The source fails to build

[archisman-panigrahi]

I downloaded the source, and tried meson builddir && cd builddir && meson compile

I got the following error

$ meson compile
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja
[19/36] Compiling C object src/pdf-metadata-editor.p/meson-generated_Document.c.o
FAILED: src/pdf-metadata-editor.p/meson-generated_Document.c.o 
cc -Isrc/pdf-metadata-editor.p -Isrc -I../src -I/usr/include/gtk-4.0 -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/cairo -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/freetype2 -I/usr/include/graphene-1.0 -I/usr/lib/graphene-1.0/include -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/fribidi -I/usr/include/sysprof-6 -I/usr/include/libpng16 -I/usr/include/pixman-1 -I/usr/include/libadwaita-1 -I/usr/include/appstream -I/usr/include/poppler/glib -I/usr/include/poppler -I/usr/include/exempi-2.0 -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -O0 -g -include config.h '-DGETTEXT_PACKAGE="pdf-metadata-editor"' -pthread -mfpmath=sse -msse -msse2 -mfpmath=sse -msse -msse2 -MD -MQ src/pdf-metadata-editor.p/meson-generated_Document.c.o -MF src/pdf-metadata-editor.p/meson-generated_Document.c.o.d -o src/pdf-metadata-editor.p/meson-generated_Document.c.o -c src/pdf-metadata-editor.p/Document.c
Document.c: In function ‘paper_clip_document_load_xmp’:
Document.c:765:40: warning: unused parameter ‘error’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_document_save_finish’:
Document.c:918:29: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
Document.c:915:53: warning: unused parameter ‘self’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_document_save_thread’:
Document.c:1188:21: warning: variable ‘_tmp10_’ set but not used [-Wunused-but-set-variable]
Document.c:1186:12: warning: unused variable ‘_inner_error1_’ [-Wunused-variable]
Document.c:1125:20: warning: variable ‘_tmp1_’ set but not used [-Wunused-but-set-variable]
Document.c: In function ‘___lambda4__g_object_notify’:
Document.c:1667:39: warning: unused parameter ‘_sender’ [-Wunused-parameter]
Document.c:1668:42: warning: unused parameter ‘pspec’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_document_deserialize_keywords’:
Document.c:1892:8: warning: unused variable ‘_keyword_collection_size_’ [-Wunused-variable]
Document.c:1835:7: warning: variable ‘_keyword_array_size_’ set but not used [-Wunused-but-set-variable]
Document.c: In function ‘paper_clip_document_load_document_finish’:
Document.c:2988:62: warning: unused parameter ‘self’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_document_create_copy_from_original_finish’:
Document.c:3144:74: warning: unused parameter ‘self’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib.h:64,
                 from /usr/include/glib-2.0/gobject/gbinding.h:30,
                 from /usr/include/glib-2.0/glib-object.h:24,
                 from src/pdf-metadata-editor.p/Document.c:24:
../src/Document.vala: In function ‘paper_clip_document_create_copy_from_original_co’:
/usr/include/glib-2.0/glib/gmessages.h:658:9: error: ‘return’ with no value, in function returning non-void [-Wreturn-mismatch]
  658 |         return; \
      |         ^~~~~~
../src/Document.vala:454:2: note: in expansion of macro ‘g_return_if_fail’
  454 |         return_if_fail (res > -1);
      |  ^      ~~~~~~~~~
Document.c:3185:1: note: declared here
Document.c: In function ‘paper_clip_document_class_init’:
Document.c:4030:42: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_document_instance_init’:
Document.c:4083:45: warning: unused parameter ‘klass’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34:
Document.c: In function ‘paper_clip_document_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
Document.c:4134:6: note: in expansion of macro ‘g_once_init_enter’
../src/Document.vala: In function ‘paper_clip_string_object_set_str’:
../src/Document.vala:472:12: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  472 |     public string str { get; set; default = ""; }
      |            ^
Document.c: In function ‘paper_clip_string_object_class_init’:
Document.c:4425:47: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_string_object_instance_init’:
Document.c:4444:50: warning: unused parameter ‘klass’ [-Wunused-parameter]
Document.c: In function ‘paper_clip_string_object_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
Document.c:4483:6: note: in expansion of macro ‘g_once_init_enter’
Document.c: In function ‘paper_clip_xmp_error_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
Document.c:4562:6: note: in expansion of macro ‘g_once_init_enter’
[21/36] Compiling C object src/pdf-metadata-editor.p/meson-generated_DateRow.c.o
DateRow.c: In function ‘_paper_clip_date_row_on_clear_button_clicked_gtk_button_clicked’:
DateRow.c:135:77: warning: unused parameter ‘_sender’ [-Wunused-parameter]
DateRow.c: In function ‘_paper_clip_date_row_on_day_selected_gtk_calendar_day_selected’:
DateRow.c:165:78: warning: unused parameter ‘_sender’ [-Wunused-parameter]
DateRow.c: In function ‘_paper_clip_date_row_on_today_button_clicked_gtk_button_clicked’:
DateRow.c:194:77: warning: unused parameter ‘_sender’ [-Wunused-parameter]
DateRow.c: In function ‘_paper_clip_date_row_on_tomorrow_button_clicked_gtk_button_clicked’:
DateRow.c:239:80: warning: unused parameter ‘_sender’ [-Wunused-parameter]
DateRow.c: In function ‘paper_clip_date_row_class_init’:
DateRow.c:388:42: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
DateRow.c: In function ‘paper_clip_date_row_instance_init’:
DateRow.c:419:45: warning: unused parameter ‘klass’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34,
                 from /usr/include/gtk-4.0/gtk/css/gtkcss.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:29,
                 from /usr/include/libadwaita-1/adwaita.h:9,
                 from src/pdf-metadata-editor.p/DateRow.c:24:
DateRow.c: In function ‘paper_clip_date_row_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
DateRow.c:455:6: note: in expansion of macro ‘g_once_init_enter’
[22/36] Compiling C object src/pdf-metadata-editor.p/meson-generated_DocumentView.c.o
DocumentView.c: In function ‘paper_clip_document_view_open_on_app_finish’:
DocumentView.c:486:38: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
DocumentView.c:483:69: warning: unused parameter ‘self’ [-Wunused-parameter]
DocumentView.c: In function ‘paper_clip_document_view_class_init’:
DocumentView.c:804:47: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
DocumentView.c: In function ‘paper_clip_document_view_instance_init’:
DocumentView.c:851:50: warning: unused parameter ‘klass’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34,
                 from /usr/include/gtk-4.0/gtk/css/gtkcss.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:29,
                 from /usr/include/libadwaita-1/adwaita.h:9,
                 from src/pdf-metadata-editor.p/DocumentView.c:24:
DocumentView.c: In function ‘paper_clip_document_view_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
DocumentView.c:906:6: note: in expansion of macro ‘g_once_init_enter’
[23/36] Compiling C object src/pdf-metadata-editor.p/meson-generated_window.c.o
window.c: In function ‘paper_clip_window_open_dropped_file_finish’:
window.c:830:38: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:827:62: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_load_dropped_file_finish’:
window.c:925:38: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:922:62: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_open_file_finish’:
window.c:1092:31: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:1089:54: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_load_document_to_view_finish’:
window.c:1326:41: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:1323:66: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_create_document_finish’:
window.c:1529:60: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_save_file_finish’:
window.c:1809:31: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:1806:54: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_save_file_as_finish’:
window.c:1994:33: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:1991:57: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_hide_progress_bar_animation_adw_animation_done’:
window.c:2231:82: warning: unused parameter ‘_sender’ [-Wunused-parameter]
../src/window.vala: In function ‘paper_clip_window_shortcuts’:
../src/window.vala:279:2: warning: ‘gtk_widget_show’ is deprecated: Use 'gtk_widget_set_visible or gtk_window_present' instead [-Wdeprecated-declarations]
  279 |             shortcuts_window.show ();
      |  ^          ~~~~
In file included from /usr/include/gtk-4.0/gtk/gtkapplication.h:26,
                 from /usr/include/gtk-4.0/gtk/gtkwindow.h:32,
                 from /usr/include/gtk-4.0/gtk/gtkaboutdialog.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:33,
                 from /usr/include/libadwaita-1/adwaita.h:9,
                 from src/pdf-metadata-editor.p/window.c:24:
/usr/include/gtk-4.0/gtk/gtkwidget.h:271:12: note: declared here
  271 | void       gtk_widget_show                (GtkWidget           *widget);
      |            ^~~~~~~~~~~~~~~
window.c: In function ‘_paper_clip_window_on_close_request_gtk_window_close_request’:
window.c:2460:74: warning: unused parameter ‘_sender’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_quit_and_save_finish’:
window.c:2510:34: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:2507:58: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_show_unsaved_warning_finish’:
window.c:2622:41: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
window.c:2619:65: warning: unused parameter ‘self’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_open_action_gsimple_action_activate_callback’:
window.c:2924:84: warning: unused parameter ‘action’ [-Wunused-parameter]
window.c:2925:79: warning: unused parameter ‘parameter’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_open_with_action_gsimple_action_activate_callback’:
window.c:2934:89: warning: unused parameter ‘action’ [-Wunused-parameter]
window.c:2935:84: warning: unused parameter ‘parameter’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_save_file_action_gsimple_action_activate_callback’:
window.c:2944:86: warning: unused parameter ‘action’ [-Wunused-parameter]
window.c:2945:81: warning: unused parameter ‘parameter’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_save_file_as_action_gsimple_action_activate_callback’:
window.c:2954:89: warning: unused parameter ‘action’ [-Wunused-parameter]
window.c:2955:84: warning: unused parameter ‘parameter’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_main_menu_action_gsimple_action_activate_callback’:
window.c:2964:89: warning: unused parameter ‘action’ [-Wunused-parameter]
window.c:2965:84: warning: unused parameter ‘parameter’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_file_dropped_gtk_drop_target_drop’:
window.c:2974:73: warning: unused parameter ‘_sender’ [-Wunused-parameter]
window.c:2976:66: warning: unused parameter ‘x’ [-Wunused-parameter]
window.c:2977:66: warning: unused parameter ‘y’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_enter_gtk_drop_target_enter’:
window.c:2988:67: warning: unused parameter ‘_sender’ [-Wunused-parameter]
window.c:2989:60: warning: unused parameter ‘x’ [-Wunused-parameter]
window.c:2990:60: warning: unused parameter ‘y’ [-Wunused-parameter]
window.c: In function ‘_paper_clip_window_on_leave_gtk_drop_target_leave’:
window.c:3001:67: warning: unused parameter ‘_sender’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_constructor’:
window.c:3025:7: warning: variable ‘_entries_size_’ set but not used [-Wunused-but-set-variable]
window.c: In function ‘paper_clip_window_class_init’:
window.c:3147:40: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
window.c: In function ‘paper_clip_window_instance_init’:
window.c:3186:43: warning: unused parameter ‘klass’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34,
                 from /usr/include/gtk-4.0/gtk/css/gtkcss.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:29:
window.c: In function ‘paper_clip_window_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
window.c:3235:6: note: in expansion of macro ‘g_once_init_enter’
window.c: In function ‘paper_clip_window_state_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
window.c:3314:6: note: in expansion of macro ‘g_once_init_enter’
window.c: At top level:
window.c:2892:1: warning: ‘paper_clip_window_get_dropped_file’ defined but not used [-Wunused-function]
window.c:2507:1: warning: ‘paper_clip_window_quit_and_save_finish’ defined but not used [-Wunused-function]
window.c:1991:1: warning: ‘paper_clip_window_save_file_as_finish’ defined but not used [-Wunused-function]
window.c:1089:1: warning: ‘paper_clip_window_open_file_finish’ defined but not used [-Wunused-function]
window.c:922:1: warning: ‘paper_clip_window_load_dropped_file_finish’ defined but not used [-Wunused-function]
window.c:827:1: warning: ‘paper_clip_window_open_dropped_file_finish’ defined but not used [-Wunused-function]
[24/36] Compiling C object src/pdf-metadata-editor.p/meson-generated_application.c.o
application.c: In function ‘paper_clip_application_real_open’:
application.c:441:8: warning: unused variable ‘_file_collection_size_’ [-Wunused-variable]
application.c: In function ‘paper_clip_application_on_query_quit_action_finish’:
application.c:692:50: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
application.c:689:75: warning: unused parameter ‘self’ [-Wunused-parameter]
application.c: In function ‘paper_clip_application_save_unsaved_managers_finish’:
application.c:1030:47: warning: variable ‘_data_’ set but not used [-Wunused-but-set-variable]
application.c:1027:76: warning: unused parameter ‘self’ [-Wunused-parameter]
../src/application.vala: In function ‘paper_clip_application_on_about_action’:
../src/application.vala:152:44: warning: passing argument 2 of ‘adw_about_dialog_set_developers’ from incompatible pointer type [-Wincompatible-pointer-types]
  152 |         var about = new Adw.AboutDialog () {
      |                                            ^     
      |                                            |
      |                                            gchar ** {aka char **}
In file included from /usr/include/libadwaita-1/adwaita.h:24,
                 from src/pdf-metadata-editor.p/application.c:24:
/usr/include/libadwaita-1/adw-about-dialog.h:115:71: note: expected ‘const char **’ but argument is of type ‘gchar **’ {aka ‘char **’}
  115 |                                                      const char     **developers);
      |                                                      ~~~~~~~~~~~~~~~~~^~~~~~~~~~
../src/application.vala:152:41: warning: passing argument 2 of ‘adw_about_dialog_set_artists’ from incompatible pointer type [-Wincompatible-pointer-types]
  152 |         var about = new Adw.AboutDialog () {
      |                                         ^~~~   
      |                                         |
      |                                         gchar ** {aka char **}
/usr/include/libadwaita-1/adw-about-dialog.h:127:68: note: expected ‘const char **’ but argument is of type ‘gchar **’ {aka ‘char **’}
  127 |                                                   const char     **artists);
      |                                                   ~~~~~~~~~~~~~~~~~^~~~~~~
application.c:1224:7: warning: variable ‘_artists_size_’ set but not used [-Wunused-but-set-variable]
application.c:1219:7: warning: variable ‘_developers_size_’ set but not used [-Wunused-but-set-variable]
application.c: In function ‘_paper_clip_application_on_about_action_gsimple_action_activate_callback’:
application.c:1497:90: warning: unused parameter ‘action’ [-Wunused-parameter]
application.c:1498:85: warning: unused parameter ‘parameter’ [-Wunused-parameter]
application.c: In function ‘_paper_clip_application_shortcuts_action_gsimple_action_activate_callback’:
application.c:1507:91: warning: unused parameter ‘action’ [-Wunused-parameter]
application.c:1508:86: warning: unused parameter ‘parameter’ [-Wunused-parameter]
application.c: In function ‘_paper_clip_application_on_query_quit_action_gsimple_action_activate_callback’:
application.c:1517:95: warning: unused parameter ‘action’ [-Wunused-parameter]
application.c:1518:90: warning: unused parameter ‘parameter’ [-Wunused-parameter]
application.c: In function ‘_paper_clip_application_on_new_window_action_gsimple_action_activate_callback’:
application.c:1527:95: warning: unused parameter ‘action’ [-Wunused-parameter]
application.c:1528:90: warning: unused parameter ‘parameter’ [-Wunused-parameter]
../src/application.vala: In function ‘paper_clip_application_constructor’:
../src/application.vala:41:82: warning: passing argument 3 of ‘gtk_application_set_accels_for_action’ from incompatible pointer type [-Wincompatible-pointer-types]
   41 |         set_accels_for_action ("app.shortcuts", { "<Ctrl>question" });
      |                                                                                  ^     
      |                                                                                  |
      |                                                                                  gchar ** {aka char **}
In file included from /usr/include/gtk-4.0/gtk/gtkwindow.h:32,
                 from /usr/include/gtk-4.0/gtk/gtkaboutdialog.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:33,
                 from /usr/include/libadwaita-1/adwaita.h:9:
/usr/include/gtk-4.0/gtk/gtkapplication.h:131:88: note: expected ‘const char * const*’ but argument is of type ‘gchar **’ {aka ‘char **’}
  131 |                                                                   const char * const  *accels);
      |                                                                   ~~~~~~~~~~~~~~~~~~~~~^~~~~~
../src/application.vala:42:83: warning: passing argument 3 of ‘gtk_application_set_accels_for_action’ from incompatible pointer type [-Wincompatible-pointer-types]
   42 |         set_accels_for_action ("app.query-quit", { "<Ctrl>q" });
      |                                                                                   ^      
      |                                                                                   |
      |                                                                                   gchar ** {aka char **}
/usr/include/gtk-4.0/gtk/gtkapplication.h:131:88: note: expected ‘const char * const*’ but argument is of type ‘gchar **’ {aka ‘char **’}
  131 |                                                                   const char * const  *accels);
      |                                                                   ~~~~~~~~~~~~~~~~~~~~~^~~~~~
../src/application.vala:43:83: warning: passing argument 3 of ‘gtk_application_set_accels_for_action’ from incompatible pointer type [-Wincompatible-pointer-types]
   43 |         set_accels_for_action ("app.new-window", { "<Ctrl>n" });
      |                                                                                   ^      
      |                                                                                   |
      |                                                                                   gchar ** {aka char **}
/usr/include/gtk-4.0/gtk/gtkapplication.h:131:88: note: expected ‘const char * const*’ but argument is of type ‘gchar **’ {aka ‘char **’}
  131 |                                                                   const char * const  *accels);
      |                                                                   ~~~~~~~~~~~~~~~~~~~~~^~~~~~
application.c:1551:7: warning: variable ‘_action_entries_size_’ set but not used [-Wunused-but-set-variable]
application.c: In function ‘paper_clip_application_class_init’:
application.c:1669:45: warning: unused parameter ‘klass_data’ [-Wunused-parameter]
application.c: In function ‘paper_clip_application_instance_init’:
application.c:1692:48: warning: unused parameter ‘klass’ [-Wunused-parameter]
In file included from /usr/include/glib-2.0/glib/gthread.h:34,
                 from /usr/include/glib-2.0/glib/gasyncqueue.h:34,
                 from /usr/include/glib-2.0/glib.h:34,
                 from /usr/include/gtk-4.0/gtk/css/gtkcss.h:29,
                 from /usr/include/gtk-4.0/gtk/gtk.h:29:
application.c: In function ‘paper_clip_application_get_type’:
/usr/include/glib-2.0/glib/gatomic.h:131:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wdiscarded-qualifiers]
  131 |     __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
      |     ^~~~~~~~~~~~~
/usr/include/glib-2.0/glib/gthread.h:272:7: note: in expansion of macro ‘g_atomic_pointer_get’
  272 |     (!g_atomic_pointer_get (location) &&                             \
      |       ^~~~~~~~~~~~~~~~~~~~
application.c:1728:6: note: in expansion of macro ‘g_once_init_enter’
application.c: At top level:
application.c:689:1: warning: ‘paper_clip_application_on_query_quit_action_finish’ defined but not used [-Wunused-function]
src/pdf-metadata-editor.p/application.c:71:20: warning: ‘paper_clip_application_properties’ defined but not used [-Wunused-variable]
   71 | static GParamSpec* paper_clip_application_properties[PAPER_CLIP_APPLICATION_NUM_PROPERTIES];
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ninja: build stopped: subcommand failed.

[Diego-Ivan]

This should be fixed as of commit https://github.com/Diego-Ivan/Paper-Clip/commit/82193146a80bfe613355706421454f879bdd496f. Make sure your local repository is up to date with upstream.