all: hide home directory in script tests (#605)

As described in:

  #603 (comment)

we currently have a situation whereby the home directory sits within the
root directory of a script test. Given that most scripts also put files
in this root directory, i.e. the script root is also the main module
root, we have a situation where files in the home directory are
contained within the main module.

We do not set GOPATH explicitly as part of our tests, hence GOPATH
defaults to being a subdirectory within the home directory, i.e. also
part of the main module.

As we are now using goproxytest, this means modules we access end up
being expanded to $HOME/go/pkg/mod.

The file watcher that is part of govim is somewhat broken (#604) and we
end up watching changes to nested modules in $HOME/go/pkg/mod.

Whilst we have raised #604 in order to fix the file watching problem, we
can also fix this problem in the short term by defining HOME as:

  $script_root/.home

At the same time, we fix a bug in the watcher whereby we were not
correctly skipping hidden directories.

Fixes #603

cmd/govim/main_test.go

@@ -81,7 +81,7 @@ func TestScripts(t *testing.T) {
 					if err := os.MkdirAll(tmp, 0777); err != nil {
 						return fmt.Errorf("failed to create temp dir %v: %v", tmp, err)
 					}
-					home := filepath.Join(e.WorkDir, "home")
+					home := filepath.Join(e.WorkDir, ".home")
 					e.Vars = append(e.Vars,
 						"TMPDIR="+tmp,
 						"GOPROXY="+proxy.URL,
@@ -90,7 +90,7 @@ func TestScripts(t *testing.T) {
 						"PLUGIN_PATH="+govimPath,
 						"CURRENT_GOPATH="+strings.TrimSpace(runCmd(t, "go", "env", "GOPATH")),
 					)
-					testPluginPath := filepath.Join(e.WorkDir, "home", ".vim", "pack", "plugins", "start", "govim")
+					testPluginPath := filepath.Join(home, ".vim", "pack", "plugins", "start", "govim")
 
 					errLog := new(testdriver.LockingBuffer)
 					outputs := []io.Writer{

cmd/govim/watcher.go

@@ -139,7 +139,7 @@ func (m *modWatcher) watch() {
 					// We have a dir
 					switch filepath.Base(path)[0] {
 					case '.', '_':
-						return nil
+						return filepath.SkipDir
 					}
 					if path != m.root {
 						// check we are not in a submodule

govim_test.go

@@ -47,11 +47,11 @@ func TestScripts(t *testing.T) {
 			},
 			Condition: testdriver.Condition,
 			Setup: func(e *testscript.Env) error {
-				home := filepath.Join(e.WorkDir, "home")
+				home := filepath.Join(e.WorkDir, ".home")
 				e.Vars = append(e.Vars,
 					"HOME="+home,
 				)
-				testPluginPath := filepath.Join(e.WorkDir, "home", ".vim", "pack", "plugins", "start", "govim")
+				testPluginPath := filepath.Join(home, ".vim", "pack", "plugins", "start", "govim")
 
 				var vimDebugLogPath, govimDebugLogPath string