SConstruct won't find implicit dependencies on files which don't yet exist

compiler.in

#!/bin/bash
echo "hello world!"

foo.in

dummy text

SConstruct

env = Environment()

# preprocess compiler.in to compiler
compiler = env.Command('compiler', 'compiler.in', 'cp $SOURCE $TARGET')
env['compiler'] = File(compiler)[0].abspath

# and then use that to compile foo.in
target = env.Command('foo', 'foo.in', '$compiler < $SOURCE > $TARGET')
Default(target)

transcript

$ scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
scons: done cleaning targets.
$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
/home/abigail/scons/compiler < foo.in > foo
sh: 1: /home/abigail/scons/compiler: not found
scons: *** [foo] Error 127
scons: building terminated because of errors.
$ scons compiler
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cp compiler.in compiler
scons: done building targets.
$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
/home/abigail/scons/compiler < foo.in > foo
scons: done building targets.
$ echo 'echo "more stuff"' >> compiler.in
$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cp compiler.in compiler
/home/abigail/scons/compiler < foo.in > foo
scons: done building targets.