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

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 <[email protected]>
Run-TryBot: Jay Conrod <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>

Author: Jay Conrod

src/cmd/go/alldocs.go

@@ -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:
 

src/cmd/go/internal/help/helpdoc.go

@@ -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.
 	`,
 }
 

src/cmd/go/internal/list/list.go

@@ -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.
 	`,
 }
 

src/cmd/go/internal/modcmd/download.go

@@ -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'.
 	`,
 }
 

src/cmd/go/internal/modcmd/edit.go

@@ -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,
 }

src/cmd/go/internal/modcmd/graph.go

@@ -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,
 }

src/cmd/go/internal/modcmd/init.go

@@ -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,
 }

src/cmd/go/internal/modcmd/tidy.go

@@ -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,
 }

src/cmd/go/internal/modcmd/vendor.go

@@ -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,
 }