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cmd/go: revise 'go help' documentation for modules

Browse Source 
Module-related help pages now contain a brief summary and point to the
reference documentation at golang.org/ref/mod for details.

Help pages for commands like 'go get' still describe the basic usage
and summarize flags but don't provide as much background detail.

Fixes #41427
Fixes #43419

Change-Id: Icacd38e0f33c352c447cc5a496c99674493abde2
Reviewed-on: https://go-review.googlesource.com/c/go/+/282615
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
This commit is contained in:
Jay Conrod 2021-01-08 11:35:35 -05:00
parent 6192b98751
commit cd6f3a54e4
16 changed files with 190 additions and 1426 deletions
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808
src/cmd/go/alldocs.go
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19
src/cmd/go/internal/help/helpdoc.go
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@ -266,7 +266,7 @@ listed in the GOPATH environment variable.
(See 'go help gopath-get' and 'go help gopath'.)
When using modules, downloaded packages are stored in the module cache.
(See 'go help module-get' and 'go help goproxy'.)
See https://golang.org/ref/mod#module-cache.
When using modules, an additional variant of the go-import meta tag is
recognized and is preferred over those listing version control systems.
@ -276,7 +276,8 @@ That variant uses "mod" as the vcs in the content value, as in:
This tag means to fetch modules with paths beginning with example.org
from the module proxy available at the URL https://code.org/moduleproxy.
See 'go help goproxy' for details about the proxy protocol.
See https://golang.org/ref/mod#goproxy-protocol for details about the
proxy protocol.
Import path checking
@ -483,6 +484,10 @@ See 'go help env' for details.
General-purpose environment variables:
GO111MODULE
Controls whether the go command runs in module-aware mode or GOPATH mode.
May be "off", "on", or "auto".
See https://golang.org/ref/mod#mod-commands.
GCCGO
The gccgo command to run for 'go build -compiler=gccgo'.
GOARCH
@ -521,20 +526,24 @@ General-purpose environment variables:
GOPATH
For more details see: 'go help gopath'.
GOPROXY
URL of Go module proxy. See 'go help modules'.
URL of Go module proxy. See https://golang.org/ref/mod#environment-variables
and https://golang.org/ref/mod#module-proxy for details.
GOPRIVATE, GONOPROXY, GONOSUMDB
Comma-separated list of glob patterns (in the syntax of Go's path.Match)
of module path prefixes that should always be fetched directly
or that should not be compared against the checksum database.
See 'go help private'.
See https://golang.org/ref/mod#private-modules.
GOROOT
The root of the go tree.
GOSUMDB
The name of checksum database to use and optionally its public key and
URL. See 'go help module-auth'.
URL. See https://golang.org/ref/mod#authenticating.
GOTMPDIR
The directory where the go command will write
temporary source files, packages, and binaries.
GOVCS
Lists version control commands that may be used with matching servers.
See 'go help vcs'.
Environment variables for use with cgo:

2
src/cmd/go/internal/list/list.go
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@ -304,7 +304,7 @@ For more about build flags, see 'go help build'.
For more about specifying packages, see 'go help packages'.
For more about modules, see 'go help modules'.
For more about modules, see https://golang.org/ref/mod.
`,
}

4
src/cmd/go/internal/modcmd/download.go
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@ -52,7 +52,9 @@ corresponding to this Go struct:
The -x flag causes download to print the commands download executes.
See 'go help modules' for more about module queries.
See https://golang.org/ref/mod#go-mod-download for more about 'go mod download'.
See https://golang.org/ref/mod#version-queries for more about version queries.
`,
}

4
src/cmd/go/internal/modcmd/edit.go
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@ -122,9 +122,7 @@ Note that this only describes the go.mod file itself, not other modules
referred to indirectly. For the full set of modules available to a build,
use 'go list -m -json all'.
For example, a tool can obtain the go.mod as a data structure by
parsing the output of 'go mod edit -json' and can then make changes
by invoking 'go mod edit' with -require, -exclude, and so on.
See https://golang.org/ref/mod#go-mod-edit for more about 'go mod edit'.
`,
}

2
src/cmd/go/internal/modcmd/graph.go
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@ -26,6 +26,8 @@ Graph prints the module requirement graph (with replacements applied)
in text form. Each line in the output has two space-separated fields: a module
and one of its requirements. Each module is identified as a string of the form
path@version, except for the main module, which has no @version suffix.
See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
`,
Run: runGraph,
}

2
src/cmd/go/internal/modcmd/init.go
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@ -27,6 +27,8 @@ Gopkg.lock), and the current directory (if in GOPATH).
If a configuration file for a vendoring tool is present, init will attempt to
import module requirements from it.
See https://golang.org/ref/mod#go-mod-init for more about 'go mod init'.
`,
Run: runInit,
}

2
src/cmd/go/internal/modcmd/tidy.go
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@ -29,6 +29,8 @@ to standard error.
The -e flag causes tidy to attempt to proceed despite errors
encountered while loading packages.
See https://golang.org/ref/mod#go-mod-tidy for more about 'go mod tidy'.
`,
Run: runTidy,
}

2
src/cmd/go/internal/modcmd/vendor.go
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@ -38,6 +38,8 @@ modules and packages to standard error.
The -e flag causes vendor to attempt to proceed despite errors
encountered while loading packages.
See https://golang.org/ref/mod#go-mod-vendor for more about 'go mod vendor'.
`,
Run: runVendor,
}

2
src/cmd/go/internal/modcmd/verify.go
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@ -31,6 +31,8 @@ modified since being downloaded. If all the modules are unmodified,
verify prints "all modules verified." Otherwise it reports which
modules have been changed and causes 'go mod' to exit with a
non-zero status.
See https://golang.org/ref/mod#go-mod-verify for more about 'go mod verify'.
`,
Run: runVerify,
}

2
src/cmd/go/internal/modcmd/why.go
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@ -48,6 +48,8 @@ For example:
# golang.org/x/text/encoding
(main module does not need package golang.org/x/text/encoding)
$
See https://golang.org/ref/mod#go-mod-why for more about 'go mod why'.
`,
}

106
src/cmd/go/internal/modfetch/fetch.go
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@ -768,90 +768,14 @@ var HelpModuleAuth = &base.Command{
UsageLine: "module-auth",
Short: "module authentication using go.sum",
Long: `
The go command tries to authenticate every downloaded module,
checking that the bits downloaded for a specific module version today
match bits downloaded yesterday. This ensures repeatable builds
and detects introduction of unexpected changes, malicious or not.
When the go command downloads a module zip file or go.mod file into the
module cache, it computes a cryptographic hash and compares it with a known
value to verify the file hasn't changed since it was first downloaded. Known
hashes are stored in a file in the module root directory named go.sum. Hashes
may also be downloaded from the checksum database depending on the values of
GOSUMDB, GOPRIVATE, and GONOSUMDB.
In each module's root, alongside go.mod, the go command maintains
a file named go.sum containing the cryptographic checksums of the
module's dependencies.
The form of each line in go.sum is three fields:
<module> <version>[/go.mod] <hash>
Each known module version results in two lines in the go.sum file.
The first line gives the hash of the module version's file tree.
The second line appends "/go.mod" to the version and gives the hash
of only the module version's (possibly synthesized) go.mod file.
The go.mod-only hash allows downloading and authenticating a
module version's go.mod file, which is needed to compute the
dependency graph, without also downloading all the module's source code.
The hash begins with an algorithm prefix of the form "h<N>:".
The only defined algorithm prefix is "h1:", which uses SHA-256.
Module authentication failures
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 the main module's go.sum file
against these precomputed checksums 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.
In day-to-day development, the checksum of a given module version
should never change. Each time a dependency is used by a given main
module, the go command checks its local cached copy, freshly
downloaded or not, against the main module's go.sum. If the checksums
don't match, the go command reports the mismatch as a security error
and refuses to run the build. When this happens, proceed with caution:
code changing unexpectedly means today's build will not match
yesterday's, and the unexpected change may not be beneficial.
If the go command reports a mismatch in go.sum, the downloaded code
for the reported module version does not match the one used in a
previous build of the main module. It is important at that point
to find out what the right checksum should be, to decide whether
go.sum is wrong or the downloaded code is wrong. Usually go.sum is right:
you want to use the same code you used yesterday.
If a downloaded module is not yet included in go.sum and it is a publicly
available module, the go command consults the Go checksum database to fetch
the expected go.sum lines. If the downloaded code does not match those
lines, the go command reports the mismatch and exits. Note that the
database is not consulted for module versions already listed in go.sum.
If a go.sum mismatch is reported, it is always worth investigating why
the code downloaded today differs from what was downloaded yesterday.
The GOSUMDB environment variable identifies the name of checksum database
to use and optionally its public key and URL, as in:
GOSUMDB="sum.golang.org"
GOSUMDB="sum.golang.org+<publickey>"
GOSUMDB="sum.golang.org+<publickey> https://sum.golang.org"
The go command knows the public key of sum.golang.org, and also that the name
sum.golang.google.cn (available inside mainland China) connects to the
sum.golang.org checksum database; use of any other database requires giving
the public key explicitly.
The URL defaults to "https://" followed by the database name.
GOSUMDB defaults to "sum.golang.org", the Go checksum database run by Google.
See https://sum.golang.org/privacy for the service's privacy policy.
If GOSUMDB is set to "off", or if "go get" is invoked with the -insecure flag,
the checksum database is not consulted, and all unrecognized modules are
accepted, at the cost of giving up the security guarantee of verified repeatable
downloads for all modules. A better way to bypass the checksum database
for specific modules is to use the GOPRIVATE or GONOSUMDB environment
variables. See 'go help private' for details.
The 'go env -w' command (see 'go help env') can be used to set these variables
for future go command invocations.
For details, see https://golang.org/ref/mod#authenticating.
`,
}
@ -865,8 +789,8 @@ regardless of source, against the public Go checksum database at sum.golang.org.
These defaults work well for publicly available source code.
The GOPRIVATE environment variable controls which modules the go command
considers to be private (not available publicly) and should therefore not use the
proxy or checksum database. The variable is a comma-separated list of
considers to be private (not available publicly) and should therefore not use
the proxy or checksum database. The variable is a comma-separated list of
glob patterns (in the syntax of Go's path.Match) of module path prefixes.
For example,
@ -876,10 +800,6 @@ causes the go command to treat as private any module with a path prefix
matching either pattern, including git.corp.example.com/xyzzy, rsc.io/private,
and rsc.io/private/quux.
The GOPRIVATE environment variable may be used by other tools as well to
identify non-public modules. For example, an editor could use GOPRIVATE
to decide whether to hyperlink a package import to a godoc.org page.
For fine-grained control over module download and validation, the GONOPROXY
and GONOSUMDB environment variables accept the same kind of glob list
and override GOPRIVATE for the specific decision of whether to use the proxy
@ -892,12 +812,6 @@ users would configure go using:
GOPROXY=proxy.example.com
GONOPROXY=none
This would tell the go command and other tools that modules beginning with
a corp.example.com subdomain are private but that the company proxy should
be used for downloading both public and private modules, because
GONOPROXY has been set to a pattern that won't match any modules,
overriding GOPRIVATE.
The GOPRIVATE variable is also used to define the "public" and "private"
patterns for the GOVCS variable; see 'go help vcs'. For that usage,
GOPRIVATE applies even in GOPATH mode. In that case, it matches import paths
@ -905,5 +819,7 @@ instead of module paths.
The 'go env -w' command (see 'go help env') can be used to set these variables
for future go command invocations.
For more details, see https://golang.org/ref/mod#private-modules.
`,
}

61
src/cmd/go/internal/modfetch/proxy.go
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@ -36,65 +36,8 @@ URLs of a specified form. The requests have no query parameters, so even
a site serving from a fixed file system (including a file:/// URL)
can be a module proxy.
The GET requests sent to a Go module proxy are:
GET $GOPROXY/<module>/@v/list returns a list of known versions of the given
module, one per line.
GET $GOPROXY/<module>/@v/<version>.info returns JSON-formatted metadata
about that version of the given module.
GET $GOPROXY/<module>/@v/<version>.mod returns the go.mod file
for that version of the given module.
GET $GOPROXY/<module>/@v/<version>.zip returns the zip archive
for that version of the given module.
GET $GOPROXY/<module>/@latest returns JSON-formatted metadata about the
latest known version of the given module in the same format as
<module>/@v/<version>.info. The latest version should be the version of
the module the go command may use if <module>/@v/list is empty or no
listed version is suitable. <module>/@latest is optional and may not
be implemented by a module proxy.
When resolving the latest version of a module, the go command will request
<module>/@v/list, then, if no suitable versions are found, <module>/@latest.
The go command prefers, in order: the semantically highest release version,
the semantically highest pre-release version, and the chronologically
most recent pseudo-version. In Go 1.12 and earlier, the go command considered
pseudo-versions in <module>/@v/list to be pre-release versions, but this is
no longer true since Go 1.13.
To avoid problems when serving from case-sensitive file systems,
the <module> and <version> elements are case-encoded, replacing every
uppercase letter with an exclamation mark followed by the corresponding
lower-case letter: github.com/Azure encodes as github.com/!azure.
The JSON-formatted metadata about a given module corresponds to
this Go data structure, which may be expanded in the future:
type Info struct {
Version string // version string
Time time.Time // commit time
}
The zip archive for a specific version of a given module is a
standard zip file that contains the file tree corresponding
to the module's source code and related files. The archive uses
slash-separated paths, and every file path in the archive must
begin with <module>@<version>/, where the module and version are
substituted directly, not case-encoded. The root of the module
file tree corresponds to the <module>@<version>/ prefix in the
archive.
Even when downloading directly from version control systems,
the go command synthesizes explicit info, mod, and zip files
and stores them in its local cache, $GOPATH/pkg/mod/cache/download,
the same as if it had downloaded them directly from a proxy.
The cache layout is the same as the proxy URL space, so
serving $GOPATH/pkg/mod/cache/download at (or copying it to)
https://example.com/proxy would let other users access those
cached module versions with GOPROXY=https://example.com/proxy.
For details on the GOPROXY protocol, see
https://golang.org/ref/mod#goproxy-protocol.
`,
}

111
src/cmd/go/internal/modget/get.go
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@ -56,85 +56,49 @@ var CmdGet = &base.Command{
UsageLine: "go get [-d] [-t] [-u] [-v] [-insecure] [build flags] [packages]",
Short: "add dependencies to current module and install them",
Long: `
Get resolves and adds dependencies to the current development module
and then builds and installs them.
Get resolves its command-line arguments to packages at specific module versions,
updates go.mod to require those versions, downloads source code into the
module cache, then builds and installs the named packages.
The first step is to resolve which dependencies to add.
To add a dependency for a package or upgrade it to its latest version:
For each named package or package pattern, get must decide which version of
the corresponding module to use. By default, get looks up the latest tagged
release version, such as v0.4.5 or v1.2.3. If there are no tagged release
versions, get looks up the latest tagged pre-release version, such as
v0.0.1-pre1. If there are no tagged versions at all, get looks up the latest
known commit. If the module is not already required at a later version
(for example, a pre-release newer than the latest release), get will use
the version it looked up. Otherwise, get will use the currently
required version.
go get example.com/pkg
This default version selection can be overridden by adding an @version
suffix to the package argument, as in 'go get golang.org/x/text@v0.3.0'.
The version may be a prefix: @v1 denotes the latest available version starting
with v1. See 'go help modules' under the heading 'Module queries' for the
full query syntax.
To upgrade or downgrade a package to a specific version:
For modules stored in source control repositories, the version suffix can
also be a commit hash, branch identifier, or other syntax known to the
source control system, as in 'go get golang.org/x/text@master'. Note that
branches with names that overlap with other module query syntax cannot be
selected explicitly. For example, the suffix @v2 means the latest version
starting with v2, not the branch named v2.
go get example.com/pkg@v1.2.3
If a module under consideration is already a dependency of the current
development module, then get will update the required version.
Specifying a version earlier than the current required version is valid and
downgrades the dependency. The version suffix @none indicates that the
dependency should be removed entirely, downgrading or removing modules
depending on it as needed.
To remove a dependency on a module and downgrade modules that require it:
The version suffix @latest explicitly requests the latest minor release of
the module named by the given path. The suffix @upgrade is like @latest but
will not downgrade a module if it is already required at a revision or
pre-release version newer than the latest released version. The suffix
@patch requests the latest patch release: the latest released version
with the same major and minor version numbers as the currently required
version. Like @upgrade, @patch will not downgrade a module already required
at a newer version. If the path is not already required, @upgrade is
equivalent to @latest, and @patch is disallowed.
go get example.com/mod@none
Although get defaults to using the latest version of the module containing
a named package, it does not use the latest version of that module's
dependencies. Instead it prefers to use the specific dependency versions
requested by that module. For example, if the latest A requires module
B v1.2.3, while B v1.2.4 and v1.3.1 are also available, then 'go get A'
will use the latest A but then use B v1.2.3, as requested by A. (If there
are competing requirements for a particular module, then 'go get' resolves
those requirements by taking the maximum requested version.)
See https://golang.org/ref/mod#go-get for details.
The 'go install' command may be used to build and install packages. When a
version is specified, 'go install' runs in module-aware mode and ignores
the go.mod file in the current directory. For example:
go install example.com/pkg@v1.2.3
go install example.com/pkg@latest
See 'go help install' or https://golang.org/ref/mod#go-install for details.
In addition to build flags (listed in 'go help build') 'go get' accepts the
following flags.
The -t flag instructs get to consider modules needed to build tests of
packages specified on the command line.
The -u flag instructs get to update modules providing dependencies
of packages named on the command line to use newer minor or patch
releases when available. Continuing the previous example, 'go get -u A'
will use the latest A with B v1.3.1 (not B v1.2.3). If B requires module C,
but C does not provide any packages needed to build packages in A
(not including tests), then C will not be updated.
releases when available.
The -u=patch flag (not -u patch) also instructs get to update dependencies,
but changes the default to select patch releases.
Continuing the previous example,
'go get -u=patch A@latest' will use the latest A with B v1.2.4 (not B v1.2.3),
while 'go get -u=patch A' will use a patch release of A instead.
When the -t and -u flags are used together, get will update
test dependencies as well.
In general, adding a new dependency may require upgrading
existing dependencies to keep a working build, and 'go get' does
this automatically. Similarly, downgrading one dependency may
require downgrading other dependencies, and 'go get' does
this automatically as well.
The -insecure flag permits fetching from repositories and resolving
custom domains using insecure schemes such as HTTP, and also bypassess
module sum validation using the checksum database. Use with caution.
@ -143,12 +107,8 @@ To permit the use of insecure schemes, use the GOINSECURE environment
variable instead. To bypass module sum validation, use GOPRIVATE or
GONOSUMDB. See 'go help environment' for details.
The second step is to download (if needed), build, and install
the named packages.
The -d flag instructs get to skip this step, downloading source code
needed to build the named packages and their dependencies, but not
building or installing.
The -d flag instructs get not to build or install packages. get will only
update go.mod and download source code needed to build packages.
Building and installing packages with get is deprecated. In a future release,
the -d flag will be enabled by default, and 'go get' will be only be used to
@ -157,31 +117,14 @@ dependencies from the current module, use 'go install'. To install a package
ignoring the current module, use 'go install' with an @version suffix like
"@latest" after each argument.
If an argument names a module but not a package (because there is no
Go source code in the module's root directory), then the install step
is skipped for that argument, instead of causing a build failure.
For example 'go get golang.org/x/perf' succeeds even though there
is no code corresponding to that import path.
Note that package patterns are allowed and are expanded after resolving
the module versions. For example, 'go get golang.org/x/perf/cmd/...'
adds the latest golang.org/x/perf and then installs the commands in that
latest version.
With no package arguments, 'go get' applies to Go package in the
current directory, if any. In particular, 'go get -u' and
'go get -u=patch' update all the dependencies of that package.
With no package arguments and also without -u, 'go get' is not much more
than 'go install', and 'go get -d' not much more than 'go list'.
For more about modules, see 'go help modules'.
For more about modules, see https://golang.org/ref/mod.
For more about specifying packages, see 'go help packages'.
This text describes the behavior of get using modules to manage source
code and dependencies. If instead the go command is running in GOPATH
mode, the details of get's flags and effects change, as does 'go help get'.
See 'go help modules' and 'go help gopath-get'.
See 'go help gopath-get'.
See also: go build, go install, go clean, go mod.
`,

484
src/cmd/go/internal/modload/help.go
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@ -12,395 +12,16 @@ var HelpModules = &base.Command{
UsageLine: "modules",
Short: "modules, module versions, and more",
Long: `
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.
Modules are how Go manages dependencies.
Module support
A module is a collection of packages that are released, versioned, and
distributed together. Modules may be downloaded directly from version control
repositories or from module proxy servers.
The go command includes support for Go modules. Module-aware mode is active
by default whenever a go.mod file is found in the current directory or in
any parent directory.
For a series of tutorials on modules, see
https://golang.org/doc/tutorial/create-module.
The quickest way to take advantage of module support is to check out your
repository, 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 go command continues to respect
a temporary environment variable, GO111MODULE, which can be set to one
of three string values: off, on, or auto (the default).
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=off, then the go command never uses
module support. Instead it looks in vendor directories and GOPATH
to find dependencies; we now refer to this as "GOPATH 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 contains a
go.mod file or is below a directory containing a go.mod file.
In module-aware mode, GOPATH no longer defines the meaning of imports
during a build, but it still stores downloaded dependencies (in GOPATH/pkg/mod)
and installed commands (in GOPATH/bin, unless GOBIN is set).
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 'go help go.mod'.
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 init' command can be used to do this:
go mod init 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. Most updates to dependencies can be performed using "go get" and
"go mod tidy". Other module-aware build commands may be invoked using the
-mod=mod flag to automatically add missing requirements and fix inconsistencies.
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. See "go help module-get".
The "go mod" command provides other functionality for use in maintaining
and understanding modules and go.mod files. See "go help mod", particularly
"go help mod tidy" and "go help mod edit".
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 may be
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.
The -mod build flag provides additional control over the updating and use of
go.mod for commands that build packages like "go build" and "go test".
If invoked with -mod=readonly (the default in most situations), the go command
reports an error if a package named on the command line or an imported package
is not provided by any module in the build list computed from the main module's
requirements. The go command also reports an error if a module's checksum is
missing from go.sum (see Module downloading and verification). Either go.mod or
go.sum must be updated in these situations.
If invoked with -mod=mod, the go command automatically updates go.mod and
go.sum, fixing inconsistencies and adding missing requirements and checksums
as needed. If the go command finds an unfamiliar import, it looks up the
module containing that import and adds a requirement for the latest version
of that module to go.mod. In most cases, therefore, one may add an import to
source code and run "go build", "go test", or even "go list" with -mod=mod:
as part of analyzing the package, the go command will resolve the import and
update the go.mod file.
If invoked with -mod=vendor, the go command loads packages from the main
module's vendor directory instead of downloading modules to and loading packages
from the module cache. The go command assumes the vendor directory holds
correct copies of dependencies, and it does not compute the set of required
module versions from go.mod files. However, the go command does check that
vendor/modules.txt (generated by "go mod vendor") contains metadata consistent
with go.mod.
If the go command is not invoked with a -mod flag, and the vendor directory
is present, and the "go" version in go.mod is 1.14 or higher, the go command
will act as if it were invoked with -mod=vendor. Otherwise, the -mod flag
defaults to -mod=readonly.
Note that neither "go get" nor the "go mod" subcommands accept the -mod flag.
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" like 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 prefix (v0.0.0- in this example) is derived from
the most recent tagged version in the commit graph before this commit.
There are three pseudo-version forms:
vX.0.0-yyyymmddhhmmss-abcdefabcdef is used when there is no earlier
versioned commit with an appropriate major version before the target commit.
(This was originally the only form, so some older go.mod files use this form
even for commits that do follow tags.)
vX.Y.Z-pre.0.yyyymmddhhmmss-abcdefabcdef is used when the most
recent versioned commit before the target commit is vX.Y.Z-pre.
vX.Y.(Z+1)-0.yyyymmddhhmmss-abcdefabcdef is used when the most
recent versioned commit before the target commit is vX.Y.Z.
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.
The string "upgrade" is like "latest", but if the module is
currently required at a later version than the version "latest"
would select (for example, a newer pre-release version), "upgrade"
will select the later version instead.
The string "patch" matches the latest available tagged version
of a module with the same major and minor version numbers as the
currently required version. If no version is currently required,
"patch" is equivalent to "latest".
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.
Note that branches and tags with names that are matched by other
query syntax cannot be selected this way. For example, the query
"v2" means the latest version starting with "v2", not the branch
named "v2".
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.
As a special case, 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.
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.
Code written before the semantic import versioning convention
was introduced may use major versions v2 and later to describe
the same set of unversioned import paths as used in v0 and v1.
To accommodate such code, if a source code repository has a
v2.0.0 or later tag for a file tree with no go.mod, the version is
considered to be part of the v1 module's available versions
and is given an +incompatible suffix when converted to a module
version, as in v2.0.0+incompatible. The +incompatible tag is also
applied to pseudo-versions derived from such versions, as in
v2.0.1-0.yyyymmddhhmmss-abcdefabcdef+incompatible.
In general, having a dependency in the build list (as reported by 'go list -m all')
on a v0 version, pre-release version, pseudo-version, or +incompatible version
is an indication that problems are more likely when upgrading that
dependency, since there is no expectation of compatibility for those.
See https://research.swtch.com/vgo-import for more information about
semantic import versioning, and see https://semver.org/ for more about
semantic versioning.
Module code layout
For now, see https://research.swtch.com/vgo-module for information
about how source code in version control systems is mapped to
module file trees.
Module downloading and verification
The go command can fetch modules from a proxy or connect to source control
servers directly, according to the setting of the GOPROXY environment
variable (see 'go help env'). The default setting for GOPROXY is
"https://proxy.golang.org,direct", which means to try the
Go module mirror run by Google and fall back to a direct connection
if the proxy reports that it does not have the module (HTTP error 404 or 410).
See https://proxy.golang.org/privacy for the service's privacy policy.
If GOPROXY is set to the string "direct", downloads use a direct connection to
source control servers. Setting GOPROXY to "off" disallows downloading modules
from any source. Otherwise, GOPROXY is expected to be list of module proxy URLs
separated by either comma (,) or pipe (|) characters, which control error
fallback behavior. For each request, the go command tries each proxy in
sequence. If there is an error, the go command will try the next proxy in the
list if the error is a 404 or 410 HTTP response or if the current proxy is
followed by a pipe character, indicating it is safe to fall back on any error.
The GOPRIVATE and GONOPROXY environment variables allow bypassing
the proxy for selected modules. See 'go help private' for details.
No matter the source of the modules, the go command checks downloads against
known checksums, to detect unexpected changes in the content of any specific
module version from one day to the next. This check first consults the current
module's go.sum file but falls back to the Go checksum database, controlled by
the GOSUMDB and GONOSUMDB environment variables. See 'go help module-auth'
for details.
See 'go help goproxy' for details about the proxy protocol and also
the format of the cached downloaded packages.
Modules and vendoring
When using modules, the go command typically satisfies dependencies by
downloading modules from their sources and using those downloaded copies
(after verification, as described in the previous section). Vendoring may
be used 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.
The command 'go mod vendor' constructs a directory named vendor in the main
module's root directory that contains copies of all packages needed to support
builds and tests of packages in the main module. 'go mod vendor' also
creates the file vendor/modules.txt that contains metadata about vendored
packages and module versions. This file should be kept consistent with go.mod:
when vendoring is used, 'go mod vendor' should be run after go.mod is updated.
If the vendor directory is present in the main module's root directory, it will
be used automatically if the "go" version in the main module's go.mod file is
1.14 or higher. Build commands like 'go build' and 'go test' will load packages
from the vendor directory instead of accessing the network or the local module
cache. To explicitly enable vendoring, invoke the go command with the flag
-mod=vendor. To disable vendoring, use the flag -mod=mod.
Unlike vendoring in GOPATH, the go command ignores vendor directories in
locations other than the main module's root directory.
For a detailed reference on modules, see https://golang.org/ref/mod.
`,
}
@ -413,87 +34,22 @@ file in its root. When the go command is run, it looks in the current
directory and then successive parent directories to find the go.mod
marking the root of the main (current) module.
The go.mod file itself is line-oriented, with // comments but
no /* */ comments. Each line holds a single directive, made up of a
verb followed by arguments. For example:
The go.mod file format is described in detail at
https://golang.org/ref/mod#go-mod-file.
module my/thing
go 1.12
require other/thing v1.0.2
require new/thing/v2 v2.3.4
exclude old/thing v1.2.3
replace bad/thing v1.4.5 => good/thing v1.4.5
retract v1.5.6
To create a new go.mod file, use 'go help init'. For details see
'go help mod init' or https://golang.org/ref/mod#go-mod-init.
The verbs are
module, to define the module path;
go, to set the expected language version;
require, to require a particular module at a given version or later;
exclude, to exclude a particular module version from use;
replace, to replace a module version with a different module version; and
retract, to indicate a previously released version should not be used.
Exclude and replace apply only in the main module's go.mod and are ignored
in dependencies. See https://golang.org/ref/mod for details.
To add missing module requirements or remove unneeded requirements,
use 'go mod tidy'. For details, see 'go help mod tidy' or
https://golang.org/ref/mod#go-mod-tidy.
The leading verb can be factored out of adjacent lines to create a block,
like in Go imports:
To add, upgrade, downgrade, or remove a specific module requirement, use
'go get'. For details, see 'go help module-get' or
https://golang.org/ref/mod#go-get.
require (
new/thing/v2 v2.3.4
old/thing v1.2.3
)
The go.mod file is designed both to be edited directly and to be
easily updated by tools. The 'go mod edit' command can be used to
parse and edit the go.mod file from programs and tools.
See 'go help mod edit'.
The go command automatically updates go.mod each time it uses the
module graph, to make sure go.mod always accurately reflects reality
and is properly formatted. For example, consider this go.mod file:
module M
require (
A v1
B v1.0.0
C v1.0.0
D v1.2.3
E dev
)
exclude D v1.2.3
The update rewrites non-canonical version identifiers to semver form,
so A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the
latest commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
The update modifies requirements to respect exclusions, so the
requirement on the excluded D v1.2.3 is updated to use the next
available version of D, perhaps D v1.2.4 or D v1.3.0.
The update removes redundant or misleading requirements.
For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0,
then go.mod's requirement of B v1.0.0 is misleading (superseded by
A's need for v1.2.0), and its requirement of C v1.0.0 is redundant
(implied by A's need for the same version), so both will be removed.
If module M contains packages that directly import packages from B or
C, then the requirements will be kept but updated to the actual
versions being used.
Finally, the update reformats the go.mod in a canonical formatting, so
that future mechanical changes will result in minimal diffs.
Because the module graph defines the meaning of import statements, any
commands that load packages also use and therefore update go.mod,
including go build, go get, go install, go list, go test, go mod graph,
go mod tidy, and go mod why.
The expected language version, set by the go directive, determines
which language features are available when compiling the module.
Language features available in that version will be available for use.
Language features removed in earlier versions, or added in later versions,
will not be available. Note that the language version does not affect
build tags, which are determined by the Go release being used.
To make other changes or to parse go.mod as JSON for use by other tools,
use 'go mod edit'. See 'go help mod edit' or
https://golang.org/ref/mod#go-mod-edit.
`,
}

5
src/cmd/go/internal/work/build.go
View File

@ -113,7 +113,10 @@ and test commands:
created with -buildmode=shared.
-mod mode
module download mode to use: readonly, vendor, or mod.
See 'go help modules' for more.
By default, if a vendor directory is present and the go version in go.mod
is 1.14 or higher, the go command acts as if -mod=vendor were set.
Otherwise, the go command acts as if -mod=readonly were set.
See https://golang.org/ref/mod#build-commands for details.
-modcacherw
leave newly-created directories in the module cache read-write
instead of making them read-only.