Quick'n'dirty cabal new-build exe-symlink script

link_cabal_exe.py

#!/usr/bin/env python

import sys
import os
import os.path
import json

plan = json.load(open("dist-newstyle/cache/plan.json"))

cabal_version = list(map(int,plan["cabal-version"].split('.')))

assert cabal_version >= [1,25]

if len(sys.argv) != 4:
    print("usage: link_cabal_exe.py pkgid exe-name symlink-file")
    sys.exit(1)

[_,pkgn,exeid,target] = sys.argv

exes = [ x.get("bin-file") for x in plan["install-plan"] if x.get("pkg-name") == pkgn and x.get("component-name") == "exe:"+exeid ]

if len(exes) > 1:
    print("WTF... found multiple entries in plan.json file")
    sys.exit(2)
elif len(exes) < 1:
    print("target not found in plan.json")
    sys.exit(2)

[exe] = exes

exe = os.path.relpath(os.path.abspath(exe), os.path.abspath(os.path.dirname(target)))

if os.path.islink(target):
    if os.readlink(target) == exe:
        #print("proper symlink exists already, nothing to do")
        sys.exit(0) # no-op

    print("Found symlink pointing to wrong destination. Resetting to proper destination...")
    os.unlink(target)

elif os.path.exists(target):
    print("ERROR: non-symlink detected at '{}'".format(target))
    sys.exit(3)

os.symlink(exe, target)