build: remove IMHEX_PLUGINS_IN_SHARE option + only allow AppImage to load plugins from inside itself

Rationale: The `IMHEX_PLUGINS_IN_SHARE` is a hack to prevent the appimage from loading plugin from system imhex installation, like /usr/lib/imhex/

In reality, I do not think people compile plugins specifically for the AppImage (plugins must be compiled for the specific imhex & compiler version the imhex binary is used), and this lets us remove the hack

CMakeLists.txt

@@ -29,7 +29,6 @@ option(IMHEX_REPLACE_DWARF_WITH_PDB     "Remove DWARF information from binaries
 option(IMHEX_STRICT_WARNINGS            "Enable most available warnings and treat them as errors"                               ON )
 option(IMHEX_DISABLE_STACKTRACE         "Disables support for printing stack traces"                                            OFF)
 ## Plugins
-option(IMHEX_PLUGINS_IN_SHARE           "Put the plugins in share/imhex/plugins instead of lib[..]/imhex/plugins (Linux only)"  OFF)
 option(IMHEX_STATIC_LINK_PLUGINS        "Statically link all plugins into the main executable"                                  OFF)
 option(IMHEX_ENABLE_PLUGIN_TESTS        "Enable building plugin tests"                                                          ON )
 option(IMHEX_INCLUDE_PLUGINS            "Semicolon-separated list of plugins to include in the build (empty = build all)"       "" )

cmake/build_helpers.cmake

@@ -175,15 +175,11 @@ macro(detectOS)
         endif()
         include(GNUInstallDirs)
 
-        if(IMHEX_PLUGINS_IN_SHARE)
-            set(PLUGINS_INSTALL_LOCATION "share/imhex/plugins")
-        else()
         set(PLUGINS_INSTALL_LOCATION "${CMAKE_INSTALL_LIBDIR}/imhex/plugins")
 
         # Add System plugin location for plugins to be loaded from
         # IMPORTANT: This does not work for Sandboxed or portable builds such as the Flatpak or AppImage release
         add_compile_definitions(SYSTEM_PLUGINS_LOCATION="${CMAKE_INSTALL_FULL_LIBDIR}/imhex")
-        endif()
 
     else ()
         message(FATAL_ERROR "Unknown / unsupported system!")

dist/AppImage/Dockerfile

@@ -51,8 +51,9 @@ CC=gcc-14 CXX=g++-14 cmake -G "Ninja"                  \
     -DIMHEX_COMMIT_HASH_LONG="${GIT_COMMIT_HASH}"                    \
     -DIMHEX_COMMIT_BRANCH="${GIT_BRANCH}"                            \
     -DIMHEX_ENABLE_LTO=${LTO}                                        \
-    -DIMHEX_PLUGINS_IN_SHARE=ON                        \
     -DIMHEX_BUNDLE_PLUGIN_SDK=OFF                                    \
+    `# To prevent using a libdir with an architecture-specific name` \
+    -DCMAKE_INSTALL_LIBDIR="lib"                                     \
     /imhex
 EOF
 

lib/libimhex/source/helpers/default_paths.cpp

@@ -97,6 +97,13 @@ namespace hex::paths {
     }
 
     static std::vector<std::fs::path> getPluginPaths() {
+        // If running from an AppImage, only allow loaded plugins from inside it
+        #if defined(OS_LINUX)
+        if(const char* appdir = std::getenv("APPDIR")) { // check for AppImage environment
+            return {std::string(appdir) + "/usr/lib/imhex"};
+        }
+        #endif
+
         std::vector<std::fs::path> paths = getDataPaths(true);
 
         // Add the system plugin directory to the path if one was provided at compile time