Fix preset dialog default dir resolving to / on Linux

Source/PluginEditor.cpp

@@ -1,6 +1,30 @@
 #include "PluginEditor.h"
 #include <BinaryData.h>
 
+namespace
+{
+    // Returns a sensible default directory for preset files. On Linux,
+    // File::getSpecialLocation (userHomeDirectory) can resolve to "/" when the
+    // home directory can't be determined, so fall back through $HOME, the user
+    // documents directory, and finally the current working directory.
+    juce::File getDefaultPresetDirectory()
+    {
+        auto test = [] (const juce::File& f) { return f.isDirectory() && f.createDirectory().wasOk(); };
+
+        if (auto* homeEnv = std::getenv ("HOME"))
+            if (test (juce::File (homeEnv)))
+                return juce::File (homeEnv);
+
+        if (test (juce::File::getSpecialLocation (juce::File::userHomeDirectory)))
+            return juce::File::getSpecialLocation (juce::File::userHomeDirectory);
+
+        if (test (juce::File::getSpecialLocation (juce::File::userDocumentsDirectory)))
+            return juce::File::getSpecialLocation (juce::File::userDocumentsDirectory);
+
+        return juce::File::getCurrentWorkingDirectory();
+    }
+}
+
 KnobLookAndFeel::KnobLookAndFeel() {
     knobOverlay = juce::ImageCache::getFromMemory(BinaryData::metalknob_png,
                                                     BinaryData::metalknob_pngSize);
@@ -907,7 +931,7 @@ juce::String MainContentComponent::currentPresetName() const {
 
 void MainContentComponent::savePresetFile() {
     auto* chooser = new juce::FileChooser("Save ChromaFlock Preset",
-        juce::File::getSpecialLocation(juce::File::userHomeDirectory)
+        getDefaultPresetDirectory()
             .getChildFile("chromaflock-" + currentPresetName().replaceCharacter(' ', '-') + ".cfl"),
         "*.cfl");
 
@@ -945,7 +969,7 @@ void MainContentComponent::savePresetFile() {
 
 void MainContentComponent::loadPresetFile() {
     auto* chooser = new juce::FileChooser("Load ChromaFlock Preset",
-        juce::File::getSpecialLocation(juce::File::userHomeDirectory),
+        getDefaultPresetDirectory(),
         "*.cfl");
 
     chooser->launchAsync(juce::FileBrowserComponent::openMode