cli/config: add synchronisation for configDir (Dir, SetDir)

commit 8a30653ed5 introduced a sync.Once
to allow for the config-directory (and home-dir) to be looked up lazily
instead of in an `init()`.

However, the package-level `configDir` variable can be set through two
separate paths; implicitly (through `config.Dir()`), and explicitly,
through `config.SetDir()`. The existing code had no synchronisation for
this, which could lead to a potential race-condition (code requesting
`config.Dir()` and code setting a custom path through `config.SetDir()`).

This patch adds synchronisation by triggering the `sync.Once` as part of
`config.SetDir()` to prevent it being triggered later (overwriting the
value that was set). It also restores the `resetConfigDir()` utility that
was removed in 379122b033, to allow resetting
the `sync.Once` for this test.

In general, we should get rid of this package-level variable, and store
it as a config on the client (passing the option to locations where its
used instead).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/config/config.go

@@ -27,6 +27,13 @@ var (
 	configDir     string
 )
 
+// resetConfigDir is used in testing to reset the "configDir" package variable
+// and its sync.Once to force re-lookup between tests.
+func resetConfigDir() {
+	configDir = ""
+	initConfigDir = new(sync.Once)
+}
+
 // Dir returns the directory the configuration file is stored in
 func Dir() string {
 	initConfigDir.Do(func() {
@@ -45,6 +52,8 @@ func ContextStoreDir() string {
 
 // SetDir sets the directory the configuration file is stored in
 func SetDir(dir string) {
+	// trigger the sync.Once to synchronise with Dir()
+	initConfigDir.Do(func() {})
 	configDir = filepath.Clean(dir)
 }
 

cli/config/config_test.go

@@ -382,3 +382,12 @@ func TestConfigPath(t *testing.T) {
 
 	SetDir(oldDir)
 }
+
+// TestSetDir verifies that Dir() does not overwrite the value set through
+// SetDir() if it has not been run before.
+func TestSetDir(t *testing.T) {
+	const expected = "my_config_dir"
+	resetConfigDir()
+	SetDir(expected)
+	assert.Check(t, is.Equal(Dir(), expected))
+}