cmd/go: stamp the pseudo-version in builds generated by go build

[4ad]

cmd/go embeds dependency version information in binaries, which is very useful. From Go 1.18 onwards, cmd/go also embeds VCS information in binaries, which makes it even more useful than it was before.

As #37475 mentions, people place version information in binaries using -ldflags='-X foo=bar', which requires an additional build wrapper. The new VCS stamping feature of cmd/go should alleviate the need for external wrapper, but I am afraid it comes short.

The version information, in the sense of Go's pseudo version is not recorded for the main module when doing go build:

: emerald:ver; go build
: emerald:ver; go version -m hello | grep 'mod.*hello'
	mod	mgk.ro/hello	(devel)	
: emerald:ver; 

The version is recorded as expected when doing go install:

: emerald:ver; go install robpike.io/ivy@latest
go: downloading robpike.io/ivy v0.1.124
: emerald:ver; go version -m `which ivy` | grep 'mod.*ivy'
	mod	robpike.io/ivy	v0.1.12	h1:qI7dnEiXhorB+za07W6qX3sG+IvBK4EUl38vUHAf53Q=
: emerald:ver; 
: emerald:ver; 

I am afraid this limitation of cmd/go will continue to force people to use external build wrappers that set -ldflags, which is rather unfortunate.

I am not the first to want main module version information in binaries, this has been already asked for in various issues, for example in #29814, which was closed as a duplicate of #37475, but it really wasn't a duplicate, as #37475 is about VCS information, and #29814 is about semantic versioning. Other examples of people asking for this feature are mvdan/sh#519 and #29228 (comment) where various workarounds were proposed.

Speaking of workarounds, the only workaround that I know that currently works would be to create a local module proxy and pass GOPROXY to go install, but that is an extremely high-overhead workaround, and go install is not a replacement for go build anyway, since go install comes with some rather severe limitations regarding how vendoring works and what you can put in go.mod, and go install doesn't support controlling GOBIN when cross-compiling.

I realize that Git tags are a local concept, and by doing the "wrong" git operations one could come up with a different pseudo-version for the same source code. I am afraid I don't have any solution or suggestion regarding this git misfeature, except to note that even in this case the hash information is recorded correctly, and in every case by the virtue of having access to the local source code the programmer can always do some local operation that has the potential to cause a version mislabeling. Git is just more prome to do this by accident, but the ability is there, always.

I don't have any stats to back this up, but from my experience most corporate source code is built by go build, not go install, and it would be great if somehow Go's notion of versioning would be stamped by go build.

CC @bcmills @mvdan @rsc

[mvdan]

At least speaking personally, for cases like mvdan/sh#519, my intent is to show something like devel ${GIT_SHA} when someone does a local Go build out of a git checkout. If someone is manually cloning and building, as opposed to the advertised and easier go install url@latest, I imagine they know what a git hash is. So what 1.18 is currently shipping with is enough for my needs.

It's true that something like a proper module version might be more useful; a git commit hash doesn't give any hint as to how old a version is, whereas a semver version prefix or a timestamp can give a starting point. So, in principle, I agree with you: 1.18 is a big step forward, but it's still unfortunate that the main module version remains as (devel) for local builds.

However, in practice, I still agree with Jay's comment in #29228 (comment); we shouldn't make such a "locally inferred version" look like a normal version, because it's reasonably likely to be wrong or cause confusion with users.

in every case by the virtue of having access to the local source code the programmer can always do some local operation that has the potential to cause a version mislabeling.

Could you give some examples? I can only think of very unlikely scenarios, such as manually corrupting the module download cache after downloading some dependencies. That cache is read-only by default, and go mod verify exists to double-check the contents too.

With the main module in a git checkout, I can think of multiple scenarios which seem more likely:

• What if I've made a commit or tag but not pushed it?
• What if I've edited some files and not committed them?
• What if two people on two computers make the same tag with different code - would they end up with the same exact module version for different software? If one of them pushes their tag to the internet, would the other's computer be affected by the mismatch?

I think that, if we are to implement something like this, the versions must be somehow different from the canonical and unique versions that get computed from fully published commits and tags. This would make it very clear that the versions are inferred from local state, and not guaranteed to be correct. As a simplistic example, imagine that tagging v1.2.3 locally results in a build whose main module version is devel v1.2.3, but when pushed and go installed, gets the version v1.2.3.

[mvdan]

we shouldn't make such a "locally inferred version" look like a normal version, because it's reasonably likely to be wrong or cause confusion with users.

To add a more concrete example: if we made the change proposed here, and locally inferred versions looked like fully published versions, I would have a harder time trusting the output of shfmt -version when my users report bugs. I would have to update the issue template to also ask: did you build from a modified git checkout?

[4ad]

Could you give some examples? I can only think of very unlikely scenarios, such as manually corrupting the module download cache after downloading some dependencies. That cache is read-only by default, and go mod verify exists to double-check the contents too.

I was thinking of the case where since Go itself doesn't expose its own concept of a version to the program, the users themselves are forced to create their own concepts of a version, either through things like VERSION files, or through some build wrappers. By definition, any such concept is under user's control, and the user can and will make mistakes. In fact, from experience, users try to naively use git tags for this which then fail for precisely the reasons you just explained.

Let me rephrase my point. Go can't enforce any useful properties for the user's notion of a version because it doesn't know about it, and as such if we make userVersion==moduleVersion, the fact that Go can't enforce any properties is neither better nor worse for the user. The user is on the hook for doing the right thing in both cases. In one case the user must properly maintain their VERSION, and in the other case the user must properly maintain their git checkouts.

The user does gain something in the latter case though. They don't have to create build wrappers.

With the main module in a git checkout, I can think of multiple scenarios [which might fail ... ] I think that, if we are to implement something like this, the versions must be somehow different from the canonical and unique versions that get computed from fully published commits and tags. [...] As a simplistic example, imagine that tagging v1.2.3 locally results in a build whose main module version is devel v1.2.3, but when pushed and go installed, gets the version v1.2.3.

I very much agree with this, with one caveat. If the locally checked-out version is identical to a published release, I would expect the version to match the release. If the locally checked-out version can not be guaranteed to match any release, then yes, it should be published with something like devel v1.2.3 (which matches what Go does, but why not v1.2.3-devel or v1.2.3-unknown, which is semver-compatible?).

Unfortunately, I can't imagine how this would work without internet access, and quite often a prerequisite of automated systems running go build is to not go to the Internet.

[4ad]

Hold on, another thought. If we always add the commit hash, and some other metadata to the main module version for local builds, essentially always making them a fully qualified Go pseudo-version, then they will always be different from the published version, so there's no potential for confusion there.

Even better, in semver terms these builds will sort before the published version, which is probably what people want.

For this, what I said earlier about

If the locally checked-out version is identical to a published release, I would expect the version to match the release.

can no longer be true, but perhaps that is ok as long as we come up with a documented and stable convention that describes versioning for local builds (as opposed to just dumping a "devel" in the metadata field).

[bcmills]

The main caveat here, I think, is unpublished tags. If I create a local, unpublished tag for, say, v1.1000.0, then my pseudo-versions will be v1.1000.0-0.2022…, but everyone else's pseudo-versions may be on an arbitrarily lower version (say, v0.8.3-0.2022….

That may or may not be a significant issue, though: if we always use a pseudo-version, we'll at least have the commit hash as a common point of reference even if the base versions differ.

[mvdan]

@4ad right, a local build can't always know what is or isn't published, as requiring a network roundtrip takes us back to square one.

Your idea of trying to stick to semver, and always using some form of pseudo-version which includes a hash, sounds good. With one caveat, though: the commit hash isn't enough to make the version unambiguous, because I can have infinite kinds of uncommitted changes that do not change the HEAD commit hash.

@bcmills good point about tags still messing with pseudo-versions, but at least if we always include a timestamp and some form of unique hash, then I think we're good. With the caveat above about uncommitted changes :)

[mvdan]

We do have another hash available to us, though, which changes whenever any input Go code changes: the build IDs used for the build cache. I seem to recall that one such ID is embedded into binaries, too.

Not ideal, as such a hash also includes build parameters like GOOS or -tags, which don't normally affect versions. But at least it fixed the problem with uncommitted files in VCS.

[4ad]

Yes, uncommitted changes should be explicit in the pseudo-version, but I think we can suffix +, just as we do with Go itself, no?

[seankhliao]

the new buildinfo already records whether the workspace is clean with vcs.modified=true|false

[seankhliao]

we could use one of +local (for clean builds) or +dirty (uncommitted changes, implies local) as the semver build id, attached to a pseudoversion which should make the situation clear enough?

So main will always have a version like

vX.Y.Z-timestamp-commit+local
vX.Y.Z-timestamp-commit+dirty

[hyangah]

What is the main motivation of encoding the local version in pseudo-version style rather than keeping those extra info (timestamp?) as extra metadata fields - if it's not guaranteed that they are always available in the origin or proxies?

It seems like the vcs.time is already there in the build info metadata.

---

BTW, I feel like the main module's version isn't sufficient to describe a tool's behavior in certain cases - go version used to go build, third-party tools dependencies, and go build's behavior change (go.work left over somewhere accidentally?) can affect a tool's behavior. So when triaging issues, I hope we develop best practice using go version -m or richer build info dump rather than relying on the main module version string.

[4ad]

What is the main motivation of encoding the local version in pseudo-version style

The main motivation is that go install does it, and many people expect to have a notion of a program's version available and want it, and because they don't have it with go build, they rely on build wrapers or other workarounds, which are undesirable in the broader Go ecosystem.

encoding the local version in pseudo-version style rather than keeping those extra info (timestamp?) as extra metadata fields

Emphasis mine.

It's not rather than, It doesn't replace the existing metadata fields. If you want to read the metadata, you should read it from those fields instead of parsing the pseudo-version. However, that metadata is useful in disambiguating builds produced by go build from published releases. Presumably we could come with some other kind of metadata for the same purpose, but since pseudo-versions are a de-facto standard in the Go ecosystem, why not reuse it?

I feel like the main module's version isn't sufficient to describe a tool's behavior in certain cases - go version used to go build, third-party tools dependencies, and go build's behavior change (go.work left over somewhere accidentally?) can affect a tool's behavior.

This sounds like an argument to always use the build ID as the version suffix instead of the VCS hash.

So when triaging issues, I hope we develop best practice using go version -m or richer build info dump rather than relying on the main module version string.

I hope so too, but again, I think that discussion is out of scope for this thread, which is more about bringing go build in line with go install and providing a solution for users that avoids build wrappers.

[rsc]

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

[maja42]

As a kind of experience report, I'm using custom build-scripts for years, solely to embed version information of the main module into the executable. When building, I attach the following information:

type BuildInfo struct {
	// Major, Minor, Patch contain the semantic version components.
	// In case of an unofficial build, this version is from a previous commit on the same branch.
	Major, Minor, Patch int
	// If true, a version-tagged commit was built.
	OfficialBuild bool

	// CommitHash is the full hash of the git commit.
	// Note that the actually built source-code is different if LocalChanges is true.
	CommitHash string
	// CommitTimestamp is the timestamp of the git commit.
	// Note that the actually built source-code is different if LocalChanges is true.
	CommitTimestamp time.Time
	// BuildTimestamp contains the timestamp when the project was built.
	BuildTimestamp time.Time

	// LocalChanges specifies if the project directory differed from the commit due to local (uncommitted) changes.
	LocalChanges bool
}

With this kind of information, I'm able to build version-strings however I like. Usually I try to match go's pseudo-version strings, but when I need to stay compatible with the version-scheme from other, non-go projects, I can do so as well.

// VersionString returns the project's semantic version number without a leading 'v'.
// Patterns:
//    <major>.<minor>.<patch>
//        Built from an officially tagged commit (without local changes)
//    0.0.0-<buildTime>
//        Unofficial build. There are no tagged commits yet.
//    <major>.<minor>.<patch*>-<buildTime>
//        Unofficial build. The commit was not tagged, or there were local changes.
//        The used patch-version is +1 compared to the last tagged commit.
//    The build timestamp (yyyymmddhhmmss) is the UTC time when the application was built / ctgover generated the version number.
func (b *BuildInfo) VersionString() string {
	preRelease := ""
        patch := p.Patch
	if !b.OfficialBuild {
		buildTime := b.BuildTimestamp.Format("20060102150405")
		preRelease = "-" + buildTime
                patch++
	}
	return fmt.Sprintf("%d.%d.%d%s", b.Major, b.Minor, patch, preRelease)
}	

The version is printed when the application is started with a -version command-line flag. But I guess go-tools could/should show the same version string.

I don't have anything against adding a build ID, but it wouldn't really solve my problem. My use cases are:

• Identify the source-code / git-commit that was built
• Identify the application's version (for example to detect available updates)
• Identify when the application was built (quickly find out if it super old)
• Compare if two applications are the same, and which one is newer

The previously raised issue that git-tags might only be local was never really an issue in my experience. Version-tags aren't made lightheartedly and are always immediately pushed to the server in the projects I work on.

I really hope we can this kind of information into a go-executable one day, because I would finally be able to get rid of all my build- and tool-scripts.

[rsc]

It sounds like @mvdan and @bcmills have some hesitation around the fact that these pseudo-versions would not correspond to any publicly available version, even though they look like those. That does seem like a reason not to do this.

We now have Git VCS info separately in the builds (as of Go 1.18; try go version -m). Do we need to add a second way to record that information?

[4ad]

It sounds like @mvdan and @bcmills have some hesitation around the fact that these pseudo-versions would not correspond to any publicly available version, even though they look like those.

We can make it unambiguously distinct, for example instead of v1.2.4-0.20191109021931-daa7c04131f5 we could use v1.2.4-0.unpublished.20191109021931-daa7c04131f5 or something like that.

We now have Git VCS info separately in the builds (as of Go 1.18; try go version -m). Do we need to add a second way to record that information?

No, we certainly only need one way to encode VCS info. The suggestion to put VCS info in the metadata field of the pseudo-version was to match the go install behavior, but putting something else there, for example the build id is probably better. The build id also works, and is meaningful when you might not have VCS info, like from a tarball, which is a pretty common case where you'd use go build for. Scratch that idea, without VCS we can't detect the version either.

[ChrisHines]

We can make it unambiguously distinct, for example instead of v1.2.4-0.20191109021931-daa7c04131f5 we could use v1.2.4-0.unpublished.20191109021931-daa7c04131f5 or something like that.

With replace statements in go.mod and the new workspace mode in Go 1.18 it is possible to build Go programs that include local versions of modules besides the main module. For those modules the go tool also lists (devel) for their version.

The new build vcs metadata only helps identify the main module. Adding vcs metadata for all local modules seems valuable and not currently supported. The format suggested above by @4ad would be more informative than (devel). Maybe also including a dirty flag if there are uncommitted local edits.

[rsc]

The new build vcs metadata only helps identify the main module. Adding vcs metadata for all local modules seems valuable and not currently supported.

This may be true, but the concern above seems to be adding vcs metadata that looks like a pseudo-version. It need not, and it probably should not. We can always add that separately; maybe that should be a different proposal. (I think this is the first comment to bring up VCS info for replaced modules that point to other local repos.)

[mvdan]

A thought: if we're only concerned about having a reliable way to always get some useful version for the main module, I think it could be an API of its own, like debug.MainVersion() string. It could first try to get the main module version from https://pkg.go.dev/runtime/debug#ReadBuildInfo, otherwise fall back to VCS information, and otherwise fall back to something that should always work, such as the binary's build ID.

I personally will be implementing logic like that to replace -ldflags=-X=main.version=... in my projects, where I use a default of var version = "(devel)". And I think it should be useful to other projects as well, at least as a good starting point.

Another option, if we want this to also work for library modules, would be debug.OwnVersion, which would do the equivalent but for the module containing the package that's making the function call. Perhaps that would cover @ChrisHines's needs. I maintain some libraries and I admit that reliably knowing my own version could help in terms of logging or capturing debug information.

If the above sounds interesting, I'll happily develop the idea further and create a new proposal. I realise it's not the same as this proposal, but I also think it could be a different solution to the same end-user problem :)

[kortschak]

@mvdan I would very much like to see something like that to replace the boiler place build lines that exist in code at work.

[4ad]

We use the semantic version of the binaries in order to compute API compatibility between different binaries. I am afraid that if your debug.MainVersion() doesn't always return some string that is compatible with semver, we will still have to resort to -ldflags=-X=....

Now, one might object to using the binary version in this way and perhaps recommend using a separately maintained API version instead that is separate from the binary version. I would tend to agree except this is outside my control. I do not have the operational liberty to change this.

[mvdan]

@amnonbc there is no need to ask every cycle. If there was progress, you would see it here. The only other way to make it happen is to volunteer yourself and learn the codebase well.

[amnonbc]

@amnonbc there is no need to ask every cycle. If there was progress, you would see it here. The only other way to make it happen is to volunteer yourself and learn the codebase well.

Fair enough. I hope to have some time to look at this over the Xmas holiday.

[andig]

I think my only slight worry then would be: programs wishing to show their information should always print the VCS info (commit, date, dirty, etc) alongside the module version, because not doing so could potentially lead to confusing edge cases for authors such as tags having been added or modified locally.

For me, the VCS info, especially the tag, plus the commit, is the single piece that I‘m looking for in this feature. If the tag is recorded as VCS info or as pseudo version wouldn‘t matter as long as I can retrieve it to remove the need for ldflags. That in turn simplifies the build process and e.g. allows to use static build config with tools like gokrazy.

[mvdan]

Here's something I think we never covered - would this stamping from VCS info always happen, or only when -buildvcs is enabled, be it via -buildvcs=true or when the default -buildvcs=auto finds the git tool and .git data to be present? I ask this in the context of #53976 (comment).

[ericrrath]

Expanding on the comment by @maja42, another use-case is vulnerability scanners. I think all these scanners work by examining the artifact, e.g. a golang binary, and extracting enough information to derive a CPE for each distinct application/library/module, and then looking up any vulnerabilities for those CPEs in whatever vuln database is used. If the scanner can't derive a CPE for a given component, then it can't lookup vulns for that component.

Trivy currently uses debug/buildinfo to derive CPEs for the dependencies, but does not look at the "main" module, possibly because it rarely sees usable values for the "main" module (pure speculation on my part).

If the debug/buildinfo fields are the canonical place to put this kind of name-and-version information, then populating it in more cases would allow the scanners to report more vulns.