Fix apt cache FD leakage and performance boost lp:1537705

[asac]

No description provided.

[asac]

test coverage decrease... would be nice if someone deep into code could write a simple test for this... if you need test case yaml its in the lp bug https://bugs.launchpad.net/snapcraft/+bug/1537705

[asac]

lool pointed out that this patch does not close cache when pkg isnt in cache... we could make this cleaner, but practically we probably always want to bail if someone asks for a build-package that isnt even known to cache, no?

[sergiusens]

I wonder if something like this is allowed (apt cache being context aware, I think it is), so mind replacing that with

with apt.Cache() as apt_cache:
    if not apt_cache[pkg].installed:
        new_package.append(pkg)

It might also be more performant to open the apt cache before looping over the packages.

[asac]

uploaded new rev with comments addressed. fwiw, i tested that it really closes the apt cache this way (before moving it out of the loop)

[asac]

ok, ran static/unit tests locally on latest push and all green... hope good enough :)

[sergiusens]

it seems my comment from before did not stick 😯

Is this a way to get only one item? If so, instead of

seen = set()
seen_add = seen.add
unique_packages = [x for x in packages if not (x in seen or seen_add(x))]

do

unique_packages = set(packages)

Or bellow in

for pkg in unique_packages:

Change that to

for pkg in set(packages):

[asac]

pushed fix

[sergiusens]

I'm closing this in favor of #268 which still keeps @asac as the author but squashed.