cmd/go: allow configuring module cache directory with GOMODCACHE

Adds a GOMODCACHE environment variable that's used by cmd/go to determine the
location of the module cache. The default value of GOMODCACHE will be
GOPATH[0]/pkg/mod, the default location of the module cache before this change.

Replace the cmd/go/internal/modfetch.PkgMod variable which previously held the
location of the module cache with the new cmd/go/internal/cfg.GOMODCACHE
variable, for consistency with many of the other environment variables that
affect the behavior of cmd/go.  (Most of the changes in this CL are due to
moving/renaming the variable.)

The value of cfg.GOMODCACHE is now set using a variable initializer. It was
previously set in cmd/go/internal/modload.Init.

The location of GOPATH/pkg/sumdb is unchanged by this CL. While it was
previously determined using the value of PkgMod, it now is determined
independently dirctly from the value of GOPATH[0].

Fixes #34527

Change-Id: Id4d31d217b3507d6057c8ef7c52af1a0606603e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/219538
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

15 files changed, 115 insertions, 61 deletions

diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 61dc6bdda6..7f8f8e92be 100644
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -236,6 +236,7 @@ var (
 	GOROOTpkg    = filepath.Join(GOROOT, "pkg")
 	GOROOTsrc    = filepath.Join(GOROOT, "src")
 	GOROOT_FINAL = findGOROOT_FINAL()
+	GOMODCACHE   = envOr("GOMODCACHE", gopathDir("pkg/mod"))
 
 	// Used in envcmd.MkEnv and build ID computations.
 	GOARM    = envOr("GOARM", fmt.Sprint(objabi.GOARM))
@@ -253,6 +254,8 @@ var (
 	GOINSECURE = Getenv("GOINSECURE")
 )
 
+var SumdbDir = gopathDir("pkg/sumdb")
+
 // GetArchEnv returns the name and setting of the
 // GOARCH-specific architecture environment variable.
 // If the current architecture has no GOARCH-specific variable,
@@ -364,3 +367,11 @@ func isGOROOT(path string) bool {
 	}
 	return stat.IsDir()
 }
+
+func gopathDir(rel string) string {
+	list := filepath.SplitList(BuildContext.GOPATH)
+	if len(list) == 0 || list[0] == "" {
+		return ""
+	}
+	return filepath.Join(list[0], rel)
+}
diff --git a/src/cmd/go/internal/clean/clean.go b/src/cmd/go/internal/clean/clean.go
index 588969ab4f..d5028de970 100644
--- a/src/cmd/go/internal/clean/clean.go
+++ b/src/cmd/go/internal/clean/clean.go
@@ -186,14 +186,14 @@ func runClean(cmd *base.Command, args []string) {
 	}
 
 	if cleanModcache {
-		if modfetch.PkgMod == "" {
+		if cfg.GOMODCACHE == "" {
 			base.Fatalf("go clean -modcache: no module cache")
 		}
 		if cfg.BuildN || cfg.BuildX {
-			b.Showcmd("", "rm -rf %s", modfetch.PkgMod)
+			b.Showcmd("", "rm -rf %s", cfg.GOMODCACHE)
 		}
 		if !cfg.BuildN {
-			if err := modfetch.RemoveAll(modfetch.PkgMod); err != nil {
+			if err := modfetch.RemoveAll(cfg.GOMODCACHE); err != nil {
 				base.Errorf("go clean -modcache: %v", err)
 			}
 		}
diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index d2d5ed9507..252025dc25 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -77,6 +77,7 @@ func MkEnv() []cfg.EnvVar {
 		{Name: "GOHOSTARCH", Value: runtime.GOARCH},
 		{Name: "GOHOSTOS", Value: runtime.GOOS},
 		{Name: "GOINSECURE", Value: cfg.GOINSECURE},
+		{Name: "GOMODCACHE", Value: cfg.GOMODCACHE},
 		{Name: "GONOPROXY", Value: cfg.GONOPROXY},
 		{Name: "GONOSUMDB", Value: cfg.GONOSUMDB},
 		{Name: "GOOS", Value: cfg.Goos},
diff --git a/src/cmd/go/internal/modconv/convert_test.go b/src/cmd/go/internal/modconv/convert_test.go
index a2a2601967..a04a13b14f 100644
--- a/src/cmd/go/internal/modconv/convert_test.go
+++ b/src/cmd/go/internal/modconv/convert_test.go
@@ -18,7 +18,6 @@ import (
 
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/modfetch"
-	"cmd/go/internal/modfetch/codehost"
 
 	"golang.org/x/mod/modfile"
 	"golang.org/x/mod/module"
@@ -42,8 +41,7 @@ func testMain(m *testing.M) int {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(dir)
-	modfetch.PkgMod = filepath.Join(dir, "pkg/mod")
-	codehost.WorkRoot = filepath.Join(dir, "codework")
+	cfg.GOMODCACHE = filepath.Join(dir, "pkg/mod")
 
 	return m.Run()
 }
diff --git a/src/cmd/go/internal/modfetch/cache.go b/src/cmd/go/internal/modfetch/cache.go
index d6ff068e7b..e3074b775e 100644
--- a/src/cmd/go/internal/modfetch/cache.go
+++ b/src/cmd/go/internal/modfetch/cache.go
@@ -26,17 +26,17 @@ import (
 	"golang.org/x/mod/semver"
 )
 
-var PkgMod string // $GOPATH/pkg/mod; set by package modload
-
 func cacheDir(path string) (string, error) {
-	if PkgMod == "" {
-		return "", fmt.Errorf("internal error: modfetch.PkgMod not set")
+	if cfg.GOMODCACHE == "" {
+		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
+		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
+		return "", fmt.Errorf("internal error: cfg.GOMODCACHE not set")
 	}
 	enc, err := module.EscapePath(path)
 	if err != nil {
 		return "", err
 	}
-	return filepath.Join(PkgMod, "cache/download", enc, "/@v"), nil
+	return filepath.Join(cfg.GOMODCACHE, "cache/download", enc, "/@v"), nil
 }
 
 func CachePath(m module.Version, suffix string) (string, error) {
@@ -63,8 +63,10 @@ func CachePath(m module.Version, suffix string) (string, error) {
 // along with the directory if the directory does not exist or if the directory
 // is not completely populated.
 func DownloadDir(m module.Version) (string, error) {
-	if PkgMod == "" {
-		return "", fmt.Errorf("internal error: modfetch.PkgMod not set")
+	if cfg.GOMODCACHE == "" {
+		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
+		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
+		return "", fmt.Errorf("internal error: cfg.GOMODCACHE not set")
 	}
 	enc, err := module.EscapePath(m.Path)
 	if err != nil {
@@ -81,7 +83,7 @@ func DownloadDir(m module.Version) (string, error) {
 		return "", err
 	}
 
-	dir := filepath.Join(PkgMod, enc+"@"+encVer)
+	dir := filepath.Join(cfg.GOMODCACHE, enc+"@"+encVer)
 	if fi, err := os.Stat(dir); os.IsNotExist(err) {
 		return dir, err
 	} else if err != nil {
@@ -131,11 +133,13 @@ func lockVersion(mod module.Version) (unlock func(), err error) {
 // user's working directory.
 // If err is nil, the caller MUST eventually call the unlock function.
 func SideLock() (unlock func(), err error) {
-	if PkgMod == "" {
-		base.Fatalf("go: internal error: modfetch.PkgMod not set")
+	if cfg.GOMODCACHE == "" {
+		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
+		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
+		base.Fatalf("go: internal error: cfg.GOMODCACHE not set")
 	}
 
-	path := filepath.Join(PkgMod, "cache", "lock")
+	path := filepath.Join(cfg.GOMODCACHE, "cache", "lock")
 	if err := os.MkdirAll(filepath.Dir(path), 0777); err != nil {
 		return nil, fmt.Errorf("failed to create cache directory: %w", err)
 	}
@@ -456,7 +460,7 @@ func readDiskStat(path, rev string) (file string, info *RevInfo, err error) {
 // just to find out about a commit we already know about
 // (and have cached under its pseudo-version).
 func readDiskStatByHash(path, rev string) (file string, info *RevInfo, err error) {
-	if PkgMod == "" {
+	if cfg.GOMODCACHE == "" {
 		// Do not download to current directory.
 		return "", nil, errNotCached
 	}
diff --git a/src/cmd/go/internal/modfetch/codehost/codehost.go b/src/cmd/go/internal/modfetch/codehost/codehost.go
index 5867288c96..d85eddf767 100644
--- a/src/cmd/go/internal/modfetch/codehost/codehost.go
+++ b/src/cmd/go/internal/modfetch/codehost/codehost.go
@@ -153,15 +153,11 @@ func ShortenSHA1(rev string) string {
 	return rev
 }
 
-// WorkRoot is the root of the cached work directory.
-// It is set by cmd/go/internal/modload.InitMod.
-var WorkRoot string
-
 // WorkDir returns the name of the cached work directory to use for the
 // given repository type and name.
 func WorkDir(typ, name string) (dir, lockfile string, err error) {
-	if WorkRoot == "" {
-		return "", "", fmt.Errorf("codehost.WorkRoot not set")
+	if cfg.GOMODCACHE == "" {
+		return "", "", fmt.Errorf("neither GOPATH nor GOMODCACHE are set")
 	}
 
 	// We name the work directory for the SHA256 hash of the type and name.
@@ -173,7 +169,7 @@ func WorkDir(typ, name string) (dir, lockfile string, err error) {
 		return "", "", fmt.Errorf("codehost.WorkDir: type cannot contain colon")
 	}
 	key := typ + ":" + name
-	dir = filepath.Join(WorkRoot, fmt.Sprintf("%x", sha256.Sum256([]byte(key))))
+	dir = filepath.Join(cfg.GOMODCACHE, "cache/vcs", fmt.Sprintf("%x", sha256.Sum256([]byte(key))))
 
 	if cfg.BuildX {
 		fmt.Fprintf(os.Stderr, "mkdir -p %s # %s %s\n", filepath.Dir(dir), typ, name)
diff --git a/src/cmd/go/internal/modfetch/codehost/git_test.go b/src/cmd/go/internal/modfetch/codehost/git_test.go
index cc32a1eb51..ba27c70f5a 100644
--- a/src/cmd/go/internal/modfetch/codehost/git_test.go
+++ b/src/cmd/go/internal/modfetch/codehost/git_test.go
@@ -57,7 +57,6 @@ func testMain(m *testing.M) int {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(dir)
-	WorkRoot = dir
 
 	if testenv.HasExternalNetwork() && testenv.HasExec() {
 		// Clone gitrepo1 into a local directory.
diff --git a/src/cmd/go/internal/modfetch/codehost/shell.go b/src/cmd/go/internal/modfetch/codehost/shell.go
index 835bc53c0d..2762c55720 100644
--- a/src/cmd/go/internal/modfetch/codehost/shell.go
+++ b/src/cmd/go/internal/modfetch/codehost/shell.go
@@ -20,6 +20,7 @@ import (
 	"strings"
 	"time"
 
+	"cmd/go/internal/cfg"
 	"cmd/go/internal/modfetch/codehost"
 )
 
@@ -29,7 +30,7 @@ func usage() {
 }
 
 func main() {
-	codehost.WorkRoot = "/tmp/vcswork"
+	cfg.GOMODCACHE = "/tmp/vcswork"
 	log.SetFlags(0)
 	log.SetPrefix("shell: ")
 	flag.Usage = usage
diff --git a/src/cmd/go/internal/modfetch/coderepo_test.go b/src/cmd/go/internal/modfetch/coderepo_test.go
index 39830948fb..f69c193b86 100644
--- a/src/cmd/go/internal/modfetch/coderepo_test.go
+++ b/src/cmd/go/internal/modfetch/coderepo_test.go
@@ -44,7 +44,7 @@ func testMain(m *testing.M) int {
 	}
 	defer os.RemoveAll(dir)
 
-	codehost.WorkRoot = dir
+	cfg.GOMODCACHE = dir
 	return m.Run()
 }
 
diff --git a/src/cmd/go/internal/modfetch/fetch.go b/src/cmd/go/internal/modfetch/fetch.go
index 187d174542..61759c0e6b 100644
--- a/src/cmd/go/internal/modfetch/fetch.go
+++ b/src/cmd/go/internal/modfetch/fetch.go
@@ -35,9 +35,10 @@ var downloadCache par.Cache
 // local download cache and returns the name of the directory
 // corresponding to the root of the module's file tree.
 func Download(mod module.Version) (dir string, err error) {
-	if PkgMod == "" {
-		// Do not download to current directory.
-		return "", fmt.Errorf("missing modfetch.PkgMod")
+	if cfg.GOMODCACHE == "" {
+		// modload.Init exits if GOPATH[0] is empty, and cfg.GOMODCACHE
+		// is set to GOPATH[0]/pkg/mod if GOMODCACHE is empty, so this should never happen.
+		base.Fatalf("go: internal error: cfg.GOMODCACHE not set")
 	}
 
 	// The par.Cache here avoids duplicate work.
@@ -456,7 +457,7 @@ func readGoSum(dst map[module.Version][]string, file string, data []byte) error
 
 // checkMod checks the given module's checksum.
 func checkMod(mod module.Version) {
-	if PkgMod == "" {
+	if cfg.GOMODCACHE == "" {
 		// Do not use current directory.
 		return
 	}
@@ -593,7 +594,7 @@ func checkSumDB(mod module.Version, h string) error {
 // Sum returns the checksum for the downloaded copy of the given module,
 // if present in the download cache.
 func Sum(mod module.Version) string {
-	if PkgMod == "" {
+	if cfg.GOMODCACHE == "" {
 		// Do not use current directory.
 		return ""
 	}
diff --git a/src/cmd/go/internal/modfetch/sumdb.go b/src/cmd/go/internal/modfetch/sumdb.go
index ff81ef687e..ef2eb213ed 100644
--- a/src/cmd/go/internal/modfetch/sumdb.go
+++ b/src/cmd/go/internal/modfetch/sumdb.go
@@ -200,8 +200,10 @@ func (c *dbClient) ReadConfig(file string) (data []byte, err error) {
 		return []byte(c.key), nil
 	}
 
-	// GOPATH/pkg is PkgMod/..
-	targ := filepath.Join(PkgMod, "../sumdb/"+file)
+	if cfg.SumdbDir == "" {
+		return nil, errors.New("could not locate sumdb file: missing $GOPATH")
+	}
+	targ := filepath.Join(cfg.SumdbDir, file)
 	data, err = lockedfile.Read(targ)
 	if errors.Is(err, os.ErrNotExist) {
 		// Treat non-existent as empty, to bootstrap the "latest" file
@@ -217,7 +219,10 @@ func (*dbClient) WriteConfig(file string, old, new []byte) error {
 		// Should not happen.
 		return fmt.Errorf("cannot write key")
 	}
-	targ := filepath.Join(PkgMod, "../sumdb/"+file)
+	if cfg.SumdbDir == "" {
+		return errors.New("could not locate sumdb file: missing $GOPATH")
+	}
+	targ := filepath.Join(cfg.SumdbDir, file)
 	os.MkdirAll(filepath.Dir(targ), 0777)
 	f, err := lockedfile.Edit(targ)
 	if err != nil {
@@ -247,7 +252,7 @@ func (*dbClient) WriteConfig(file string, old, new []byte) error {
 // GOPATH/pkg/mod/cache/download/sumdb,
 // which will be deleted by "go clean -modcache".
 func (*dbClient) ReadCache(file string) ([]byte, error) {
-	targ := filepath.Join(PkgMod, "cache/download/sumdb", file)
+	targ := filepath.Join(cfg.GOMODCACHE, "cache/download/sumdb", file)
 	data, err := lockedfile.Read(targ)
 	// lockedfile.Write does not atomically create the file with contents.
 	// There is a moment between file creation and locking the file for writing,
@@ -261,7 +266,7 @@ func (*dbClient) ReadCache(file string) ([]byte, error) {
 
 // WriteCache updates cached lookups or tiles.
 func (*dbClient) WriteCache(file string, data []byte) {
-	targ := filepath.Join(PkgMod, "cache/download/sumdb", file)
+	targ := filepath.Join(cfg.GOMODCACHE, "cache/download/sumdb", file)
 	os.MkdirAll(filepath.Dir(targ), 0777)
 	lockedfile.Write(targ, bytes.NewReader(data), 0666)
 }
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 19a47bd54f..664a2a1594 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -26,7 +26,6 @@ import (
 	"cmd/go/internal/lockedfile"
 	"cmd/go/internal/modconv"
 	"cmd/go/internal/modfetch"
-	"cmd/go/internal/modfetch/codehost"
 	"cmd/go/internal/mvs"
 	"cmd/go/internal/search"
 
@@ -178,17 +177,6 @@ func Init() {
 		base.Fatalf("$GOPATH/go.mod exists but should not")
 	}
 
-	oldSrcMod := filepath.Join(list[0], "src/mod")
-	pkgMod := filepath.Join(list[0], "pkg/mod")
-	infoOld, errOld := os.Stat(oldSrcMod)
-	_, errMod := os.Stat(pkgMod)
-	if errOld == nil && infoOld.IsDir() && errMod != nil && os.IsNotExist(errMod) {
-		os.Rename(oldSrcMod, pkgMod)
-	}
-
-	modfetch.PkgMod = pkgMod
-	codehost.WorkRoot = filepath.Join(pkgMod, "cache/vcs")
-
 	cfg.ModulesEnabled = true
 	load.ModBinDir = BinDir
 	load.ModLookup = Lookup
@@ -225,13 +213,6 @@ func Init() {
 
 func init() {
 	load.ModInit = Init
-
-	// Set modfetch.PkgMod and codehost.WorkRoot unconditionally,
-	// so that go clean -modcache and go mod download can run even without modules enabled.
-	if list := filepath.SplitList(cfg.BuildContext.GOPATH); len(list) > 0 && list[0] != "" {
-		modfetch.PkgMod = filepath.Join(list[0], "pkg/mod")
-		codehost.WorkRoot = filepath.Join(list[0], "pkg/mod/cache/vcs")
-	}
 }
 
 // WillBeEnabled checks whether modules should be enabled but does not
diff --git a/src/cmd/go/internal/modload/query_test.go b/src/cmd/go/internal/modload/query_test.go
index 15470e2685..247e4c40d2 100644
--- a/src/cmd/go/internal/modload/query_test.go
+++ b/src/cmd/go/internal/modload/query_test.go
@@ -15,8 +15,6 @@ import (
 	"testing"
 
 	"cmd/go/internal/cfg"
-	"cmd/go/internal/modfetch"
-	"cmd/go/internal/modfetch/codehost"
 
 	"golang.org/x/mod/module"
 )
@@ -36,8 +34,7 @@ func testMain(m *testing.M) int {
 
 	os.Setenv("GOPATH", dir)
 	cfg.BuildContext.GOPATH = dir
-	modfetch.PkgMod = filepath.Join(dir, "pkg/mod")
-	codehost.WorkRoot = filepath.Join(dir, "codework")
+	cfg.GOMODCACHE = filepath.Join(dir, "pkg/mod")
 	return m.Run()
 }
 
diff --git a/src/cmd/go/testdata/script/mod_gomodcache.txt b/src/cmd/go/testdata/script/mod_gomodcache.txt
new file mode 100644
index 0000000000..67a8f07b2c
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_gomodcache.txt
@@ -0,0 +1,59 @@
+# Test GOMODCACHE
+env GO111MODULE=on
+
+# Explicitly set GOMODCACHE
+env GOMODCACHE=$WORK/modcache
+go env GOMODCACHE
+stdout $WORK[/\\]modcache
+go get -d rsc.io/quote@v1.0.0
+exists $WORK/modcache/cache/download/rsc.io/quote/@v/v1.0.0.info
+grep '{"Version":"v1.0.0","Time":"2018-02-14T00:45:20Z"}' $WORK/modcache/cache/download/rsc.io/quote/@v/v1.0.0.info
+
+# Ensure GOMODCACHE doesn't affect location of sumdb, but $GOMODCACHE/cache/download/sumdb is still written
+exists $GOPATH/pkg/sumdb
+! exists $WORK/modcache/sumdb
+exists $WORK/modcache/cache/download/sumdb
+
+# Test that the default GOMODCACHE is $GOPATH[0]/pkg/mod
+env GOMODCACHE=
+go env GOMODCACHE
+stdout $GOPATH[/\\]pkg[/\\]mod
+go get -d rsc.io/quote@v1.0.0
+exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.0.0.info
+grep '{"Version":"v1.0.0","Time":"2018-02-14T00:45:20Z"}' $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.0.0.info
+
+# If neither GOMODCACHE or GOPATH are set, GOPATH defaults to the user's $HOME/go, so GOMODCACHE becomes $HOME/go/pkg/mod
+[windows] env USERPROFILE=$WORK/home # Ensure USERPROFILE is a valid path (rather than /no-home/ so we don't run into the logic that "uninfers" GOPATH in cmd/go/main.go
+[!windows] env HOME=$WORK/home
+env GOMODCACHE=
+env GOPATH=
+go env GOMODCACHE
+stdout $HOME[/\\]go[/\\]pkg[/\\]mod
+
+# If GOMODCACHE isn't set and GOPATH starts with the path list separator, it's an error.
+env GOMODCACHE=
+env GOPATH=${:}$WORK/this/is/ignored
+! go env GOMODCACHE
+stderr 'missing \$GOPATH'
+
+# If GOMODCACHE isn't set and GOPATH has multiple elements only the first is used.
+env GOMODCACHE=
+env GOPATH=$WORK/first/path${:}$WORK/this/is/ignored
+go env GOMODCACHE
+stdout $WORK[/\\]first[/\\]path[/\\]pkg[/\\]mod
+
+env GOMODCACHE=$WORK/modcache
+go mod download rsc.io/quote@v1.0.0
+exists $WORK/modcache/cache/download/rsc.io/quote/@v/v1.0.0.info
+
+# Test that the following work even with GO111MODULE=off
+env GO111MODULE=off
+
+# Cleaning modcache
+exists $WORK/modcache
+env GOMODCACHE=$WORK/modcache
+go clean -modcache
+! exists $WORK/modcache
+
+-- go.mod --
+module m
diff --git a/src/internal/cfg/cfg.go b/src/internal/cfg/cfg.go
index 0d227ecd10..bdbe9df3e7 100644
--- a/src/internal/cfg/cfg.go
+++ b/src/internal/cfg/cfg.go
@@ -46,6 +46,7 @@ const KnownEnv = `
 	GOINSECURE
 	GOMIPS
 	GOMIPS64
+	GOMODCACHE
 	GONOPROXY
 	GONOSUMDB
 	GOOS