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extended forwards compatibility for Go #57001
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Updated link to design doc: https://go.dev/design/57001-gotoolchain. |
I just want to note that the potential for confusion here is high. |
I'm not sure about that. What I hope will be a common mode of usage is that you install some update-aware Go toolchain on your machine and then from that point on just edit go or toolchain lines in your go.mod in various projects and never explicitly update the locally installed Go toolchain ever again. The Go toolchain becomes a detail managed inside go.mod just like all the other inputs to your build. In that mode of usage, this reporting would print on literally every go command that gets run, which is too noisy. |
I think the combination of auto-upgrading and not allowing old toolchains to build new code will change the Go ecosystem to either no longer support multiple versions of Go, or to delay experimenting with new language features. Where previously a Go module could target Go 1.21 but make use of 1.22 features in optional, build-tagged files, it can no longer do so. To be allowed to use Go 1.22 language features, the go.mod has to specify Auto-uprading makes this seem fine at first: anyone who needs Go 1.22 will get it for free, automatically. However, I don't think auto-upgrading can be assumed to be pervasive. For one, most people who hack on Go at least occasionally will be using GOTOOLCHAIN=local, pointed at a git checkout. Furthermore, I predict that some Linux distributions will patch their Go packages to disable the automatic upgrading, as it side-steps their packages and some are allergic to that. This'll lead to users who are left behind even more than they're now due to slow-moving distributions. |
I personally have a few reservations about this proposal. Firstly, I don't feel that the Go version in It's very possible to enable a newer version of Go in This pattern seems common enough; Secondly, the automatic download/execution of binary releases of Go seems really surprising. I feel like it's going to be very awkward for Linux distributions to lose control of the toolchain in use without environment variables (especially if they patch Go). I do wonder how many distros might patch Go entirely to force There are also systems where the binaries downloaded from This part of the proposal is being compared to module dependency management itself. I strongly feel that modules work really, really well in comparison to other languages' package management scenarios (like (I mentioned some of this in #55092 (comment), but my thread seems to have been missed as all of the threads around it were replied to.) |
I spoke to @ianlancetaylor about his concerns. For most commands, you can always run For
I think it should continue to be shorthand for that, which would mean ignoring the In the case where
|
This is true. Older versions of the module will still support Go 1.21, of course. It's just the latest version of the module that only supports Go 1.22. I don't think it's a sure thing that this is a problem. The same happens today for dependencies, of course, and it seems to be fine. I agree that making it easier to update to a new Go toolchain may well result in people updating more quickly.
People who hack on Go will be using I agree that some Linux distributions are likely to patch Go to default to |
@zikaeroh, Alpine should not have problems running standard Go distributions starting in Go 1.20. I am not sure about NixOS. The only thing it should need is a libc.so.6 for the dynamic linker to resolve. Or maybe we should build the distribution cmd/go with -tags netgo and then it wouldn't even need that. I wonder what that would break... |
My (rudimentary) understanding is that |
x/tools/gopls only tests that far back because they want to build with what's on people's machines. If what's on people's machines knew how to fetch a newer toolchain then we'd have stopped needing to support older versions long ago. I think that one reason people are slow to update to new Go versions because it is too difficult. What's difficult is managing Go installations. This proposal removes that difficulty, which in turn should make it easier for people to keep up with newer versions. |
Regarding Linux distributions setting GOTOOLCHAIN=local by default (which I think would be fine), I'm curious whether they apply similar rules to rustup or nvm. Does anyone know? |
I guess I'm confused; my impression was that the hardest problem in upgrading was not obtaining a new version of Go, but making sure that the Go code works for that new version of Go, which is the backwards compatibility proposal (not this one). I would be very interested to know what proportion of Go users obtain Go via a package manager (versus If all of those users are going to end up getting
On Arch, you can either install the Arch doesn't package |
We should describe what happens if we drop an existing port (per https://go.dev/wiki/PortingPolicy). Presumably the go command 1.N will see "go 1.N+1", try to download the binaries for 1.N+1, fail, and then give an error and stop the build. For cases like NixOS I think we would have to expect users on that system to set |
This proposal has been added to the active column of the proposals project |
I filed #57007 for building cmd/go without libc.so.6, which I think would make NixOS happy. I agree that it should be possible to build a toolchain with GOTOOLCHAIN=local as the default, but I don't think most package managers should do this. For example I don't think it makes sense for user-installed package managers like Chocolatey or Homebrew to do this at all. They are not as pedantic about "we are the only way to install software on your machine!" as the operating system-installed package managers are, and they should not be going out of their way to break what will end up being a core feature of the Go experience. I also think a fair number of Go developers still use the installers we provide, and those of course will have the GOTOOLCHAIN=auto default. |
Yes, exactly. And we can give a good error. |
Go's backward compatibility is already very good. To the extent that it needs work, the backwards compatibility proposal will make it even better. That will leave actually getting the upgraded Go toolchain as the hardest problem. My experience maintaining other machines where I build Go programs but don't do Go development has been that I don't upgrade often at all because it is annoying to go download and unpack the right tar files. If all it took was editing a go.mod, I would do that far more often. Another point that I forgot to make in the doc is that setting the Go toolchain in go.mod means that all developers working on a project will agree on the toolchain version, without other special arrangements. This was of course one of the big improvements of modules and moving out of GOPATH, for dependency versions. The same property can be provided for the Go toolchain version. This would also mean that if you are moving back and forth between two projects that have chosen different Go toolchain versions as their standard toolchain, you get the right one for that project automatically by virtue of just being in that project. You don't have to change your PATH each time you switch, or maintain a global symlink in $HOME/bin, or remember to type 'go1.18 build' in one place and 'go1.19 build' in the other, or any other kludge. It just does the right thing. |
In a CI/CD environment, I don't think this feature would be useful. I would expect that job to be configured to use the correct Go version in the first place. Downloading a newer toolchain might not work anyway due to firewall restrictions. And as others have mentioned, using an older compiler with On another note, while the go directive in go.mod controls language features like octal literals and generics, today it has no bearing on the standard library implementation. My expectation is that if I run
We build our own version of the toolchain and distribute it to our developers, rather than using what is on golang.org. So this would not address that problem for us, especially because it sounds like such a toolchain will default to Another use case is if I am writing a library and want to easily test it with multiple go versions on my local machine. It would be convenient if I could just do something like |
I find this to conflict with the idea from the original proposal that it's a minimum version; if my project says "go 1.13" because that's the minimum, I very likely do not want to use that version of Go for development. A newer toolchain will be faster and behave better when called by tooling like gopls or other analyzers (regardless of the version of Go that gopls is compiled with). Or, I will definitely want to publish binaries using the absolute latest version of Go possible. For example, esbuild says "go 1.13", but the actual binaries published to npm are from Go 1.19. If 1.13 this were to be the expected development version, that wouldn't be very optimal. |
To be honest I am fine with: |
I feel like this proposal also doesn't really address this problem. To me, it sounds like both of these features are fundamentally mis-designed. If I am publishing a library on GitHub, then I should be specifying a range of minor versions (e.g, 1.17+), and then it tests with the latest patch release of each of them as part of my merge gate. Since the go.mod file cannot be relied upon to denote the lower or the upper bound, it really has no bearing on this, except possibly as the default lower bound. Separately, if I am publishing an actual binary as a release artifact, then I should be specifying the Go version (for build reproducibility), but the go.mod should not be considered at all.
Existing versions of the Go compiler already do not fail just because the |
I don't think this is a concern here. This proposal does not say that newer Go versions should download an older Go toolchain. It says that older Go versions should download a newer Go toolchain. When a newer Go version sees an older "go" line in go.mod, it will emulate the language features of the older Go language (that is already true today). |
I agree; that was my original interpretation of the proposal. It just seemed like the followups implied otherwise. (That is how pinning tends to work in other languages like node.) |
Change https://go.dev/cl/450916 mentions this issue: |
As others here have explained, this proposal would cause a lot of problems for CI/CD, for package management, for conditionally using newer features in older codebases with conditional compilation, ... The version of go in go.mod is now a minimum, which is fine. Rather than a magic environment variable, I would add a new command, go upgrade, that can upgrade the go compiler if installed locally from the official packages, but gives a helpful message if one should upgrade using the package manager in stead. |
FWIW I only mentioned This also is not exclusive to language features; I recall a series of CLs updating the
Which to me very much supports the idea that (I apparently forgot to actually submit this reply days ago, oops.) |
This seems like a bad idea to me. Other text file formats include a line identifying the tool version that created the file, and do not imply that older versions cannot process the file properly. So the current behavior is not without precedent. (Examples of these other formats aren't springing to mind, but it wasn't a novel concept when I first saw it in go.mod). This change assumes that upgrading the toolchain will always be beneficial and regressions will never happen. That stance doesn't seem much different to me than that of a certain OS, where users can be forced to reboot for an update - with no possibility to defer or skip the update. With a language rather than an OS, this behavior may be less infuriating and less disruptive for most users, but I think it's still unacceptable. If a change is to be made, I would instead deprecate the If I understand correctly, the |
@mark-pictor-csec I think you just described the actual proposal. minimum_go is spelled 'go'. It sets the minimum Go toolchain version that must be used to compile the module, whether used directly (via git clone + cd into it + run go commands) or indirectly (as a module dependency). recommended_go is spelled 'toolchain'. It only applies when code is used directly by cd'ing into the module. It is ignored when the module is used indirectly as a required dependency. It is not true that the proposal "assumes that upgrading the toolchain will always be beneficial and regressions will never happen." In fact I have gone out of my way in the past to explain why that's false. See for example https://research.swtch.com/vgo-mvs. Instead, the proposal, like Go modules as a whole, puts the user in control of which toolchain they use. There are no gremlins going around updating the Go toolchain behind your back. You only get a new go toolchain when you explicitly make a change to your go.mod file to indicate that. This is the same behavior as other modules: you keep getting the one listed in go.mod, even if there are newer ones, until you explicitly upgrade. |
Change https://go.dev/cl/518415 mentions this issue: |
We do not index std as a whole module ever. When working in the main Go repo, files in package change often, so we don't want to pay the cost of reindexing all of std when what we really need is just to reindex strings. Per-package indexing works better for that case. When using a released Go toolchain, we don't have to worry about the whole module changing, but if we switch to whole-module indexing at that point, we have the potential for bugs that only happen in released toolchains. Probably not worth the risk. For similar reasons, we don't index the current work module as a whole module (individual packages are changing), so we use the heuristic that we only do whole-module indexing in the module cache. The new toolchain modules live in the module cache, though, and our heuristic was causing whole-module indexing for them. As predicted, enabling whole-module indexing for std when it's completely untested does in fact lead to bugs (a very minor one). This CL turns off whole-module indexing for std even when it is in the module cache, to bring toolchain module behavior back in line with the other ways to run toolchains. Updates #57001. For #61873. Change-Id: I5012dc713f566846eb4b2848facc7f75bc956eb9 Reviewed-on: https://go-review.googlesource.com/c/go/+/504119 TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Bryan Mills <[email protected]> Auto-Submit: Russ Cox <[email protected]> Run-TryBot: Russ Cox <[email protected]> (cherry picked from commit a7b1793) Reviewed-on: https://go-review.googlesource.com/c/go/+/518415 Reviewed-by: Russ Cox <[email protected]> Run-TryBot: Bryan Mills <[email protected]> Auto-Submit: Dmitri Shuralyov <[email protected]>
Change https://go.dev/cl/519216 mentions this issue: |
Match the behavior as implemented in CL 518675 and CL 518815, and ready to be released in the next set of minor releases. For golang/go#57001. Change-Id: I4404530994e636173f636aefb83bd64e208eba3c Reviewed-on: https://go-review.googlesource.com/c/website/+/519216 Auto-Submit: Dmitri Shuralyov <[email protected]> Reviewed-by: Dmitri Shuralyov <[email protected]> Reviewed-by: Bryan Mills <[email protected]> Run-TryBot: Dmitri Shuralyov <[email protected]> TryBot-Result: Gopher Robot <[email protected]>
I don't understand why the default is "auto", all our CI jobs are failing now because they require running The default should be The ci jobs for running |
@gaby Thanks for reporting, but this is a closed issue and it's not appropriate to investigate here. Both |
Change https://go.dev/cl/546635 mentions this issue: |
…go install' flags When the argument to 'go install' or 'go run' looks like a versioned package, we make a best effort to switch to a toolchain compatible with the module containing that package, by fetching its go.mod file and checking the go version it specifies. At this point in the code, we have not yet parsed the arguments given on the command line: instead, we just make a best effort to find one we can use to select a toolchain version. Since that toolchain may be newer, the command to install it may also include flags that are only supported by that Go version — and we don't want to fail due to an error that would be resolved by switching to a more appropriate toolchain. So at this point in the code we can't parse the flags in a way that will surface errors, but we want to make a best effort to parse the ones that we know about. It turns out that “parse the flags we know about” is already a familiar problem: that's also what we do in 'go test', so we can reuse the cmdflag library from that to do the best-effort pass of parsing. If it turns out that we don't need to switch toolchains after all, cmd/go's main function will parse the flags again, and will report any errors at that point. This fixes a regression, introduced in CL 497879, which caused 'go install -modcacherw pkg@version' to unset the write bit for directories created while selecting the toolchain to use. Fixes #64282. Updates #57001. Change-Id: Icc409c57858aa15c7d58a97a61964b4bc2560547 Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest Reviewed-on: https://go-review.googlesource.com/c/go/+/546635 LUCI-TryBot-Result: Go LUCI <[email protected]> Auto-Submit: Bryan Mills <[email protected]> Reviewed-by: Michael Matloob <[email protected]>
Change https://go.dev/cl/550055 mentions this issue: |
Change https://go.dev/cl/550237 mentions this issue: |
Change https://go.dev/cl/551215 mentions this issue: |
…n' and 'go install' flags" This caused other problems, and for the purposes of the Go 1.22 release, we can just roll back to the Go 1.21 behavior and then decide in January what the correct path forward is. Revert of CL 546635. Unfixes #64282. Fixes #64738. For #57001. This reverts commit e44b8b1. Change-Id: I78753c76dcd0bc6dbc90caa17f73248c42e5f64a Reviewed-on: https://go-review.googlesource.com/c/go/+/551215 LUCI-TryBot-Result: Go LUCI <[email protected]> Auto-Submit: Russ Cox <[email protected]> Reviewed-by: Daniel Martí <[email protected]> Reviewed-by: Than McIntosh <[email protected]>
…go install' flags When the argument to 'go install' or 'go run' looks like a versioned package, we make a best effort to switch to a toolchain compatible with the module containing that package, by fetching its go.mod file and checking the go version it specifies. At this point in the code, we have not yet parsed the arguments given on the command line: instead, we just make a best effort to find one we can use to select a toolchain version. Since that toolchain may be newer, the command to install it may also include flags that are only supported by that Go version — and we don't want to fail due to an error that would be resolved by switching to a more appropriate toolchain. So at this point in the code we can't parse the flags in a way that will surface errors, but we want to make a best effort to parse the ones that we know about. It turns out that “parse the flags we know about” is already a familiar problem: that's also what we do in 'go test', so we can reuse the cmdflag library from that to do the best-effort pass of parsing. If it turns out that we don't need to switch toolchains after all, cmd/go's main function will parse the flags again, and will report any errors at that point. This fixes a regression, introduced in CL 497879, which caused 'go install -modcacherw pkg@version' to unset the write bit for directories created while selecting the toolchain to use. Fixes golang#64282. Updates golang#57001. Change-Id: Icc409c57858aa15c7d58a97a61964b4bc2560547 Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest Reviewed-on: https://go-review.googlesource.com/c/go/+/546635 LUCI-TryBot-Result: Go LUCI <[email protected]> Auto-Submit: Bryan Mills <[email protected]> Reviewed-by: Michael Matloob <[email protected]>
…n' and 'go install' flags" This caused other problems, and for the purposes of the Go 1.22 release, we can just roll back to the Go 1.21 behavior and then decide in January what the correct path forward is. Revert of CL 546635. Unfixes golang#64282. Fixes golang#64738. For golang#57001. This reverts commit e44b8b1. Change-Id: I78753c76dcd0bc6dbc90caa17f73248c42e5f64a Reviewed-on: https://go-review.googlesource.com/c/go/+/551215 LUCI-TryBot-Result: Go LUCI <[email protected]> Auto-Submit: Russ Cox <[email protected]> Reviewed-by: Daniel Martí <[email protected]> Reviewed-by: Than McIntosh <[email protected]>
Part of this change forces The below patch forces diff --git a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
index 35fd1f534c..75017ba708 100644
--- a/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
+++ b/src/cmd/vendor/golang.org/x/mod/modfile/rule.go
@@ -969,2 +969,3 @@ func (f *File) Cleanup() {
func (f *File) AddGoStmt(version string) error {
+ version = lazyregexp.New(`1\.(\d*)\.\d*`).ReplaceAllString(version, "1.$1.0")
if !GoVersionRE.MatchString(version) { You can apply it using the following Nix expression: go.overrideAttrs (old: {
patches = (old.patches or []) ++ [
# Save your fetch as the file below.
./go-always-init-mod-with-0-patch.patch
];
doCheck = false;
}) |
Many people believe the
go
line in thego.mod
file specifies which Go toolchain to use. This proposal would correct this widely held misunderstanding by making it reality. At the same time, the proposal would improve forward compatibility by making sure that old Go toolchains never try to build newer Go programs.Define the “work module” as the one containing the directory where the go command is run. We sometimes call this the “main module”, but I am using “work module” in this document for clarity.
Updating the
go
line in thego.mod
of the work module, or thego.work
file in the current workspace, would change the minimum Go toolchain used to run go commands. A newtoolchain
line would provide finer-grained control over Go toolchain selection.An environment variable
GOTOOLCHAIN
would control this new behavior. The default,GOTOOLCHAIN=auto
, would use the information ingo.mod
. Setting GOTOOLCHAIN to something else would override thego.mod
.GOTOOLCHAIN=local
would force use of the locally installed toolchain, and other values would choose specific releases. For example, to test the package in the current directory with Go 1.17.2:As part of this change, older Go toolchains would refuse to try to build newer Go code. The new system would arrange that normally this would not come up - the new toolchain would be used automatically. But if forced, such as when using
GOTOOLCHAIN=local
, the older Go toolchain would no longer assume it can build newer Go code. This in turn would make it safe to revisit and fix for loop scoping (discussion #56010).See my talk on this topic at GopherCon for more background.
See the design document for details.
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