Add initial support for the XDG Base Directory spec

Spec version 0.7 from https://standards.freedesktop.org/basedir-spec/basedir-spec-0.7.html
(latest as of this commit).

Three virtual methods are added to OS for the various XDG paths we will use:
- OS::get_data_path gives XDG_DATA_HOME, or if missing:
  ~/.local/share on X11, ~/Library/Application Support/ on macOS and %APPDATA% on Windows
- OS::get_config_path gives XDG_CONFIG_HOME, or if missing:
  ~/.config on X11, ~/Library/Application Support/ on macOS and %APPDATA% on Windows
- OS::get_cache_path gives XDG_CACHE_HOME, or if missing:
  ~/.cache on X11, ~/Library/Caches on macOS and %APPDATA% on Windows

So for Windows there are no changes, for Linux we follow the full split spec
and for macOS stuff will move from ~/.godot to ~/Library/Application Support/Godot.

Support for system-wide installation of templates on Unix was removed for now,
as it's a bit hackish and I don't think anyone uses it.

user:// will still be OS::get_data_path() + "/godot/app_userdata/$name" by
default, but when using the application/config/use_shared_user_dir option
it will now use XDG_DATA_HOME/$name, e.g. ~/.local/share/MyGame.

For now everything still goes in EditorSettings::get_settings_dir(), but
this will be changed in a later commit to make use of the new splitting
where relevant.

Part of #3513.

8 files changed, 170 insertions, 10 deletions

diff --git a/platform/haiku/os_haiku.cpp b/platform/haiku/os_haiku.cpp
index 0c34e39655..4d5dfeddb5 100644
--- a/platform/haiku/os_haiku.cpp
+++ b/platform/haiku/os_haiku.cpp
@@ -314,3 +314,36 @@ bool OS_Haiku::_check_internal_feature_support(const String &p_feature) {
 
 	return p_feature == "pc" || p_feature == "s3tc";
 }
+
+String OS_Haiku::get_config_path() const {
+
+	if (has_environment("XDG_CONFIG_HOME")) {
+		return get_environment("XDG_CONFIG_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".config");
+	} else {
+		return ".";
+	}
+}
+
+String OS_Haiku::get_data_path() const {
+
+	if (has_environment("XDG_DATA_HOME")) {
+		return get_environment("XDG_DATA_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".local/share");
+	} else {
+		return get_config_path();
+	}
+}
+
+String OS_Haiku::get_cache_path() const {
+
+	if (has_environment("XDG_CACHE_HOME")) {
+		return get_environment("XDG_CACHE_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".cache");
+	} else {
+		return get_config_path();
+	}
+}
diff --git a/platform/haiku/os_haiku.h b/platform/haiku/os_haiku.h
index 86148f1fb4..4ee54fb48d 100644
--- a/platform/haiku/os_haiku.h
+++ b/platform/haiku/os_haiku.h
@@ -117,6 +117,10 @@ public:
 	virtual int get_power_percent_left();
 
 	virtual bool _check_internal_feature_support(const String &p_feature);
+
+	virtual String get_config_path() const;
+	virtual String get_data_path() const;
+	virtual String get_cache_path() const;
 };
 
 #endif
diff --git a/platform/osx/os_osx.h b/platform/osx/os_osx.h
index 1df847eb79..aa8ee1fe83 100644
--- a/platform/osx/os_osx.h
+++ b/platform/osx/os_osx.h
@@ -154,6 +154,11 @@ public:
 
 	virtual MainLoop *get_main_loop() const;
 
+	virtual String get_config_path() const;
+	virtual String get_data_path() const;
+	virtual String get_cache_path() const;
+	virtual String get_godot_dir_name() const;
+
 	virtual String get_system_dir(SystemDir p_dir) const;
 
 	virtual bool can_draw() const;
diff --git a/platform/osx/os_osx.mm b/platform/osx/os_osx.mm
index 49d94da9e1..391c697ae9 100644
--- a/platform/osx/os_osx.mm
+++ b/platform/osx/os_osx.mm
@@ -36,6 +36,7 @@
 #include "print_string.h"
 #include "sem_osx.h"
 #include "servers/visual/visual_server_raster.h"
+#include "version_generated.gen.h"
 
 #include <Carbon/Carbon.h>
 #import <Cocoa/Cocoa.h>
@@ -1340,6 +1341,43 @@ MainLoop *OS_OSX::get_main_loop() const {
 	return main_loop;
 }
 
+String OS_OSX::get_config_path() const {
+
+	if (has_environment("XDG_CONFIG_HOME")) {
+		return get_environment("XDG_CONFIG_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file("Library/Application Support");
+	} else {
+		return ".";
+	}
+}
+
+String OS_OSX::get_data_path() const {
+
+	if (has_environment("XDG_DATA_HOME")) {
+		return get_environment("XDG_DATA_HOME");
+	} else {
+		return get_config_path();
+	}
+}
+
+String OS_OSX::get_cache_path() const {
+
+	if (has_environment("XDG_CACHE_HOME")) {
+		return get_environment("XDG_CACHE_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file("Library/Caches");
+	} else {
+		return get_config_path();
+	}
+}
+
+// Get properly capitalized engine name for system paths
+String OS_OSX::get_godot_dir_name() const {
+
+	return String(_MKSTR(VERSION_SHORT_NAME)).capitalize();
+}
+
 String OS_OSX::get_system_dir(SystemDir p_dir) const {
 
 	NSSearchPathDirectory id = 0;
diff --git a/platform/windows/os_windows.cpp b/platform/windows/os_windows.cpp
index 8c290127a0..146e2e76ea 100644
--- a/platform/windows/os_windows.cpp
+++ b/platform/windows/os_windows.cpp
@@ -47,6 +47,7 @@
 #include "servers/visual/visual_server_wrap_mt.h"
 #include "stream_peer_winsock.h"
 #include "tcp_server_winsock.h"
+#include "version_generated.gen.h"
 #include "windows_terminal_logger.h"
 
 #include <process.h>
@@ -2131,6 +2132,43 @@ MainLoop *OS_Windows::get_main_loop() const {
 	return main_loop;
 }
 
+String OS_Windows::get_config_path() const {
+
+	if (has_environment("XDG_CONFIG_HOME")) { // unlikely, but after all why not?
+		return get_environment("XDG_CONFIG_HOME");
+	} else if (has_environment("APPDATA")) {
+		return get_environment("APPDATA");
+	} else {
+		return ".";
+	}
+}
+
+String OS_Windows::get_data_path() const {
+
+	if (has_environment("XDG_DATA_HOME")) {
+		return get_environment("XDG_DATA_HOME");
+	} else {
+		return get_config_path();
+	}
+}
+
+String OS_Windows::get_cache_path() const {
+
+	if (has_environment("XDG_CACHE_HOME")) {
+		return get_environment("XDG_CACHE_HOME");
+	} else if (has_environment("TEMP")) {
+		return get_environment("TEMP");
+	} else {
+		return get_config_path();
+	}
+}
+
+// Get properly capitalized engine name for system paths
+String OS_Windows::get_godot_dir_name() const {
+
+	return String(_MKSTR(VERSION_SHORT_NAME)).capitalize();
+}
+
 String OS_Windows::get_system_dir(SystemDir p_dir) const {
 
 	int id;
@@ -2167,18 +2205,17 @@ String OS_Windows::get_system_dir(SystemDir p_dir) const {
 	ERR_FAIL_COND_V(res != S_OK, String());
 	return String(szPath);
 }
-String OS_Windows::get_user_data_dir() const {
 
-	String an = get_safe_application_name();
-	if (an != "") {
+String OS_Windows::get_user_data_dir() const {
 
-		if (has_environment("APPDATA")) {
+	String appname = get_safe_application_name();
+	if (appname != "") {
 
-			bool use_godot = ProjectSettings::get_singleton()->get("application/config/use_shared_user_dir");
-			if (!use_godot)
-				return (OS::get_singleton()->get_environment("APPDATA") + "/" + an).replace("\\", "/");
-			else
-				return (OS::get_singleton()->get_environment("APPDATA") + "/Godot/app_userdata/" + an).replace("\\", "/");
+		bool use_godot_dir = ProjectSettings::get_singleton()->get("application/config/use_shared_user_dir");
+		if (use_godot_dir) {
+			return get_data_path().plus_file(get_godot_dir_name()).plus_file("app_userdata").plus_file(appname).replace("\\", "/");
+		} else {
+			return get_data_path().plus_file(appname).replace("\\", "/");
 		}
 	}
 
diff --git a/platform/windows/os_windows.h b/platform/windows/os_windows.h
index f3b8f0e5fd..5e0c240dba 100644
--- a/platform/windows/os_windows.h
+++ b/platform/windows/os_windows.h
@@ -253,8 +253,14 @@ public:
 
 	virtual void enable_for_stealing_focus(ProcessID pid);
 	virtual void move_window_to_foreground();
-	virtual String get_user_data_dir() const;
+
+	virtual String get_config_path() const;
+	virtual String get_data_path() const;
+	virtual String get_cache_path() const;
+	virtual String get_godot_dir_name() const;
+
 	virtual String get_system_dir(SystemDir p_dir) const;
+	virtual String get_user_data_dir() const;
 
 	virtual void release_rendering_thread();
 	virtual void make_rendering_thread();
diff --git a/platform/x11/os_x11.cpp b/platform/x11/os_x11.cpp
index 412e22b5f7..c1d744215d 100644
--- a/platform/x11/os_x11.cpp
+++ b/platform/x11/os_x11.cpp
@@ -1941,6 +1941,39 @@ bool OS_X11::_check_internal_feature_support(const String &p_feature) {
 	return p_feature == "pc" || p_feature == "s3tc";
 }
 
+String OS_X11::get_config_path() const {
+
+	if (has_environment("XDG_CONFIG_HOME")) {
+		return get_environment("XDG_CONFIG_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".config");
+	} else {
+		return ".";
+	}
+}
+
+String OS_X11::get_data_path() const {
+
+	if (has_environment("XDG_DATA_HOME")) {
+		return get_environment("XDG_DATA_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".local/share");
+	} else {
+		return get_config_path();
+	}
+}
+
+String OS_X11::get_cache_path() const {
+
+	if (has_environment("XDG_CACHE_HOME")) {
+		return get_environment("XDG_CACHE_HOME");
+	} else if (has_environment("HOME")) {
+		return get_environment("HOME").plus_file(".cache");
+	} else {
+		return get_config_path();
+	}
+}
+
 String OS_X11::get_system_dir(SystemDir p_dir) const {
 
 	String xdgparam;
diff --git a/platform/x11/os_x11.h b/platform/x11/os_x11.h
index 0ea5bbfdb6..67f3807d99 100644
--- a/platform/x11/os_x11.h
+++ b/platform/x11/os_x11.h
@@ -213,6 +213,10 @@ public:
 	virtual void make_rendering_thread();
 	virtual void swap_buffers();
 
+	virtual String get_config_path() const;
+	virtual String get_data_path() const;
+	virtual String get_cache_path() const;
+
 	virtual String get_system_dir(SystemDir p_dir) const;
 
 	virtual Error shell_open(String p_uri);