Issue #12640: run in-build GIMP binary through a debugger when gdb is available.

It is not in fact a fix for #12640, only an improvement to our build
script, wrapping our calls to GIMP executables and outputting a
backtrace on a crash. This way, when people report issues during one of
the relevant calls, we may be able to diagnose.

It won't be useful for other types of failures (when the process doesn't
crash, but e.g. the script is wrong or other non-fatal bugs in GIMP).

meson.build

@@ -1951,7 +1951,8 @@ subdir('app-tools')
 # tool.
 
 gimp_run_env=environment()
-gimp_run_env.set('GIMP_GLOBAL_BUILD_ROOT', meson.global_build_root())
+gimp_run_env.set('GIMP_GLOBAL_BUILD_ROOT',  meson.global_build_root())
+gimp_run_env.set('GIMP_GLOBAL_SOURCE_ROOT', meson.global_source_root())
 
 if meson.can_run_host_binaries() and have_gobject_introspection
   if enable_console_bin

tools/debug-in-build-gimp.py

@@ -0,0 +1,8 @@
+def my_signal_handler (event):
+  if (isinstance(event, gdb.SignalEvent)):
+    gdb.write("Eeeeeeeeeeeek: in-build GIMP crashed!\n")
+    gdb.execute('info threads')
+    gdb.execute("thread apply all backtrace full")
+
+gdb.events.stop.connect(my_signal_handler)
+gdb.execute("run")

tools/in-build-gimp.sh

@@ -24,7 +24,13 @@ if [ -n "$GIMP_TEMP_UPDATE_RPATH" ]; then
   unset IFS
 fi
 
-cat /dev/stdin | $GIMP_SELF_IN_BUILD "$@"
+if command -v gdb; then
+  echo RUNNING: cat /dev/stdin "|" gdb --batch -x "$GIMP_GLOBAL_SOURCE_ROOT/tools/debug-in-build-gimp.py" --args $GIMP_SELF_IN_BUILD "$@"
+  cat /dev/stdin | gdb --return-child-result --batch -x "$GIMP_GLOBAL_SOURCE_ROOT/tools/debug-in-build-gimp.py" --args $GIMP_SELF_IN_BUILD "$@"
+else
+  echo RUNNING: cat /dev/stdin "|" $GIMP_SELF_IN_BUILD "$@"
+  cat /dev/stdin | $GIMP_SELF_IN_BUILD "$@"
+fi
 
 if [ -n "$GIMP_TEMP_UPDATE_RPATH" ]; then
   export IFS=":"