Revert "cmd/go: change the default value of GO111MODULE to 'on'"

This reverts commit cf469165
(CL 162698).

Reason for revert: broke make.bash bootstrapping from head.

Change-Id: I3de6d26b1af9038c6b92dec88667bfa734060a41
Reviewed-on: https://go-review.googlesource.com/c/go/+/166985Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/help_test.go

@@ -12,14 +12,9 @@ import (
 	"testing"
 
 	"cmd/go/internal/help"
-	"cmd/go/internal/modload"
 )
 
 func TestDocsUpToDate(t *testing.T) {
-	if !modload.Enabled() {
-		t.Skipf("help.Help in GOPATH mode is configured by main.main")
-	}
-
 	buf := new(bytes.Buffer)
 	// Match the command in mkalldocs.sh that generates alldocs.go.
 	help.Help(buf, []string{"documentation"})

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

@@ -17,7 +17,6 @@ import (
 	"unicode/utf8"
 
 	"cmd/go/internal/base"
-	"cmd/go/internal/modload"
 )
 
 // Help implements the 'help' command.
@@ -36,10 +35,8 @@ func Help(w io.Writer, args []string) {
 		usage := &base.Command{Long: buf.String()}
 		cmds := []*base.Command{usage}
 		for _, cmd := range base.Go.Commands {
-			// Avoid duplication of the "get" documentation.
-			if cmd.UsageLine == "module-get" && modload.Enabled() {
-				continue
-			} else if cmd.UsageLine == "gopath-get" && !modload.Enabled() {
+			if cmd.UsageLine == "gopath-get" {
+				// Avoid duplication of the "get" documentation.
 				continue
 			}
 			cmds = append(cmds, cmd)

src/cmd/go/internal/modload/help.go

@@ -19,25 +19,34 @@ 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.
 
-Module support
+Preliminary module support
 
-Go 1.13 includes official support for Go modules,
-including a module-aware 'go get' command.
-Module-aware mode is active by default.
+Go 1.11 includes preliminary 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 preliminary),
+and then at a later point we may remove support for work
+in GOPATH and the old 'go get' command.
 
-For more fine-grained control, Go 1.13 continues to respect
+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, auto, or on (the default).
-If GO111MODULE=on or is unset, 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, 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.
-If GO111MODULE=off, then the go command never uses
-module support. Instead it looks in vendor directories and GOPATH
+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.
 
 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)

src/cmd/go/internal/modload/init.go

@@ -34,7 +34,7 @@ import (
 
 var (
 	cwd            string // TODO(bcmills): Is this redundant with base.Cwd?
-	mustUseModules = true
+	MustUseModules = mustUseModules()
 	initialized    bool
 
 	modRoot     string
@@ -70,6 +70,16 @@ func BinDir() string {
 	return filepath.Join(gopath, "bin")
 }
 
+// mustUseModules reports whether we are invoked as vgo
+// (as opposed to go).
+// If so, we only support builds with go.mod files.
+func mustUseModules() bool {
+	name := os.Args[0]
+	name = name[strings.LastIndex(name, "/")+1:]
+	name = name[strings.LastIndex(name, `\`)+1:]
+	return strings.HasPrefix(name, "vgo")
+}
+
 var inGOPATH bool // running in GOPATH/src
 
 // Init determines whether module mode is enabled, locates the root of the
@@ -86,13 +96,14 @@ func Init() {
 	switch env {
 	default:
 		base.Fatalf("go: unknown environment setting GO111MODULE=%s", env)
-	case "auto":
-		mustUseModules = false
-	case "on", "":
-		mustUseModules = true
+	case "", "auto":
+		// leave MustUseModules alone
+	case "on":
+		MustUseModules = true
 	case "off":
-		mustUseModules = false
-		return
+		if !MustUseModules {
+			return
+		}
 	}
 
 	// Disable any prompting for passwords by Git.
@@ -139,7 +150,7 @@ func Init() {
 		}
 	}
 
-	if inGOPATH && !mustUseModules {
+	if inGOPATH && !MustUseModules {
 		if CmdModInit {
 			die() // Don't init a module that we're just going to ignore.
 		}
@@ -156,8 +167,8 @@ func Init() {
 	} else {
 		modRoot = findModuleRoot(cwd)
 		if modRoot == "" {
-			if !mustUseModules {
-				// GO111MODULE is 'auto', and we can't find a module root.
+			if !MustUseModules {
+				// GO111MODULE is 'auto' (or unset), and we can't find a module root.
 				// Stay in GOPATH mode.
 				return
 			}
@@ -256,7 +267,7 @@ func init() {
 // (usually through MustModRoot).
 func Enabled() bool {
 	Init()
-	return modRoot != "" || mustUseModules
+	return modRoot != "" || MustUseModules
 }
 
 // ModRoot returns the root of the main module.
@@ -289,7 +300,7 @@ func die() {
 	if os.Getenv("GO111MODULE") == "off" {
 		base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
 	}
-	if inGOPATH && !mustUseModules {
+	if inGOPATH && !MustUseModules {
 		base.Fatalf("go: modules disabled inside GOPATH/src by GO111MODULE=auto; see 'go help modules'")
 	}
 	if cwd != "" {

src/cmd/go/main.go

@@ -49,7 +49,7 @@ func init() {
 		fix.CmdFix,
 		fmtcmd.CmdFmt,
 		generate.CmdGenerate,
-		modget.CmdGet,
+		get.CmdGet,
 		work.CmdInstall,
 		list.CmdList,
 		modcmd.CmdMod,
@@ -89,10 +89,17 @@ func main() {
 		base.Usage()
 	}
 
+	if modload.MustUseModules {
+		// If running with modules force-enabled, change get now to change help message.
+		*get.CmdGet = *modget.CmdGet
+	}
+
 	if args[0] == "get" || args[0] == "help" {
-		if modload.Init(); !modload.Enabled() {
-			// Replace module-aware get with GOPATH get if appropriate.
-			*modget.CmdGet = *get.CmdGet
+		// Replace get with module-aware get if appropriate.
+		// Note that if MustUseModules is true, this happened already above,
+		// but no harm in doing it again.
+		if modload.Init(); modload.Enabled() {
+			*get.CmdGet = *modget.CmdGet
 		}
 	}
 

src/cmd/go/mkalldocs.sh

@@ -8,6 +8,6 @@ set -e
 go build -o go.latest
 # If the command used to generate alldocs.go changes, update TestDocsUpToDate in
 # help_test.go.
-GO111MODULE='' ./go.latest help documentation >alldocs.go
+./go.latest help documentation >alldocs.go
 gofmt -w alldocs.go
 rm go.latest

src/cmd/go/testdata/script/mod_find.txt

@@ -17,7 +17,7 @@ cd $GOPATH/src/example.com/x/y
 ! go mod init
 stderr 'go: modules disabled inside GOPATH/src by GO111MODULE=auto; see ''go help modules'''
 
-env GO111MODULE=
+env GO111MODULE=on
 
 # Derive module path from location inside GOPATH.
 cd $GOPATH/src/example.com/x/y

src/cmd/go/testdata/script/mod_gobuild_import.txt

@@ -24,18 +24,12 @@ exec $WORK/testimport.exe other/x/y/z/w .
 stdout w2.go
 
 # GO111MODULE=on outside GOPATH/src
-env GO111MODULE=
-exec $WORK/testimport.exe other/x/y/z/w .
-stdout w2.go
 env GO111MODULE=on
 exec $WORK/testimport.exe other/x/y/z/w .
 stdout w2.go
 
 # GO111MODULE=on in GOPATH/src
 cd $GOPATH/src
-env GO111MODULE=
-exec $WORK/testimport.exe x/y/z/w .
-stdout w1.go
 env GO111MODULE=on
 exec $WORK/testimport.exe x/y/z/w .
 stdout w1.go