cmd/go: warn about non-use of go.mod in legacy go get

It's important for a smooth transition for non-module users
not to change operation in GOPATH/src by default in Go 1.11,
even if go.mod exists in a downloaded dependency.

Even so, users create go.mod and then are confused about
why 'go get' commands seem to behave oddly, when in fact
they are getting the old 'go get'.

Try to split the difference by printing a warning in 'go get'
when run in a tree that would normally be considered a
module if only it were outside GOPATH/src.

Change-Id: I55a1cbef127f3f36de54a8d7b93e1fc64bf0a708
Reviewed-on: https://go-review.googlesource.com/124859
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 4e69da567b7ca86caeff47bc1dc7e7f408f2e284..9dd90ee871d319269d419f5122e929a7323b466f 100644 (file)
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -73,6 +73,11 @@ var (
        // in module-aware mode (as opposed to GOPATH mode).
        // It is equal to modload.Enabled, but not all packages can import modload.
        ModulesEnabled bool
+
+       // GoModInGOPATH records whether we've found a go.mod in GOPATH/src
+       // in GO111MODULE=auto mode. In that case, we don't use modules
+       // but people might expect us to, so 'go get' warns.
+       GoModInGOPATH string
 )
 
 func init() {

diff --git a/src/cmd/go/internal/get/get.go b/src/cmd/go/internal/get/get.go
index 36aa171c7f91dfaef4b7adecb6b41aec7b2ed5a1..0789d5bb3cbbbb50429c05304531dbbbaa7cb0b7 100644 (file)
--- a/src/cmd/go/internal/get/get.go
+++ b/src/cmd/go/internal/get/get.go
@@ -118,6 +118,11 @@ func runGet(cmd *base.Command, args []string) {
                // Should not happen: main.go should install the separate module-enabled get code.
                base.Fatalf("go get: modules not implemented")
        }
+       if cfg.GoModInGOPATH != "" {
+               // Warn about not using modules with GO111MODULE=auto when go.mod exists.
+               // To silence the warning, users can set GO111MODULE=off.
+               fmt.Fprintf(os.Stderr, "go get: warning: modules disabled by GO111MODULE=auto in GOPATH/src;\n\tignoring %s;\n\tsee 'go help modules'\n", base.ShortPath(cfg.GoModInGOPATH))
+       }
 
        work.BuildInit()
 

diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 602d33acb30689169ae6efa978d781d223a7dca4..dfab6578a968b565b7a9dd4c2c5e396615e2d4a1 100644 (file)
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -153,6 +153,9 @@ func Init() {
        } else {
                if inGOPATH && !MustUseModules {
                        // No automatic enabling in GOPATH.
+                       if root, _ := FindModuleRoot(cwd, "", false); root != "" {
+                               cfg.GoModInGOPATH = filepath.Join(root, "go.mod")
+                       }
                        return
                }
                root, _ := FindModuleRoot(cwd, "", MustUseModules)

diff --git a/src/cmd/go/testdata/script/mod_get_warning.txt b/src/cmd/go/testdata/script/mod_get_warning.txt
new file mode 100644 (file)
index 0000000..36b5434
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_get_warning.txt
@@ -0,0 +1,10 @@
+# go get in GO111MODULE=auto should warn when not using modules and go.mod exists
+
+env GO111MODULE=auto
+mkdir z
+cd z
+! go get # fails because no code in directory, not the warning
+stderr 'go get: warning: modules disabled by GO111MODULE=auto in GOPATH/src;\n\tignoring ..[/\\]go.mod;\n\tsee ''go help modules'''
+
+-- go.mod --
+module x