chapter-08.srt

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Chapter 08.
Making Target dependencies build.

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JC: So in order for that to work, we just need to....

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The second target has been
given its dependencies as input,

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So we should just be able
to tell them to build themselves.

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So if we go back into our target class then build.

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And we've got this dependencies
thing that we've not stored.

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[Silence]

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So build could call update or...

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Not necessarily going to update them,
I'm going to make sure they're up to date.

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ensure_updated_dependencies

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And then let's extract that
into something called build_self.

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So build is now a sort of sequence of high level
things you need to do, and this is how to do each one.

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[Silence]

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We have def ensure_updated_dependencies.

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So we should be able to go in
and say dependencies.each &:build.

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And they will build themselves.

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These things here, which are
primary resources we already created,

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they don't have any build
instructions and should work OK.

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This is why I made it so it was
OK to have no instructions,

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because you need to be able to
model things that already exist.

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This should go off and tell file a and b
to build themselves, which will do nothing.

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And then this will tell the first
target and file c to build themselves.

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The first target will run this command here and
once those are done, run this command here.

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And everything should be OK.

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TS: Does it work?

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JC: It works. Hurrah!
TS: Amazing!

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JC: Right, so we've got an integration test
and all that we've changed to do that

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is quite a lot of things. (Laughter)

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I don't know if all these unit tests should
be on the build method, or on build_self.

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I don't want to specify the
implementation of target

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but I want to specify it's
relationship with other things.

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The important thing is when you build one target, it
will tell those dependencies to build themselves.

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That's the minimum abstract
thing that needs to be checked.

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I don't want to tell it how its
private method should be organized.

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It's more about, what's its interaction with other
stuff and that is that it calls build on them.

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In terms of unit tests...
fakemake target_spec... so build.

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This is all about running instructions and stuff.

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But before we get to running
instructions we have dependencies.

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I'm not sure if it makes sense to write
a test for when there are no dependencies.

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These tests are already implicitly
for when there are no dependencies.

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And if there are none there's no other target for
you to say that it should or should not call build on.

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So let's make a test for when there are dependencies.

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[Silence]

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We can have several of them and in
this case the order shouldn't be important.

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Or rather you should construct your
dependency tree so the order doesn't matter.

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If c depends on a and b, but b has to happen
after a then you should just say b depends on a.

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That will ensure that that happens first.

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So... The first dependency is a double.

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And the second dependency is also a double.

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This does let us check that if the first dependency
fails then we don't call the second dependency.

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That isn't really a requirement, it's
accidental because the order doesn't matter.

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So we should say it should tell all
its dependencies to build themselves.

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So we expect first_dep to receive build once.

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And likewise for the second_dep.

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And, what's our target here?

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Our target is FakeMake::Target.new
with a pathname (that won't matter yet).

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And the dependencies, second dep and no
instructions because we're not testing that here.

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That looks OK, so when we call target build it
should tell each of the targets to build themselves.

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Oops, I've lost my other shell.

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Path again...

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[Silence]

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OK that looks good.

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This is a good place to commit. It's a new
feature: we have dependency management.

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Let's have a look at what we've changed.

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We've added dependencies to target class and made
it so that the target will build its dependencies.

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If you have a tree of targets
they will recursively build themselves.

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And we've added tests for those things.

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[Silence]

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OK.

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TS: I was surprised to see when you ran that unit test,

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it looks like there was some
output on stdout during the test,

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which wasn't what I expected to see.

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JC: You're right we're printing the commands.

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We'll still have an issue with system, because
system inherits stdout from the ruby process.

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Cat happens to not emit any output; well it does,
but we're piping it into a file, so it's fine.

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But we are still echoing stuff.

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TS: But this wasn't happening before right?

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When you ran the unit test before
it was just a line of green dots.

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JC: Yes.

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I've let these targets in the
integration tests use stdout.

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and I can maybe stop them from doing that.

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It's a bit frustrating in that I could have
used puts and set $stdout to StringIO,

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but then the tests wouldn't emit any output.

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It's one of those isolation things.

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I want this thing that prints
stuff to print to a black hole.

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But I want the tests that are running the
process to still be able to talk to stdout.

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We can get around that by passing
in an output like we did before.

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We'll call it stdout here to make
it a bit more clear what its role is.

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And then that can take it as an argument.
Although not all of them will need it.

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Only the ones that run code need it.

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[Silence]

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I'm not having a very good typing day today. [Laughter]

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Private method puts called for; that's interesting.

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Oh! I've called it output sorry, I forgot what
I called it. It's called stdout in this test.

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OK that's better, outputs gone away.
TS: Great.