fully support relocatable binaries, improving AppImages

* You can now specify `--with-scitecodatadir` as a relative path,
  that will be interpreted relative to the binary's location.
* Win32 binaries already were relocatable, but this was a Windows-specific
  hack. Win32 binaries are now built with `--with-scitecodatadir=.`
  since everything is in a single directory.
* Ubuntu packages are now also built `--with-scitecodatadir=../share/sciteco`.
  This is not crucial for ordinary installations, but is meant for AppImage creation.
* Since AppImages are now built from relocatable packages,
  we no longer need the unionfs-workaround from pkg2appimage.
  This should fix the strange root contents when autocompleting in
  AppImage builds.
* This might also fix the appimage.github.io CI issues.
  I assume that because I could reproduce the issue on FreeBSD's
  Linuxulator in dependence of pkg2appimage's "union"-setting.
  See https://github.com/AppImage/appimage.github.io/pull/3402
* Determining the binary location actually turned out be hard and
  very platform-dependant. There are now implementations for Windows
  (which could also read argv[0]), Linux and generic UNIX (which
  works on FreeBSD, but I am not sure about the others).
  I believe this could also be useful on Mac OS to create app bundles,
  but this needs to be tested - currently the Mac OS binaries are
  installed into fixed locations and don't use relocation.

1 files changed, 85 insertions, 0 deletions

diff --git a/src/file-utils.c b/src/file-utils.c
index 3f8f721..b7e5418 100644
--- a/src/file-utils.c
+++ b/src/file-utils.c
@@ -19,6 +19,7 @@
 #include "config.h"
 #endif
 
+#define _GNU_SOURCE
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
@@ -35,6 +36,10 @@
 #include <glib.h>
 #include <glib/gstdio.h>
 
+#ifdef G_OS_UNIX
+#include <dlfcn.h>
+#endif
+
 #include "sciteco.h"
 #include "qreg.h"
 #include "interface.h"
@@ -179,6 +184,86 @@ teco_file_is_visible(const gchar *path)
 
 #endif /* !G_OS_WIN32 */
 
+#ifdef G_OS_WIN32
+
+gchar *
+teco_file_get_program_path(void)
+{
+	TCHAR buf[MAX_PATH];
+	if (!GetModuleFileNameW(NULL, buf, G_N_ELEMENTS(buf))
+		return g_get_current_dir();
+	g_autofree gchar *exe = g_utf16_to_utf8(buf, -1, NULL, NULL, NULL);
+	return g_path_get_dirname(exe);
+}
+
+#elif defined(__linux__)
+
+gchar *
+teco_file_get_program_path(void)
+{
+	gchar buf[PATH_MAX];
+	ssize_t len = readlink("/proc/self/exe", buf, sizeof(buf)-1);
+	if (G_UNLIKELY(len < 0))
+		/* almost certainly wrong */
+		return g_get_current_dir();
+	buf[len] = '\0';
+
+	return g_path_get_dirname(buf);
+}
+
+#elif defined(G_OS_UNIX)
+
+/*
+ * At least works on FreeBSD, even though it also has
+ * sysctl(KERN_PROC_PATHNAME).
+ * We assume it works on all other UNIXes as well.
+ */
+gchar *
+teco_file_get_program_path(void)
+{
+	Dl_info info;
+	return dladdr(teco_file_get_program_path, &info)
+		? g_path_get_dirname(info.dli_fname) : g_get_current_dir();
+}
+
+#else /* !G_OS_WIN32 && !__linux__ && !G_OS_UNIX */
+
+/*
+ * This is almost guaranteed to be wrong,
+ * meaning that SciTECO cannot be made relocatable on these platforms.
+ * It may be worth evaluating argv[0] on these platforms.
+ */
+gchar *
+teco_file_get_program_path(void)
+{
+	return g_get_current_dir();
+}
+
+#endif
+
+/**
+ * Get the datadir.
+ *
+ * By default it is hardcoded to an absolute path at
+ * build time.
+ * However, you can also build relocateable binaries
+ * where the datadir is relative to the program's executable.
+ *
+ * @note Beginning with glib v2.58, we could directly use
+ * g_canonicalize_filename().
+ */
+gchar *
+teco_file_get_datadir(void)
+{
+	if (g_path_is_absolute(SCITECODATADIR))
+		return g_strdup(SCITECODATADIR);
+
+	/* relocateable binary - datadir is relative to binary */
+	g_autofree gchar *program_path = teco_file_get_program_path();
+	g_autofree gchar *datadir = g_build_filename(program_path, SCITECODATADIR, NULL);
+	return teco_file_get_absolute_path(datadir);
+}
+
 /**
  * Perform tilde expansion on a file name or path.
  *