Linux: Save Bookmarks under XDG_STATE_HOME

An installation path like "/usr/share/tangerine/" might be read-only.

Define the CPP macro `TANGERINE_SELF_CONTAINED` to use a path relative
to the executable, instead. Currently, Windows always uses
`TANGERINE_SELF_CONTAINED`, but support for both options could be
useful there, too.

CMakeLists.txt

@@ -15,6 +15,7 @@ include(GNUInstallDirs)
 
 option(EMBED_LUA "Embed Lua support" ON)
 option(EMBED_RACKET "Embed Racket support" OFF)
+option(SELF_CONTAINED "Use directory tree instead of XDG_STATE_HOME" OFF)
 
 set(INSTALL_PKG_SUBPATH "tangerine" CACHE PATH
 	"Subdirectory to form PKGDATADIR from DATADIR")
@@ -149,6 +150,7 @@ set_target_properties(tangerine
 	RUNTIME_OUTPUT_DIRECTORY
 	$<PATH:APPEND,${CMAKE_BINARY_DIR},${CMAKE_INSTALL_BINDIR}>)
 target_compile_definitions(tangerine PRIVATE
+	$<$<BOOL:${SELF_CONTAINED}>:"TANGERINE_SELF_CONTAINED">
 	"TANGERINE_PKGDATADIR_FROM_BINDIR=${PKGDATADIR_FROM_BINDIR}")
 target_link_libraries(tangerine PRIVATE
 	fmt

tangerine/installation.cpp

@@ -17,9 +17,24 @@
 #include "whereami.h"
 #include <iostream>
 
+#if !_WIN64
+#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <cerrno>
+#include <cstring>
+const char *const TangerineAppID =
+	// TODO: consider a reverse-dns name with the escaping recommended in:
+	// https://docs.gtk.org/gio/type_func.Application.id_is_valid.html
+	// See rationale in: https://docs.gtk.org/gtk4/migrating-3to4.html#set-a-proper-application-id
+	"tangerine";
+std::optional<std::filesystem::path> GetXDGStateHome();
+#endif
+
 
 StatusCode TangerinePaths::PopulateInstallationPaths()
 {
+	std::filesystem::path ExecutablePath;
 	{
 		int Length = wai_getExecutablePath(NULL, 0, NULL);
 		if (Length > -1)
@@ -44,20 +59,142 @@ StatusCode TangerinePaths::PopulateInstallationPaths()
 		}
 	}
 
-	ExecutableDir = ExecutablePath.parent_path();
+	std::filesystem::path ExecutableDir = ExecutablePath.parent_path();
 
 #ifdef TANGERINE_PKGDATADIR_FROM_BINDIR
 #define STRINGIFY(x) #x
 #define EXPAND_AS_STR(x) STRINGIFY(x)
-	PkgDataDir = ExecutableDir / std::filesystem::path(EXPAND_AS_STR(TANGERINE_PKGDATADIR_FROM_BINDIR));
+	std::filesystem::path PkgDataDir = ExecutableDir / std::filesystem::path(EXPAND_AS_STR(TANGERINE_PKGDATADIR_FROM_BINDIR));
 #undef EXPAND_AS_STR
 #undef STRINGIFY
 #else
-	PkgDataDir = ExecutableDir;
+	std::filesystem::path PkgDataDir = ExecutableDir;
 #endif
 
 	ShadersDir = PkgDataDir / std::filesystem::path("shaders");
 	ModelsDir = PkgDataDir / std::filesystem::path("models");
 
+#if defined(TANGERINE_SELF_CONTAINED)
+	BookmarksPath = PkgDataDir / std::filesystem::path("bookmarks.txt");
+#elif !_WIN64
+	if (std::optional<std::filesystem::path> HomeDir = GetXDGStateHome())
+	{
+		BookmarksPath = HomeDir.value() / std::filesystem::path(TangerineAppID) / std::filesystem::path("bookmarks.txt");
+	}
+	else
+	{
+		BookmarksPath = std::nullopt;
+	}
+#else // Shouldn't get here: handled in "installation.h".  Using %APPDATA% / CSIDL_APPDATA / FOLDERID_RoamingAppData might be useful, though.
+# error "Windows currently requires TANGERINE_SELF_CONTAINED."
+#endif
+
 	return StatusCode::PASS;
 }
+
+
+#if !_WIN64
+std::optional<std::filesystem::path> GetHomeDir() {
+	// Based on `rktio_expand_user_tilde()`.
+	// License: (Apache-2.0 OR MIT)
+
+	// $HOME overrides everything.
+	if (const char *Home = std::getenv("HOME"))
+	{
+		return std::filesystem::path(Home);
+	}
+
+	// $USER and $LOGNAME (in that order) override `getuid()`.
+	const char *AltUserVar = "USER";
+	const char *AltUser = std::getenv(AltUserVar);
+	if (!AltUser)
+	{
+		AltUserVar = "LOGNAME";
+		AltUser = std::getenv(AltUserVar);
+	}
+
+	/* getpwnam(3) man page says: "If one wants to check errno after the
+	   call, it should be set to zero before the call." */
+	errno = 0;
+	struct passwd *Passwd = AltUser ? getpwnam(AltUser) : getpwuid(getuid());
+	int PasswdError = errno;
+
+	// Did we find it?
+	if (Passwd && Passwd->pw_dir)
+	{
+		if (0 != PasswdError)
+		{
+			std::cout << "Warning: Found home directory, but " << (AltUser ? "getpwnam" : "getpwuid") << " reported an error.\n";
+		}
+		else
+		{
+			// No warning
+			return std::filesystem::path(Passwd->pw_dir);
+		}
+	}
+	else if (Passwd)
+	{
+		std::cout << "Warning: User exists, but does not have a home directory.\n";
+	}
+	else
+	{
+		std::cout << "Warning: Could not find home directory: user not found.\n";
+	}
+
+	// Add warning details:
+	// Was `getuid()` overridden?
+	if (AltUser)
+	{
+		std::cout << "   user: " << AltUser << " (from $" << AltUserVar << ");\n";
+	}
+	// Report system error.
+	if (0 != PasswdError)
+	{
+		std::cout << "  error: " << std::strerror(PasswdError) << "\n";
+		std::cout << "  errno: " << PasswdError << "\n";
+	}
+	else
+	{
+		std::cout << "  errno: not set by " << (AltUser ? "getpwnam" : "getpwuid") << "\n";
+	}
+
+	if (Passwd && Passwd->pw_dir)
+	{
+		return std::filesystem::path(Passwd->pw_dir);
+	}
+	else
+	{
+		return {};
+	}
+}
+
+std::optional<std::filesystem::path> GetXDGStateHome()
+{
+	// Based on `rktio_system_path()`.
+	// License: (Apache-2.0 OR MIT)
+
+	const char *EnvVar = "XDG_STATE_HOME";
+	const char *DefaultSubpath = ".local/state";
+
+	// Check the environment variable.
+	if (const char *FromEnv = std::getenv(EnvVar))
+	{
+		std::filesystem::path Candidate = std::filesystem::path(FromEnv);
+		// We must ignore the environment variable if it is not an absolute path.
+		if (Candidate.is_absolute()) {
+			return Candidate;
+		}
+	}
+
+
+	// Environment variable was unset or is invalid.
+	if (std::optional<std::filesystem::path> Home = GetHomeDir())
+	{
+		return Home.value() / std::filesystem::path(DefaultSubpath);
+	}
+	else
+	{
+		return {};
+	}
+}
+#endif /* !_WIN64 */

tangerine/installation.h

@@ -15,17 +15,21 @@
 
 #pragma once
 #include <filesystem>
+#include <optional>
 #include "embedding.h"
 #include "errors.h"
 
+#ifndef TANGERINE_SELF_CONTAINED
+# ifdef _WIN64
+#  define TANGERINE_SELF_CONTAINED
+# endif
+#endif
 
 struct TangerinePaths
 {
 	StatusCode PopulateInstallationPaths();
 
-	std::filesystem::path ExecutablePath;
-	std::filesystem::path ExecutableDir;
-	std::filesystem::path PkgDataDir;
 	std::filesystem::path ShadersDir;
 	std::filesystem::path ModelsDir;
+	std::optional<std::filesystem::path> BookmarksPath;
 };

tangerine/tangerine.cpp

@@ -1747,11 +1747,10 @@ void RenderUI(SDL_Window* Window, bool& Live)
 
 void LoadBookmarks()
 {
-	std::filesystem::path BookmarksPath =
-                // FIXME might be read-only
-                Installed.ExecutableDir / "bookmarks.txt";
-	if (std::filesystem::is_regular_file(BookmarksPath))
+	std::optional<std::filesystem::path> MaybeBookmarksPath = Installed.BookmarksPath;
+	if (MaybeBookmarksPath && std::filesystem::is_regular_file(MaybeBookmarksPath.value()))
 	{
+		std::filesystem::path BookmarksPath = MaybeBookmarksPath.value();
 		std::ifstream BookmarksFile;
 		BookmarksFile.open(BookmarksPath);
 		std::string Bookmark;
@@ -1772,12 +1771,16 @@ void LoadBookmarks()
 
 void SaveBookmarks()
 {
-	std::filesystem::path BookmarksPath =
-		// FIXME might be read-only
-		Installed.ExecutableDir / "bookmarks.txt";
+	std::optional<std::filesystem::path> MaybeBookmarksPath = Installed.BookmarksPath;
+	if (!MaybeBookmarksPath)
+	{
+		return;
+	}
+	std::filesystem::path BookmarksPath = MaybeBookmarksPath.value();
 	const std::vector<std::string>& Bookmarks = ifd::FileDialog::Instance().GetFavorites();
 	if (Bookmarks.size() > 0)
 	{
+		std::filesystem::create_directories(BookmarksPath.parent_path());
 		std::ofstream BookmarksFile;
 		BookmarksFile.open(BookmarksPath);
 		for (const std::string& Bookmark : Bookmarks)