$ >output/source.txt                                                                                                                                                                                                          
 
$ ~/scons/bin/scons --dry-run --debug=duplicate --taskmastertrace=trace.txt -f SConstruct.error                                                                                                                              
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
dup: no src for output/source.txt, unlinking old variant copy
scons: building associated VariantDir targets: output
scons: *** [output/target.txt] Source `output/source.txt' not found, needed by target `output/target.txt'.
scons: building terminated because of errors.
 
$ more trace.txt
 
Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <no_state   0   'output'> and its children:
Taskmaster:        <no_state   0   'output/source.txt'>
Taskmaster:        <no_state   0   'output/target.txt'>
Taskmaster:      adjusted ref count: <pending    1   'output'>, child 'output/source.txt'
Taskmaster:      adjusted ref count: <pending    2   'output'>, child 'output/target.txt'
Taskmaster:     Considering node <no_state   0   'output/source.txt'> and its children:
Taskmaster: Evaluating <pending    0   'output/source.txt'>
 
Task.make_ready_current(): node <pending    0   'output/source.txt'>
Task.prepare():      node <up_to_date 0   'output/source.txt'>
Task.executed_with_callbacks(): node <up_to_date 0   'output/source.txt'>
Task.postprocess():  node <up_to_date 0   'output/source.txt'>
Task.postprocess():  removing <up_to_date 0   'output/source.txt'>
Task.postprocess():  adjusted parent ref count <pending    1   'output'>
 
Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <no_state   0   'output/target.txt'> and its children:
Taskmaster:        <up_to_date 0   'output/source.txt'>
Taskmaster:        <no_state   0   '/bin/cp'>
Taskmaster:      adjusted ref count: <pending    1   'output/target.txt'>, child '/bin/cp'
Taskmaster:     Considering node <no_state   0   '/bin/cp'> and its children:
Taskmaster: Evaluating <pending    0   '/bin/cp'>
 
Task.make_ready_current(): node <pending    0   '/bin/cp'>
Task.prepare():      node <up_to_date 0   '/bin/cp'>
Task.executed_with_callbacks(): node <up_to_date 0   '/bin/cp'>
Task.postprocess():  node <up_to_date 0   '/bin/cp'>
Task.postprocess():  removing <up_to_date 0   '/bin/cp'>
Task.postprocess():  adjusted parent ref count <pending    0   'output/target.txt'>
 
Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <pending    0   'output/target.txt'> and its children:
Taskmaster:        <up_to_date 0   'output/source.txt'>
Taskmaster:        <up_to_date 0   '/bin/cp'>
Taskmaster: Evaluating <pending    0   'output/target.txt'>
 
Task.make_ready_current(): node <pending    0   'output/target.txt'>
Task.prepare():      node <executing  0   'output/target.txt'>
Task.failed_stop():  node <executing  0   'output/target.txt'>
Taskmaster:        removing node <executing  0   'output/target.txt'> from the pending children set
 
Taskmaster:        removing parent <pending    0   'output'> from the pending children set
 
Task.postprocess():  node <failed     0   'output/target.txt'>
 
Taskmaster: Looking for a node to evaluate
Taskmaster:        removing node <no_state   0   '.'> from the pending children set
 
Taskmaster: No candidate anymore.