MODULES: lib1, lib2, lib3, main

STEP 0:
    libs: lib1, lib2, lib3, main
    dirty js modules: lib1, lib2, lib3, main
    dirty js files:   lib1/l11, lib1/l12, lib2/l21, lib3/l3, main/m, main/m.export
STEP 1:
    libs: lib1, lib2, lib3, main
    dirty js modules: lib1, lib2, lib3, main
    dirty js files:   lib2/l21, lib2/l22, lib3/l3, main/m
STEP 2:
    libs: lib1, lib2, lib3, main
    dirty js modules: lib1, lib2, lib3, main
    dirty js files:   lib1/l12_n, lib2/l21, lib3/l3, main/m