explicit dependency not being picked correctly with scons - build

Question

I have a scons build environment set up something like :
--SConstruct [Top level file]
--dir1
--Sconscript
--src
--inc
--dir2
--Sconscript
--src
--inc
[dir1]
building dir1 results in several .so being generated, lets say libdir1_a.so, libdir1_b.so, libdir1_c.so etc.
all these shared libs ar eplaced in some folder - $install/dir1/lib/
[dir2]
when building src for dir2, it needs one library to be linked from dir1, libdir1_b.so
I use
env.Depends(dir2_target, $install/dir1/lib/libdir1_b.so)
to specify the dependency.
However, when building source sin dir2 it fails saying explicit dependency not found.
What do i need to do to make sure dir1 builds before dir ?

Answer 1

The solution for your use case is to not use explicit dependencies. The Depends function is not needed here. SCons is smart enough to figure out these types of dependencies.
Here is a working example, because that always makes an explanation better!
>> scons --version
SCons by Steven Knight et al.:
script: v2.3.6.rel_2.3.5:3347:d31d5a4e74b6[MODIFIED], 2015/07/31 14:36:10, by bdbaddog on hpmicrodog
engine: v2.3.6.rel_2.3.5:3347:d31d5a4e74b6[MODIFIED], 2015/07/31 14:36:10, by bdbaddog on hpmicrodog
engine path: ['/usr/lib/scons/SCons']
Copyright (c) 2001 - 2015 The SCons Foundation
>> tree
.
├── dir1
│   ├── include
│   │   ├── dir1_a.h
│   │   ├── dir1_b.h
│   │   └── dir1_c.h
│   ├── SConscript
│   └── src
│   ├── dir1_a.cpp
│   ├── dir1_b.cpp
│   └── dir1_c.cpp
├── dir2
│   ├── include
│   │   └── dir2_a.h
│   ├── SConscript
│   └── src
│   └── dir2_a.cpp
└── SConstruct
6 directories, 11 files
>> find . -type f | xargs awk 'FNR==1{print FILENAME; }{ print }'
./dir2/src/dir2_a.cpp
#include <dir2_a.h>
#include <dir1_a.h>
#include <iostream>
void dir2_a::myhello() {dir1_a::hello();}
./dir2/include/dir2_a.h
#include <iostream>
namespace dir2_a { void myhello();}
./dir2/SConscript
Import('env')
local_env = env.Clone()
local_env.Append(CPPPATH=['include', '#include'],
LIBPATH=['#lib'],
LIBS=['dir1_a'],
RPATH=['$$$$\\{ORIGIN}/.'])
liba = local_env.SharedLibrary('src/dir2_a.cpp')
Install('#lib', [liba])
Install('#include', Glob('include/*.h'))
./SConstruct
env = Environment()
Export('env')
SConscript('dir1/SConscript')
SConscript('dir2/SConscript')
./dir1/src/dir1_a.cpp
#include <dir1_a.h>
#include <iostream>
void dir1_a::hello() {std::cout << "A" << std::endl;}
./dir1/src/dir1_b.cpp
#include <dir1_b.h>
#include <iostream>
void dir1_b::hello() {std::cout << "B" << std::endl;}
./dir1/src/dir1_c.cpp
#include <dir1_c.h>
#include <iostream>
void dir1_c::hello() {std::cout << "C" << std::endl;}
./dir1/include/dir1_c.h
#include <iostream>
namespace dir1_c { void hello();}
./dir1/include/dir1_b.h
#include <iostream>
namespace dir1_b { void hello();}
./dir1/include/dir1_a.h
#include <iostream>
namespace dir1_a { void hello();}
./dir1/SConscript
Import('env')
local_env = env.Clone()
local_env.Append(CPPPATH='include')
liba = local_env.SharedLibrary('src/dir1_a.cpp')
libb = local_env.SharedLibrary('src/dir1_b.cpp')
libc = local_env.SharedLibrary('src/dir1_c.cpp')
Install('#lib', [liba, libb, libc])
Install('#include', Glob('include/*.h'))
>> scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
g++ -o dir1/src/dir1_a.os -c -fPIC -Idir1/include dir1/src/dir1_a.cpp
g++ -o dir1/src/dir1_b.os -c -fPIC -Idir1/include dir1/src/dir1_b.cpp
g++ -o dir1/src/dir1_c.os -c -fPIC -Idir1/include dir1/src/dir1_c.cpp
g++ -o dir1/src/libdir1_a.so -shared dir1/src/dir1_a.os
g++ -o dir1/src/libdir1_b.so -shared dir1/src/dir1_b.os
g++ -o dir1/src/libdir1_c.so -shared dir1/src/dir1_c.os
Install file: "dir1/include/dir1_a.h" as "include/dir1_a.h"
g++ -o dir2/src/dir2_a.os -c -fPIC -Idir2/include -Iinclude dir2/src/dir2_a.cpp
Install file: "dir1/src/libdir1_a.so" as "lib/libdir1_a.so"
g++ -o dir2/src/libdir2_a.so -shared -Wl,-rpath=$\{ORIGIN}/. dir2/src/dir2_a.os -Llib -ldir1_a
Install file: "dir1/include/dir1_b.h" as "include/dir1_b.h"
Install file: "dir1/include/dir1_c.h" as "include/dir1_c.h"
Install file: "dir2/include/dir2_a.h" as "include/dir2_a.h"
Install file: "dir1/src/libdir1_b.so" as "lib/libdir1_b.so"
Install file: "dir1/src/libdir1_c.so" as "lib/libdir1_c.so"
Install file: "dir2/src/libdir2_a.so" as "lib/libdir2_a.so"
scons: done building targets.
>> tree
.
├── dir1
│   ├── include
│   │   ├── dir1_a.h
│   │   ├── dir1_b.h
│   │   └── dir1_c.h
│   ├── SConscript
│   └── src
│   ├── dir1_a.cpp
│   ├── dir1_a.os
│   ├── dir1_b.cpp
│   ├── dir1_b.os
│   ├── dir1_c.cpp
│   ├── dir1_c.os
│   ├── libdir1_a.so
│   ├── libdir1_b.so
│   └── libdir1_c.so
├── dir2
│   ├── include
│   │   └── dir2_a.h
│   ├── SConscript
│   └── src
│   ├── dir2_a.cpp
│   ├── dir2_a.os
│   └── libdir2_a.so
├── include
│   ├── dir1_a.h
│   ├── dir1_b.h
│   ├── dir1_c.h
│   └── dir2_a.h
├── lib
│   ├── libdir1_a.so
│   ├── libdir1_b.so
│   ├── libdir1_c.so
│   └── libdir2_a.so
└── SConstruct
8 directories, 27 files
>> ldd lib/libdir2_a.so
linux-vdso.so.1 (0x00007ffdb53a5000)
libdir1_a.so => ./libdir1_a.so (0x00007f0707bd7000)
libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f070782f000)
libm.so.6 => /lib64/libm.so.6 (0x00007f070752d000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f0707316000)
libc.so.6 => /lib64/libc.so.6 (0x00007f0706f54000)
/lib64/ld-linux-x86-64.so.2 (0x000055bd342e4000)
If you want to see that the dependency tree is really being automatically setup, just execute the following...
>> scons --tree=prune
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
g++ -o dir1/src/dir1_a.os -c -fPIC -Idir1/include dir1/src/dir1_a.cpp
g++ -o dir1/src/dir1_b.os -c -fPIC -Idir1/include dir1/src/dir1_b.cpp
g++ -o dir1/src/dir1_c.os -c -fPIC -Idir1/include dir1/src/dir1_c.cpp
g++ -o dir1/src/libdir1_a.so -shared dir1/src/dir1_a.os
g++ -o dir1/src/libdir1_b.so -shared dir1/src/dir1_b.os
g++ -o dir1/src/libdir1_c.so -shared dir1/src/dir1_c.os
Install file: "dir1/include/dir1_a.h" as "include/dir1_a.h"
g++ -o dir2/src/dir2_a.os -c -fPIC -Idir2/include -Iinclude dir2/src/dir2_a.cpp
Install file: "dir1/src/libdir1_a.so" as "lib/libdir1_a.so"
g++ -o dir2/src/libdir2_a.so -shared -Wl,-rpath=$\{ORIGIN}/. dir2/src/dir2_a.os -Llib -ldir1_a
Install file: "dir1/include/dir1_b.h" as "include/dir1_b.h"
Install file: "dir1/include/dir1_c.h" as "include/dir1_c.h"
Install file: "dir2/include/dir2_a.h" as "include/dir2_a.h"
Install file: "dir1/src/libdir1_b.so" as "lib/libdir1_b.so"
Install file: "dir1/src/libdir1_c.so" as "lib/libdir1_c.so"
Install file: "dir2/src/libdir2_a.so" as "lib/libdir2_a.so"
+-.
+-SConstruct
+-dir1
| +-dir1/SConscript
| +-dir1/include
| | +-dir1/include/dir1_a.h
| | +-dir1/include/dir1_b.h
| | +-dir1/include/dir1_c.h
| +-dir1/src
| +-dir1/src/dir1_a.cpp
| +-dir1/src/dir1_a.os
| | +-dir1/src/dir1_a.cpp
| | +-dir1/include/dir1_a.h
| | +-/bin/g++
| +-dir1/src/dir1_b.cpp
| +-dir1/src/dir1_b.os
| | +-dir1/src/dir1_b.cpp
| | +-dir1/include/dir1_b.h
| | +-/bin/g++
| +-dir1/src/dir1_c.cpp
| +-dir1/src/dir1_c.os
| | +-dir1/src/dir1_c.cpp
| | +-dir1/include/dir1_c.h
| | +-/bin/g++
| +-dir1/src/libdir1_a.so
| | +-[dir1/src/dir1_a.os]
| +-dir1/src/libdir1_b.so
| | +-[dir1/src/dir1_b.os]
| +-dir1/src/libdir1_c.so
| +-[dir1/src/dir1_c.os]
+-dir2
| +-dir2/SConscript
| +-dir2/include
| | +-dir2/include/dir2_a.h
| +-dir2/src
| +-dir2/src/dir2_a.cpp
| +-dir2/src/dir2_a.os
| | +-dir2/src/dir2_a.cpp
| | +-include/dir1_a.h
| | | +-dir1/include/dir1_a.h
| | +-dir2/include/dir2_a.h
| | +-/bin/g++
| +-dir2/src/libdir2_a.so
| +-[dir2/src/dir2_a.os]
| +-lib/libdir1_a.so
| +-[dir1/src/libdir1_a.so]
+-include
| +-[include/dir1_a.h]
| +-include/dir1_b.h
| | +-dir1/include/dir1_b.h
| +-include/dir1_c.h
| | +-dir1/include/dir1_c.h
| +-include/dir2_a.h
| +-dir2/include/dir2_a.h
+-lib
+-[lib/libdir1_a.so]
+-lib/libdir1_b.so
| +-[dir1/src/libdir1_b.so]
+-lib/libdir1_c.so
| +-[dir1/src/libdir1_c.so]
+-lib/libdir2_a.so
+-[dir2/src/libdir2_a.so]
scons: done building targets.