cmd/go: move module cache from $GOPATH/src/mod to $GOPATH/pkg/mod

Using $GOPATH/src/mod confuses too many tools.
$GOPATH/pkg/mod seems better for now.
It's also next to dep's cache, $GOPATH/pkg/dep.
If we do eliminate GOPATH/pkg for holding .a files (#4719)
then we could still keep it around for pkg/mod.
(Or we could move the module cache again then.)

Fixes #26401.
Fixes #26635.

Change-Id: I18f7da216ed9f490eded3c00d837fb086ae5b6a4
Reviewed-on: https://go-review.googlesource.com/126755
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/go/internal/clean/clean.go

@@ -153,10 +153,10 @@ func runClean(cmd *base.Command, args []string) {
 	}
 
 	if cleanModcache {
-		if modfetch.SrcMod == "" {
+		if modfetch.PkgMod == "" {
 			base.Fatalf("go clean -modcache: no module cache")
 		}
-		if err := removeAll(modfetch.SrcMod); err != nil {
+		if err := removeAll(modfetch.PkgMod); err != nil {
 			base.Errorf("go clean -modcache: %v", err)
 		}
 	}

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

@@ -377,7 +377,7 @@ See https://golang.org/doc/code.html for an example.
 GOPATH and Modules
 
 When using modules, GOPATH is no longer used for resolving imports.
-However, it is still used to store downloaded source code (in GOPATH/src/mod)
+However, it is still used to store downloaded source code (in GOPATH/pkg/mod)
 and compiled commands (in GOPATH/bin).
 
 Internal Directories

src/cmd/go/internal/load/pkg.go

@@ -434,7 +434,7 @@ func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPo
 
 	if strings.HasPrefix(path, "mod/") {
 		// Paths beginning with "mod/" might accidentally
-		// look in the module cache directory tree in $GOPATH/src/mod/.
+		// look in the module cache directory tree in $GOPATH/pkg/mod/.
 		// This prefix is owned by the Go core for possible use in the
 		// standard library (since it does not begin with a domain name),
 		// so it's OK to disallow entirely.

src/cmd/go/internal/modconv/convert_test.go

@@ -39,7 +39,7 @@ func testMain(m *testing.M) int {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(dir)
-	modfetch.SrcMod = filepath.Join(dir, "src/mod")
+	modfetch.PkgMod = filepath.Join(dir, "pkg/mod")
 	codehost.WorkRoot = filepath.Join(dir, "codework")
 
 	return m.Run()

src/cmd/go/internal/modfetch/cache.go

@@ -22,17 +22,17 @@ import (
 
 var QuietLookup bool // do not print about lookups
 
-var SrcMod string // $GOPATH/src/mod; set by package modload
+var PkgMod string // $GOPATH/pkg/mod; set by package modload
 
 func cacheDir(path string) (string, error) {
-	if SrcMod == "" {
-		return "", fmt.Errorf("internal error: modfetch.SrcMod not set")
+	if PkgMod == "" {
+		return "", fmt.Errorf("internal error: modfetch.PkgMod not set")
 	}
 	enc, err := module.EncodePath(path)
 	if err != nil {
 		return "", err
 	}
-	return filepath.Join(SrcMod, "cache/download", enc, "/@v"), nil
+	return filepath.Join(PkgMod, "cache/download", enc, "/@v"), nil
 }
 
 func CachePath(m module.Version, suffix string) (string, error) {
@@ -54,8 +54,8 @@ func CachePath(m module.Version, suffix string) (string, error) {
 }
 
 func DownloadDir(m module.Version) (string, error) {
-	if SrcMod == "" {
-		return "", fmt.Errorf("internal error: modfetch.SrcMod not set")
+	if PkgMod == "" {
+		return "", fmt.Errorf("internal error: modfetch.PkgMod not set")
 	}
 	enc, err := module.EncodePath(m.Path)
 	if err != nil {
@@ -71,7 +71,7 @@ func DownloadDir(m module.Version) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	return filepath.Join(SrcMod, enc+"@"+encVer), nil
+	return filepath.Join(PkgMod, enc+"@"+encVer), nil
 }
 
 // A cachingRepo is a cache around an underlying Repo,
@@ -287,7 +287,7 @@ 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 SrcMod == "" {
+	if PkgMod == "" {
 		// Do not download to current directory.
 		return "", nil, errNotCached
 	}

src/cmd/go/internal/modfetch/fetch.go

@@ -28,9 +28,9 @@ 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 SrcMod == "" {
+	if PkgMod == "" {
 		// Do not download to current directory.
-		return "", fmt.Errorf("missing modfetch.SrcMod")
+		return "", fmt.Errorf("missing modfetch.PkgMod")
 	}
 
 	// The par.Cache here avoids duplicate work but also
@@ -53,7 +53,7 @@ func Download(mod module.Version) (dir string, err error) {
 			if _, err := os.Stat(zipfile); err == nil {
 				// Use it.
 				// This should only happen if the mod/cache directory is preinitialized
-				// or if src/mod/path was removed but not src/mod/cache/download.
+				// or if pkg/mod/path was removed but not pkg/mod/cache/download.
 				fmt.Fprintf(os.Stderr, "go: extracting %s %s\n", mod.Path, mod.Version)
 			} else {
 				if err := os.MkdirAll(filepath.Dir(zipfile), 0777); err != nil {
@@ -200,7 +200,7 @@ func readGoSum(file string, data []byte) {
 
 // checkSum checks the given module's checksum.
 func checkSum(mod module.Version) {
-	if SrcMod == "" {
+	if PkgMod == "" {
 		// Do not use current directory.
 		return
 	}
@@ -264,7 +264,7 @@ func checkOneSum(mod module.Version, h string) {
 // 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 SrcMod == "" {
+	if PkgMod == "" {
 		// Do not use current directory.
 		return ""
 	}

src/cmd/go/internal/modfetch/proxy.go

@@ -77,10 +77,10 @@ archive.
 
 Even when downloading directly from version control systems,
 the go command synthesizes explicit info, mod, and zip files
-and stores them in its local cache, $GOPATH/src/mod/cache/download,
+and stores them in its local cache, $GOPATH/pkg/mod/cache/download,
 the same as if it had downloaded them directly from a proxy.
 The cache layout is the same as the proxy URL space, so
-serving $GOPATH/src/mod/cache/download at (or copying it to)
+serving $GOPATH/pkg/mod/cache/download at (or copying it to)
 https://example.com/proxy would let other users access those
 cached module versions with GOPROXY=https://example.com/proxy.
 `,

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

@@ -50,7 +50,7 @@ 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/src/mod)
+during a build, but it still stores downloaded dependencies (in GOPATH/pkg/mod)
 and installed commands (in GOPATH/bin, unless GOBIN is set).
 
 Defining a module

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

@@ -170,9 +170,9 @@ func Init() {
 func init() {
 	load.ModInit = Init
 
-	// Set modfetch.SrcMod unconditionally, so that go clean -modcache can run even without modules enabled.
+	// Set modfetch.PkgMod unconditionally, so that go clean -modcache can run even without modules enabled.
 	if list := filepath.SplitList(cfg.BuildContext.GOPATH); len(list) > 0 && list[0] != "" {
-		modfetch.SrcMod = filepath.Join(list[0], "src/mod")
+		modfetch.PkgMod = filepath.Join(list[0], "pkg/mod")
 	}
 }
 
@@ -233,17 +233,17 @@ func InitMod() {
 		base.Fatalf("$GOPATH/go.mod exists but should not")
 	}
 
-	srcV := filepath.Join(list[0], "src/v")
-	srcMod := filepath.Join(list[0], "src/mod")
-	infoV, errV := os.Stat(srcV)
-	_, errMod := os.Stat(srcMod)
-	if errV == nil && infoV.IsDir() && errMod != nil && os.IsNotExist(errMod) {
-		os.Rename(srcV, srcMod)
+	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.SrcMod = srcMod
+	modfetch.PkgMod = pkgMod
 	modfetch.GoSumFile = filepath.Join(ModRoot, "go.sum")
-	codehost.WorkRoot = filepath.Join(srcMod, "cache/vcs")
+	codehost.WorkRoot = filepath.Join(pkgMod, "cache/vcs")
 
 	if CmdModInit {
 		// Running go mod init: do legacy module conversion

src/cmd/go/internal/modload/query_test.go

@@ -29,7 +29,7 @@ func testMain(m *testing.M) int {
 		log.Fatal(err)
 	}
 	defer os.RemoveAll(dir)
-	modfetch.SrcMod = filepath.Join(dir, "src/mod")
+	modfetch.PkgMod = filepath.Join(dir, "pkg/mod")
 	codehost.WorkRoot = filepath.Join(dir, "codework")
 	return m.Run()
 }

src/cmd/go/testdata/addmod.go

@@ -97,13 +97,13 @@ func main() {
 			continue
 		}
 		path, vers, dir := f[0], f[1], f[2]
-		mod, err := ioutil.ReadFile(filepath.Join(gopath, "src/mod/cache/download", path, "@v", vers+".mod"))
+		mod, err := ioutil.ReadFile(filepath.Join(gopath, "pkg/mod/cache/download", path, "@v", vers+".mod"))
 		if err != nil {
 			log.Printf("%s: %v", arg, err)
 			exitCode = 1
 			continue
 		}
-		info, err := ioutil.ReadFile(filepath.Join(gopath, "src/mod/cache/download", path, "@v", vers+".info"))
+		info, err := ioutil.ReadFile(filepath.Join(gopath, "pkg/mod/cache/download", path, "@v", vers+".info"))
 		if err != nil {
 			log.Printf("%s: %v", arg, err)
 			exitCode = 1

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

@@ -6,16 +6,16 @@ go mod edit -fmt
 go list -mod=readonly
 env GOPROXY=file:///nonexist
 go list
-grep v1.5.1 $GOPATH/src/mod/cache/download/rsc.io/quote/@v/list
+grep v1.5.1 $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/list
 
 # Use download cache as file:/// proxy.
 [windows] stop # TODO: file://$WORK puts backslashes in the URL
 env GOPATH=$WORK/gopath2
 env GOPROXY=file:///nonexist
 ! go list
-env GOPROXY=file://$WORK/gopath1/src/mod/cache/download
+env GOPROXY=file://$WORK/gopath1/pkg/mod/cache/download
 go list
-grep v1.5.1 $GOPATH/src/mod/cache/download/rsc.io/quote/@v/list
+grep v1.5.1 $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/list
 
 -- $WORK/x/go.mod --
 module x

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

-# Test that GOPATH/src/mod is excluded
+# Test that GOPATH/pkg/mod is excluded
 env GO111MODULE=off
 ! go list mod/foo
 stderr 'disallowed import path'

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

@@ -10,12 +10,12 @@ go list -f '{{.Dir}}' rsc.io/quote
 stdout '.*mod[\\/]rsc.io[\\/]quote@v1.5.2$'
 
 # downloaded dependencies are read-only
-exists -readonly $GOPATH/src/mod/rsc.io/quote@v1.5.2
-exists -readonly $GOPATH/src/mod/rsc.io/quote@v1.5.2/buggy
+exists -readonly $GOPATH/pkg/mod/rsc.io/quote@v1.5.2
+exists -readonly $GOPATH/pkg/mod/rsc.io/quote@v1.5.2/buggy
 
 # go clean -modcache can delete read-only dependencies
 go clean -modcache
-! exists $GOPATH/src/mod/rsc.io/quote@v1.5.2
+! exists $GOPATH/pkg/mod/rsc.io/quote@v1.5.2
 
 # list {{.Dir}} shows replaced directories
 cp go.mod2 go.mod

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

@@ -9,14 +9,14 @@ go list -f '{{.ImportPath}}' $GOROOT/src/math
 stdout ^math$
 go list -f '{{.ImportPath}}' .
 stdout ^x$
-go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/quote@v1.5.2
+go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/quote@v1.5.2
 stdout '^rsc.io/quote$'
-go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.0
+go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.0
 stdout '^rsc.io/sampler$'
 go get rsc.io/sampler@v1.3.1
-go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.1
+go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.1
 stdout '^rsc.io/sampler$'
-! go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.0
+! go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.0
 stderr 'outside available modules'
 
 -- go.mod --

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

@@ -2,25 +2,25 @@ env GO111MODULE=on
 
 # initial standalone module should use no downloaded modules
 go list -deps -f {{.Dir}}
-! stdout 'src[\\/]mod'
+! stdout 'pkg[\\/]mod'
 
 # v2 import should use a downloaded module
 # both without an explicit go.mod entry ...
 cp tmp/use_v2.go x.go
 go list -deps -f {{.Dir}}
-stdout 'src[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
+stdout 'pkg[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
 
 # ... and with one ...
 cp tmp/use_v2.mod go.mod
 go list -deps -f {{.Dir}}
-stdout 'src[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
+stdout 'pkg[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
 
 # ... and even if there is a v2 module in a subdirectory.
 mkdir v2
 cp x.go v2/x.go
 cp tmp/v2.mod v2/go.mod
 go list -deps -f {{.Dir}}
-stdout 'src[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
+stdout 'pkg[\\/]mod[\\/]rsc.io[\\/]quote[\\/]v2@v2.0.1$'
 
 -- go.mod --
 module rsc.io/quote

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

@@ -3,12 +3,12 @@ env GO111MODULE=on
 # With good go.sum, verify succeeds by avoiding download.
 cp go.sum.good go.sum
 go mod verify
-! exists $GOPATH/src/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
+! exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
 
 # With bad go.sum, verify succeeds by avoiding download.
 cp go.sum.bad go.sum
 go mod verify
-! exists $GOPATH/src/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
+! exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
 
 # With bad go.sum, sync (which must download) fails.
 # Even if the bad sum is in the old legacy go.modverify file.
@@ -16,14 +16,14 @@ rm go.sum
 cp go.sum.bad go.modverify
 ! go mod tidy
 stderr 'checksum mismatch'
-! exists $GOPATH/src/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
+! exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
 
 # With good go.sum, sync works (and moves go.modverify to go.sum).
 rm go.sum
 cp go.sum.good go.modverify
 go mod tidy
-exists $GOPATH/src/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
-exists $GOPATH/src/mod/rsc.io/quote@v1.1.0/quote.go
+exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.zip
+exists $GOPATH/pkg/mod/rsc.io/quote@v1.1.0/quote.go
 ! exists go.modverify
 
 # go.sum should have the new checksum for go.mod
@@ -50,7 +50,7 @@ grep '^rsc.io/quote v1.1.0/go.mod ' go.sum
 grep '^rsc.io/quote v1.1.0 ' go.sum
 
 # sync should ignore missing ziphash; verify should not
-rm $GOPATH/src/mod/cache/download/rsc.io/quote/@v/v1.1.0.ziphash
+rm $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.ziphash
 go mod tidy
 ! go mod verify