) for details.

When running go install, it fails to lock the module cache because it’s read-only:

go: failed to lock file at /ro/gopath/pkg/mod/cache/lock

So far so good—it’s reasonable to not continuing when the side lock can’t be acquired. But, when specifying -mod=readonly, I’m getting:

go: updates to go.mod needed, disabled by -mod=readonly

I don’t know that go install should error out here. Certainly it could just continue with whatever changes needed just being retained in memory? As a user, I’m interested in the binary installation, not the side effect updates.

Thanks for considering,

@bcmills bcmills added this to the Go1.14 milestone Jul 28, 2019

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