bootloader: splash: use absolute library paths in onedir mode

In onedir mode, the Tcl and Tk shared library need to be loaded
using an absolute path instead of relative one (i.e., just library
basename). While the latter seems to work on Windows, it does not
work on Linux, where we end up trying to load the library from
system-wide library directories (and fail if system has no Tcl/Tk
installed).

bootloader/src/pyi_splash.c

@@ -334,20 +334,28 @@ pyi_splash_extract(ARCHIVE_STATUS *archive_status, SPLASH_STATUS *splash_status)
         }
     }
 
+    /* Alter the paths inside SPLASH_STATUS to load the the libraries from the
+     * correct place */
     if (extracted) {
-        /* Alter the paths inside SPLASH_STATUS to load the the libraries from the
-         * correct place */
+        /* Onefile mode; the libraries were extracted into a sub-directory of
+         * temppath */
         pyi_path_join(run_dir, archive_status->temppath, splash_status->rundir);
+    } else {
+        /* Onedir mode; we also need to adjust the paths to shared libraries so that
+         * the absolute paths are used. On Windows, we could seemingly get away with
+         * using just library base name, but not so on Linux, where we would end up
+         * trying to load system-wide library instead of the bundled one. */
+        strncpy(run_dir, archive_status->homepath, PATH_MAX);
+    }
 
-        strncpy(tmp, splash_status->tcl_libpath, PATH_MAX);
-        pyi_path_join(splash_status->tcl_libpath, run_dir, tmp);
+    strncpy(tmp, splash_status->tcl_libpath, PATH_MAX);
+    pyi_path_join(splash_status->tcl_libpath, run_dir, tmp);
 
-        strncpy(tmp, splash_status->tk_libpath, PATH_MAX);
-        pyi_path_join(splash_status->tk_libpath, run_dir, tmp);
+    strncpy(tmp, splash_status->tk_libpath, PATH_MAX);
+    pyi_path_join(splash_status->tk_libpath, run_dir, tmp);
 
-        pyi_path_basename(tmp, splash_status->tk_lib);
-        pyi_path_join(splash_status->tk_lib, run_dir, tmp);
-    }
+    pyi_path_basename(tmp, splash_status->tk_lib);
+    pyi_path_join(splash_status->tk_lib, run_dir, tmp);
 
 cleanup:
     free(tmp_toc);

news/6664.bugfix.rst

@@ -0,0 +1,3 @@
+(Linux) Fix the splash screen in onedir build loading system-installed
+Tcl/Tk  shared libraries instead of bundled ones (and failing if the
+system has no Tcl/Tk installed).