cmd/go: fix error messages for go mod download in GOPATH mode

Checks if modules are enabled in GOPATH mode.
Error message returned when no version is provided. Relevant tests
updated. Test for GO111MODULE=off added.

Fixes #27783

Change-Id: I12cdaced5fa38a9c49c0ecfed4c479eb86ed061f
Reviewed-on: https://go-review.googlesource.com/c/go/+/179998
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/cmd/go/internal/modcmd/download.go b/src/cmd/go/internal/modcmd/download.go
index 9f8c410b82f78b9e3619cd597922609b7682e4f8..71b660d6fde326e7f468794db4a5f1c8673fff43 100644 (file)
--- a/src/cmd/go/internal/modcmd/download.go
+++ b/src/cmd/go/internal/modcmd/download.go
@@ -5,6 +5,7 @@
 package modcmd
 
 import (
+       "cmd/go/internal/cfg"
        "encoding/json"
        "os"
 
@@ -67,6 +68,13 @@ type moduleJSON struct {
 }
 
 func runDownload(cmd *base.Command, args []string) {
+       // Check whether modules are enabled and whether we're in a module.
+       if cfg.Getenv("GO111MODULE") == "off" {
+               base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
+       }
+       if !modload.HasModRoot() && len(args) == 0 {
+               base.Fatalf("go mod download: no modules specified (see 'go help mod download')")
+       }
        if len(args) == 0 {
                args = []string{"all"}
        }

diff --git a/src/cmd/go/testdata/script/mod_off.txt b/src/cmd/go/testdata/script/mod_off.txt
index bc0a7861f4b6ca7f3f7819112610a997323b43c0..cada6deb1dd871182c255821aebd7d723d695c10 100644 (file)
--- a/src/cmd/go/testdata/script/mod_off.txt
+++ b/src/cmd/go/testdata/script/mod_off.txt
@@ -9,6 +9,8 @@ stderr 'go mod init: modules disabled by GO111MODULE=off; see ''go help modules'
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 ! go mod verify
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
+! go mod download
+stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 
 # Same result in an empty directory
 mkdir z
@@ -19,6 +21,8 @@ stderr 'go mod init: modules disabled by GO111MODULE=off; see ''go help modules'
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 ! go mod verify
 stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
+! go mod download
+stderr 'go: modules disabled by GO111MODULE=off; see ''go help modules'''
 
 -- sample.go --
 package sample