#!/usr/bin/python
#
# Given a file, compute its list of unused ELF dependencies.  Unlike
# ldd -r -u, take the complete load stack into account.
#
# For example.  evolution is linked against (among many other things)
# libnspr4.so and libdl.so.2.  ldd -r -u correctly notes that libdl is
# an unused direct dependency, since evo does not call into libdl itself.
# However, libnspr4.so _does_ call into libdl, so libdl isn't unused, 
# just not directly used.
#
# In implementation news: who needs data structures when you can memoize.

import os
import sys

# ldd's output is transitively complete, which is pleasant.  by this i mean,
# it doesn't just print out the DT_NEEDED from the binary, but recurses down
# those to find everything else downstream of it.

_depstable = {}

def deps(name):
    ret = []
    if name in _depstable.keys():
	return _depstable[name]
    file = os.popen("/usr/bin/ldd %s" % name)
    for line in file:
	line = line.partition("=>")[2].partition("(")[0].strip()
	if line:
	    ret.append(line)
    _depstable[name] = ret
    return ret

_uddtable = {}

# ldd -r -u, however, is not recursive.
def unused_direct_deps(name):
    ret = []
    if name in _uddtable.keys():
	return _uddtable[name]
    file = os.popen("/usr/bin/ldd -r -u %s 2>/dev/null" % name)
    for line in file:
	line = line.strip()
	if not line.startswith("/"):
	    continue
	ret.append(line)
    _uddtable[name] = ret
    return ret

def used_direct_deps(name):
    used = set(deps(name)).difference(set(unused_direct_deps(name)))
    return used

_udtable = {}

def used_deps(name):
    if name in _udtable.keys():
	return _udtable[name]
    all = set(deps(name))
    definite = used_direct_deps(name)
    for i in all:
	definite.update(used_deps(i))
    _udtable[name] = definite
    return _udtable[name]

def unused_deps(name):
    all = set(deps(name))
    return all.difference(used_deps(name))

for i in sys.argv[1:]:
    if not os.access(i, os.F_OK):
	continue
    foo = unused_deps(i)
    if not len(foo):
	continue
    print "%s:" % i
    for j in foo:
	print "    %s" % j
    print