evas_filter_parser: add a workaround for in-tree runs

Without this, the prefix would get pointed to something like
/path/to/efl/build/share/evas, which is not a valid path when
building. That would cause the docs build to fail.

doc/meson.build

@@ -114,7 +114,11 @@ foreach text_filter_property : text_filter_properties
   filter_code = run_command('cat', join_paths(meson.source_root(), 'src', 'examples', 'evas', 'filters', 'filter_'+name+'.lua'))
 
   doc_target += custom_target('preview_text_filters_'+name,
-                  command: [env, 'EFL_RUN_IN_TREE=1', preview_text_filter.full_path(), text, filter_code.stdout(), '@OUTPUT@', font, size],
+                  command: [
+                    env, 'EFL_RUN_IN_TREE=1',
+                    'EFL_EVAS_FILTER_LUA_PREFIX=' + join_paths(meson.source_root(), 'src', 'lib', 'evas'),
+                    preview_text_filter.full_path(), text, filter_code.stdout(), '@OUTPUT@', font, size
+                  ],
                   depends: preview_text_filter,
                   output:  'filter_'+name+'.png',
                   build_by_default: false

src/lib/evas/filters/evas_filter_parser.c

@@ -2262,7 +2262,13 @@ static char *_lua_color_code = NULL;
 static inline void
 _lua_import_path_get(char *path, size_t len, const char *name)
 {
-   const char *pfx = _evas_module_datadir_get();
+   const char *pfx = NULL;
+   /* a hack for in-tree runs, can point this to src/lib/evas */
+   if (getenv("EFL_RUN_IN_TREE"))
+     pfx = getenv("EFL_EVAS_FILTER_LUA_PREFIX");
+   /* the real path not for in-tree runs */
+   if (!pfx)
+     pfx = _evas_module_datadir_get();
    size_t r = 0;
 
 #ifdef FILTERS_DEBUG