% scons -Q --debug=stacktrace scons: *** [prog.o] Source `prog.c' not found, needed by target `prog.o'. scons: internal stack trace: File "bootstrap/src/engine/SCons/Job.py", line 199, in start task.prepare() File "bootstrap/src/engine/SCons/Script/Main.py", line 190, in prepare return SCons.Taskmaster.OutOfDateTask.prepare(self) File "bootstrap/src/engine/SCons/Taskmaster.py", line 198, in prepare executor.prepare() File "bootstrap/src/engine/SCons/Executor.py", line 431, in prepare raise SCons.Errors.StopError(msg % (s, self.batches[0].targets[0]))