waf cross-project dependencies - waf

Question

I have a trivial waf project:
$ root
|-- a
| `-- wscript
|-- b
| `-- wscript
`-- wscript
Root wscript is
def configure(conf):
pass
def build(bld):
bld.recurse('a b')
a wscript is
def build(bld):
bld (rule = 'touch ${TGT}', target = 'a.target' )
b wscript is
def build(bld):
bld (rule = 'cp ${SRC} ${TGT}', source='a.target', target='b.target')
What I'm trying to achieve is have a build system that first touches a.target, then copies it to b.target. I want to have rules for a.target and b.target to stay in their respective wscript files.
When I'm trying to launch it, I get the following error instead:
source not found: 'a.target' in bld(target=['b.target'], idx=1, tg_idx_count=2, meths=['process_rule', 'process_source'], rule='cp ${SRC} ${TGT}', _name='b.target', source='a.target', path=/<skip>/waf_playground/b, posted=True, features=[]) in /<skip>/waf_playground/b
If I put both rules into a single wscript file, everything works like a charm.
Is there a way for a target to depend on a another target defined in other wscript?

Answer 1

When you specify source/target, that is expressed relative to the current wscript file.
$ waf configure build
...
source not found: 'a.target' in bld(source='a.target, ...)
...
$ tree build
build/
├── a
│ └── a.target
...
Knowing that, the fix is to refer to the a.target source file correctly in b/wscript:
def build(bld):
bld (rule = 'cp ${SRC} ${TGT}', source='../a/a.target', target='b.target')
The task now correctly finds the source file:
$ waf build
Waf: Entering directory `.../build'
[1/2] Creating build/a/a.target
[2/2] Compiling build/a/a.target
Waf: Leaving directory `.../build'
'build' finished successfully (0.055s)
$ tree build
build/
├── a
│   └── a.target
├── b
│   └── b.target
...