It seems that Go upstream is making great progress on the vgo and Go modules. It looks like it might help us with better tracking the versioned dependencies(there will be some data in the repositories) and could force upstream to more properly declare their dependencies and actually making them more likely to do versioned releases. On the down side we will have to add support for this now format in to the tooling ;).

What do you think?

You can now test the go modules on the master and go1.11 branch of Go/GC. You can obtain it by regular means from upstream, if you are running rawhide/29 fedora you get it out of the box and if you are on Fedora < 29 you can grab it from my COPR repo(https://copr.fedorainfracloud.org/coprs/jcajka/golang-rawhide/) where I'm building Golang/GC from master.

Original upstream announcement email follows.

JC

----- Forwarded Message ----- From: "Russ Cox" rsc@golang.org To: "golang-dev" golang-dev@googlegroups.com Cc: "Paul Jolly" paul@myitcv.io, "Bryan C. Mills" bcmills@google.com, nototon@gmail.com Sent: Thursday, July 12, 2018 11:20:34 PM Subject: [golang-dev] go modules have landed

As of CL 123580, submitted a few minutes ago, the development copy of the go command, in the main go repository, has support for Go modules. There are various minor known issues, but quite a lot works very well.

There's still more to be done but this is a key milestone: if you run on the bleeding edge, you can play with modules just by using "go". Work on the module support will now be done exclusively in the main repo. We will automatically export the main repo to the x/vgo repo when we have a snapshot we want to make available to people using "vgo".

The open issues have moved from the vgo milestone to the Go 1.11 milestone, but labeled with the new 'modules https://github.com/golang/go/labels/modules' label.

A note on terminology: Go 1.11 is not shipping with "vgo support". It is shipping with "Go module support". Vgo was only ever the prototype/demo of that module support. Just like all the other features we've introduced to the go command over the past ten years, the goal for this one is to fit so well into the rest of the go command fabric that the seams are invisible - module support is just part of "go", the same way that, say, race detector support or GOPATH support is.

Speaking of GOPATH, the go command automatically chooses between using modules and using GOPATH depending on where it is run. If a go command runs outside GOPATH/src and there is a go.mod file in the current directory or one of its parent directories, then modules are enabled (otherwise not):

$ mkdir /tmp/hello $ cd /tmp/hello $ echo module hello >go.mod $ cat >hello.go <<EOF package main

import "rsc.io/quote"

func main() { println(quote.Glass()) } EOF $ go run . I can eat glass and it doesn't hurt me. $ cat go.mod module hello

require rsc.io/quote v1.5.2 $ go list -m all hello golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c rsc.io/quote v1.5.2 rsc.io/sampler v1.3.0 $

For more information, see 'go help modules', which I've included at the end of this mail.

Many thanks to everyone in the community who has helped us get to this point, but especially to Paul Jolly for really hammering on the module support and filing tons of great bugs, and to Baokun Lee for a steady sequence of helpful CLs. Thanks also to Bryan Mills for helping work out a lot of important details in the past few weeks.

Thanks again, and keep the bug reports coming.

Best, Russ

*go help modules*

A module is a collection of related Go packages. Modules are the unit of source code interchange and versioning. The go command has direct support for working with modules, including recording and resolving dependencies on other modules. Modules replace the old GOPATH-based approach to specifying which source files are used in a given build.

*Experimental module support*

Go 1.11 includes experimental support for Go modules, including a new module-aware 'go get' command. We intend to keep revising this support, while preserving compatibility, until it can be declared official (no longer experimental), and then at a later point we may remove support for work in GOPATH and the old 'go get' command.

The quickest way to take advantage of the new Go 1.11 module support is to check out your repository into a directory outside GOPATH/src, create a go.mod file (described in the next section) there, and run go commands from within that file tree.

For more fine-grained control, the module support in Go 1.11 respects a temporary environment variable, GO111MODULE, which can be set to one of three string values: off, on, or auto (the default). If GO111MODULE=off, then the go command never uses the new module support. Instead it looks in vendor directories and GOPATH to find dependencies; we now refer to this as "GOPATH mode." If GO111MODULE=on, then the go command requires the use of modules, never consulting GOPATH. We refer to this as the command being module-aware or running in "module-aware mode". If GO111MODULE=auto or is unset, then the go command enables or disables module support based on the current directory. Module support is enabled only when the current directory is outside GOPATH/src and itself contains a go.mod file or is below a directory containing a go.mod file.

*Defining a module*

A module is defined by a tree of Go source files with a go.mod file in the tree's root directory. The directory containing the go.mod file is called the module root. Typically the module root will also correspond to a source code repository root (but in general it need not). The module is the set of all Go packages in the module root and its subdirectories, but excluding subtrees with their own go.mod files.

The "module path" is the import path prefix corresponding to the module root. The go.mod file defines the module path and lists the specific versions of other modules that should be used when resolving imports during a build, by giving their module paths and versions.

For example, this go.mod declares that the directory containing it is the root of the module with path example.com/m, and it also declares that the module depends on specific versions of golang.org/x/text and gopkg.in/yaml.v2:

module example.com/m require ( golang.org/x/text v0.3.0 gopkg.in/yaml.v2 v2.1.0 )

The go.mod file can also specify replacements and excluded versions that only apply when building the module directly; they are ignored when the module is incorporated into a larger build. For more about the go.mod file, see https://research.swtch.com/vgo-module.

To start a new module, simply create a go.mod file in the root of the module's directory tree, containing only a module statement. The 'go mod' command can be used to do this:

go mod -init -module example.com/m

In a project already using an existing dependency management tool like godep, glide, or dep, 'go mod -init' will also add require statements matching the existing configuration.

Once the go.mod file exists, no additional steps are required: go commands like 'go build', 'go test', or even 'go list' will automatically add new dependencies as needed to satisfy imports.

*The main module and the build list*

The "main module" is the module containing the directory where the go command is run. The go command finds the module root by looking for a go.mod in the current directory, or else the current directory's parent directory, or else the parent's parent directory, and so on.

The main module's go.mod file defines the precise set of packages available for use by the go command, through require, replace, and exclude statements. Dependency modules, found by following require statements, also contribute to the definition of that set of packages, but only through their go.mod files' require statements: any replace and exclude statements in dependency modules are ignored. The replace and exclude statements therefore allow the main module complete control over its own build, without also being subject to complete control by dependencies.

The set of modules providing packages to builds is called the "build list". The build list initially contains only the main module. Then the go command adds to the list the exact module versions required by modules already on the list, recursively, until there is nothing left to add to the list. If multiple versions of a particular module are added to the list, then at the end only the latest version (according to semantic version ordering) is kept for use in the build.

The 'go list' command provides information about the main module and the build list. For example:

go list -m # print path of main module go list -m -f={{.Dir}} # print root directory of main module go list -m all # print build list

*Maintaining module requirements*

The go.mod file is meant to be readable and editable by both programmers and tools. The go command itself automatically updates the go.mod file to maintain a standard formatting and the accuracy of require statements.

Any go command that finds an unfamiliar import will look up the module containing that import and add the latest version of that module to go.mod automatically. In most cases, therefore, it suffices to add an import to source code and run 'go build', 'go test', or even 'go list': as part of analyzing the package, the go command will discover and resolve the import and update the go.mod file.

Any go command can determine that a module requirement is missing and must be added, even when considering only a single package from the module. On the other hand, determining that a module requirement is no longer necessary and can be deleted requires a full view of all packages in the module, across all possible build configurations (architectures, operating systems, build tags, and so on). The 'go mod -sync' command builds that view and then adds any missing module requirements and removes unnecessary ones.

As part of maintaining the require statements in go.mod, the go command tracks which ones provide packages imported directly by the current module and which ones provide packages only used indirectly by other module dependencies. Requirements needed only for indirect uses are marked with a "// indirect" comment in the go.mod file. Indirect requirements are automatically removed from the go.mod file once they are implied by other direct requirements. Indirect requirements only arise when using modules that fail to state some of their own dependencies or when explicitly upgrading a module's dependencies ahead of its own stated requirements.

Because of this automatic maintenance, the information in go.mod is an up-to-date, readable description of the build.

The 'go get' command updates go.mod to change the module versions used in a build. An upgrade of one module may imply upgrading others, and similarly a downgrade of one module may imply downgrading others. The 'go get' command makes these implied changes as well. If go.mod is edited directly, commands like 'go build' or 'go list' will assume that an upgrade is intended and automatically make any implied upgrades and update go.mod to reflect them.

The 'go mod' command provides other functionality for use in maintaining and understanding modules and go.mod files. See 'go help mod'.

*Pseudo-versions*

The go.mod file and the go command more generally use semantic versions as the standard form for describing module versions, so that versions can be compared to determine which should be considered earlier or later than another. A module version like v1.2.3 is introduced by tagging a revision in the underlying source repository. Untagged revisions can be referred to using a "pseudo-version" of the form v0.0.0-yyyymmddhhmmss-abcdefabcdef, where the time is the commit time in UTC and the final suffix is the prefix of the commit hash. The time portion ensures that two pseudo-versions can be compared to determine which happened later, the commit hash identifes the underlying commit, and the v0.0.0- prefix identifies the pseudo-version as a pre-release before version v0.0.0, so that the go command prefers any tagged release over any pseudo-version.

Pseudo-versions never need to be typed by hand: the go command will accept the plain commit hash and translate it into a pseudo-version (or a tagged version if available) automatically. This conversion is an example of a module query.

*Module queries*

The go command accepts a "module query" in place of a module version both on the command line and in the main module's go.mod file. (After evaluating a query found in the main module's go.mod file, the go command updates the file to replace the query with its result.)

A fully-specified semantic version, such as "v1.2.3", evaluates to that specific version.

A semantic version prefix, such as "v1" or "v1.2", evaluates to the latest available tagged version with that prefix.

A semantic version comparison, such as "<v1.2.3" or ">=v1.5.6", evaluates to the available tagged version nearest to the comparison target (the latest version for < and <=, the earliest version for > and >=).

The string "latest" matches the latest available tagged version, or else the underlying source repository's latest untagged revision.

A revision identifier for the underlying source repository, such as a commit hash prefix, revision tag, or branch name, selects that specific code revision. If the revision is also tagged with a semantic version, the query evaluates to that semantic version. Otherwise the query evaluates to a pseudo-version for the commit.

All queries prefer release versions to pre-release versions. For example, "<v1.2.3" will prefer to return "v1.2.2" instead of "v1.2.3-pre1", even though "v1.2.3-pre1" is nearer to the comparison target.

Module versions disallowed by exclude statements in the main module's go.mod are considered unavailable and cannot be returned by queries.

For example, these commands are all valid:

go get github.com/gorilla/mux@latest # same (@latest is default for 'go get') go get github.com/gorilla/mux@v1.6.2 # records v1.6.2 go get github.com/gorilla/mux@e3702bed2 # records v1.6.2 go get github.com/gorilla/mux@c856192 # records v0.0.0-20180517173623-c85619274f5d go get github.com/gorilla/mux@master # records current meaning of master

*Module compatibility and semantic versioning*

The go command requires that modules use semantic versions and expects that the versions accurately describe compatibility: it assumes that v1.5.4 is a backwards-compatible replacement for v1.5.3, v1.4.0, and even v1.0.0. More generally the go command expects that packages follow the "import compatibility rule", which says:

"If an old package and a new package have the same import path, the new package must be backwards compatible with the old package."

Because the go command assumes the import compatibility rule, a module definition can only set the minimum required version of one of its dependencies: it cannot set a maximum or exclude selected versions. Still, the import compatibility rule is not a guarantee: it may be that v1.5.4 is buggy and not a backwards-compatible replacement for v1.5.3. Because of this, the go command never updates from an older version to a newer version of a module unasked.

In semantic versioning, changing the major version number indicates a lack of backwards compatibility with earlier versions. To preserve import compatibility, the go command requires that modules with major version v2 or later use a module path with that major version as the final element. For example, version v2.0.0 of example.com/m must instead use module path example.com/m/v2, and packages in that module would use that path as their import path prefix, as in example.com/m/v2/sub/pkg. Including the major version number in the module path and import paths in this way is called "semantic import versioning". Pseudo-versions for modules with major version v2 and later begin with that major version instead of v0, as in v2.0.0-20180326061214-4fc5987536ef.

The go command treats modules with different module paths as unrelated: it makes no connection between example.com/m and example.com/m/v2. Modules with different major versions can be used together in a build and are kept separate by the fact that their packages use different import paths.

In semantic versioning, major version v0 is for initial development, indicating no expectations of stability or backwards compatibility. Major version v0 does not appear in the module path, because those versions are preparation for v1.0.0, and v1 does not appear in the module path either.

As a special case, for historical reasons, module paths beginning with gopkg.in/ continue to use the conventions established on that system: the major version is always present, and it is preceded by a dot instead of a slash: gopkg.in/yaml.v1 and gopkg.in/yaml.v2, not gopkg.in/yaml and gopkg.in/yaml/v2.

See https://research.swtch.com/vgo-import and https://semver.org/ for more information.

*Module verification*

The go command maintains, in the main module's root directory alongside go.mod, a file named go.sum containing the expected cryptographic checksums of the content of specific module versions. Each time a dependency is used, its checksum is added to go.sum if missing or else required to match the existing entry in go.sum.

The go command maintains a cache of downloaded packages and computes and records the cryptographic checksum of each package at download time. In normal operation, the go command checks these pre-computed checksums against the main module's go.sum file, instead of recomputing them on each command invocation. The 'go mod -verify' command checks that the cached copies of module downloads still match both their recorded checksums and the entries in go.sum.

*Modules and vendoring*

When using modules, the go command completely ignores vendor directories.

By default, the go command satisfies dependencies by downloading modules from their sources and using those downloaded copies (after verification, as described in the previous section). To allow interoperation with older versions of Go, or to ensure that all files used for a build are stored together in a single file tree, 'go mod -vendor' creates a directory named vendor in the root directory of the main module and stores there all the packages from dependency modules that are needed to support builds and tests of packages in the main module.

To build using the main module's top-level vendor directory to satisfy dependencies (disabling use of the usual network sources and local caches), use 'go build -getmode=vendor'. Note that only the main module's top-level vendor directory is used; vendor directories in other locations are still ignored.